832 STATR BOARD OF AGRICULTURE. 



Table 4 and in the acconipanyinjj^ Figure 4. Tlu^ numcn'cal data were 

 obtained bv treating a f^oil Avilli an excess of KOll and then titrating 

 Avith Ca(0n)2 in the usnal manner. 



TABLE 4. THE FREEZING POINT DEPRESSION OF ALKALINE SOIL TO WHICH W^AS 



ADDED Ca(OH)2. 

 Reagents. Depression. 



2 gm. soil plus 10 c. c. water 015°C 



plus 1 c. c. Ca(OH)2 016 



plus 2 c. c. Ca(0H)2 024 



The third principle, therefore, is also established by the preceding 

 data. As will be noticed the depression commenced to rise when only 

 1 c. c. Ca(OH)o was added, while before this soil was saturated with 

 KOH it required 9 c. c. of Ca(0H)2 of the same strength before the 

 freezing point depression started to rise. 



The curve illustrating the third principle is named and will be referred 

 to as the alkaline or no-lime-requirement curve. 



Going back for a moment to the first type of curve, the acid curve, the 

 question may be raised, may there not be other substances, besides acids 

 and acid salts, which upon reacting with Ca(OH)„, give the same type 

 of curve? Before attempting to answer this question it is necessary first 

 to consider the cause or causes which produce this type of curve. 



According to the ionic theory, acids, bases, and salts or electrolytes, 

 tend to break up or dissociate into ions, and the degree of dissociation 

 varies markedly in the various electrolytes. Besides other properties, 

 each ion causes the same amount of depression of the freezing point as a 

 molecule. The larger the number of ions, therefore, there is present in a 

 solution, the greater will be the freezing point depression. Since the 

 various acids, bases, and salts, dissociate differently at the same mole- 

 cular concentration their depression of the freezing point will necessar- 

 ily be different. 



In the light of the ionic theory, therefore, the reason for the gradual 

 decrease in the depression of the acids and acid salts upon adding to 

 them various amounts of Ca(OH)o until the neutralization point is 

 reached and then commences to rise with further addition of the hydrate, 

 becomes at once clear and self-evident. Thus, for instance, consider the 

 case of HCl. This acid at the concentration employed possesses a definite 

 degree of dissociation and hence also a freezing point depression. Upon 

 the addition of a small amount of Ca(iO'H)o part of the acid combines 

 with the Ca to form CaCL. The CaCL evidently has a lower degree of 

 dissociation than that of either HCl and Ca(0H)2, and consequently 

 the lowering of the freezing point is decreased. This decrease continues 

 until all the acid is completely neutralized and there is present only 

 CaCL and HjO. Since the degree of dissociation of CaCl is less than 

 that of either HCl and Ca(OH)o the minimum lowering of the freezing 

 point is registered at the point of neutralization. Upon further addition 

 of Ca(0H)2 after the neutralization is reached, the Ca(OH)o remains in 

 solution, and since it possesses a greater degree of dissociation than the 

 CaCl,, causes an ascent in the depression. 



Any salt, therefore, formed by the reaction between any acid and any 

 base will give the same type of curve as that between HCl and Ca(0H)2 

 provided the salt thus formed has a lower degree of dissociation than 

 either of the acid and base. It might be stated in this connection that 



