848 STATE BOARD OF AGRICULTURE]. 



colloidal hydrated silica, acid aliimino-silicates, silicic acid, and insoluble 

 organic matter, in the case of the mineral soils, in the case of peats and 

 mucks, however, it might be partly assigned to the soluble organic 

 acids and humus substances, and partly to organic insoluble acids and 

 humus substances. 



Hence, the acidity or lime requirement of soils might he asoHhed almost 

 entirely to insoluble hydrated siUoic acid, acid alumino-silicates, silica, 

 and organic insoluble substances in the case of the mineral soils, and to 

 organic soluble acids and huinns substances, and organic insoluble acids 

 and humus substances in the case of peats and mucks. 



Inferring once more to the absorption curve of the mineral soils, it 

 will be at once concluded that no exchange of bases takes place in the 

 soil, when it is treated with Ca(0H)2, until it is saturated with this 

 base. Hence, w^hile an exchange of bases may take place when the soil is 

 treated with a neutral salt, such an exchange does not immediately occur 

 when a free base is used. 



Another very interesting phenomenon in connection with the absorp- 

 tion curve is the fact that the depression of the freezing point remains 

 constant with the increase in the volume of water present. Thus, just 

 before the soil is completely saturated or satisfied with Ca(0H)2, the 

 volume of water is increased in some cases almost twice and yet the 

 lowering of the freezing point is the same. It appears that when the 

 solution of the soil is very dilute the freezing point depression is not 

 perceptibly affected even with considerable increase in the volume of 

 water. Thus 2 grams of soil in 10 c. c. of Avater give a. lowering of the 

 freezing point of .010° O. Practically the same lowering of the freezing 

 point is obtained when the same quantitv of soil is treated with 20 c. c. 

 of water. Even in pure salt solutions the freezing point depression re- 

 mains almost constant with large dilutions, if the original solutions are 

 very dilute. Thus, MgSO^ at a certain concentration gave a depression 

 of .010° C. Upon adding to 10 c. c. of this solution 10 c. c. of water, the 

 depression changed to .008° C, or a difference of only .002° C. These re- 

 sults might be expected in the case of electrolytes. 



Before concluding this part of the investigation, on the lime require- 

 ment of soils, a brief discussion should be devoted to the character of the 

 reaction that is involved between the Ca(OH)o and the various soils, 

 that is to say, is the reaction a chemical or a physical one? It should 

 be at once stated that it appears to be both but the major part appears 

 to be chemical. That probably it is not entirely physical may be men- 

 tioned the following facts: (1) The quantity of lime taken up by the 

 various soils is too great to be accounted for entirely by surface 

 phenomena; surface alone does not appear to be the predominant cause 

 of the absorption because kaolin and quartz sand may be ground almost 

 as fine as many of the clay loams here employed and yet their lime re- 

 quirement is practically negligible. (2) The curves obtained are not 

 adsorption curves; the adsorption curves are smooth equilibrium curves 

 and consequently do not have such abrupt breaks as indicated in the 

 foregoing curves. (3) There is no fundamental reason why the phe- 

 nomenon cannot be chemical. 



Lastly, the question may be asked, is it necessary and economical to 

 add to the soil all the amount of lime according to the freezing point 

 method, it requires? As previously declared, this question will ulti- 



