 Reagents used in assaying This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to find out how to volunteer, please contact LibriVox.org. From a textbook of assaying for the use of those connected with minds by C and J. J. Beringer published in 1904, Chapter 6. Reagents. Acids etc. Acetic acid C2H4O2 specific gravity 1.044 containing 33% real acid. An organic acid forming a class of salts, acidates, which are for the most part soluble in water and which are on the ignition leave the oxide or carbonate of the metal. It is almost always used in those cases where mineral acids are objectionable. To convert, for example, a solution of a substance in hydrochloric acid into a solution of the same in acetic acid, alkali should be added in excess and then acetic acid. Many compounds are insoluble in acetic acid which are soluble in mineral acids such as ferric phosphate, ferric arsenate, zinc sulfide, zinc sulfide, calcium oxalate etc. so that the use of acetic acid is valuable in some separations. The commercial acid is strong enough for most purposes and is used without dilution. Aquaridia is a mixture of one part by measure of nitric acid and three parts of hydrochloric acid. The acids react forming what is practically a solution of chlorine. The mixture is best made when wanted and is chiefly used for the solution of gold and platinum and for opening up sulfides. When solutions in Aquaridia are evaporated, chlorides are left. Bromine, BR, specific gravity 3.0. Practically pure bromine. It is a heavy reddish brown liquid and very volatile. It boils at 60 degrees centigrade and consequently must be kept in a cool place. It gives off brown irritating vapours which render its use very objectionable. Generally it answers the same purpose as Aquaridia and is employed where the addition of nitric acid to a solution has to be specially avoided. It is also used for dissolving metals only from ores which contain metallic oxides not desired in the solution. Bromine water is simply bromine shaken up with water till no more is dissolved. Carbonic acid, CO2, a heavy gas somewhat soluble in water. It is mainly used for providing an atmosphere in which substances may be dissolved, titrated etc. without fear of oxidation. It is also used in titrating arsenic assays with iodine when a feeble acid is required to prevent the absorption of iodine by the alkaline carbonate. It is prepared when wanted in solution by adding a gram or so of bicarbonate of soda and then as much acid as will decompose as bicarbonate mentioned. When a quantity of the gas is wanted it is prepared in an apparatus like that used for sulfurated hydrogen by acting on fragments of marble or limestone with dilute hydrochloric acid. Citric acid C6H8O7.H2O is an organic acid which occurs in colourless crystals soluble in less than their weight of water. The solution must be freshly prepared as it gets mouldy when kept. It forms a comparatively unimportant class of salts, citrates. It is used in the determination of phosphoric acid, chiefly for the purpose of preventing the precipitation of phosphates of iron and alumina by ammonia and in a few similar cases. The commercial crystals are used. They should be free from sulfuric acid and leave no ash on ignition. Hydrochloric acid HCl in water. Specific gravity 1.16. It contains 32% of hydrogen chloride. It is sometimes called muriatic acid and when impure, spirit of salt. The acid solution should be colourless and free from arsenic, iron and sulfuric acid. It forms an important family of salts, the chlorides. It is the best acid for dissolving metallic oxides and carbonates and is always used by the assayer when oxidising agents are to be avoided. The acid is used without dilution when no directions are expressly given to dilute it. It has no action on the following metals, gold, platinum, arsenic and mercury. It very slightly attacks antimony, bismuth, lead, silver and copper. Tin is more soluble in it but with difficulty whilst iron, zinc, nickel, cobalt, cadmium and aluminium easily dissolve with evolution of hydrogen and the formation of the lower chloride if the metal forms more than one class of salts. All the metallic oxides except a few of the native and rarer oxides are dissolved by it with the formation of chlorides of the metal and water. Dilute hydrochloric acid is made by diluting the strong acid with an equal volume of water. This is used for dissolving precipitates obtained in the general course of analysis and the more easily soluble metals. Hydrochloric acid, a solution in water may be purchased in gutter, percher or lead bottles. It is of variable strength and doubtful purity. It must always be examined quantitatively for the residue left on evaporation. It is used occasionally for the examination of silicates. It attacks silica forming fluoride of silicon which is a gas. When the introduction of another base will not interfere with the assay the substance may be mixed in the platinum dish with fluoride of ammonium or of potassium or of calcium and hydrochloric acid instead of treating it with the commercial acid. It is only required in special work. The fumes and acid are dangerous and of course glass or porcelain vessels cannot be used with it. Iodine, I. This can be obtained in commerce quite pure and is often used for standardizing. It is very slightly soluble in water but readily dissolves in potassium iodide solution. It closely resembles chlorine and bromine in its properties and can be used for dissolving metals without at the same time attacking any oxide which may be present. It is chiefly used as an oxidizing agent in volumetric work being sharp in its reactions and easily detected in minute quantities. It cannot be used in alkaline solutions since it reacts with the hydrates and even with the carbonates to form iodides and iodates. Iodine is soluble in alcohol. Nitric acid HNO3 specific gravity 1.42 boiling point 121 degrees centigrade contains 70% by weight of hydrogen nitrate. It is convenient to remember that one cc of this contains one gram of real acid. It combines the properties of an acid and of an oxidizing agent. One cc contains 0.76 gram of oxygen most of which is very loosely held and easily given up to metals and other oxidizable substances. Consequently it will dissolve many metals etc upon which hydrochloric acid has no action. All sulfides that of mercury accepted are attacked by it and for the most part rendered soluble. It has no action on gold or platinum and very little on aluminium. The strong acid at the ordinary temperature does not act on iron or tin and in most cases it acts better when diluted. Some nitrates being insoluble in nitric acid form a protecting coat to the metal which hinders further action. Where the strong acid does act the action is very violent so that generally it is better to use the dilute acid. When iron has been immersed in strong nitric acid it not only remains unacted on but assumes a passive state so that if after being wiped it is then placed in the dilute acid it will not dissolve. Tin and antimony are converted into insoluble oxides while other metals with the exception of those already mentioned dissolve as nitrates. During the solution of the metal red fumes are given off which mainly consist of nitrogen per oxide. The solution is often coloured brown or green because of dissolved oxides of nitrogen which must be got rid of by boiling. Generally some ammonium nitrate is formed especially in the cases of zinc, iron and tin when these are acted on by cold dilute acid. Sulphur, phosphorus and arsenic are converted into sulphuric phosphoric and arsenic acids respectively when boiled with the strong acid. Dilute nitric acid. Dilute one volume of the strong acid with two of water. Oxalic acid. H2C2O4.2H2O. This is an organic acid in colourless crystals. It forms a family of salts the oxalates. It is used in standardising being a crystallised and permanent acid. It can be readily weighed. It is also used in separations many of the oxalates being insoluble. For general use make a 10% solution. Use the commercially pure acid. On ignition the acid should leave no residue. Sulphurated hydrogen. Hydro-sulfuric acid. SH2. A gas largely used in assaying since by its action it allows of the metals being conveniently classed into groups. It is soluble in water. This liquid dissolving at the ordinary temperature about three times its volume of the gas. The solution is only useful for testing. In separations a current of the gas must always be used. It is best prepared in an apparatus like that shown in figure 32 by acting on ferrous sulphide with dilute hydrochloric acid. When iron has to be subsequently determined in the assay solution the gas should be washed by bubbling it through water in the smaller bottle but for most purposes washing can be dispensed with. The gas is very objectionable and operations with it must be carried out in a cupboard with a good draft. When the precipitation has been completed the apparatus should always be washed out. The effect of this acid on solutions of the metals is to form sulphides. All the metallic sulphides are insoluble in water but some are soluble in alkaline and some acid solutions. If sulphurated hydrogen is passed through an acid solution containing the metals till no further precipitation takes place a precipitate will be formed containing sulphides insoluble in the acid. On filtering adding ammonia to render the filtrate alkaline and again passing the gas a further precipitate will be obtained consisting of sulphides insoluble in an alkaline solution but not precipitable in an acid one. The filtrate may also contain sulphides not precipitable in an acid solution which are soluble in an alkaline one. These will be thrown down on neutralizing. Again the metals precipitated in the acid solution form sulphides which may be divided into groups. The one consisting of those which are soluble and the other of those which are not soluble in alkalis. This classification is shown in the following summary. 1. Precipitable in an acid solution. A. Soluble in alkalis. Sulfides of arsenic and timony, tin, gold, platinum, iridium, molybdenum, tellurium and selenium. B. Insoluble in alkalis. Sulfides of silver, lead, mercury, bismuth, copper, cadmium, palladium, rhodium, osmium and ruthenium. 2. Not precipitated in an acid solution but thrown down in an alkaline one. Sulfides of manganese, zinc, iron, nickel, copper, indium, tellurium and gallium. These can again be divided into those which are dissolved by dilute acids and those which are not. 3. Not precipitated in an acid or alkaline solution but thrown down on neutralizing the latter. Sulfides of vanadium and tungsten. Sulfurated hydrogen is a strong reducing agent. Ferric salts are thereby quickly reduced to ferrous. In hot solutions, nitric acid is decomposed. These changes are marked by a precipitation of sulfur and the student must be careful to pass the gas sufficiently long and not be too hasty in concluding that no sulfide will form because it does not at once make its appearance. The best indication that it has been passed long enough is the smell of the gas in the solution after shaking. The reagent used may be regarded as a saturated solution of sulfur dioxide in water. It may be purchased and keeps for a long time. It may be made by heating copper with sulfuric acid and passing the gas formed into water. The heat should be withdrawn when the gas is coming off freely. It is used as a reducing agent and should not be diluted. Sulfuric acid H2SO4. Specific gravity 1.84 containing 96% of real acid H2SO4. This acid forms insoluble sulfates with salts of lead, strontium and barium. It has a high boiling point, 290 degrees centigrade and when evaporated with salts of the more volatile acids converts them into sulfates. When nitrates or chlorides are objectionable in a solution evaporation with sulfuric acid removes them. In working with this acid caution is necessary since on mixing with water great heat is evolved and if either the acid or water has been previously heated a serious accident may result. In diluting the acid it should be poured into cold water. Glass vessels containing boiling sulfuric acid should be handled as little as possible and should not be cooled under the tap. The action of diluted sulfuric acid on metals closely resembles that of dilute hydrochloric acid. Magnesium, aluminium, iron, zinc, nickel, cobalt, manganese and cadmium dissolve with evolution of hydrogen in the cold acid or when warmed. The action of hot and strong sulfuric acid is altogether different. It acts as an oxidizing agent and is itself reduced to sulfur dioxide or even to sulfur. Following metals are attacked in this way copper, bismuth, mercury, silver, ant money, tin and lead. Gold, platinum and arsenic are not affected. This property is made use of in parting silver from gold and platinum. Metallic sulphides are similarly attacked but this method of opening up minerals has the disadvantage of giving rise to the formation of anhydrous sulfates of iron etc which are not readily dissolved when afterwards diluted. The use of sulfuric acid in assaying is for these reasons to be avoided. Its chief use is as a drying agent since it has a strong affinity for water. Air under a belger may be kept dry by means of a basin of sulfuric acid and gases bubbled through it are freed from water vapor. Dilute sulfuric acid. This is made by diluting one volume of the strong acid with four of water. Tartaric acid C4H6O6. A crystallized organic acid soluble in less than its own weight of water or in less than three parts of alcohol. It is used for the same purpose as citric acid is. The solution is made when required. Bases, salts etc. Alcohol C6H6O. Commercial alcohol of specific gravity 0.838. It contains 84% by weight of alcohol. It should burn with a non-luminous flame and leave no residue. It is used for washing precipitates where water is inapplicable and for facilitating drying. Ammonia NH3. Commercial ammonia, a solution having a specific gravity of 0.88 to 0.89 and containing about 33% of ammonia. It is used as an alkali, more commonly than soda or potash since an excess of it is easily removed by boiling. The salts of ammonium formed by it may be removed by igniting or by evaporating in a porcelain dish with an excess of nitric acid. It differs in a marked way from soda or potash in its solvent action on the oxides or hydrates of the metals. Salts of the following metals are soluble in an ammoniical solution in the presence of ammonic chloride, copper, cadmium, silver, nickel, cobalt, manganese, zinc, magnesium, sodium, potassium and the alkaline earths. Dilutamonia is made by diluting one volume of commercial ammonia with two of water. The dilutamonia is always used, but in assays for copper a stronger solution, one of strong ammonia to one of water, is required. Ammonic carbonate AM2CO3. Reader's note AM being an abbreviation for NH4, end reader's note, is prepared by dissolving one part of the commercial sesquicarbonate of ammonia in four parts of water and adding one part of strong ammonia. Ammonic carbonate HAMCO3 is prepared by saturating a solution of the sesquicarbonate of ammonia with carbon dioxide. Ammonic chloride AMCl use the commercial salt in a 20% solution in water. The salt should leave no residue on ignition. Ammonic molybdate. The solution is prepared as follows. Dissolve 100 grams of the powdered commercial salt in 200 cc of dilutamonia and pour the solution in a slow stream into 750 cc of dilute nitric acid. Make up to one litre and allow the mixture to settle before using. It is used for the purpose of separating phosphoric acid from bases and from other acids and also as a test for phosphates and arsenates. In using this solution the substance must be dissolved in nitric acid and a considerable excess of the reagent added. 50 cc is sufficient to precipitate 0.1 gram P2O5. Reader's note, phosphorus pentoxide, end reader's note. When the phosphate is in excess no precipitate will be got. The precipitate is phosphomolibdate of ammonia. Ammonic nitrate AMNO3 is used in the separation of phosphoric acid by the molybdate method and occasionally for destroying organic matter. It is soluble in less than its own weight of water. The solution is made when wanted. Ammonic oxalate AM2C2O4.2H2O is used chiefly for the separation of lime. The solution is made by dissolving 15 grams of the salt in 100 cc of water. Ammonic sulfide may be purchased in the state of a strong solution. It is yellow and contains the disulfide S2AM2. It serves the same purpose as is obtained by passing a current of sulfuretted hydrogen through an ammoniacle solution, but has the disadvantage of loading the solution with sulfur, which is precipitated when the solution is subsequently acidified. It is useful for dissolving the lower sulfide of tin, SNS. Baric carbonate BA-CO3 is sometimes used for precipitating the weaker bases. It should be prepared when wanted by precipitating a solution of baric chloride with ammonic carbonate and washing. The moist precipitate is used without drying. Baric chloride BA-CL2.2H2O. A crystallized salt soluble in two and a half parts of water. It is used for the detection and separation of sulfates. Make a 10% solution. Black flux. A mixture of finely divided carbon with carbonate of potash or with carbonates of potash and soda. It is prepared by heating tartar over a shell salt until no more combustible gas is given off. One gram will reduce about two grams of lead from litharge. Borax NA2B407.10H2O. It is chiefly used as a flux in dry assaying, as already described. It is also used in testing before the blowpipe. Many metallic oxides impart a characteristic color to a bead of borax in which they have been fused. Calcium chloride. The crystallized salt is CACL2.6H2O. Dried at 200 degrees centigrade, it becomes CACL2.2H2O. And when fused it becomes dehydrated. The fused salt broken up into small lumps is used for drying gases. It combines with water giving off much heat and dissolves in a little more than its own weight of water. Strong solutions may be used in baths in which temperatures above the boiling point of water are required. One part of the salt and two of water gives a solution boiling at 112 degrees, and a solution of two parts of the salt in one of water boils at 158 degrees. The salt is very little used as a reagent. Calcium chloride, or fluospa, CaF2. The mineral is used as a flux in dry assaying. It renders slags which are thick from the presence of phosphates, etc. Very fluid. Mixed with hydrochloric acid, it may sometimes be used instead of hydrofluoric acid. Calcium carbonate, CaCO3. It is precipitated in a pure state by a monic carbonate from a solution of calcium chloride. It is used for standardizing. In the impure state, as marble or limestone, it is used in the preparation of carbonic acid. Calcium hydrate, or lime water. This is used in testing for carbon dioxide and in estimating the amount of that gas present in air. It may be made by slaking quick lime and digesting the slaked lime with water. 100 cc of water at 15 degrees centigrade dissolves 0.1368 grams of the hydrate, CaH2O2, and hot water dissolves still less. Milk of lime is slaked lime suspended in water. Cobalt nitrate, CO, Brackets NO3, closed brackets twice, .6H2O. It is used in a 10% solution for the detection of oxides of zinc, aluminium, etc. on ignition with which it forms characteristically coloured compounds. Copper, Cu. Pure copper, as obtained by electrolysis, can be purchased. This only should be used. Copper oxide, CuO. It occurs as a black, heavy and gritty powder, and is used for the oxidation of carbon and hydrogen in organic substances. It should be ignited and cooled out of contact with air just before using, since it is hygroscopic. Oxide of copper, which has been used, may be again utilised after calcination. Copper sulfate, CuSO4.5H2O, contains 25.4% of copper. It is used in the outer cell of a Daniel battery. Commercial salt is used for this purpose. The recrystallised and pure salt is used for preparing the anhydrous sulfate, which is used for detecting moisture in gases. For this purpose, it is dried at 200 degrees centigrade till no trace of green or blue colour remains. It must be prepared when wanted. It may be conveniently used in the form of pumice stone saturated with the solution of the salt and dried. Traces of moisture develop a green colour. Ferric chloride, Fe2Cl6. When crystallised, Fe2Cl6.6H2O. The solution is prepared as described under iron. The commercial salt contains arsenic, and since the chief use of ferric chloride is for the determination of this substance, it must be purified. Ferric sulfate, Fe2Cl6H2O, is a yellowish-white delicuosent salt. It is used as an indicator in volumetric silver assaying, and for the separation of iodine from bromine. It may be purchased as iron alum, Am2Fe2O4Cl4H2O, but it is best prepared by adding strong sulphuric acid to ferric hydrate in equivalent proportions. Use it as a solution containing 2 or 3% of iron. Ferrous sulfate, FeSo4.7H2O. The granulated form is best, and can be purchased pure. It is used for standardising. It keeps better in crystals than in solution. It is readily soluble in water, but the solution is best made with the help of a little free acid. As a reagent, use a 10% solution. The crystals should be clear bluish green. If their colour is dark green, brown or blue, they should be rejected. Ferrous sulfide, FeS, is used for the preparation of sulphurated hydrogen. It may be purchased and broken in small lumps, nut size for use. Fusion mixture, K2CO3.NA2CO3 is a mixture of pedacic and sodic carbonates in the proportions of 13 of the former to 10 of the latter by weight. It is hygroscopic. A mixture of the bicarbonates is better, being purer and less apt to get damp. Gallic acid, C7H6O5.H2O is an organic acid occurring as a pale, fawn-coloured crystalline powder soluble in 100 parts of cold water or in 3 parts of boiling water. It is used for the determination of antimony. A 10% solution in warm water is made when required. Hydrogen H is a gas. It is obtained by acting on zinc with dilute hydrochloric or sulphuric acid. It is used as a reducing agent and for providing an atmosphere free from oxygen. It reduces metallic oxides at a high temperature. It must be freed from water, and special precautions should be taken to prevent an admixture with air. It is generally required in a current which can be continued for an hour or more without interruption. The preparation can be conveniently carried out in the apparatus shown, figure 33. A quart bottle is half filled with cheat zinc and connected with bulbs filled with sulphuric acid and with a calcium chloride tube. The last is connected with the apparatus through which the gas has to be passed. Dilute hydrochloric acid mixed with a few cubic centimetres, 20cc to 1 pint, of stannous chloride solution to fix any dissolved oxygen is placed in the funnel, and let into the bottle by opening the stopcock when required. Care must be taken to let the hydrogen escape for some time before starting the reduction. Gold AU Gold obtained by cupoling and parting is for most purposes sufficiently pure. It is best kept in the shape of foil. When the purer metal is required, gold should be dissolved in aqua regia. The solution evaporated to a paste diluted, allowed to stand and filtered. The filtered solution is acidified with hydrochloric acid, warmed and precipitated with sodium sulfite. The precipitate is collected, washed and fused on charcoal. Iron FE The soft wire, thin, is used for standardising. Rods are used in dry assays as a desulfurising agent. Steel must not be used, since it is not pure, and contains a variable amount of iron. Lead PB Granulated lead or lead foil is used in the dry assay for silver and gold, and in the preparation of lead salts. It can be obtained very pure, but always contains more or less silver, one or two milligrams in 100 grams. The amount of silver it contains must be determined and recorded. Lead Acetate PB Open Brackets C2H3O2 Close Brackets x2.3H2O is used as a test, especially for the detection and estimation of sulfuretted hydrogen. Prepare a 10% solution for use. Lead Nitrate PB Open Brackets NO3 Close Brackets x2 can be purchased pure. It is used for standardising. Lead Dioxide PBO2 occurs as a dark brown powder. It is used as an oxidising agent and for absorbing sulfurous oxide. It can be prepared by digesting red lead with warm dilute nitric acid, washing and drying the residue. Lithage PBO It can be purchased as a yellow, heavy powder. It is used in dry assaying as a flux, as a desulfurising agent, and also as a source of lead. It always contains some silver, the amount of which must be determined. Litmus This is an organic colouring matter, which is turned red by acids and blue by alkalis. For ordinary purposes, it is best used as litmus paper, which may be purchased in small books. A solution is prepared by digesting 15 or 20 grams of the commercial litmus in 100 cc of water on the water bath. After being allowed to settle, it is filtered and made just faintly red with acetic acid. Then there is added a drop or two of a solution of soda and 10 cc of alcohol. It should be kept in a loosely covered bottle. Magnesia MGO It may be purchased as calcined magnesium. It is used for making magnesium mixture and should be kept in a corked, wide-mouthed bottle. Magnesia mixture Dissolve 22 grams of magnesium in about a quarter of a litre of dilute hydrochloric acid, avoiding excess. Add 5 grams of magnesium, boil and filter. Add 300 grams of amonic chloride and 250 cc of strong ammonia, and dilute with water to 2 litres. It should be kept in a stoppered wind chester. Magnesium sulfate MGS04.7H20 It can be purchased very pure and is occasionally used as a standard salt. Manganese dioxide MNO2 It is used in the preparation of chlorine. The commercial article is not pure, but is sufficiently so for this purpose. Marble CaCO3 Fragments of the white crystalline variety only should be used. It is used as a source of lime and of carbon dioxide. Mercury HG This can be purchased pure. It should have a bright surface, flow without a tail, and leave no residue on ignition. It is used as a standard for amalgamation and as a confining liquid in gas analysis. Nucuric chloride HGCl2 May be purchased pure. Make a 5% solution in water. It is used for destroying an excess of stannous chloride for removing sulfurated hydrogen from solution and as a test for stannous salts. Microcosmic salt HAMNAP04.H20 When fused, an AP03 is formed. It is used in testing for metallic oxides and silica before the blowpipe. The crystals are sometimes used as a standard for phosphoric acid. Nestler's Solution Mode of preparation Dissolve 35 grams of potassium iodide in 100cc of water. Dissolve 17 grams of mercuric chloride in 300cc of water. And pour this solution into that of the iodide till a permanent precipitate is produced. Make up to 1 liter with a 20% solution of potash. Admercuric chloride till a precipitate is again formed. Allow to settle and decant. It is used for detecting ammonia. Niter This is potassium nitrate. Platinum chloride 2HCl.PTCL4 In the crystallized form it has 6H20. It may be made as follows. Take 5 grams of clean platinum scrap and dissolve in a flask at a gentle heat in 50cc of hydrochloric acid with the occasional addition of some nitric acid. Evaporate to a paste and then dissolve in 100cc of water. It is used for separating and determining potassium. Phenolphthalein is an organic compound used as an indicator, more especially in determining the weaker acids. It cannot be used in the presence of ammonia. Dissolve half a gram in 100cc of dilute alcohol. Potassium bicarbonate KHCl3 It may be purchased pure. On ignition it leaves the carbonate K2Cl3 which may be used as a standard. Potassium cyanide KCN It is used in the dry assay as a reducing agent. The commercial sort is very impure. Purchase that sold as potassium cyanide. Open brackets, gold, closed brackets. Potassium bichromate K2CR207 It may be purchased nearly pure. It is used as an oxidizing agent for determining iron and as a test solution. For this last purpose a 10% solution is prepared. Potassium chlorate KClO3 Can be purchased pure. It is used with hydrochloric acid as a substitute for aqua regia. Potassium ferrocyanide K4FE Open brackets CN Close brackets X6.3H20 Or Yellow Praciate of Potash Is used as a test, as an indicator, and for the determination of zinc. Make a 5% solution Potassium ferrocyanide K6FE2 Open brackets CN Close brackets X12 Or Red Praciate of Potash Is used for testing And as an indicator Make a 5% solution when wanted as it decomposes on keeping. Potassium hydrate KHO Purchase that purified with alcohol. It is an alkali and is used for absorbing carbonic acid etc. Potassium iodide Ki It may be purchased nearly pure. It is used as a test and for dissolving iodine. It should be used in a 10% solution freshly made. The solution decomposes on exposure to light with separation of iodine. Potassium nitrate KN03 can be purchased pure. It is used in the dry way as an oxidizing agent. It is very fusible. It decomposes at a low temperature into potassium nitrite KN02 and free oxygen. And at a higher temperature leaves potash K20. It oxidizes sulfur and carbon with explosive violence. This action may be moderated by mixing the nitre with carbonate of soda, common salt or some other inert body. Potassium nitrite KN02 The commercial article is not pure but is sufficiently so for the purpose required. A saturated solution is used in the separation of cobalt. The solution is made when wanted. Potassium permanganate KM04 This salt may be purchased sufficiently pure. It is much used as an oxidizing agent. Potassium bisulfate KHS04 is used as a dry reagent for opening up minerals. It fuses and at a much higher temperature is converted into potassium sulfate with loss of sulfuric acid. Potassium sulfosionate KCNS is used for the detection and determination of traces of ferric iron as also in the separation of silver and copper from some of the other metals. Make a 10% solution. It should show no colour on the addition of hydrochloric acid. Red lead PB304 is used in the dry assay as a flux instead of lithage from which it differs in containing a little more oxygen. When acted on by nitric acid a brown residue of lead dioxide is left, nitrate of lead going into solution. Like lithage it always carries silver about 2mg in 100g. Silver AG Pure silver in foil is required as a standard. It may be prepared as follows. Dissolve scrap silver in dilute nitric acid and decant off any residue. Dilute the solution with hot water and add hydrochloric acid until there is no further precipitate. Stir. Allow the precipitate to settle. Decant and wash. Dry the precipitate. Mix it with twice its bulk of carbonate of soda and fuse the mixture in a crucible until tranquil. Clean the button and roll or hammer it into foil. Sodium acetate NaC2H3O2.3H2O The crystals may be purchased sufficiently pure. Make a 20% solution in water. It is used for replacing mineral acids by acetic acid. Sodium acetate and acetic acid. A solution is used in the determination of phosphates and arsenates. 100g of the salt is dissolved in 500cc of acetic acid and diluted with water to 1l. Sodium bicarbonate NaHCO3 is used as a flux in dry methods. On ignition it leaves the carbonate Na2CO3 which is used as a standard reagent. Make a 20% solution of the carbonate for use. It should be free from chlorides or sulfates or if impure the amount of impurities must be determined. Sodium hydrate NaHO It may be purchased in sticks which should be kept in a well-corked bottle. It is sometimes called caustic soda. It is a strong alkali. It is used for neutralizing acid solutions and for separations where ammonia is unsuitable. Make a 5% solution for use. Sodium hypo sulfite Na2S2O3.5H2O It may be purchased pure. It is generally known as hypo. It is used as a standard. Sodium sulfite Na2S3.7H2O is used as a reducing agent. Sodium phosphate Na2HPO4.12H2O The crystals may be purchased pure but they effloresce in dry air with loss of water. It is used as a standard and for precipitating magnesium etc. Make a 10% solution. Stannous chloride SnCl22H2O The crystals are best purchased. If kept dry and free from air they are fairly permanent. A solution is made by dissolving 20g in 10cc of hydrochloric acid and diluting to 1L. The solution is not permanent. It is a strong reducing agent and is chiefly used in solution for this purpose. Tin Sn. Grain Tin should be purchased. It is not pure but contains 99.5% of the metal. The chief impurity is copper. It can be used as a standard. When acted on with hot hydrochloric acid it slowly dissolves more rapidly in contact with platinum and forms stannous chloride. Uranium Acetate U02 Open Brackets C2H302 Close Brackets x2.H2O It is best purchased in crystals. The solution is used for the determination of phosphates and arsenates. A solution of 3% strength is occasionally used as an indicator. Uranium Nitrate U02 Open Brackets N03 Close Brackets x2.H2O This salt is very soluble in water and is sometimes used instead of the acetate which is somewhat difficult to dissolve. Water H2O Spring or well water is sufficiently pure for most purposes. 100cc will leave a residue of from 10 to 30mg so that where a salt has to be dissolved out evaporated and weighed it should be replaced by distilled water. Rainwater, melted snow etc always leave less residue than spring water but in other respects they are often dirtier. Distilled water is best prepared in the office, a glass or tin condenser being used. Zinc ZN It is sold in a granulated form or in sticks. It generally contains over 1% of lead with a little iron and arsenic. It is used for separating metals from their solutions and generally as a reducing agent. For the preparation of hydrogen and in most other cases scrap sheet zinc may be used. Zinc Oxide ZNO The commercial oxide sometimes contains carbonate. Zinc Sulfate ZNSO4.7H2O It is occasionally used as a standard and can be purchased nearly pure. End of reagents salts etc from a textbook of assaying by C and JJ Berringer Reinforced Concrete by Edward Godfrey This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer please visit LibriVox.org This reading by Deborah Lynn Readers note This extract is the beginning of the text and contains the author's paper only. For soporific purposes I retained the list of men whose discussion follows this extract. End of Readers Note American Society of Civil Engineers instituted 1852 Transactions Paper number 1169 Some Muted Questions in Reinforced Concrete Design Footnote A By Edward Godfrey M Period AM Period SOC Period C Period E Period With discussion by Messers Joseph Wright S. Bent Russell J. R. Worcester L. J. Mench Walter W. Clifford J. C. Meem George H. Myers Edwin Thatcher C. A. P. Turner Paul Chapman E. P. Goodrich Albin H. Byer John C. Ostrup Harry F. Porter John Stephen Sewell Sanford E. Thompson And Edward Godfrey Not many years ago physicians had certain rules and practices by which they were guided as to when and where to bleed a patient in order to relieve or cure him. What of those rules and practices today? If they were logical why have they been abandoned? It is the purpose of this paper to show that reinforced concrete engineers have certain rules and practices which are no more logical than those governing the bloodletting of former days. If the writer fails in this by reason of the more weighty arguments on the other side of the questions he propounds he will at least have brought out good reasons which will stand the test of logic for the rules and practices which he proposes to condemn and which at the present time are quite lacking in the voluminous literature on this comparatively new subject. Destructive criticism has recently been decried in an editorial in an engineering journal. Some kinds of destructive criticism are of the highest benefit. When it succeeds in destroying error it is reconstructive. No reform was ever accomplished without it and no reformer ever existed who was not a destructive critic. If showing up errors and faults is destructive criticism we cannot have too much of it. In fact we cannot advance without it. If engineering practice is to be purged of its inconsistencies and absurdities it will never be done by dwelling on its excellencies. Reinforced concrete engineering has fairly leaped into prominence and apparently into full growth but it still wears some of its swaddling bands. Some of the garments which it borrowed from sister forms of construction in its short infancy still cling to it. And while these were perhaps the best makeshifts under the circumstances they fit badly and should be discarded. It is some of these misfits and absurdities which the writer would like to bring prominently before the engineering profession. Illustration figure one. The first point to which attention is called is illustrated in figure one. It concerns sharp bends in reinforcing rods in concrete. Figure one shows a reinforced concrete design. One held out in nearly all books on the subject as a model. The reinforcing rod is bent up at a sharp angle and then may or may not be bent again and run parallel with the top of the beam. At the bend is a condition which resembles that of a hog chain or truss rod around a queen post. The reinforcing rod is the hog chain or the truss rod. Where is the queen post? Suppose this rod has a section of one square inch and an inclination of 60 degrees with the horizontal and that its unit stress is 16,000 pounds per square inch. The forces A and B are then 16,000 pounds. The force C must also be 16,000 pounds. What is to take this force C of 16,000 pounds? There is nothing but concrete. At 500 pounds per square inch this force would require an area of 32 square inches. Will some advocate of this type of design please state where this area can be found? It must of necessity be in contact with the rod and for structural reasons because of the lack of stiffness in the rod it would have to be close to the point of bend. If analogy to the queen post fails so completely because of the almost complete absence of the post why should not this borrowed garment be discarded? If this same rod be given a gentle curve of a radius 20 or 30 times the diameter of the rod the side unit pressure will be from 120th to 130th of the unit stress on the steel. This being the case and being a simple principle of mechanics which ought to be thoroughly understood it is astounding that engineers should perpetrate the gross error of making a sharp bend in a reinforcing rod under stress. The second point to which attention is called may also be illustrated by figure one. The rod mark three is also like the truss rod of a queen post truss in appearance because it ends over the support and has the same shape but the analogy ends with appearance for the function of a truss rod in a queen post truss is not performed by such a reinforcing rod in concrete for other reasons than the absence of a post. The truss rod receives its stress by a suitable connection at the end of the rod and over the support of the beam. The reinforcing rod in the standard beam ends abruptly at the very point where it is due to receive an important element of strength an element which would add enormously to the strength and safety of many a beam if it could be introduced. Of course a reinforcing rod in a concrete beam receives its stress by increments imparted by the grip of the concrete but these increments can only be imparted where the tendency of the concrete is to stretch. This tendency is greatest near the bottom of the beam and when the rod is bent up to the top of the beam it is taken out of the region where the concrete has the greatest tendency to stretch. The function of this rod as reinforcement of the bottom flange of the beam is interfered with by bending it up in this manner as the beam is left without bottom flange reinforcement as far as that rod is concerned from the point of bend to the support. It is true that there is a shear or a diagonal tension in the beam and the diagonal portion of the rod is apparently in a position to take this tension. This is just such a force as the trust rod in a queen post trust must take. Is this reinforcing rod equipped to perform this office? The beam is apt to fail in the line AB. In fact it is apt to crack from shrinkage on this or almost any other line and to leave the strength dependent on the reinforcing steel. Suppose such a crack should occur. The entire strength of the beam would be dependent on the grip of the short end of rod three to the right of the line AB. The grip of this short piece of rod is so small and precarious considering the important duty it has to perform that it is astounding that designers having any care for the permanence of their structures should consider for an instant such features of design much less incorporate them in a building in which life and property depend on them. The third point to which attention is called is the feature of design just mentioned in connection with the bent up rod. It concerns the anchorage of rods by the embedment of a few inches of their length in concrete. This most flagrant violation of common sense has its most conspicuous example in large engineering works where of all places better judgment should prevail. Many retaining walls have been built and described in engineering journals in papers before engineering societies of the highest order and in books enjoying the greatest reputation which have as an essential feature a great number of rods which cannot possibly develop their strength and might as well be of much smaller dimensions. These rods are the vertical and horizontal rods in the counter fort of the retaining wall shown at A in figure two. This retaining wall consists of a front curtain wall and a horizontal slab joined at intervals by ribs or counter forts. The manifest and only function of the rib or counter fort is to tie together the curtain wall and the horizontal slab. That it is or should be of concrete is because the steel rods which it contains need protection. It is clear that failure of the retaining wall could occur by rupture through the section AB or through BC. It is also clear that apart from the cracking of the concrete of the rib the only thing which would produce this rupture is the pulling out of the short ends of these reinforcing rods. Riders treat the triangle ABC as a beam but there is absolutely no analogy between this triangle and a beam. Designers seem to think that these rods take the place of so-called shear rods in a beam and that the inclined rods are equivalent to the rods in a tension flange of a beam. It is hard to understand by what process of reasoning such results can be attained. Any clear analysis leading to these conclusions would certainly be a valuable contribution to the literature on the subject. It is scarcely possible, however, that such analysis will be brought forward for it is the apparent policy of the reinforced concrete analyst to jump into the middle of his proposition without the encumbrance of a premise. There is positively no evading the fact that this wall could fail as stated by rupture along either AB or BC. It can be stated just as positively that a set of rods running from the front wall to the horizontal slab and anchored into each in such a manner as would be adopted were these slabs suspended on the rods is the only rational and the only efficient design possible. This design is illustrated at B in figure two. Illustration figure two. The fourth point concerns shear in steel rods embedded in concrete. For decades, specifications for steel bridges have gravely given a unit shear to be allowed on bridge pins and every bridge engineer knows or ought to know that if a bridge pin is properly proportioned for bending and bearing, there is no possibility of its being weak from shear. The centers of bearings cannot be brought close enough together to reduce the size of the pin to where its shear need be considered because of the width required for bearing on the parts. Concrete is about one-thirtieth as strong as steel in bearing. There is therefore somewhat less than one-thirtieth of a reason for specifying any shear on steel rods embedded in concrete. The gravity of the situation is not so much the serious manner in which this unit of shear and steel is written in specifications and building codes for reinforced concrete work. It does not mean anything in specifications for steel work because it is ignored, but it is apparent when designers soberly use these absurd units and proportion shear rods accordingly. Many designers actually proportion shear rods for shear. Sheer in the steel at units of 10,000 or 12,000 pounds per square inch and the blame for this dangerous practice can be laid directly to the literature on reinforced concrete. Sheer rods are given as standard features in the design of reinforced concrete beams. In the joint report of the committee of the various engineering societies, a method for proportioning shear members is given. The stress or shear per shear member is the longitudinal shear which would occur in the space from member to member. No hint is given as to whether these bars are in shear or tension. In fact, either would be absurd and impossible without greatly overstressing some other part. This is just a sample of the state of the literature on this important subject. Sheer bars will be taken up more fully in subsequent paragraphs. The fifth point concerns vertical stirrups in a beam. These stirrups are conspicuous features in the designs of reinforcing concrete beams. Explanations of how they act are conspicuous in the literature on reinforced concrete by its total absence. By stirrups are meant the so-called shear rods strung along a reinforcing rod. They are usually U-shaped and looped around the rod. It is common practice to count these stirrups in the shear taking the horizontal shear in a beam. In a plate girder, the rivets connecting the flange to the web take the horizontal shear or the increment to the flange stress. Compare two three-quarter inch rivets tightly driven into holes in a steel angle with a loose vertical rod three quarters of an inch in diameter looped around a reinforcing rod in a concrete beam. In direct comparison of methods of design in steel and reinforced concrete as they are commonly practiced is obtained. These stirrups can take but little hold on the reinforcing rods and this must be through the medium of the concrete and they can take but little shear. Some writers however hold the opinion that the stirrups are in tension and not in shear and some are bold enough to compare them with the vertical tension members of a how-truss. Imagine a how-truss with the vertical tension members looped around the bottom cord and run up to the top cord without any connection or hooked over the top cord. Then compare such a truss with one in which the end of the rod is upset and receives a nut and large washer bearing solidly against the cord. This gives a comparison of methods of design in wood and reinforced concrete as they are commonly practiced. Anchorage or grip in the concrete is all that can be counted on in any event to take up the tension of these stirrups but it requires an embedment of from 30 to 50 diameters of a rod to develop its full strength. Take 30 to 50 diameters from the floating end of these shear members and in some cases nothing or less than nothing will be left. In any case the point at which the shear member or stirrup is good for its full value is far short of the centroid of compression of the beam where it should be. In most cases it will be nearer the bottom of the beam. In a how-truss the vertical tension members having their end connections near the bottom cord would be equivalent to these shear members. The sixth point concerns the division of stress into shear members. Briefly stated the common method is to assume each shear member as taking the horizontal shear occurring in the space from member to member. As already stated this is absurd if stirrups could take shear this method would give the shear per stirrup but even advocates of this method acknowledge that they cannot. To apply the common analogy of a truss each shear member would represent a tension web member in the truss and each would have to take all the shear occurring in a section through it. If for example shear members were spaced half the depth of a beam apart each would take half the shear by the common method. If shear members take vertical shear or if they take tension what is between the two members to take the other half of the shear. There is nothing in the beam but concrete and the tension rod between the two shear members. If the concrete can take the shear why use steel members it is not conceivable that an engineer should seriously consider a tension rod in a reinforced concrete beam as carrying the shear from stirrup to stirrup. The logical deduction from the proposition that shear rods take tension is that the tension rods must take shear and that they must take the full shear of the beam and not only a part of it. For these shear rods are looped around or attached to the tension rods and since tension in the shear rods would logically be imparted through the medium of this attachment there is no escaping the conclusion that a large vertical force the shear of the beam must pass through the tension rod. If the shear member really relieves the concrete of the shear it must take it all if as would be allowable the shear rods take but a part of the shear leaving the concrete to take the remainder that carried by the rods should not be divided again as is recommended by the common method. Bulletin number 29 of the University of Illinois experiment station shows by numerous experiments and reiterates again and again that shear rods do not act until the beam has cracked and partly failed. This being the case a shear rod is an illogical element of design. Any element of a structure which cannot act until failure has started is not a proper element of design. In a steel structure a bent plate which would straighten out under a small stress and then resist final rupture would be a menace to the rigidity and stability of the structure. This is exactly analogous to shear rods which cannot act until failure has begun. When the man who tears down by criticism fails to point out the way to build up he is a destructive critic. If under the circumstances designing with shear rods had the virtue of being the best thing to do with the steel and concrete disposed in a beam as far as experience and logic in their present state could decide nothing would be gained by simply criticizing this method of design. But logic and tests have shown a far simpler more effective and more economical means of disposing of the steel in a reinforced concrete beam. In shallow beams there is little need of provision for taking shear by any other means than the concrete itself. The rider has seen a reinforced slab support a very heavy load by simple friction for the slab was cracked close to the supports. In slabs shear is seldom provided for in the steel reinforcement. It is only when beams begin to have a depth approximating one tenth of the span that the shear in the concrete becomes excessive and provision is necessary in the steel reinforcement. Years ago the rider recommended that in such beams some of the rods be curved up toward the ends of the span and anchored over the support. Such reinforcement completely relieves the concrete of all shearing stress for the stress in the rod will have a vertical component equal to the shear. The concrete will rest in the rod as a saddle and the rod will be like the cable of a suspension span. The concrete should be in separate blocks with vertical joints and still the load would be carried safely. By end anchorage is not meant an inch or two of embedment in concrete for an iron vice would not hold a rod for its full value by such means. Neither does it mean a hook on the end of the rod. A threaded end with a bearing washer and a nut and a lock nut to hold a washer in place is about the only effective means and it is simple and cheap. Nothing is as good for this purpose as plain round rods for no other shape affords the same simple and effective means of end connection. In a line of beams end to end the rods may be extended into the next beam and their act to take the top flange tension while at the same time finding anchorage for the principal beam stress. The simplicity of this design is shown still further by the absence of a large number of little pieces in a beam box as these must be held in their proper places and as they interfere with the pouring of the concrete. It is surprising that the simple and unpatented method of design has not met with more favor and has scarcely been used even in tests. Some time ago the writer was asked by the head of an engineering department of a college for some ideas for the students to work up for theses and suggested that they test beams of this sort. He was met by the astounding and fatuous reply that such would not be reinforced concrete beams. There would certainly be concrete beams and just to certainly be reinforced. Bulletin 29 of the University of Illinois Experiment Station contains a record of tests of reinforced concrete beams of this sort. They failed by the crushing of the concrete or by failure in the steel rods and nearly all the cracks were in the middle third of the beams whereas beams rich in shear rods cracked principally in the end thirds that is in the neighborhood of the shear rods. The former failures are ideal and are easier to provide against. A cracking of beam near the middle of the span is of little consequence whereas one near the support is a menace to safety. The seventh point of common practice to which attention is called is the manner in which bending moments in so-called continuous beams are juggled to reduce them to what the designer would like to have them. This has come to be almost a matter of taste and is done with as much precision or reason as geologists guess at the age of a fossil in millions of years. If a line of continuous beams be loaded uniformly the maximum moments are negative and are over the supports. Whoever heard of a line of beams in which the reinforcement over the supports was double that at mid-spans. The end support of such a line of beams cannot be said to be fixed but is simply supported. Hence the end beam would have a negative bending moment over next to the last support equal to that of a simple span. Whoever heard of a beam being reinforced for this. The common practice is to make a reduction in the bending moment at the middle of the span to about that of a line of continuous beams regardless of the fact that they may not be continuous or even contiguous and in spite of the fact that the loading of only one gives quite different results and may give results approaching those of a simple beam. If the beams be designed as simple beams taking the clear distance between supports as the span and not the centers of bearings or the centers of supports and if a reasonable top reinforcement be used over these supports to prevent cracks every requirement of good engineering is met. Under extreme conditions such construction might be heavily stressed in the steel over the supports. It might even be overstressed in this steel but what could happen not failure for the beams are capable of carrying their load individually and even if the rods over the supports were severed a thing impossible because they cannot stretch out sufficiently the beams would stand. Continuous beam calculations have no place whatever in designing stringers of a steel bridge though the end connections will often take a very large moment and if calculated as continuous will be bound to be strained to a very much larger moment. Whoever heard of a failure because of continuous beam action in the stringers of a bridge why cannot reinforced concrete engineering be placed on the same sound footing as structural engineering. The eighth point concerns the spacing of rods in a reinforced concrete beam. It is common to see rods bunched in the bottom of such a beam with no regard whatever for the ability of the concrete to grip the steel or to carry the horizontal shear incident to their stress to the upper part of the beam as an illustration of the logic and analysis applied in discussing the subject of reinforced concrete. One well-known authority on the premise that the unit of adhesion to rod and of shear are equal derives a rule for the spacing of rods. His reasoning is so false and his rule is so far from being correct that two-thirds would have to be added to the width of beam in order to make it correct. An error of 66% may seem trifling to some minds where reinforced concrete is considered but errors of one-tenth this amount in steel design would be caused for serious concern. It is reasoning of the most elementary kind which shows that if shear and adhesion are equal the width of a reinforced concrete beam should be equal to the sum of the peripheries of all reinforcing rods gripped by the concrete. The width of the beam is the measure of the shearing area above the rods taking the horizontal shear to the top of the beam and the peripheries of the rods of the measure of the gripping or adhesion area. Analysis which examines a beam to determine whether or not there is sufficient concrete to grip the steel and to carry the shear is about at the vanishing point in nearly all books on the subject. Such misleading analysis as that just cited is worse than nothing. The ninth point concerns the T-beam. Excessively elaborate formulas are worked out for the T-beam and haphazard guesses are made as to how much of the floor slab may be considered in the compression flange. If a fraction of this mental energy were directed toward a logical analysis of the shear and gripping value of the stem of the T-beam it would be found that when the stem is given its proper width little if any of the floor slab will have to be counted in the compression flange for the width of concrete which will grip the rods properly will take the compression incident to their stress. The tenth point concerns elaborate theories and formulas for beams and slabs formulas are commonly given with 25 or 30 constants and variables to be estimated and guessed at and are based on assumptions which are inaccurate and untrue. One of these assumptions is that the concrete is initially unstressed. This is quite out of reason for the shrinkage of the concrete on hardening puts stress in both concrete and steel. One of the coefficients of the formulas is that of the elasticity of the concrete. No more variable property of concrete is known than its coefficient of elasticity which may vary from one million to five million or six million. It varies with the intensity of stress with the kind of aggregate used with the amount of water used in mixing and with the atmospheric condition during setting. The unknown coefficient of elasticity of concrete and the non-existent condition of no initial stress videate entirely formulas supported by these two props. Here again destructive criticism would be vicious if these mathematical gymnasts were giving the best or only solution which present knowledge could produce or if the critic did not point out a substitute. The substitute is so simple of application in such agreement with experiments and so logical in its derivation that it is surprising that it has not been generally adopted. The neutral axis of reinforced concrete beams under safe loads is near the middle of the depth of the beams. If in all cases it be taken at the middle of the depth of the concrete beam and if variation of intensity of stress in the concrete be taken as uniform from this neutral axis up the formula for the resisting moment of a reinforced concrete beam becomes extremely simple and no more complex than that for a rectangular wooden beam. The eleventh point concerns complex formulas for chimneys. It is a simple matter to find the tensile stress in that part of a plain concrete chimney between two radii on the windward side. If in this space there is inserted a rod which is capable of taking that tension at a proper unit the safety of the chimney is assured as far as that tensile stress is concerned. Why should frightfully complex formulas be proposed which bring in the unknowable modulus of elasticity of concrete and can only be solved by stages or dependence on the calculations of someone else. The twelfth point concerns deflection calculations. As is well known deflection does not play much of a part in the design of beams. Sometimes however the passing requirement of a certain floor construction is the amount of deflection under a given load. Professor Gitano Lanza has given some data on recorded deflections of reinforced concrete beams. Footnote B. He has also worked out the theoretical deflections on various assumptions. An attempt to reconcile the observed deflections with one of several methods of calculating stresses led him to the conclusion that the observations made thus far are not sufficient to furnish the means for determining the actual distribution of the stresses and hence for the deduction of reliable formula for the computation of the direct stresses, shearing stresses, diagonal stresses, deflections, position of the neutral axis, etc under a given load. Professor Lanza might have gone further and said that the observations made thus far are sufficient to show the hopelessness of deriving a formula that will predict accurately the deflection of a reinforced concrete beam. The wide variation shown by two beam tests cited by him in which the beams were identical is in itself proof of this. Taking the data of these tests and working out the modulus of elasticity from the recorded deflections as though the beams were of plain concrete, values are found for this modulus which are not out of agreement with the value of that variable modulus as determined by other means. Therefore, if the beams be considered as plain concrete beams and an average value be assumed for the modulus or coefficient of elasticity, a deflection may be found by a simple calculation which is an average of that which may be expected. Here again simple theory is better than complex because of the ease with which it may be applied and because it gives results which are just as reliable. The thirteenth point concerns the elastic theory as applied to a reinforced concrete arch. This theory treats a reinforced concrete arch as a spring. In order to justify its use, the arch or spring is considered as having fixed ends. The results obtained by the intricate methods of the elastic theory and the simple method of the equilibrium polygon are too nearly identical to justify the former when the arch is taken as hinged at the ends. The assumption of fixed ends in an arch is a most extravagant one because it means that the abutments must be rigid that is capable of taking bending moments. Rigidity in an abutment is only affected by a large increase in bulk whereas strength in an arch ring is greatly augmented by the addition of a few inches to its thickness. By the elastic theory, the arch ring does not appear to need as much strength as by the other method, but additional stability is needed in the abutments in order to take the bending moments. This latter feature is not dwelt on by the elastic theorists. In the ordinary arch, the criterion by which the size of abutment is gauged is the location of the line of pressure. It is difficult and expensive to obtain depth enough in the base of the abutment to keep this line within the middle third when only the thrust of the arch is considered. If, in addition to the thrust, there is a bending moment which, for many conditions of loading, further displaces the line of pressure toward the critical edge, the difficulty and expense are increased. It cannot be gained said that a few cubic yards of concrete added to the ring of an arch will go much further toward strengthening the arch than the same amount of concrete added to the two abutments. In reinforced concrete there are ample grounds for the contention that the carrying out of a nice theory based on nice assumptions and the exact determination of ideal stresses is of far less importance than the building of a structure which is in every way capable of performing its function. There are more than ample grounds for the contention that the ideal stresses worked out for a reinforced concrete structure are far from realization in this far from ideal material. Apart from the objection that the elastic theory, instead of showing economy by cutting down the thickness of the arch ring, would show the very opposite if fully carried out. There are objections of greater weight, objections which strike at the very foundation of the theory as applied to reinforced concrete. In the elastic theory, as in the intricate beam theory commonly used, there is the assumption of an initial unstressed condition of the materials. This is not true of a beam and is still further from the truth in the case of an arch. Besides shrinkage of the concrete which always produces unknown initial stresses, there is a still more potent cause of initial stress, namely the settlement of the arch when the forms are removed. If the initial stresses are unknown, ideal determinations of stresses can have little meaning. The elastic theory stands or falls according as one is able or unable to calculate accurately the deflection of a reinforced concrete beam and it is an impossibility to calculate this deflection even approximately. The tests cited by Professor Lanza show the utter disagreement in the matter of deflections. Of those tested, two beams which were identical showed results almost 100% apart. A theory grounded on such a shifting foundation does not deserve serious consideration. Professor Lanza's conclusions quoted under the 12th point have special meaning and force when applied to a reinforced concrete arch. The actual distribution of the stresses cannot possibly be determined and complex cloaks of arithmetic cannot cover this fact. The elastic theory, far from being a reliable formula, is false and misleading in the extreme. The 14th point refers to temperature calculations in a reinforced concrete arch. These calculations have no meaning whatever. To give the grounds for this assertion would be to reiterate much of what has been said under the subject of the elastic arch. If the unstressed shape of an arch cannot be determined because of the unknown effect of shrinkage and settlement, it is a waste of time to work out a slightly different unstressed shape due to temperature variation, and it is a further waste of time to work out the supposed stresses resulting from deflecting that arch back to its actual shape. If no other method of finding the approximate stresses in an arch existed, the elastic theory might be classed as the best available, but this is not the case. There is a method which is both simple and reliable. Accuracy is not claimed for it, and hence it is in accord with the more or less uncertain materials dealt with. Complete safety, however, is assured, for it treats the arch as a series of blocks, and the cementing of these blocks into one mass cannot weaken the arch. Reinforcement can be proportioned in the same manner as for chimneys by finding the tension exerted to pull these blocks apart and then providing steel to take that tension. The fifteenth point concerns steel in compression in reinforced concrete columns or beams. It is common practice, and it is recommended in the most pretentious works on the subject, to include in the strength of a concrete column slender longitudinal rods embedded in the concrete, to quote from one of these works. The compressive resistance of a hooped member exceeds the sum of the following three elements. One, the compressive resistance of the concrete without reinforcement. Two, the compressive resistance of the longitudinal rods stressed to their elastic limit. Three, the compressive resistance which would have been produced by the imaginary longitudinal at the elastic limit of the hooping metal. The volume of the imaginary longitudinal is being taken as 2.4 times that of the hooping metal. This does not stand the test, either of theory or practice. In fact, it is far from being true. Its departure from the truth is great enough, and of serious enough moment, to explain some of the worst accidents in the history of reinforced concrete. It is a nice theoretical conception that the steel and the concrete act together to take the compression, and that each is accommodating enough to take just as much of the load as will stress it to just the right unit. Here again, initial stress plays an important part. The shrinkage of the concrete tends to put the rods in compression. The load adds more compression on the slender rods, and they buckle because of the lack of any adequate stiffening, long before the theorist's ultimate load is reached. There is no theoretical or practical consideration which would bring in the strength of the hoops after the strength of the concrete between them has been counted. All the compression of a column must of necessity go through the disc of concrete between the two hoops and the longitudinal steel. No additional strength in the hoops can affect the strength of this disc with a given spacing of the hoops. It is true that shorter discs will have more strength, but this is a matter of the spacing of the hoops and not of their sectional area as the above quotation would make it appear. Besides being false theoretically, this method of investing phantom columns with real strength is woefully lacking in practical foundation. Even the assumption of reinforcing value to the longitudinal steel rods is not at all borne out in tests. Designers add enormously to the calculated strength of concrete columns when they insert some longitudinal rods. It appears to be the rule that real columns are weakened by the very means which these designers invest with reinforcing properties. Whether or not it is the rule, the mere fact that many tests have shown these so-called reinforced concrete columns to be weaker than similar plain concrete columns is amply sufficient to condemn the practice of assuming strength which may not exist. Of all parts of a building, the columns are the most vital. The failure of one column will, in all probability, carry with it many others stronger than itself, whereas a weakened failing slab or beam does not put an extra load in shock on the neighboring parts of a structure. In bulletin number 10 of the University of Illinois Experiment Station, footnote C, a plain concrete column, 9 by 9 inches by 12 feet, stood an ultimate crushing load of 2,004 pounds per square inch. Column 2, identical in size and having four, five-eight-inch rods embedded in the concrete, stood 1,557 pounds per square inch, so much for longitudinal rods without hoops. This is not an isolated case, but appears to be the rule, and yet, in reading the literature on the subject, one would be led to believe that longitudinal steel rods in a plain concrete column add greatly to the strength of the column. A paper by Mr. M. O. Withy, before the American Society for Testing Materials in 1909, gave the results of some tests on concrete steel and plain concrete columns. The term concrete steel is used because this particular combination is not reinforced concrete. One group of columns, namely W1 to W3, 10 and a half inches in diameter, 102 inches long and circular in shape, stood an average ultimate load of 2,600 pounds per square inch. These columns were a plain concrete. Another group, namely E1 to E3, were octagonal in shape with a short diameter, 12 inches, their length being 120 inches. These columns contained nine longitudinal rods, five-eight-inch in diameter, and one-quarter inch steel rings every foot. They stood an ultimate load averaging 2,438 pounds per square inch. This is less than the column with no steel and with practically the same ratio of slenderness. In some tests on columns made by the Department of Buildings of Minneapolis, Minnesota, footnote D, test A was a nine-by-nine inch column, nine feet six inches long with 10 longitudinal round rods, one-half inch in diameter, and one-and-a-half inch by three-sixteenths inch circular bands having two half-inch rivets in the splice, spaced four inches apart, the circles being seven inches in diameter. It carried an ultimate load of 130,000 pounds, which is much less than half the compressive resistance of a hooped member, worked out according to the authoritative quotation before given. Another similar column stood a little more than half that compressive resistance. Five of the 17 tests on the concrete steel columns made at Minneapolis stood less than the plain concrete columns. So much for the longitudinal rods and for hoops, which are not close enough to stiffen the rods, and yet in reading the literature on the subject, anyone would be led to believe that longitudinal rods and hoops add enormously to the strength of a concrete column. The sixteenth indictment against common practice is in reference to flat slabs supported on four sides. Grashof's formula for flat plates has no application to reinforced concrete slabs because it is derived for a material strong in all directions and equally stressed. The strength of concrete intention is almost nil, at least it should be so considered. Poisson's ratio, so prominent in Grashof's formula, has no meaning whatever in steel reinforcement for a slab because each rod must take tension only, and instead of a material equally stressed in all directions, there are generally sets of independent rods in only two directions. In a solution of the problem given by a high English authority, the slab is assumed to have a bending moment of equal intensity along its diagonal. It is quite absurd to assume an intensity of bending clear into the corner of a slab, and on the very support equal to that at its center. A method published by the writer some years ago has not been challenged. By this method strips are taken across the slab, and the moment in them is found considering the limitations of the several strips in deflection imposed by those running at right angles therewith. This method shows as tests demonstrate that when the slab is oblong, reinforcement in the long direction rapidly diminishes in usefulness. When the ratio is one to one-and-a-half, reinforcement in the long direction is needless, since that in the short direction is required to take its full amount. In this way, French and other regulations give false results and fail to work out. If the writer is wrong in any or all of the foregoing points, it should be easy to disprove his assertions. It would be better to do this than to ridicule or ignore them, and it would be even better than to issue reports signed by authorities which commend the practices herein condemned. Footnotes. Footnote A presented at the meeting of March 16, 1910. Footnote B stresses in reinforced concrete beams. Journal American Society of Mechanical Engineers mid-October 1909. Footnote C, page 14, column 8. Footnote D, Engineering News, December 3, 1908. End of selection.