 continue with the geomaterial characterization with subtopics as chemical characterization. Though we have discussed how to determine P H T D S that is total dissolved solids electrical conductivity of the soil solutions B O D and C O D. Sulphide and chloride contents can cation exchange capacity followed by pore solution sampling. So, most of the lecture today's lecture will be discussed will I will try to cover most of the techniques used for pore solution sampling followed by most probably in the next lecture or if possible today I will be talking about corrosion potential of soils, sorption desorption continue with that followed by thermal characterization and electrical characterization. This is just to remind you that the characterization is still going on and we are still stuck up with chemical characterization part. Now, to start with P H determination this is the unit which is known as water quality analyzer and this water quality analyzer unit is connected to some electrodes. These electrodes are basically glass-calomel electrodes you must have used them also earlier for determining P H of the solution of soils. The only thing is that you have to prepare soil solutions with different liquid to solid ratios which is also known as L by S. So, depending upon different L by S P H values may change may not change truly speaking P H value should remain same for different L by S, but it so happens if you keep on increasing more and more liquid into the solution P H may also alter because of more opportunity which oxides may get to react with water and sometimes when you are working with oxides in the materials which are amphoteric in nature which have dual you know behavior when they come in contact with water P H may definitely change. Now, this instrument is a very good tool to determine P H of the soil solution essentially what you have to do is you have to prepare a soil solution corresponding to a liquid solid ratio and then filter out the liquid part and that liquid part is normally kept in this beaker the glass-calomel electrode is dipped into this and then you can read out reading directly. However, you have to be very careful that P H normally gets influenced by the temperature. So, this instrument also records temperature simultaneously and normally at room temperature that is 25 degree centigrade the P H values are reported. So, you can apply the correction depending upon the values which you are obtaining if the temperature is not same as 25 degree. You can use this water quality analyzer also for determining total dissolved solids which is an indicative of turbidity of the solution if you cannot use a UV spectrophotometer then this is also good technique. You can determine electrical conductivity of the solution of the soil corresponding to different L by S ratio and then ultimately electrical conductivity can also be linked with tedious of the suspension in the material. You can find out chemical oxygen demand as well as biological oxygen demand and based on these parameters you can again classify the soil and later on we will notice that these parameters are very handy in defining the corrosion potential of the soil mass. So, particularly P H and electrical conductivity and sometimes another word which is used as redox potential I will be talking about that later on. So, this is a simple device to determine all these parameters and different liquid solid ratios. Now, most of the time when you are working as a geotechnical engineer for site investigation your profession demands that you should understand what is the concentration of chloride and sulphide ions in the soil as well as in the groundwater. Can you guess where these type of studies would be more useful or applicable that is right particularly nearby the seashores or to estimate in very gross terms what is the degree of contamination of the soil mass of the groundwater. Particularly in Bombay region when you are doing piling activities it is mandatory to understand what type of soils and what type of groundwater conductivity and chloride and sulphide concentrations are available. And then what will happen suppose if I determine that the concentration is very high. So, what you should do then as a protective measure then you should use some sulphate resistance emits. So, this is where the sulphate resistance emits becomes mandatory. Then you can also coat the piles by using some polymers or the raisins or some epoxies. So, the normal practice is the pile should be protected against any corrosion due to water or soil which is having a very high concentration of chloride and sulphates. So, here the normal procedure is that you take soil sample dissolve it in water and make a liquid solid ratio of 2 is to 1 that is all by s equal to 2. And we go for indirect titration and that titration is done with the help of ion exchange units which are known as indian easy test kits. So, these test kits are very useful basically this is an ion exchange resin and if you drop it in the solution of soil mass or soil solution their color changes. So, depending upon the number of drops which you have added to the solution of a particular resin you can find out roughly what is the concentration of chloride and sulphide ions in the soil mass. So, it is a sort of a titration technique very helpful for people who are working in field and those who want to estimate the what amount of chloride and sulphides are present and this can also help you in determining what is the corrosion potential of the soil. Now, in my previous lecture I had talked about the cation exchange capacity of the soil mass, but I did not talk about the whole methodology of determination of CEC, but you have noticed that CEC is a parameter on which lot of things depend and for the entire property of the soil mass depends. So, with this in view I thought of covering the steps which are normally adopted for determining CEC of the soil mass. Basically what is CEC the classical definition is that this is the holding capacity of the soil of any contaminants or cations. So, that means this is an amount of cations a soil can hold easily. Now, this is where I was using the term parking of the cations on the soil grains alright and all of you are aware by this time that CEC plays a very important role in soil contaminant interaction. You can also put it as that this is the summation of exchangeable ions that is sodium ion, potassium ion, calcium ion and ferric or ferrous ions on the soil grains. So, factors affecting CEC are basically the charge carrying capacity of the soil. Now, my question to you is how would you determine the charge carrying capacity of the soil? We always assume that clays have negatively charged particles, but then the question is how would you estimate that what is the amount of the charge which is available on the grains of the soil? Is there any method which comes to your mind? There is a method known as zeta potential determination, zeta potential ZETA. So, essentially zeta potential describes how much charge is available on the surface of grains of the soil. Now, if you go in these type of studies you can very easily answer the questions that why clays cannot be compacted beyond a certain limit. So, apart from a double layer formation because of the negatively charged particles you cannot put two particles together just because of the mechanical energy. So, there is a limitation of the compaction process, but if you remember if you go for some energy principle and if you expose the soil mass to some energy field particularly electric or electromagnetic then what happens? This double layer of water surrounding the grains of the soil gets reduced and soils can be compacted very easily. So, based on this technique the genesis of electro kinetic remediation takes place or the consolidation which is accelerated due to electric field application. So, this is important factor that CEC gets influenced by the charge carrying capacity of the soil. I think you can notice this point that as the clay particles are negatively charged when they come in contact with the cations there is a sort of a neutralization of the charge on the surface clear. So, this is the bond which is formed at the time of soil contaminant interaction and rather than contaminant if you are dealing only with water then there is a dipole formation or a double layer formation of water. CEC will also depend upon the pH of the solution. So, on both sides of the pH equal to 7 that is acidic and basic environment the soil exhibits active behavior. So, this part you may come across later on when I will talk about the influence of pH on the corrosion potentials of the soils. Ionic strength of the pore solution the type of cations the type of ions which are present in the pore solution will also influence the cation exchange capacity of the soil and of course, the presence of the salts. Now, there are two codes normally which are followed one is IS 2720 and the EPA SW 846 which are followed to determine the CEC of the soil sample normally we follow IS 2720. So, the sample is first treated with the H 2 O 2 and what it does if you treat the sample as 2 O 2 it will remove the organic contents and boil thoroughly for 1 hour. So, this way you can get rid of all the organic contents which are present in the soil mass. You should notice here that why you want to do this type of treatment to the soil. If organic content is too much the reactivity of the soil will be more or less it will be less that is one of the reasons why you cannot stabilize organic and marine soils. It is very difficult to stabilize them you got the point. So, organic soils cannot be stabilized so easily first of all they themselves are not stable second is their water holding capacity is very high. So, even if you put the cement in them what is going to happen cement will not get any water out of the soil to get cured and to form a bond because these soils will not release water so easily. So, this type of mechanism goes on. So, that is the reason that you have to remove organic contents from the soil to determine its real potential. So, the treated sample is oven dried with 5 gram and it is mixed with 50 ml of 1 normal sodium acetate solution with pH 5. Now, this mixture is digested in a boiling water bath for 30 minutes with intermittent stirring and later centrifuge at a speed of 5000 to 6000 rpm for 15 minutes. The supernatant fluid or liquid is discarded and the sample settled at the bottom of the centrifuge tube is again treated with 50 ml of 1 normal sodium acetate C S 3 CO H is acetic acid. So, C S 3 CO Na is sodium acetate solution again with pH 5 and centrifuged repeat this process thrice. So, as to ensure exchange of calcium ions in the soil by sodium ions. So, this is the first step where you are replacing all the sodium ions with sorry calcium ions with sodium ions why because you are using sodium acetate solution. So, is the leaching of calcium ions out of the sample of the soil and all those calcium ions gets replaced by sodium ions. What we will have to do next is we will have to replace the sodium ions which are getting fixed on the soil by treating it with some other chemical. So, this is the first step of the process. Now, this sample is treated with 1 normal calcium chloride solution. So, this is where sodium is being replaced by calcium ions and is again digested and centrifuged this process is repeated thrice. So, as to ensure exchange of sodium ions with calcium ions. Sangita is realizing that it is a very tough task. Most of things require a lot of patience as I say again and again. Now, this sample is again washed with sodium acetate why you are doing this now. You are trying to check whether further sodium can replace calcium or not if not your process is done, but if there is a change your process is not done you have to repeat the process again. So, this sample is treated again with 50 ml of 1 normal sodium acetate solution of PS 7 and again digested and centrifuged this operation is performed thrice. The resulting supernatant from the last three steps is collected in 250 ml volumetric flask and the concentration of calcium and present in the solution is determined using AAS that is atomic absorption spectrophotometer. Now, once you have done this you can obtain CEC. So, CEC is milli equivalence per 100 gram which is defined as concentration of calcium ions or sodium ions micrograms per milliliter multiplied by 100 into volume of the extract into dilution that is L by S divided by equivalent weight of the cation into 1000 into weight of the soil in grams. Just to give you some idea about what are the CECs of different minerals and hope you will appreciate why some minerals are very active and why some minerals are not active. This table gives you a clear picture if you find out the minerals by using XRD X-ray diffraction technique. For monponylite the CEC is 18.6 and for cationite and elite CEC comes out to approximately 5. So, almost it is 3 to 4 times difference between the cation exchange capacity of the clays itself alright. So, because cationite and elite itself is a clay and monponylite is also a clay mineral but this is one of the reasons why water absorption capacity of monponylite is much more higher than kilonite. But in classical geomechanics we always say that what type of bonds are available in monponylite the van der Waal forces is it not. So, because of van der Waal forces the water absorption capacity is more that is where we have not talked about the chemical potential of the soil or chemical aspects of the material. So, by putting cation exchange capacity also in conjunction with the platelet theory you can find out what would be the total potential of the soil towards its activity or reactivity with contaminants or the environment is this clear. Now, this CEC value can be utilized for the classification of the soil. So, this seems to be a very good tool if you want to differentiate between coarse grained soils and fine grained soils and within fine grained soils also you think or you imagine a situation where each mineral is specified with a CEC value. So, the moment you get the CEC value you need not to go for even XRD analysis which again is a very costly and expensive procedure. So, what you can do is you can up scribe this number and you can say that this soil has more predominance of monponylite and so on. So, this again seems to be a good classification scheme based on chemical composition of the soil mass.