 8. of the Romance of Modern Chemistry of the various classes into which chemical compounds may be divided, acids form one of the largest and most important. They get their name from the sour taste which is supposed to characterize them, but this characteristic is by no means From the chemist's point of view, all acids are similar in that they contain the element hydrogen, this hydrogen being replaceable by a metal. In many cases we can actually follow the replacement of the hydrogen in an acid by a metal, as for example, when a few pieces of magnesium ribbon, iron wire, or granulated zinc are put into hydrochloric acid, spirits of salt, as the druggist may call it. The acid and the metal attack each other, the latter disappears gradually and turns out the hydrogen which comes bubbling off as a gas. What takes place might be expressed as follows. Metal plus acid goes to a salt plus hydrogen, the salt left in solution being magnesium chloride, iron chloride, or zinc chloride, according as magnesium, iron, or zinc was the metal taken. The corrosive acid is, in a sense, destroyed by the metal, and the plumber's description of zinc chloride as killed spirits of salt is therefore quite to the point. The behavior of acids in attacking or corroding metals is very general and even domestic illustrations are available. Vinegar is a household article, but it is well to remember that it contains a fair amount of acetic acid, which, although not so powerful as sulfuric or hydrochloric acid, is yet able to exhibit the corrosive action which is characteristic of acids in general. A drop of vinegar left on the surface of a copper saucepan will betray itself before long by the appearance of verdigris. This is acetate of copper, the salt produced by the action of the acetic acid in the vinegar on the copper of the saucepan. The widow of man has hit upon methods of utilizing this corrosive action of acids on metals, and if properly guided it becomes a process of engraving. Suppose we have a plate of copper on which we wish to trace some design. One simple way of doing this is to coat the plate completely with a thin film of wax or other substance, which is not affected by acids, and then with a sharp steel point to scratch the required design through the wax. This means that the metal surface is exposed, where the steel point has removed the wax, so that if the plate is immersed in an acid bath, say of aquafortis, nitric acid, the metal is eaten away along the lines traced by the engraver. When the wax is dissolved, the metal plate is then found to bear the design intended, the depth of the lines depending on the length of time during which the plate has been left in the bath. Such etching of metals is characteristic of acids generally, but there is another kind of etching, namely unglass, which can be affected by one acid only, that is to say it is a specific action. This very peculiar property is possessed by hydrofluoric acid, a compound of hydrogen and the element fluorine, which is combined with lime in the mineral fluorospar. If a piece of glass is coated with paraffin wax, and a design is traced upon this with a sharp pointed instrument, then on exposure to the vapor of hydrofluoric acid, the glass is eaten away at the places where the wax has been removed. In this way, the design traced upon the wax is reproduced on the glass, the surface however, being deadened where the acid vapor has acted. If it is desired to etch without deadening the surface, the glass is immersed in a solution of hydrofluoric acid. This treatment leaves the glass polished and clear, even where it has been etched. The process of etching on glass is invaluable to the maker of scientific instruments, for it is frequently desirable to have figures marked on glass apparatus itself, rather than on any scale attached to the apparatus. An ink is actually sold, containing the ingredients necessary to produce hydrofluoric acid, and mere writing with this on a piece of glass apparatus is sufficient to leave an impression. The constituent of glass attacked by hydrofluoric acid is silica. This is the oxide of the element silicon, and forms a very large proportion of the rocks in the earth's crust. Sand, for example, is impure silica, and the behavior of hydrofluoric acid towards silica is well illustrated by allowing it to act on powdered sand in a leaden vessel. The sand gradually disappears, because the silicon in it forms a gaseous compound with the fluorine contained in the hydrofluoric acid. It is difficult to realize that the essential constituent of sand may be converted into a vapor, but that is what is affected by the action of the hydrofluoric acid. Bearing in mind this corrosive action of hydrofluoric acid on glass, we see that it would be inadvisable to keep a solution of the acid in any glass vessel. As a matter of fact, it is usually sold in gutta percha bottles. The more powerful acids have a destructive and corrosive action not only on metals, but on many other substances also, notably on organic materials. The most outstanding in this respect is sulfuric acid, or oil of vitriol, an innocent enough looking liquid, which, however, is extraordinarily destructive of animal and vegetable tissue, and requires very careful handling. If a drop of it gets on the skin and is not at once washed off, a very painful wound is produced. Occasional newspaper reports show that there are people who regard vitriol throwing as a proper way of settling old scores, but from what has been said it will be understood that it is a diabolical proceeding and is very rightly scheduled as a crime. The destructive action of sulfuric acid on vegetable tissue is seen when a drop falls on wood. The latter turns black and has a charred appearance, just as if it had been burned. Sulfuric acid is characterized by an extraordinary fondness for water. If cold sulfuric acid is added to cold water in a glass vessel, the warmth of their meeting is quite remarkable, and the vessel becomes too hot to hold. Further, if a dish containing a little sulfuric acid is left exposed to the air, the bulk of the liquid gradually increases, and if left long enough, the dish would overflow, the reason being that the sulfuric acid absorbs from the air as much moisture as possible, and so becomes diluted. The affinity of sulfuric acid for water is much utilized by chemists in order to render gases absolutely free from moisture. A current of hydrogen which is being evolved by the action of a metal on hydrochloric acid comes off fully charged with water vapor, but if it is made to bubble through sulfuric acid, the water molecules are seized by the acid and the hydrogen is obtained dry. So thorough is the scrutiny that scarce a single water molecule escapes. One property characteristic of acids generally is their power to make carbonates effervesce. Here again, domestic resources will be sufficient to supply us with an illustration, for most houses can furnish vinegar and washing soda. As has been said already, vinegar contains a certain proportion of acetic acid, and washing soda is nothing else than carbonate of soda. When therefore we pour a little vinegar on washing soda, we bring together an acid and a carbonate, and the result is the usual one, namely effervescence due to the liberation of carbon dioxide. This production of gas which occurs when an acid and a carbonate are brought together is applied very ingeniously in the chemical fire engine. The essential parts of this engine are a large closed tank charged with a solution of bicarbonate of soda, and inside the tank a leaden jar containing sulfuric acid. At the proper moment, the acid is tipped into the soda solution, and the carbon dioxide which is generated exerts a pressure sufficient to force water a considerable distance or height. The advantage of this fire engine is obviously that the chemical forces may be brought into play instantaneously. There is no necessity to wait until the steam is up. The action between an acid and a carbonate may be used in another way in the direct extinction of small fires. It is well known that combustion is not possible in an atmosphere of carbon dioxide, hence if we can surround a piece of burning wood for example with such an atmosphere we may smother the fire. This is the object of the fire grenades which are to be seen hanging in factories and public buildings. They contain the substances necessary for the production of carbon dioxide, and these are brought together by throwing down and breaking the glass vessel in which they are contained. The reader is doubtless aware that much of our building material consists of limestone, the chief constituent of which is carbonate of lime. Bath, stone, and dolomite, for example, are affected by acids in exactly the same way as ordinary carbonates, and in as much as the air in our large towns contains some acid constituents derived mostly from the sulfur and coal, calcareous or chalky stones like this are liable to disintegration. The houses of parliament and York Minster furnish examples of the way in which a calcareous building stone decays under the influence, amongst other factors, of the acid constituents of the atmosphere. Bearing in mind another general characteristic of acids, we have a very simple clue to a conjuring trick which seems marvelous to the uninitiated. It is found that certain vegetable products assume one definite color in the presence of acids and another color in the presence of alkalis, which, as we shall see presently, are the exact opposites of acids in many respects. A solution of litmus, for example, is turned red by acids and blue by alkalis, while a solution of phenolphthalein is colorless in the presence of acid and intensely red in the presence of alkalis. These substances are called indicators and are of the greatest use in chemical work because they enable the chemist to neutralize any solution that is neither acid nor alkaline. In the conjuring trick a series of glasses are rinsed out alternately with acid and alkali, and then water containing some phenolphthalein is poured from the first glass into the second, from the second into the third, and so on. What the spectator sees and marvels at is a colorless liquid becoming suddenly red on being poured into an apparently empty glass, and the same red liquid becoming colorless again when poured into another also apparently empty glass. As a class, alkalis are the opposite of acids, not only in regard to the indicators just mentioned, but in many other respects. The addition of an alkali to an acid destroys or neutralizes the characteristic properties of the latter, and if the right quantity is added, the solution then contains nothing but a salt, a kind of neutral substance which does not exhibit the behavior either of an acid or of an alkali. The process of neutralization may be represented in the following way. Acid plus alkali goes to a salt plus water, from which it will be seen that the same sort of body is produced in this way as is formed by the action of an acid on a metal. In certain circumstances an alkali may obviously be used as an antidote to an acid. If for instance a drop of an acid is allowed to fall on clothing, the production of a stain and ultimately a hole may be prevented by the immediate application of an alkali, for the salt which is thus formed is quite harmless so far as any action on the cloth is concerned, and may be washed out with water. Again, if any acid has been swallowed, an alkaline substance is the thing to take. In both cases, however, the right alkaline substance must be chosen, otherwise the cure may be worse than the disease. For certain alkalis have a very powerful action on animal and vegetable tissues, destroying such things as skin and paper. Two alkalis of this description are caustic soda and caustic potash, which although extensively used in the manufacture of hard and soft soap respectively, are perhaps not so familiar to most people as the so-called mild alkalis, carbonate of soda, and carbonate of potash. What has been said about an alkali acting as an antidote to an acid will enable the reader to understand that air containing carbon dioxide may be purified by passing over caustic soda. For carbon dioxide is an acid gas, and as such is readily absorbed by an alkali. Hence, it is possible to devise an arrangement whereby a person may breathe in a closed space without suffering from accumulated carbon dioxide. It is only necessary that oxygen should be supplied to replace what is absorbed in the lungs, and that the exhaled air should be freed from carbon dioxide by contact with alkali before it is again inhaled. Both these conditions are fulfilled in the so-called oxygen-respirating apparatus. This consists of a bag of air carried on the breast and connected by various tubes with, one, the mouth and nostrils, two, a compartment filled with alkali, and three, cylinders containing compressed oxygen and carried on the back. Anyone provided with a portable apparatus of this description is independent of the surrounding atmosphere and may therefore venture into places entrance into which would ordinarily mean certain death. An equipment of this kind was used with success in the rescue work at Courier where, as the reader may remember, a very serious mind disaster occurred not very long ago. But we must return to the question of the well-known alkali's. Solutions of these substances are soapy to the touch and are extremely useful for cleaning purposes. One thing, however, which should not be cleaned with alkali is the modern aluminum wear used for cooking. Of the few metals which are dissolved by alkali's, aluminum is one. Potash furnishes an interesting illustration of a useful substance coming from unlikely sources, of which two may be mentioned. Wood contains a certain proportion of potash, absorbed from the soil by way of food, and in countries which are well-timbered, potash is extracted from wood ashes, in which there may be as much as 10% of the alkali. Its very name is derived from the fact that the wood ashes are dissolved in water, and the solution is evaporated down in iron pots. Another and still more strange source from which potash is derived is the fatty matter in the fleece of sheep. This suent, as it is called, contains quite an appreciable amount of the potassium salt of an organic acid, and when this is extracted, evaporated, and strongly heated, potash is left behind. Besides the mild and caustic alkali's which have just been described, there is what is known as the volatile alkali, ammonia. Although this substance is the gas composed of nitrogen and hydrogen, it is an alkali just as much as caustic potash or washing soda. It neutralizes acids and exerts the same effects as other alkali's on litmus or phenyl phthalane. One of the most remarkable properties of ammonia gas is its extreme solubility in water. If a flask quite full of the gas is uncorked with the mouth under water, the latter will rush in and occupy the whole of the flask just as if there had been nothing there at all. Measurements have been made of the solubility, and it has been found that one cubic inch of water will absorb at the ordinary temperature as much as 700 cubic inches of ammonia gas. The solution so obtained may therefore be regarded as a convenient and compact form of ammonia, and it is this which is supplied to us when we ask for ammonia at the shops. The liquid we buy contains a large proportion of water, but it would clearly be impracticable to buy and sell ammonia in the pure gaseous state. This convenient way of handling a substance in solution instead of in the pure under-duded state is employed also in the case of some acids. Oil of vitriol, to be sure, is almost pure sulfuric acid, but aquafortis is only a solution of nitric acid and spirits of salt as a rule does not contain more than one-third of its weight of hydrogen chloride, which is itself a gas. Ammonia as an alkali has the power of neutralizing acids, and an interesting experiment which shows that the process of neutralization leads to the formation of an entirely new substance, a salt, is the following. A glass cylinder is filled with ammonia gas and closed with a glass plate. A similar cylinder is filled with hydrogen chloride, and the two are placed mouth to mouth with the glass plate between them. If the glass plate is slipped out, the colorless alkaline gas in the one cylinder and the colorless acid gas in the other immediately rush upon each other, and a white powdery substance, sal-ammoniac, is produced. Here we have the interesting case of two gases uniting to form a solid, entirely different in character from the original reacting substances. Lime is another alkaline body of which enormous quantities are required in the arts and the manufacturers, and yet the majority of people know very little about its valuable properties. Lime is the oxide of the metal calcium, and is obtained by strongly heating carbonate of lime, which nature supplies in profuse measure and in such various forms as marble, limestone, and chalk. We may note that from the point of view of ultimate chemical composition, chalk is as good as marble. It is only the poor brother in the family. By dropping a little acid on marble, limestone, or chalk, we can satisfy ourselves that they give an ever-vescence of carbon dioxide. As a matter of fact, carbonate of lime is just a neutral salt formed by the union of the alkaline lime and the acidic carbon dioxide. This salt, however, differs from other common salts, because when it is heated it gives off its acidic component, the carbon dioxide, while the lime remains behind. This chemical change is carried out on the large scale when limestone is strongly heated in lime kilns. The process is termed lime burning. The reader must not suppose that lime burns in the sense that a piece of coal does. This term refers only to the strong heating to which the limestone is subjected. The product of lime burning is called quicklime, but for a great many purposes, such as the preparation of building mortar, this must be converted into slaked lime by the action of water. The slaking of lime is a beautiful example of the changes brought about by a simple chemical action. For if a little water is sprinkled on one of the hard lumps of quicklime obtained from a lime kiln, some remarkable effects are observed. For a minute or two, nothing is apparent, but presently, steam rises from the lime, and if the observer touches the mass with his hand, he will realize that much heat is being generated. The chemical forces at work are such that the hard lump of lime splits up and crumbles down to a soft powder, which is absolutely dry in spite of the added water. The secret of this striking phenomenon is that a new chemical compound has been formed. The water has united with the quicklime to produce slaked lime, hence its disappearance. The slaking of lime is accompanied by a considerable increase in bulk, and this fact has been occasionally applied in the blasting of coal in fiery mines, where the use of ordinary explosives is dangerous. A so-called cartridge of quicklime is pressed into a cavity drilled in the coal, and water is then forced in by a pump. The result is that the lime slakes, and the force of the expansion which accompanies the slaking process, is such as to split the surrounding masses of coal. An excellent example of this, of the chemical energy latent even in the most commonplace materials. We do not usually associate anything very striking with such matter-effect substances as lime and water, and yet in their own quiet way they can together do the work for which the aid of a high explosive is generally requisitioned. Lime is very extensively employed in the preparation of building mortar. For this purpose, sand and slaked lime are used, and they are made up together with water until the mixture has a pasty consistency. The setting of mortar, which occurs a few days after it has been made and applied, is simply a process of drying by exposure to the atmosphere. But even after the mortar has set it undergoes a further change. It gradually hardens. This process of hardening is a chemical one, and is due to the slow absorption of carbon dioxide from the atmosphere. It can easily be shown that lime has the power of absorbing carbon dioxide, for if lime water, which is simply a clear solution of slaked lime, is exposed to the air for some time, a white film of chalk collects on the surface. So also the lime in mortar gradually absorbs carbon dioxide, becoming converted into the hard carbonate of lime. It will of course take a very long time for the hardening to be complete, but the examination of ancient mortar from Greek and Roman ruins has shown that in these cases, the carbon dioxide absorbed from the atmosphere has been sufficient to convert all slaked lime into the carbonate. In fact, by pouring a little acid on a piece of old mortar, anyone can see that it contains a carbonate. Every stone or brick wall, therefore, in which mortar has been used, must be pictured as the scene of a slow, imperceptible chemical change, a change which will probably go on as long as the wall lasts. END OF CHAPTER VIII CHAPTER IX NATURAL WATERS AND WHAT THEY MAY CONTAIN It was a commonly accepted idea among the ancients that fire, air, earth, and water were the four elements, the simplest forms which matter could assume. This conclusion was not reached as a result of experiments, of unsuccessful attempts to get at something more simple, for the ancient philosophers never made any chemical experiments at all. So far as they concern themselves with the science, they were what we might call study table chemists, and they thought it a much finer thing to make theories than to make experiments. To indulge in the latter practice was regarded as an occupation quite below the level of a philosopher. Now all this has changed, and in the last two centuries men have used the experimental method with infinite skill and patience to ring from nature many of her most valuable secrets. Amongst other things it has been discovered that water is not an element, as the ancients thought, but is capable of being broken down into yet simpler and more elementary substances, hydrogen and oxygen. So far then the ancients were wrong, but at the same time they were correct in regarding water as one of the first ranked substances in nature, not only because it is so abundant, but because it is so absolutely essential to life of all kinds. From the chemist's point of view, water is an exceptionally interesting substance, for in the first place it furnishes an excellent example of the thoroughgoing alteration which matter may undergo when it takes part in chemical processes. Think of it, hydrogen and oxygen, the elements which combine chemically to form water, are gaseous, invisible substances, which we may mix without any obvious change taking place. In the mixture neither gas interferes with the other, and each retains its own characteristics and properties. But bring a lighted taper or match near the mouth of the vessel which contains the gases, and what is the result? The gases which have up to this point been in peaceful contact are stimulated to mortal combat, a loud explosion occurs, and the gases are destroyed, leaving behind only the sweat of battle in the shape of a few drops of water. One has seen a conjurer converting handkerchiefs into rabbits, and a pack of cards into thin air, but his feats are tricks, after all, and the more genuine cause of wonder is to be found in the marvelous things which nature has to show. Among these marvels are such changes as that by which hydrogen and oxygen are converted into water, a substance with absolutely new properties and characteristics. Water, however, is interesting in other ways. Has the reader ever observed that ice floats in water? He may have seen it, but not perceived it. Probably the fact has just been accepted as a matter of course, without any inkling of its importance. But the truth is that water is somewhat eccentric in this respect. Generally speaking, when any substance is exposed to lower and lower temperatures, and thereby passes from the condition of a gas to that of a liquid, and from the condition of a liquid to that of a solid, it shrinks and becomes more dense. That is, a given bulk of the substance weighs more and more. Water, however, is peculiar. As the temperature falls, it changes from steam to liquid water, and from liquid water to ice. But there is not throughout these changes a continuous increase of density. Water does indeed become more and more dense down to a certain point, 39 degrees Fahrenheit, but here it reverses its behavior. It expands and becomes lighter as it gets colder. So it comes about that ice is lighter than the water from which it freezes, and accordingly floats on the surface of the water. A little thought will show how significant this fact is in the economy of nature. For the preservation of life in our lakes and seas during a severe winter is possible only because the surface ice protects the water underneath from freezing. The same fact, however beneficial in its consequences in the realm of nature, is liable to put us moderns sometimes to considerable inconvenience. We fit our houses with water pipes, and it is only when the grip of winter has been unusually severe and our pipes are burst that we learn that nature will have her way in spite of our devices. Since ice occupies more space than the same weight of water, the pipes are burst when the water freezes, although it is not till the thought comes that the damage is revealed to us. Now the waters with which nature supplies us, not always very regularly, according to our way of thinking, are never pure from the chemist point of view. Many of them are fresh and quite suitable for drinking purposes, but even they contain substances which make them a little different from pure water. Thus it is well known that practically all natural waters contain in solution an appreciable amount of solid matter. A large part of this solid matter may be deposited when the water is boiled, and a glance inside the kitchen kettle will, in many cases at least, suffice to show that this is the case. The so-called furring of a kettle is simply due to the solid matter depositing when the water boils. The same thing happens in engine boilers, and the incrustation or scale that forms on the plates of the boiler is a cause of serious trouble, for it is very difficult to remove the scale without damaging the boiler, and so long as it is allowed to remain, extra heat must be supplied to the boiler if the output of steam is to be maintained. The extra heat is required because the scale is a bad conductor of heat. It has been found that a boiler incrustation one quarter of an inch in thickness involves a consumption of fuel fifty percent greater than would be required if the boiler plates were clean. Different natural waters contain quite different amounts of dissolved solid matter. Some, such as sea water, contain a great deal. Others, such as rainwater, contain very little. A good idea of the relative average amounts of solid matter contained in fresh waters from various sources will be obtained by a glance at the accompanying diagram. The heights of the columns are proportional to the amounts of solid matter in the various waters. Deep well waters contain, on the average, about half an ounce of solid matter for every thousand ounces of water, and the proportion of solid matter in the other fresh waters may be roughly gauged from the diagram. If the amount of solid in sea water were to be represented in the same way, a column eighty times as high as the highest in the diagram would have to be introduced. This obviously must be left to the imagination of the reader. To the ordinary individual, waters are familiar as hard or soft, and this classification gives a rough idea of the amount of solid dissolved in the water. Hard waters contain a large amount of solid. Soft waters, which require but little soap to make a lather, are those which are comparatively free from dissolved solid. The question next arises, what are the solids that we find in the various natural waters and where do they come from? If sea water is left out of account for the present, it may be said that the main substances occurring in natural waters are sulfate and carbonate of lime and magnesia to a less extent. The proportion of these substances held in solution by a water depends on its history. As a matter of fact, carbonate of lime, chalk, is not soluble in pure water, but only in water charged with carbon dioxide. If now the reader recollects that there is opportunity for rain to become charged with carbon dioxide from the atmosphere, he will understand that the water which falls on the surface of the earth and percolates through the soil and the rocks will have the power of dissolving from these the carbonate of lime which they contain, as well as more soluble substances. When this water comes to the surface again in a well or spring, it is found to be hard. But the simple process of boiling may render it comparatively soft, since in this operation the carbon dioxide with which the water is charged is boiled out, and the carbonate of lime being no longer soluble is deposited. That the furring in the aforementioned kitchen kettle is caused by a carbonate is shown by the effervescence which occurs on the addition of a little hydrochloric acid, spirits of salt, as it is commonly called. Apart from actual boiling, mere exposure of such a hard water to the air will deprive it of its carbon dioxide by evaporation, and insofar as the carbon dioxide is removed, insofar is a deposit of carbonate of lime produced. This is the way in which these curious excretances known as stalactites and stalagmites are formed. Water which has percolated through some depths of soil and rock and become hard in the process may arrive at the roof of some underground cavern. The drops which their form are subject to evaporation, and part of the carbon dioxide with which they are charged is removed. This leads to the deposition of chalk and a tiny contribution is made to the growth of the stalactite. A further quantity of carbon dioxide evaporates as the drops fall on the floor of the cavern, a further deposit of chalk is formed, and a tiny contribution is made to the growth of the stalagmite column. Another very interesting natural phenomenon closely related to the formation of stalactites and stalagmites is the action of what are known as petrifying springs. If a wicker basket, for example, is exposed to the action of such a spring, it is gradually impregnated and coated with a stony-like substance. The explanation is that the water of a petrifying spring is hard and contains a considerable quantity of carbonate of lime in solution. When the water comes to the surface, it deposits carbonate of lime because it loses by evaporation some of the carbon dioxide in virtue of which it has the power of dissolving that substance. This deposition of calcareous matter may take place on any objects such as leaves or twigs exposed to the play of the water, but it is thought by some people that certain bog mosses or water plants are specially effective in causing decomposition of the carbonic acid and thereby inducing the deposition of a crust of carbonate of lime on their stems and branches. Most of the water which has percolated through the soil and the rocks and thereby collected a certain amount of solid matter finds its way into streams and rivers and ultimately into lakes and seas. It will be obvious that the amount of solid matter in the sea and in lakes which have no outlet must be gradually increasing since the supply of water is roughly balanced by continual evaporation from the surface. The rate of increase of the solids in seawater is very small because of the enormous quantity of water, but in the case of an inland lake in a hot climate where there are heavy rains alternating with periods of rapid evaporation, the amount of dissolved solid is very high and increases fairly rapidly. The Dead Sea is a case in point. Its waters are exceedingly brackish and contain no less than about a quarter of their weight of solid matter, mostly sodium chloride, common salt, washed out from the neighboring hills. The presence of so much solid makes the water of the Dead Sea considerably heavier bulk for bulk than freshwater. It is so dense that eggs will float in it and it will not allow the human body to sink. Ordinary seawater also is somewhat denser than freshwater and its superior buoyancy is possibly known already to the reader by personal experience. Much of the water which is distributed over the surface of the globe is quite unsuitable for the use of man. All brackish waters come under this category and many an unfortunate sailor who has been cast adrift at sea has realized the bitter truth that there was water everywhere but not a drop to drink. Even from seawater, however, it is possible to obtain pure water by the process of distillation. The water is boiled in a suitable vessel and the steam is led away through a cooled pipe, at the end of which the condensed water may be collected in a pure state. The solids dissolved in the seawater are not volatile and are accordingly left behind in the boiler. At the present day much of the fresh water required on board our great ocean liners is obtained by subjecting seawater to distillation. When one thinks of it, nature herself is constantly making use of this process. The evaporation that continually takes place from the surface of the ocean is really a slow distillation. The water vapor condenses into clouds and falls, some of it at least, as rain on the surface of the land. Rain is a natural distilled water. For many domestic and industrial purposes it is necessary to purify even ordinary fresh water, especially when it is hard. This process of softening water may be affected in several ways. It has already been stated that mere boiling will diminish the hardness of a water, but even water that has been boiled will not at once give a lather with soap. Instead of giving an immediate lather, a curd is formed, evidence that the sulfate of lime still remaining in the water is being removed or precipitated by the soap. Only after this removal is complete will the soap form a lather. The lime in hard water may be removed also by the addition of sodium carbonate, washing soda as it is commonly called, or of lime water. If the water is to be obtained free from the deposit of chalk which both these substances produce, it must be allowed to stand in tanks and then run off after the precipitate has settled to the bottom. Occasionally the impurities in a water are of an organic nature, and these may be such as to render the water unsafe for drinking purposes. This organic matter may come from decomposing vegetable substances where it may be of animal origin and come from sewage or surface drainage. Sometimes our senses of taste and smell will warn us of this, but in the last resort we must depend on a chemical and bacteriological examination of the water. Such an examination will reveal, in the case of a polluted water, an unduly high amount of nitrogenous compounds, and possibly also large numbers of disease germs. To make the water safe it must either be filtered through sand or unglazed porcelain, or it must be sterilized by boiling. All germs seem to find exposure to boiling water a somewhat trying experience, and few survive the ordeal. This will be clear from a special example which has been put on record. A particular water of bad quality was found to contain 460,000 germs per cubic centimeter. Exposure to a temperature of 194 degrees Fahrenheit for 10 minutes reduced the number to 26, and even these hardy individuals had to give up when the water was boiled for 10 minutes. As the palatable quality of a water depends on the quantity of dissolved gases such as oxygen and carbon dioxide, the device of boiling it renders it somewhat insipid. If this is considered a disadvantage, it can be made more palatable by aeration, that is, by shaking it for a little while with air. Besides the various kinds of fresh water and the brackish water of our seas and inland lakes, nature supplies us here and there with waters of a peculiar kind. Distinguish not so much by the quantity of matter which they contain, as by the fact that this matter is of an unusual kind. These are the so-called mineral waters, which in many cases at least come from considerable depths below the surface, and are frequently hot on that account. Some of the well-known mineral waters are alkaline and contain carbonate of soda, notably those which are charged with extra-large quantities of carbon dioxide, such as Apollonaris and Celsar waters. Carbon dioxide has been forced into these waters under high pressure far below ground, and when they come to the surface and under the lower pressure which prevails there, they cannot contain themselves as it were, and so are marked by their characteristic effervescence. Here and there one finds iron or chalibiate springs. Carbonate of iron, like carbonate of lime, is not soluble in pure water, but is taken up by water charged with carbon dioxide. Thus it is possible to obtain a water which holds in solution a considerable quantity of otherwise insoluble iron. When such a water comes to the surface, it loses some of the carbon dioxide with which it is charged, and the channel down which the water runs away is tinged a yellowish or reddish color owing to the action of the oxygen in the air on the carbonate of iron deposited from the spring water. Saline springs containing sulfate of magnesia and sulfate of soda are frequently found. The waters of these springs are bitter and act as purgatives. It is interesting to note that sulfate of magnesia is commonly known as epsom salts, on account of the fact that it was found in the spring at epsom by a London physician of the 17th century. There are springs of this class in other parts of England, but the best known spas at which bitter waters are available are sedlits, fredrick-chow, and kissing-gin. Other mineral waters which are peculiar are those which contain sulfur in some form or other. The springs at harrigay and strathpeffer are the best known of the kind in this country. Owing to the sulfurated hydrogen and the sulfite of soda which these waters contain, they have an unpleasant taste and smell, but they are much valued for their medicinal properties. Those happy individuals, however, who have hitherto escaped the ills to which flesh is air, will have no desire to cultivate a closer acquaintance with sulfur springs. Chapter 10 of the Romance of Modern Chemistry This Libervox recording is in the public domain. The Romance of Modern Chemistry by James C. Phillip. Chapter 10. Chemical Changes Which Produce Light and Heat To the popular mind a chemical laboratory is suggestive of explosions, reactions which result in the very evident production of light and heat, and sound into the bargain. But it is not necessary to visit a chemical laboratory in order to observe chemical changes which produce light and heat, for we are all chemists to some extent at our own firesides. When we strike a match or light a fire, we make a chemical experiment, but the red flower is so familiar to us that we miss the meaning and the marvel of it. The making of fire is one of the oldest chemical achievements of the human race, and in our modern world the part played by combustion is of enormous importance. A little thought will show it is on those chemical changes which produce light and heat that we depend for a great many of our modern social conveniences. Where does the power come from which drives our motor cars? Why from the combustion of petrol? Further, when a man stands on the foot plate of a flying Scotchman or in the engine room of the Mauritania, he begins to understand what wonders in the way of locomotion we owe to the combustion of coal. Ah yes, some reader may say, but we are going in for electricity nowadays, are we not? We are lighting our streets with electric light instead of gas, and our railways are being electrified. That is all quite true, but even then we have not got rid of combustion as the source of nearly all our energy. Except where water power is available, the introduction of electricity means simply that the combustion has been centralized. Instead of burning gas at each street lamp, we burn coal or gas at some central furnace, and use up the energy of combustion in driving a dynamo. Instead of having a fire on each locomotive, we have again a central furnace at the power station. Hence the production of energy, whatever its form, still depends almost exclusively on the time-honored process of combustion. Now although the various things which are burned for the purpose of producing light and heat are outwardly very different, gas, coal, power-fin, oil, candles, wood, methylated spirits, petroleum, peat, etc., the process of combustion is essentially the same in each case. The substances just mentioned are alike in containing carbon and hydrogen, either in the form of the elements themselves or in the form of compounds, and the process of combustion is simply the chemical combination of these two elements with the oxygen of the atmosphere. Hence if we understand what happens in the combustion of a candle, for example, we should be able to give an intelligent explanation of what takes place in a paraffin oil lamp or in a coal fire. When the carbon and hydrogen in a candle combined with the oxygen of the atmosphere, the products are our old friends carbon dioxide and water. Carbon dioxide is an invisible gas, as the reader will remember, and the water formed in the flame is given off as an invisible vapor. The candle therefore gradually disappears as it burns, leaving little or no trace behind. To the superficial observer, the fact that the candle disappears and leaves nothing tangible in exchange might seem to throw doubt on the law of conservation of matter, according to which matter cannot be destroyed. But it will be admitted that the law would still be fulfilled if the disappearance of so much matter in one form were compensated by the production of an equivalent amount in another form, and the reader who has followed the argument of the foregoing chapters will recognize that some forms of matter are invisible. The fact is the invisible products of the combustion of a candle, that is, the carbon dioxide and the water vapor, weigh more than the candle. This is only natural, for just as it takes two to make a quarrel, so there are two parties to a combustion, namely the combustible substance, in this case the candle, and the supporter of combustion, the oxygen from the air. As the combustion consists in a combination of the carbon and hydrogen of the candle with the oxygen of the air, the products are necessarily heavier than either the candle or the oxygen separately. The chemists can easily show that this is so, by absorbing and weighing the carbon dioxide and water, but it will be sufficient for our purpose to show that each of these substances is present in the gases arising from a candle flame. In order to show that carbon dioxide is one product of a candle flame, we may fix a small piece of candle on a wire, light the candle, and lower it into a glass jar, into which we have previously poured a little lime water. When the candle has been allowed to burn in the jar for 10 or 15 seconds, it is taken out. The jar is closed by a cork, and the contents are shaken. It will then be seen that the lime water has become turbid, showing that the air left in the jar after the burning of the candle contained carbon dioxide. The production of water in the flame of a burning candle may be very readily demonstrated with domestic apparatus. A tumbler of cold water, the colder the better, is carefully wiped on the outside, so that it is perfectly dry, and is then held a little above the candle flame. The outside of the tumbler at once becomes cloudy, owing to the condensation of tiny drops of water. The extent to which carbonaceous fuel is converted into carbon dioxide and water depends on the supply of the air which supports the combustion. If for any reason the supply of air is cut off, combustion ceases. Hence it comes that a candle cannot continue to burn in a closed space for more than a very short time. Not only does it exhaust the oxygen, but by its own combustion it produces substances which are unfavorable to a continuance of the process. In an atmosphere of carbon dioxide and water vapor, no combustion is possible. On the other hand, the more air or oxygen we supply to the burning fuel, the more complete is the combustion. The oldest method of supplying more air to burning fuel, and thereby securing more complete combustion, is the familiar one of making a draft. The difference between an oil lamp flame with the chimney off, and the same flame with the chimney on, is due to the draft which the chimney makes. This draft means an inrush of air at the bottom of the chimney, and a better supply of oxygen to the flame of the burning oil. Perhaps the reader has tried sometimes to fan the flickering flame of a newly lit flyer by holding a newspaper in front of the upper part of the grate. The result of this is that the chimney draft sucks the air right through the fuel, which is thereby fed more perfectly with the oxygen it so badly needs. If the newspaper were not there, the bulk of the air which is drawn up the chimney would come in through the upper part of the grate front, without passing through the fuel. The village blacksmith, too, when he makes his bellows roar, is in quest of more rapid combustion, and consequently, more intense heat. Imperfect combustion is responsible for the smoke that hangs like a pall over so many of our large cities. We in England insist on having the cheery but unscientific open fireplace, with the result that the fuel is imperfectly burned, and our chimneys pour a constant stream of smoke into the atmosphere. Smoke is charged not only with finely divided carbon and soot, but also with oily and tarry vapor, whereas if there were perfect combustion, nothing but invisible gases would leave the chimney. Just imagine what that would mean. Apart from the saving in fuel, we should never require the services of the chimney sweep, and we should be spared many of the grimy fogs which come, especially in London, to clog our breathing organs and to depress our spirits. Why should it be so uneconomical and unscientific to burn coal in such open fireplaces as are common in England? The key to the answer lies in the fact that when coal is heated, it first gives off a quantity of inflammable gas, and it is really this gas which burns when we put coal on a fire. But, unfortunately, in our open fires, the fresh coal is put on the top, so that the gas which comes out of the coal as it gets warmed up is in a part of the fire where the supply of oxygen is limited. Not only has a considerable portion of the oxygen been used up in the combustion of the glowing fuel at the bottom of the grate, but the carbon dioxide which is produced there, and which ascends through the freshly added fuel, makes it impossible to get perfect combustion of the latter. Hence it comes that quite a respectable fraction of our best household coal simply goes up the chimney unburnt, to become subsequently a nuisance to ourselves and our neighbors. The abolition of smoke is a consummation devoutly to be hoped for, and considerable advance has already been made in that direction. Improvement has been affected chiefly in the diminution of smoke emitted from factory chimneys. For this we are indebted, partly at least, to the introduction of mechanical stokers which feed coal into factory furnaces so that the fresh fuel is put where it has an excellent supply of oxygen. The mechanical stoker subsequently moves the coal onto other and hotter parts of the furnace, and it has the further advantage that it obviates the necessity of opening the furnace doors, an operation which involves the admission of a draft of cold air. Appliances have been devised for securing more perfect combustion in house fires by introducing the coal from below, but none of these have come into general use. The adoption of such a plan would involve the reconstruction of all our fireplaces. Another method of getting rid of the smoke nuisance is to subject the coal to destructive heating in a gas works, and to use the gas so obtained for heating purposes instead of coal. This is the plan that will probably be adopted in the long run. A gas stove is however much less fascinating than a coal fire. Sentiment clings round the old fireside, and the institution will die hard. When gas or a candle burns in the air, the supply of oxygen is not sufficient for complete combustion of the carbon and the hydrogen, except in the outermost envelope of the flame, and the fact that we get any light at all from an ordinary gas or candle flame is due to a host of unburnt particles of carbon in the interior. These particles are raised to a white heat by the flame, and so make it luminous. That the ordinary gas or candle flame contains particles of carbon may be very easily shown by holding a cold surface just into the top of the flame, when a deposit of soot that is carbon in a finely divided form is obtained. When the supply of air to a gas flame is increased by mixing the gas with air just before it reaches the actual place where it is burned, then the combustion is more complete, the flame is hotter and no longer luminous. The particles of carbon which ordinarily make the flame luminous are now all converted into carbon dioxide, even in the interior of the flame by the extra oxygen supplied. This is the principle of the well-known Bunsen burner, which finds application now not only in the laboratory but in our houses on incandescent burners and gas stoves. A simple Bunsen burner is shown in the accompanying diagram. The current of gas which rushes out at the central nozzle sucks in air through the surrounding holes at the bottom of the burner, while the mixture of air and gas ascends and is burned at the top of the tube. The flame is very hot, gives out almost no light, and if a cold surface is put into the flame, no soot is deposited. This kind of flame is therefore especially suitable for heating and cooking purposes, for blackening of the utensils is avoided. The part played by the air in such a burner can be very simply demonstrated. If the burner is lighted and the observer puts his fingers over the air inlet holes at the bottom of the tube, the flame, instead of giving practically no light, becomes luminous at once. If the reader will take the trouble, this little experiment may be carried out with an ordinary incandescent burner. The air inlet holes are easily discovered, and if the burner is lit on some occasion, when the mantle has been removed, the effect of letting in or shutting off the extra supply of air is very evident. It has been already stated that an ordinary gas or candle flame is luminous because it contains particles of unburnt carbon which are raised to incandescence and so emit light. If this is so, then we may expect that if we take a non-luminous flame, like that of a Bunsen burner, and introduce into it some solid substance which can stand a very high temperature without melting, this flame will become a source of light. This is exactly the principle which has been applied in our modern incandescent burners. As has just been pointed out, the flame of an incandescent burner, apart from the mantle, is quite without luminosity, and the mantle is simply an infusible substance which is raised to incandescence by the heat of the flame. A similar device used to be much in vogue for the exhibition of lantern slides in the so-called limelight. By allowing a very hot flame to play on a little lump of lime, the latter is raised to white heat and emits a very powerful light. In an electric glow lamp, the light proceeds from a carbon filament raised to incandescence, but in this case the source of heat is an electric current, not a flame of burning gas. The electric glow lamp furnishes at the same time an interesting illustration of what has been said about there being two parties to a combustion. The filament in the lamp is made of carbon. There it is glowing brightly, and yet apparently it suffers no wastage. It appears to burn, but it is not consumed. Why is this? Because the other party to a combustion, the oxygen, is absent on this occasion. The lamp has been rendered vacuous during the process of manufacture. That is, the air which it contained was removed, and so no combustion is possible. The tender little filament is protected by its glass cage from the hordes of oxygen molecules that would be only too ready to fall upon it if they had the chance. It must not be supposed that the term combustion is to be applied exclusively to those cases where carbonaceous fuel is burned. Many other substances combine readily with the oxygen of the air, and the chemical change involved in this combination produces light and heat. Everybody who has seen an underground cavern illuminated by the burning of magnesium ribbon knows what an intense light is emitted in this process, and the process is essentially the same as the burning of a piece of charcoal. When charcoal is burned, oxide of carbon, carbon dioxide, is produced. When magnesium is burned, oxide of magnesium, magnesium is produced. The burning of magnesium illustrates very excellently one or two points which have been mentioned already. In the first place, it shows what fundamental changes those substances undergo which take part in a chemical action. We start with a piece of metallic ribbon and the invisible air, and there is left behind a soft white powdery mass of magnesium. In the second place, the intense light observed when magnesium burns is due to the presence of little particles of infusible magnesium which are rendered incandescent by the great heat of the chemical action. Again, it is easy to show that just as the carbon dioxide and water produced by the combustion of a candle are heavier than the candle, so the white powder produced by the burning of a piece of magnesium ribbon weighs more than the ribbon. The discovery that the products of combustion are heavier than the combustible substance was really a very important one in the history of chemistry. For up to about 120 years ago, it was generally supposed that a combustible substance contained something called phlogiston which came out of the substance when it was burned. It was the famous French chemist Lavoisier who finally overthrew this theory and emphasized the fact that instead of losing anything when it was burned, a combustible substance actually became heavier. The meaning of the term combustion has been extended in the foregoing paragraphs so that the burning of coal and the burning of magnesium are brought under the same category. We may now extend the term still further to cover many chemical processes which although they do not very obviously produce light and heat yet depend essentially on the same chemical phenomenon, namely the combination of some substance with the oxygen of the atmosphere. These are the cases of slow combustion and may be referred to generally as oxidation processes. One of these processes which without producing any light produces a good deal of heat is the respiration of animals. What goes on in our bodies through the agency of the lungs and the blood is neither more nor less than a combustion in the course of which the carbon compounds in the body, the fat, etc., are burned to carbon dioxide and water. It is very easy to show that air expired from the lungs is heavily charged with carbon dioxide. Ordinary fresh air contains so little of this gas that a pint bottle full produces no milkiness when shaken up with a little lime water. But if the air which we breathe or blow out from our lungs is made to bubble through a little lime water, a very marked turbidity appears. Exact measurements have shown that whereas fresh air contains three to four parts by volume of carbon dioxide in 10,000, the air which issues from the lungs is charged to the extent of 400 to 450 parts carbon dioxide in 10,000. A little carbon dioxide is also given off through the skin and it is computed that the total carbon dioxide evolved by the lungs and skin is about three-quarters of a cubic foot per hour. An ordinary gas burner produces about one and a half cubic feet of carbon dioxide in the same time so that as far as the contamination of the air in a room is concerned, a gas burner is equal to two men. Another change which comes under the same category as respiration in which we might describe as a slow combustion is the rusting of iron. Rusting is the combination of the metal with the oxygen of the air and is thus exactly parallel to the burning of magnesium ribbon except that it takes so much longer. The total heat evolved in the process of rusting is not any less than it would be if the oxidation took place rapidly. It is only spread over such a long time that the evolution of heat at any particular moment is not noticeable. Rusting is an example of spontaneous oxidation. It is not necessary to strike a match to start the process. Rusting is only too ready, as we often know to our cost, to start on its own account. It is indeed essential that carbon dioxide and moisture should be present before rusting can take place. But these substances are both present to some extent in ordinary air and the only way to keep iron from rusting is either to paint it or to plate it with some other metal which is less ready to hold traffic with the air. Metals which are commonly used for this purpose are zinc, tin, and nickel. Galvanized iron and tin plate, which are manufactured in such large quantities, are simply iron which has been coated with zinc and tin respectively in order to protect it from corrosion. Every cyclist knows that so long as the nickel plating of his handlebars is intact there is very little tendency to tarnish, but that whenever the protective layer of nickel has been removed rust is not long in putting in an appearance. CHAPTER 11 HOW FIRE IS MADE In the foregoing chapter it has been said that the making of fire is one of the oldest achievements of the human race. So old is it that there is no trustworthy evidence of any tribe which was ignorant of fire and its uses. There is nothing impossible in the supposition that there may have been such a tribe, but we have no proof. It should be remembered that man must have been familiar with fire on the large scale even before he knew how to produce it himself. For we may presume that lightning and volcanic eruptions have always been features of life on the earth. Apart however from these exceptional manifestations the primeval man must one day have discovered how to produce fire with the ordinary means at his disposal. The reader can imagine the amazement and delight, perhaps the alarm, of the first human being who succeeded in making fire for himself, and of those who afterwards made an independent discovery of the same thing. How it was actually done we can only conjecture, but we shall probably get fairly near the true answer if we discover the methods of making fire which have been practiced among primitive tribes even in comparatively recent times. The ancients solved the problem of the original discovery of fire in a manner that has the merit of simplicity, even if it does not commend itself to the scientific mind of this twentieth century. They suppose that fire had been stolen from heaven by Prometheus, who carried it off in a hollow tube, while according to another account he obtained it by holding a rod close to the sun. A fairy story, some reader will say, and certainly one feels that the ancients, having looked at the difficulty, simply told a pretty tale and passed by on the other side. All the chemical methods of producing fire, those namely which are now employed, are comparatively new, and up till about a century ago only what we might call mechanical methods were available. Friction, for example, as everybody knows, produces heat, and one of the oldest ways of producing fire consisted in rubbing one stick against another until the wood inflamed. In some primitive tribes a stick was pushed backwards and forwards in a groove in a piece of wood. Sometimes the one stick was used as a drill, and was rapidly rotated in a hole cut out of a fixed block. Evidence of the extraordinary dexterity with which these fire sticks can be manipulated by savages is found in Captain Cook's description of the production of fire among some Australian tribes. He writes, To produce fire they take two pieces of dry soft wood, one a stick about eight to nine inches long, the other flat, the stick they shape into an obtuse point at one end, and pressing it upon the other turn it nimbly by holding it between both their hands as we do a chocolate mill, often shifting their hands up and then moving them down upon it to increase the pressure as much as possible. By this method they get fire in less than two minutes, and from the smallest spark they increase it with great speed and dexterity. How we should grumble nowadays if we had to work hard for two minutes before getting a light. The chances are that the savage would beat the civilized man at this game, and we moderns would probably require much more than two minutes to produce fire with these primitive appliances. Another elementary way of making fire is to strike flint and steel together, allowing the sparks which are thrown off to fall among some easily ignited material such as tinder. This latter substance consists of the element carbon in a finely divided condition, and is obtained by charring fragments of linen. The tinder, although it is not actually inflamed by a spark, glows with sufficient heat to ignite sulfur-tipped wooden splints, spunks as they used to be called. The flint and steel method of obtaining fire for domestic and other purposes was known to the Greeks and Romans, and was the one commonly in use in most countries up to the end of the 18th century. Even the inhabitants of such an out-of-the-way place as Tierra del Fuego have for centuries been accustomed to get fire in this way, only instead of steel they used pyrites, a mineral compound of iron and sulfur. It appears in fact that this mineral got its name from the use which was originally made of it in this way. Both flint and pyrites received the name of firestone. Another curious device which may be employed in making fire depends on the fact that if air is suddenly compressed, heat is produced. A simple instrument based on this principle, and known as a fire syringe, or pneumatic tinder box, is to be found in any list of scientific apparatus. It consists of a glass tube fitted at both ends with brass caps, through one of which moves a rod with a piston attached. If a piece of tinder is put in the bottom end of the tube, and the air in the tube is compressed by rapidly pushing down the piston, the tinder ignites. A similar apparatus, with a tube however of hard wood or ivory, has actually been found in use in Burma. Among the mechanical methods of producing fire we must not forget to reckon the lens or burning glass, by which the rays of the sun may be focused at a point. Combustible material, which will not ignite when merely exposed to the sun, will at once take fire if brought to the point at which the heat is thus concentrated. The burning lens was known to the Greeks, and is commonly used by the Chinese. Some readers may remember the story according to which Archimedes, during the siege of Syracuse, set the Roman fleet on fire with the aid of burning glasses. It is rather a tall story, not confirmed by the historians, but it serves at least to show that the use of the lens in the production of fire was familiar to the ancient world. All the foregoing methods of obtaining fire are physical or mechanical methods, and it was not until 1805 that an attempt was made to employ a chemical method for the purpose. In that year a certain Frenchman showed that splints of wood coated with sulfur and tipped with a mixture of chloride of potash and sugar would ignite when brought into contact with sulfuric acid, oil of vitriol, as it is commonly called. The chemical action which takes place spontaneously between the acid, the chloride of potash and the sugar is accompanied by the evolution of so much heat that ignition takes place, the sulfur first and then the wood bursting into flame. The first really practical Lucifer matches were made in England about 1827. They consisted of wooden splints or sticks of cardboard coated with sulfur, and tipped with a mixture of sulfide of antimony, chloride of potash and gum. They were ignited by being drawn between two folds of glass paper tightly pressed together, and a piece of this paper was supplied with each box. These matches required much pressure for ignition, and as they were liable to throw off sparks they required careful handling. A chilling per box of 84 was the price, and it is instructive to compare this figure with the cost nowadays, when we can get as many as 400 for a penny. The great modern development of the match industry began with the introduction of phosphorus. This element was discovered and its properties were known long before, but its application in the manufacture of matches began in the 30s of the last century. Phosphorus in the ordinary condition is a wax-like substance which melts at 111 degrees Fahrenheit and takes fire very readily just above its melting point. It is, in fact, this property of very ready ignition, which makes phosphorus valuable in the manufacture of matches. The slightest friction will cause it to catch fire, and hence if a splint of wood tipped with some mixture containing phosphorus is rubbed against a rough surface, for example sandpaper, it will ignite immediately. The ignition is much facilitated by mixing the phosphorus with an oxidizing agent, that is a substance which contributes to the combustion of the phosphorus by supplying it with oxygen. Solpeter, Chlorate of Potash, and Red Lead, which all contain a high percentage of oxygen, are the substances chiefly used for this purpose. In addition to these two essential constituents of a match tipping mixture, namely the phosphorus and the oxidizing agent, there are also binding ingredients, generally glue, coloring matters, such as ultramarine or vermilion, and gritty material such as powdered glass or fine sand, the object of which is to increase the susceptibility of the mixture to friction. In order that this splint might be sure to catch when the match was struck, it was at one time customary to dip it in sulfur before tipping with the phosphorus mixture. The combustion of the latter lasts only a moment. The sulfur, on the other hand, burns slowly and allows a little more time and opportunity for the wood to catch. Sulfur coated splints are out of date now and are met with only in cheap matches of continental manufacture. Instead of sulfur, paraffin is frequently used. It acts similarly as a go-between for the explosive mixture at the tip and the wooden splint. The use of ordinary phosphorus in matches has many disadvantages. Their dangers have been impressed on many of us by the dreadful story of Harriet and the matches, and their use has most certainly led to numerous fires. In addition to this objection, there is the fact that phosphorus is poisonous. Workers in match factories, who are exposed to the vapor of phosphorus, are liable to a painful and often incurable disease of the jawbone. In the earlier periods of the manufacture of phosphorus matches, there was considerable mortality from this cause, but it has been found that when close attention is paid to ventilation and cleanliness, the danger is exceedingly slight. The objections to the use of ordinary phosphorus can, however, be met in another way. Curiously enough, phosphorus is an element which exists in two forms, just as an actor may represent two different characters in the same play, so phosphorus is sometimes a pale yellow waxy solid, very poisonous and very easily inflamed. At other times it is a red powder, not poisonous, and much less readily ignited. Regarding superficially, these two substances are absolutely different, but they are really the same element in different garb, and chemists have found a way of changing yellow phosphorus into red, or red into yellow. This matter has already been discussed at length in Chapter 5. Soon after red phosphorus was discovered, it was suggested that the disadvantages of using the ordinary yellow phosphorus in matches might be avoided by substituting the red form, on account of its being non-poisonous and less readily inflamed. Attempts were accordingly made to tip matches with mixtures containing red phosphorus, but these were not very successful. A certain suite, however, ultimately proposed that, instead of putting the red phosphorus at the end of the match, it might be put on the surface on which the match was to be rubbed. This idea was worked out with complete success, and has led to what are now known as safety matches. These matches will not ignite with ordinary friction on a rough surface. They will strike only on the prepared surface on the box, consisting very generally of red phosphorus, gum, and powdered glass. In order still further to diminish risk of fire, the stems of safety matches are frequently soaked in some chemical, such as alum or magnesium sulfate, so that when the burning match is blown out, the wood immediately ceases to glow. A splint of ordinary dry wood, on the other hand, will continue to glow for a little after it has ceased to burn. This, the reader, can easily verify for himself. The number of matches manufactured nowadays is enormous. It is estimated that in England alone, 500 millions are turned out daily, and that for each million of matches about one pound of phosphorus is required. The 40 or 50 tons of phosphorus annually used in England for tipping matches are obtained from bones, which contain a large proportion of phosphate of lime. The high rate at which matches are turned out has become possible only by the introduction of ingenious labor-saving machinery, and no one who has not been through a match factory can realize how much is done in this direction. Another curious device for the production of fire was brought out by Doberreiner in 1823. The lamp known by his name is no longer used, but it was based on a very interesting principle, and therefore deserves consideration. We have seen that hydrogen is a combustible gas, and if we bring a light close to a nozzle from which hydrogen is escaping, it will take fire, that is, the hydrogen combines with the oxygen of the air at a high temperature, forming water vapor. At ordinary temperatures, on the other hand, hydrogen and oxygen are generally indifferent to each other. There is, however, one substance which is able to promote the union of hydrogen and oxygen even under these conditions, namely, spongy platinum. That is, platinum in a very finely divided condition. Platinum is usually a compact white metal, heavier than gold, but by special chemical treatment it can be obtained as a dark porous powder, and in this condition it is extremely active. If, instead of bringing a flame to the nozzle from which hydrogen is issuing, we hold a little spongy platinum in the gas, the metal begins to glow, and presently the hydrogen catches fire. A very pretty instance this of what is known as catalytic action, a term denoting the curious effect some substances have in promoting a chemical action without themselves being altered thereby. The platinum, for instance, which induces the hydrogen and oxygen to combine so readily, is found to be unchanged at the end, and this is the case also in other processes where finely divided platinum behaves as a catalytic agent. Its action has evidently something to do with the very large surface which is exposed by the porous, finely divided metal, but opinions differ as to the correct explanation. Some think that the gases condense in the surface of the platinum, and are thus brought into closer contact, the platinum surface acting as a sort of bird lime for the flying molecules. Others consider that the platinum first lays hold of the oxygen molecules to form a compound, and then meekly delivers them over to the hydrogen with the net result that water is formed, and the platinum is left as it was at the beginning with nothing to show for its labor. Although Doper Reiner's lamp has gone out in more senses than one, there are some modern devices based on the same principle. Many incandescent burners used to be provided with a little piece of platinum above the jet so that when the gas was turned on it would light without the help of a match. This arrangement has gone out of use now, largely because the platinum rapidly deteriorates in efficiency and finally loses its power of igniting the gas. Another piece of apparatus based on the same principle is a cigar lighter, which is sold at the present time. This consists of a small metal vessel provided with a cap. The vessel holds some volatile spirit, and attached to the cap there is a piece of very fine platinum wire. When this is held in the vapor of the spirit, while air has access to the vessel, the spirit combines with the oxygen under the influence of the platinum. Heat is produced, the platinum glows, and finally the spirit bursts into flame. Reference has just been made to the very high catalytic power of platinum when it is in a finely divided condition. Generally speaking, it may be said that finely divided matter behaves differently in many respects from compact matter of the same kind. It is for example a consequence of the law of gravitation that solid particles in the air soon fall to the ground, but if they are infinitesimally small, they may travel quite a long distance without coming to earth. Thus the beautiful sunsets seen in England in 1883 were attributed to the presence of very fine dust in the atmosphere carried all the way from a volcanic eruption on the other side of the globe. In regard also to combustion, finely divided substances have somewhat peculiar manners. Everybody would regard iron and lead as elements of the most staid and sober temperament, and yet it is possible to obtain these metals in a state of such fine division that when they are thrown out of any vessel into the air they take fire of their own accord. The finely divided substance has relatively a much greater surface than the compact substance, and the rate of rusting or oxidation is therefore so much increased that incandescence is observed. The process of combustion, which is slow under ordinary conditions, becomes very rapid. The phenomenon might be described as spontaneous combustion, but the reader should clearly understand that the chemical change which takes place when finely divided iron or lead take fire in air is exactly the same as when they rust. The only difference is that the latter change is spread over a much longer time. There are other cases in which combustion appears to take place without any obvious cause and to which the term spontaneous is applied. Stacks of hay occasionally take fire of their own accord, and heaps of cotton waste or rags impregnated with oil have been frequently found to exhibit a similar behavior. But however spontaneous the occurrence may seem to be, there is in each case a sufficient reason for the combustion. In the first case, the hay has been stacked while still moist, and in these circumstances fermentation sets in. Now fermentation is a chemical change of the constituents of the hay, promoted by the presence of minute organisms, and this change, like most chemical reactions, is accompanied by the evolution of heat. If the hay were lying out in the open, this heat would be dissipated at once, but in the inside of a stack it cannot escape so easily. It accumulates more and more as the fermentation process goes on, and ultimately the temperature rises so high that the hay takes fire. The explanation is different in the case of the oily rags or cotton waste. Many oils are readily oxidized by the oxygen of the air, and when such oils are spread over the extensive surface of rags or waste, the oxidation takes place very rapidly. The rags and waste being bad conductors, the heat generated in the oxidation is rapidly accumulated, and finally leads to the so-called spontaneous combustion. In both these cases, the chemical change involved is a slow combustion at the beginning and becomes rapid at the end, only because the heat generated in the process has been unable to escape. With rising temperature, a chemical change invariably becomes quicker and quicker. Hence, as the heat accumulates in the hay or the cotton waste, the chemical forces become more and more impetuous, and ultimately lead to a general conflagration. The affair, in fact, resembles the accumulation of money at compound interest. Haystacks are not the sort of thing that the ordinary individual can experiment with, but there is one very simple example of the way in which the heat effect accompanying a slow combustion may be accumulated. If iron filings are mixed with sawdust and a little water is added, then, after a few hours, steam will be seen to come off from the mixture. Now, the heat evolved during rusting cannot be detected in ordinary circumstances, but in this little experiment, the non-conducting sawdust allows the heat to accumulate until it is obvious to the senses. There was another kind of spontaneous combustion in which people believed at one time, namely, the spontaneous combustion of human beings. It was supposed that a living human body might be consumed by fire spontaneously generated in the internal organs. In the philosophical transactions of the Royal Society for 1744, for example, one finds a communication to the following effect. About seventeen years ago, three noblemen whose names for decency's sake I will not publish, drank by emulation strong liquors, and two of them died, scorched and suffocated by a flame forcing itself from the stomach. So widespread was the belief in the possible spontaneous combustion of human beings, that the great chemist Liebig thought it was worthwhile to deal with the question, and to record his view that, while a fat dead body charged with alcohol may perhaps burn, a living body in which the blood is circulating cannot take fire spontaneously. The story of this curious belief shows how easy it is, firstly, to make wrong observations, and secondly, even when the facts have been correctly ascertained, to rush at the first explanation which suggests itself. End of Chapter 11 Chapter 12 of the Romance of Modern Chemistry This LibriVox recording is in the public domain. The Romance of Modern Chemistry by James C. Philip. Chapter 12. Nature's Stores of Fuel. It is all very well to be able to make fire, but our achievements in this direction would be of little use if nature did not supply us liberally with combustible substances or fuels. So far as combination with oxygen and production of heat and light are concerned, a great many substances may be called fuels, but the name is generally restricted to those which contain the element carbon in some form, and which are obtained in large quantities on or under the surface of the earth. Some reference has already been made to these carbonaceous fuels, but much more remains to be said on this interesting topic. The process of combustion is perhaps the most fundamental chemical change with which we are acquainted, and to our modern world, with all its travel, industry, and social life, the production and maintenance of fire are almost as essential as air and water are to the human body. In some cases, the fuels supplied by nature are available directly for man's use, without any other than the simplest treatment. Wood and peat, for example, need only to be cut and dried before they are in condition for burning, while in the case of coal, the only necessary preliminary is the cutting and raising to the surface. These three fuels, wood, peat, and coal, represent three stages in the history of the vegetable world. Living wood, apart from the large amount of water which it contains, consists chiefly of cellulose, a compound of the three elements, carbon, hydrogen, and oxygen. If the wood dies and is allowed to lie in the soil where it has grown, a remarkable series of chemical changes sets in. In many cases, the fallen forests and jungles of the past have been submerged and then covered over with alluvial deposits of clay and sand, so that what was once a luxuriant vegetation on the surface is now buried many feet below. Now when wood or any other vegetable matter containing cellulose is kept below water or in a moist soil, the relative proportions of the carbon, hydrogen, and oxygen which made up the cellulose begin to change. Decomposition and fermentation set in, the hydrogen is gradually eliminated in the form of marsh gas, a combustible compound of carbon and hydrogen, and the oxygen in the form of carbon dioxide. Anyone who pokes a stick into a stagnant pool at the bottom of which vegetable matter is decomposing will observe bubbles of gas rising to the surface. These bubbles have been examined by chemists and are found actually to contain carbon dioxide and marsh gas. The result of these slow changes extending over a long period is that instead of cellulose there is left a carbonaceous mass containing a very much higher percentage of carbon than the original wood. If the decomposition has been going on for a very long time and at some depth below the surface, the product is a compact coal containing relatively small quantities of hydrogen and oxygen. Vegetable matter of more recent date will not have been carbonized to the same extent and will have reached the stage represented by brown coal or lignite. Pete again is vegetable matter, chiefly moss, which has been undergoing decomposition and carbonization for a very much shorter time and which being on the surface has not been subjected to the same pressure as coal and is therefore less compact. A few figures will show how the amounts of hydrogen and oxygen diminish regularly as we pass from wood to a hard coal like anthracite. To make the figures comparable, the amount of carbon is put as equal to 100 in each case. Wood, carbon 100, hydrogen 12, oxygen 83, peat carbon 100, hydrogen 9, oxygen 56, lignite carbon 100, hydrogen 8, oxygen 42, bituminous coal, carbon 100, hydrogen 6, oxygen 21, anthracite, carbon 100, hydrogen 3, oxygen 2. Corresponding to the gradual alteration in composition, there is a change also in the way these fuels behave when they are burned. For a brightly blazing fire there is nothing like wood, the reason being that, when it is heated, quantities of inflammable gas are given off, hence wood catches fire much more easily than the other solid fuels, and when it has ignited it burns with a larger amount of flame, for flame is simply burning gas. The inflammable vapors given off from heated wood consist to a large extent of hydrocarbons, that is compounds of carbon and hydrogen. Wood therefore, which has undergone an age-long decay and which has in the process lost the greater part of its hydrogen, will be able to yield little or no inflammable gas when heated. Take anthracite for example, a species of coal which is largely mined in whales. It contains a very high proportion of carbon, and very little hydrogen and oxygen. When heated it gives off practically no inflammable vapor, and this makes it very difficult to ignite. For the same reason, even when it has been successfully ignited, it burns with very little flame or smoke. These characteristics make anthracite unsuitable for domestic use. It can be kept burning, only in a strong draft, and is accordingly chiefly employed in boiler furnaces. The solid fuels which have been considered in the foregoing paragraphs are all directly supplied by nature, and are to be had more or less for the gathering. In this little island we pick up over two hundred million tons of coal every year, and we may well ask how long this will continue to be possible. Shall we be able to draw upon nature's stores for an indefinite period? Is it time to consider what we should do if the coal supply of the world ran out? Before attempting to answer these questions we must recall the fact that nature supplies us also with liquid fuel, yielding it to us with a very slight expenditure of energy on our part. It has long been known that in certain countries there were indications of the presence of oil in the Earth's crust, but it was only forty or fifty years ago that a systematic search was made. About that time a certain American engineer drove an iron pipe from the surface down through the rock and was surprised to find that when the pipe had gone down about thirty-four feet oil rose nearly to the top. He had in fact struck oil. This discovery, of course, led to other attempts to tap the subterranean oil stores, with the result that today whole districts in the United States and Russia, the two countries which supply by far, the greater part of the world's liquid fuel, are given over to oil bearing. Sometimes the oil has to be pumped up like water from a well, but in other cases the oil in the internal reservoirs is under pressure, and so soon as an opening is provided it spouts out with great force. It might be thought an easy matter to collect the oil which comes up these wells, but it is frequently very difficult, especially when the boring has just been made, and the oil is forced out under pressure. A certain well in Baku, the Russian oil-bearing district, tapped in 1886, began to spout with such vehemence that the whole surrounding country was deluged. For a time nothing could be done to stop the outflow, and many thousand tons of oil were lost. The great pressure which sometimes exists in the subterranean reservoirs was well shown by another fountain, which burst out a few months later and rose to a height of 350 feet. The escape in this case was so great that it formed an extensive petroleum lake and overflowed into the Caspian Sea. The crude petroleum obtained from the American or Russian oil wells must be subjected to chemical treatment before it is ready for the market. It is distilled, and the volatile portions of the oil are thus separated from the heavier portions. The reader would be quite surprised to find what a number of distinct products can thus be separated from natural petroleum by the simple process of distillation. The most volatile portions of the petroleum yield naphtha and petrol, the latter substance now largely in demand in these days of motorcars. The petroleum, which distills over a somewhat higher temperature, is used for illuminating purposes, and it is in this form of lamp oil that the bulk of the American petroleum ultimately comes to the market. After the petroleum suitable for lighting has been distilled off, there is next obtained a heavy oily portion which may be used as a fuel or for lubricating purposes. While, last of all, there is a residue from which may be extracted such useful substances as Vaseline and paraffin wax, the latter employed very largely in the manufacture of candles. Closely allied to the petroleum of Pennsylvania or Baku is so-called natural gas, which in fact frequently makes its appearance along with the petroleum. From the chemical point of view it is extremely similar to petroleum, consisting largely of hydrocarbons. These, however, are still more volatile than the hydrocarbons present in petroleum, and are therefore not found in a liquid condition. In the United States enormous quantities of natural gas are obtained, so much so that in many districts the manufacture of coal gas for lighting and heating purposes is quite superfluous. We do not, however, require to travel to the United States to find natural gas. There is actually a supply of it in England, although not on a large scale. It was discovered in 1893 as a borehole was being sunk at Heathfield in Sussex for the purpose of obtaining water. When the boring had reached a depth of over two hundred feet, no water had been got, but an inflammable gas issued from the borehole. Some three years later another boring was made in the same neighborhood, and at a depth of three hundred twelve feet gas was met with inconsiderable quantity. The supply was under great pressure, for when ignited it gave a flame sixteen feet high. Obviously one of nature's gasometers had been tapped, and since then this natural gas has been used regularly in the immediate neighborhood for lighting and heating purposes to the extent of about one thousand cubic feet per day. The gas consists almost exclusively of methane or marsh gas, the simplest compound of carbon and hydrogen. The origin of solid fuel has already been discussed and is fairly evident, but it is much more difficult to specify the source of all the petroleum which has been obtained so abundantly during the last forty years. Some authorities assign it to an inorganic origin and suppose that the hydrocarbons of which petroleum consists have been produced by the action of water on carbides. These substances are compounds of metals with carbon and are decomposed by water in such a way that the carbon of the carbide forms a new compound, a hydrocarbon, with the hydrogen in the water. Many readers doubtless are familiar with one carbide which is in common use, namely calcium carbide. This substance on contact with water generates acetylene, a hydrocarbon which has many advantages as an illuminating gas. Bicycle lamps, for example, are made in which acetylene is burned, the gas being prepared in the lamp by allowing water to drop on lumps of calcium carbide. So it may be supposed that water, penetrating through fissures in the crust of the earth, has acted on subterranean masses of carbides with the production of petroleum. Another explanation which on the whole has more support regards petroleum as derived from an organic source, animal rather than vegetable. According to this view, the animal remains of past ages have undergone a change whereby all nitrogenous and other matters except the fats were removed. Subsequently these fats being subjected to distillation by the combined action of heat and pressure, or of pressure alone, yielded the petroleum which we get today. In connection with all these fuel supplies, coal, petroleum, and natural gas, a question of the utmost importance arises to which reference has already been made. We are using up these fuels at an enormous rate and there is no reason to suppose that the stores are being replenished at anything like the rate at which they are being consumed. In this respect, we are, in fact, living on our capital, and moreover, we do not know what is its amount. Estimates have indeed been made of the probable duration of our coal supplies, and royal commissions have dealt with the subject. The authorities are divided, but on the whole, it seems we may reckon on our coal-lasting for the matter of five hundred years or thereabouts, even when allowance is made for the probable increase in the consumption. It must be remembered also for our comfort that new coal fields are occasionally discovered, as was the case recently in the county of Kent. The Kentish Collarys mean a substantial addition to our coal capital, and they may outlast the older ones in the north so that someday it may be necessary to carry coals even to Newcastle. Estimates like the forgoing are based on the actual inspection of the seams of coal, which have been discovered, their thickness and extent, but who will be bold enough to say how long the subterranean reservoirs will keep us supplied with oil and gas? Human eyes have never seen, nor ever will see, what these hidden reservoirs contain. As a matter of fact, signs are not wanting that the stock of petroleum and natural gas is beginning to run short. The output of oil it is true is increasing, but this is due not to any natural increase given by the existing wells, but to an increase in their number. The oil-yielding wells are very short-lived, and as new ones are continually being opened the available oil fields will soon be entirely covered. We must not forget to include in our fuel capital the vast stock of timber on the surface of the globe and the enormous quantities also of peat found in many countries. How far may we regard these as reliable sources of fuel? Wood is, of course, burned in many countries where there is a large extent of forest, but it would be absolute madness to use up all our timber in this way. It is the vegetation of the world which, as we shall see, is the necessary counterpart of animal life, and gradually to cut down all the forest on the face of the globe would be a suicidal policy. Besides, there is a large demand for timber for architectural and constructive purposes, and even as matters are at present, the forest-covered land of North America and Europe is being laid bare at a rapidly increasing rate. Trees do not grow in a hurry, and once the primeval forests are cut down, the keeping up of a supply of timber by planting trees is hardly feasible. And what about peat? In Ireland alone there are over one million acres of peat bogs, and it is estimated that an acre of a bog of an average depth of even eight feet would yield about 1,250 tons of dried peat. In Russia there are about one hundred million acres of bogs, so that altogether the fuel stored up in the form of peat must be very considerable. What militates against the use of peat as a fuel is the very large amount of moisture which it holds. When freshly dug it may contain as much as eighty to ninety percent of water, and the problem is how best to get rid of this and obtain the fiber of the peat in a condition fit for burning. The usual method of exposing the wet peat to air until it is dry requires much time and space. It is further a very bulky fuel, and probably owing to these causes the output of peat has never been much greater than sufficed for local demands. In recent years, however, great advances have been made in the utilization of peat. Methods have been devised of squeezing out the water by mechanical means, and compressing the combustible fibers into briquettes. These are not only more compact than the air-dried peat, but also have a higher heating power. It is conceivable that in the distant future of the world's history there may come a time when, apart from timber, the natural stores of fuel, coal, peat, petroleum, and natural gas are completely or almost exhausted. What then? Necessity is the mother of invention, and we may be sure that before things shall have come to such a pass the ingenuity of man will discover a way out of the difficulty. As a matter of fact there are already indications that alcohol is to be the fuel of the future. In the form of methylated spirit it is used to a very small extent at the present day, but it looks as if it were to survive as a fuel when all others have gone. When every oil well is dry, when a piece of coal can be seen only in a museum, and when the peat bogs are no more, then alcohol, if no better substance has been discovered in the meantime, will come to its own as a fuel. All very nice, the reader may say, but how is the alcohol to be produced in the large quantities which will be necessary? By the simple and time-honored operations of growing potatoes, wheat, rice, beetroot, and similar substances, from these alcohol may be obtained by fermentation, as will be shown in a future chapter. To those who doubt whether alcohol could be used as fuel, say in driving an engine, the best reply is that the thing has been done. Experiments have shown that alcohol can be employed with satisfactory results, in place of petrol, and it has certain advantages over the latter fuel, such as greater safety in handling. At present, while the natural fuel is so abundant, the price of alcohol would prohibit its general use as a fuel, but it is at least a comfort to know that we have something promising in reserve. In the foregoing chapter we have discussed the various natural fuels which are available for use without any more than a slight preliminary treatment. There are however other substances commonly classed as fuels, to which no reference has yet been made, for example charcoal, coke, and coal gas. Although these substances are to be regarded as fuels, they do not belong to the same category as wood, peat, coal, or petroleum. Unlike the latter fuels, they are not obtained directly from nature, they are produced secondarily from the natural fuels by special treatment. Generally speaking, the secondary fuels, charcoal, coke, and coal gas, are obtained by the process of destructive distillation. This operation sounds rather alarming, but it is one which most boys have performed on a small scale, and the principle of it is comparatively simple. In ordinary distillation, where a liquid is converted into a vapor, and this vapor is condensed by passing through a cooled tube, any products obtained in the distillate were already present in the original liquid. The products however of a dry or destructive distillation are not present as such in the original substance, they are only produced by its chemical decomposition. The little experiment in destructive distillation which many readers have probably made consists in filling the bowl of a clay pipe with little bits of coal, blocking up the mouth of the bowl with clay, and then heating it in a fire. When this is done a gas will be found issuing from the end of the pipe stem, which will burn with a luminous flame. This gas is essentially the same as coal gas, and the method by which it has been obtained is destructive distillation, the process by which also charcoal, coke, and coal gas are obtained from the natural fuels. It is of course necessary that the natural fuels which are undergoing destructive distillation should be excluded from contact with air during the process, otherwise combustion would take place. What occurs then is that the carbon compounds in the natural fuel are chemically decomposed by the action of heat, the atoms of carbon, hydrogen, and oxygen are rearranged, and new products are formed which did not exist as such in the original fuel. The chemical decomposition which takes place in the dry distillation of wood or coal is exceedingly complex, and the number of products that can ultimately be obtained is very large indeed. But although this is so, the first crude products are only four in number, namely gas, watery liquid, tar, and residue. These differing in character according as wood or coal is being subjected to distillation. In the case of wood the process is sometimes carried out by stacking the wood, burning part of it, and using the heat so obtained to decompose the rest. This is a wasteful method so far as most of the products are concerned, for no provision is made to catch those which are volatile. The residue is known as wood charcoal, and consists very largely of carbon with small quantities of hydrogen, oxygen, and nitrogen, and a little ash or mineral matter. Such a primitive method of converting wood into charcoal is frequently replaced by a more scientific procedure in which the wood is heated in closed vessels or retorts, and provision is made for collecting or condensing any volatile matter. In considering the use of wood as a fuel, we have seen that its ready combustibility is due to its giving off inflammable vapor. It is therefore not surprising to find that when wood is heated out of contact with air, a quantity of gas is obtained. The main constituents of this gas are carbon dioxide, carbon monoxide, and marsh gas. The two latter are combustible, and although the gas has not much illuminating value, it may be used to heat the retorts. This is a simple example of the way in which the byproducts of a manufacturing operation may be utilized so as to diminish the cost of production. The volatile matter obtained by subjecting wood to dry distillation not only yields a combustible gas, but condenses partly to a tar and partly to a watery liquid. The latter yields acetic acid, the acid of vinegar, and wood spirit. This consists largely of methyl alcohol, and is added to rectified spirits of wine in order to produce methylated spirit. The object of thus denaturing ordinary alcohol is to provide a spirit which may be employed for industrial purposes and which at the same time is not drinkable. Leather the latter condition is fulfilled is doubtful, for it is said that such methylated spirit is consumed as a beverage to the injury of the revenue. Accordingly the bulk of methylated spirit now sold has a small admixture of mineral naphtha or light petroleum to render the taste more objectionable. When coal is subjected to destructive distillation, the effects are in general the same as those obtained with wood, but the character of the products differs in some important particulars. The gas which is given off on heating coal is of much more use for illuminating purposes, and is in fact, after purification, nothing else than the common coal gas used throughout our towns. This consists largely of hydrogen and marsh gas, together with some carbon monoxide and small quantities of heavy hydrocarbons which are responsible for the illuminating power. In the crude gas which comes from the retorts there are several undesirable constituents which must be removed before the gas can be supplied to the public. In addition to carbon, hydrogen and oxygen, coal contains small quantities of the elements nitrogen and sulfur, and these appear to some extent in the coal gas in the form of ammonia, a compound of nitrogen and hydrogen, and sulfur-rated hydrogen, a compound of sulfur and hydrogen. The ammonia collects mostly in the watery liquid, which accordingly becomes alkaline, in contrast with the acid watery liquid obtained in the destructive distillation of wood. The last traces of ammonia are removed from coal gas by scrubbers, towers packed with coke or brushwood over which a constant stream of water is trickling. The current of gas goes in the opposite direction, and as ammonia is very soluble in water it is all removed before the gas issues at the top. The sulfur-rated hydrogen resulting from the above process, if it were allowed to remain in the coal gas, would unburning produce sulfur dioxide, and this in anything more than a small quantity would be a very objectionable addition to the atmosphere. The gas is accordingly passed through a series of purifiers containing slaked lime and iron oxide. The reader is already familiar with the first of these as being an alkaline substance in virtue of which it readily absorbs anything of an acid nature which passes through the purifiers. Now both carbon dioxide, a little of which is sure to be present in the gas, and sulfur-rated hydrogen, are substances of an acid nature, and one would therefore expect them to be fixed by the lime. Sulfur-rated hydrogen, however, is not absorbed by lime when it is mixed with carbon dioxide, so in order to ensure the complete removal of the former, the coal gas must also be passed over iron oxide. This substance, generally in the form of Irish bog ore, is at first very active in holding back the sulfur-rated hydrogen, but as it absorbs more and more it gets exhausted, being gradually converted into sulfide of iron. A course of fresh air, however, is found to have a beneficial effect on its activity, hence the exhausted or spent oxide of iron is taken out of the purifiers and spread on the ground for a time. During this rescue, the sulfide of iron enters into a chemical reaction with the oxygen of the air, with the result that the element sulfur is liberated and iron oxide is regenerated. The material is then again capable of actively absorbing sulfur-rated hydrogen, and is therefore returned to the purifiers until exhausted a second time. This process of revivifying the iron oxide may be repeated a good many times until the material has picked up about half its own weight of sulfur. It will then have lost its effectiveness as a purifier of coal gas, and is accordingly sold to the sulfuric acid manufacturer. As the proportion of sulfur in the original coal is not more than one or two percent, this is a very instructive instance of the value of gathering up the fragments. Even the very impurities in coal gas are made to contribute to the cost of its production. This remark covers also the ammonia which is found in crude coal gas. As has been stated already, the destructive distillation of coal converts some of the nitrogen which it contains into ammonia, and this has turned out to be a very valuable byproduct of coal gas manufacture. From the watery liquid, in which it mostly collects, the ammonia is driven out by a current of steam. It is then passed into sulfuric acid, forming sulfate of ammonia, and the crystals of this substance are fished out from time to time. On the average, a ton of coal yields twenty pounds of ammonium sulfate. The latter substance fetches a good price as a manure, about ten pounds per ton, and it makes, therefore, a very substantial contribution to the expense of producing coal gas. Other byproducts obtained in the manufacture of coal gas are tar and coke. From coal tar, so many interesting and useful substances are prepared that a special chapter must be devoted to their consideration, where we shall see that even from this uninviting and unpromising material many beautiful products may be extracted. Coke is the residue in the retorts after all gas, tar, and ammonia have been driven off. The mineral matter or ash in the original coal is not volatile, so that it remains in the coke, which contains about ninety percent of carbon and small quantities of hydrogen, oxygen, nitrogen, and sulfur. Gas coke is used as a fuel, although the reader will understand that since the volatile combustible gases have been removed, it is difficult to burn. In domestic use it must be mixed with coal, but in furnaces where there is a powerful draft it is very satisfactory by itself and gives off no smoke. Large quantities of gas coke are employed in lime and cement burning. Such are the chief products of the destructive distillation of coal in the manufacture of coal gas. As a fuel, coal gas, if not particularly cheap, is comparatively clean and certainly very convenient. Hitherto it has been used principally for lighting purposes, and we can best appreciate its convenience in that respect from the standpoint of our great-great grandfathers. What seemed to them the marvel about coal gas was that no wick was required as in the lamps and candles with which they were familiar, so marvelous did they find it, that it was regarded as rather uncanny and the lighting of gas lamps was at first thought to be a perilous undertaking. Nowadays electricity is a competitor with gas as an illuminant, but the latter is being increasingly employed as a fuel and may be said to hold its own. In England there is a decided preference for the old-fashioned cheery open coal fire, with all its accompaniments of ash, soot, and smoke. There is little doubt, however, that the gas fire or stove is gradually coming into favor on account both of its cleanliness and its convenience. In estimating the chances that coal gas will hold its own with electricity as a lighting and heating agent, the very important part played by the byproducts of the gasworks must not be forgotten. Here, as in so many cases, it is the byproducts which settle the question whether a given manufacturer will pay or not. Coke, which has been referred to as a byproduct in the manufacture of coal gas, is prepared in large quantities for its own sake. It is extensively used in metallurgical operations, that is, in the production of metals from their ores. The coke required for this purpose must be specially dense, and as free as possible from sulfur and ash. Gas coke does not adequately fulfill these conditions, and in Great Britain, as much as 12 million tons of coal are destructively distilled every year in special ovens in order to get coke suitable for metallurgical purposes. This is frequently described as oven coke. The use of coke in metallurgical operations is readily understood. In iron smelting, for instance, the ore consists mainly of iron oxide, and when this is heated in the blast furnace with coke, the oxygen prefers to be in partnership with the carbon rather than with the iron, so that the latter is liberated and is obtained from the blast furnace as molten metal. Coal is not the only naturally occurring substance that is subjected to destructive distillation. In Scotland, there is a very considerable industry founded on the winning of fuel oil by the destructive distillation of shale. This is a carbonaceous substance which differs from coal in that it contains a very much larger proportion, sometimes as much as 70% of mineral matter or ash. By the destructive distillation of a ton of shale, about 30 gallons of crude oil can be obtained, which by further treatment is made to yield paraffin oil, lubricating oil, and paraffin wax. Attempts have been made also to subject peat to destructive distillation, but these have generally ended in failure. The difficulties, however, are now being overcome, and quite recently, a promising development has taken place in South Germany, where a plant has been put down beside an extensive peat bog and is turning out tar, paraffin, ammonia, and coke. If this process should be found commercially sound, we may yet see the peat bogs of Ireland being converted into productive ground, while at the same time a new industry will be available for the people. Leaving out of account for the moment the tar, ammonia, and sulfur obtained as byproducts in the destructive distillation of coal, we may regard the net result of the operation as giving us for fuel, coke and coal gas, instead of coal. Now whereas coal is an exceedingly dirty fuel, both coke and coal gas are clean fuels, burning without smoke. Bearing this in mind, we might ask the question whether it would not be possible to modify the destructive distillation of coal in such a way as to obtain a coke-like product, which would, however, still retain enough gas-producing material to make it readily inflammable, and which would at the same time be a smokeless fuel. Experiments made during the last four or five years have shown that this is possible when the temperatures of the retorts, instead of being raised to 1600 or 1700 degrees Fahrenheit, as is usual in gasworks, is kept about 800 degrees. The quantity of gas given off during the heating is not so large, but the half-cooked coal left in the retorts, containing as it does a certain proportion of volatile matter, is a smokeless, easily ignited fuel. This product is now on the market, under the name of coalite. The convenience of gaseous fuel for many purposes has stimulated efforts on the part of chemists to convert carbon entirely into combustible gaseous products. It was discovered long ago that when a current of steam is passed through red-hot carbon, an inflammable gas is produced. The chemical reaction involved is very simple. The water is decomposed by the red-hot carbon, and the latter appropriates the oxygen, forming carbon monoxide. The hydrogen of the water is left in the free state, and issues from the furnace along with the carbon monoxide. Since both these gases are combustible, the reader will perceive that the simple passage of steam over red-hot carbon means the conversion of a solid into a gaseous fuel. The product is called water gas, a term which must be carefully distinguished from water vapor. The latter is, of course, not combustible. Simple as the foregoing process may seem to be on paper, many difficulties were experienced in making it work on a large scale. The decomposition of steam by carbonaceous fuel requires a large amount of heat, and it was soon found impracticable to supply this by external heating of the retorts, containing the coke or coal. The device was accordingly adopted of heating the fuel internally by its partial combustion. Air is blown into the retort containing the ignited fuel, which is raised to incandescence by the heat given out in its own combustion. Then, as soon as this condition is attained, the air blast is shut off and steam is blown into the retort. The formation of water gas at once begins, and is continued until the temperature falls below a certain limit, when the steam blast is shut off and air is once again blown in. It must be understood that the two parts of this operation, the air blow and the steam blow, are complementary to each other, the heat evolved in the first stage supplying the energy required in the second stage. Water gas, the mixture of hydrogen and carbon monoxide, burns with a non-luminous flame, and if it is to be used for illuminating purposes, must either be carbureted, that is provided with hydrocarbons to render its flame luminous, or used with incandescent mantles. In America, water gas is frequently used in place of coal gas. In this country it is never supplied alone for lighting purposes, but is often mixed with coal gas. One objection to its use is the excessively poisonous nature of carbon monoxide, referred to in a previous chapter. On this ground it is considered unsafe to distribute to the public coal gas which contains more than about 16% of carbon monoxide. Has the reader ever realized what an enormous amount of energy is stored up in a pound of coal, or a cubic foot of coal gas? When the fuel is burned, this latent energy becomes manifest in the form of heat, and it is actually found that the heat given out when one pound of coal is burned would be sufficient to raise the temperature of seven tons of water, one degree Fahrenheit, say from 60 to 61 degrees. Now heat is convertible into other forms of energy and may, for example, be transformed into mechanical energy. Thus it has been shown that the quantity of heat which would raise the temperature of one pound of water from 60 to 61 degrees would, if converted into mechanical energy, be able to raise a weight of 772 pounds through one foot, or what is the same thing, a weight of one pound through 772 feet. By means of this mechanical equivalent of heat, as it has been called, someone has calculated that if the energy latent in one pound of coal were converted without loss into mechanical energy, it would do as much as five or six horses working for an hour. But one must admit that this is quite an ideal process. Even in the best engines we can employ to convert the latent energy of fuel into mechanical energy, only a portion of the heat reappears in the form of useful work. In this respect, the internal combustion engine, such as is used on a motor car, is much superior to the steam engine by which we convert only about 10% of the heat value of the coal into power. The power of different fuels to give out heat when burned, the calorific power as it is called, varies very considerably. The heat given out in the combustion of one pound of coal, for example, is nearly twice as great as that liberated when one pound of dried wood is burned. The calorific power of petroleum, on the other hand, is nearly 30% greater than that of coal. And selecting a fuel, however, many other factors have to be borne in mind besides the calorific power. The prudent engineer has to consider the bulk of the fuel, its cost, its handling, and the readiness with which it may be fed into the engine. It is the total effect of all these factors on the balance sheet that is the important thing from the commercial point of view. From what source has all the energy lay in in naturally occurring fuels been derived? George Stevenson, when he was asked what drove his locomotive, replied that it was bottled up sunshine and he was not far wrong. The reader will ask how the bottling process was carried out, but that is another story, which must be postponed to a later chapter.