846 STATE BOARD OF AGRICULTURE. 



TAHLE 7. THE FREEZING POINT DEPRESSION OF SOILS TO WHICH WERE ADDED 



VARIOUS QUANTITIES OF Ca(0H)2. 

 Reagents. Depression. 



2 gm. Soil No. 3 plus 10 c. c. water 009°C 



plus 5 c. c. N/25 Ca(0H)2 009 



plus 1 c. c. N/25 Ca(0H)2 010 



plus 2 c. c. N/25 Ca{OH)2 016 



2 gm. Soil No. 4 plus 10 c. c. water 010°C 



plus 8 c. c. N/25 Ca(OH)2 010 



plus 1 c. c. N/25 Ca(0H)2 012 



plus 3 c. c. N/25 Ca(OH)2 020 



2 gm. Soil No. 9 plus 10 c. c. water OOg'C 



plus 3 c. c. N/25 Ca(0H)2 009 



plus 1 c. c. N/25 Ca(OH)2 010 



plus 3 c. c. N/25 Ca(0H)2 019 



1 gm. Peat No. 30 plus 10 c. c. water 010°C 



plus 14 c. c. N/25 Ca(0H)2 001 



plus 1 c. c. N/25 Ca(OH)2 002 



plus 5 c. c. N/25 Ca(0H)2 012 



It is clearly evident that both the absorption and acid curves are ob- 

 tained. It will be noted, however, that only the peats gave an acid curve, 

 while the mineral soils yielded the absorption curve. Since the above 

 examples are presented to typify the general character of curve that all 

 the different soils in their natural condition yielded, then it will at 

 once be inferred that only the peats and mucks yielded the acid curve while 

 the mineral soils gave the absorption cuiwe. Indeed nearly 80 different 

 mineral soils have been tested by the freezing point method both for 

 their lime requirement and nature of their acidity and in no case was 

 an acid curve obtained. This array of soils included some of the most 

 acid soils of the Rhode Island and Pennsylvania experimental plots. 

 On the other hand, most of the peats, which numbered only 15, and col- 

 lected at random, gave an acid curve. 



Although none of the 80 mineral soils tested failed to give an acid 

 curve, it cannot be concluded that universally all mineral soils will act 

 alike. On the contrary there are probably some mineral soils which 

 would give an acid curve, but it is believed that such soils are rare. On 

 the other hand, probably all the mineral soils under humid conditions can 

 be induced, by certain treatments, to give an acid curve, as will be 

 subsequently shown. 



The curve yielded by the mineral soils and designated for convenience 

 an absorption curve is of great significance and warrants a thorough 

 consideration. Indeed, this type of curve throws light upon the nature 

 of the acidity of mineral soils, and also upon the theory of exchange of 

 bases in soils. 



In the first place this absorption curve shows that the Ca(0H)2 is 

 removed from solution or taken up by the soil as fast as it is added and 

 is rendered inactive as far as the freezing point depression is concerned, 

 until a certain point is reached and then it begins to remain in solution, 

 or if it is still taken up, it replaces something else, most likely another 

 bas"^. Now the substance which uses up the Ca(0H)2 must be in the 

 solid phase and not in the liquid phase, for if it were in the liquid phase 

 the depression would not remain constant. If the substance were in 

 solution it would take part in the depression produced by the soil plus 

 the water. Upon the addition of Ca(0H)2 a reaction would take place. 

 If the reaction resulted in an insoluble product the substance would 

 be removed from the solution and thus decrease the freezing point de- 

 pression. If, on the other hand, the reaction resulted in a soluble com- 



