G14 



STATE BOARD OF AGRICULTURE. 



Table 7. Solubility of Various Salts at 20° C. 



Name of Salt. 



Grams of Salt 



dissolved in 100 



gm. of water. 



NaNOs 



KNO3 



CaCNOaVj. . 

 Mg(N03)2.. 



KCl 



NaCl 



CaClz 



K2SO4 



CaS04 



MgS04 



Ca(HC03)2. 

 Mg(HC03)2. 

 NaHCOn... 

 CaH4(P04)2, 



(NH4)2S04. 



83.7 



31.6 



54.8(19) 



42.33(19) 



34.07 



35.82 



74.00 



11.11 



36.2 



9.60 



'75!4' ' 



(19) at 18° C 



Since the formation of tlief*e salts is eomparatively slow and their 

 accumulation to any extent is prevented by the excessive and frequent 

 rains in the humid regions, their amount in the soil solution is relatively 

 small and does not form a saturated solution, probably, not even at a low 

 moisture content. Those of course that form a saturated solution are 

 separated in the solid phase. At a hiuh moisture content, therefore, 

 these salts are diluted and would cause only a small lowering of the 

 freezing point, but as the water content is reduced they become more 

 concentrated and they would cause a correspondingly greater lowering 

 of the freezing point. That is exactly what the experimental results 

 show. Hence, the experimental data agree almost perfectly with the 

 hypothesis. 



The foregoing hypothesis, however, does not explain why the lowering 

 of the freezing point increases in a geometric progression while the 

 moisture content decreases in an arithmetic progression, and not fol- 

 low a direct invere ]U'0]»ortionality ratio, (approximately), as might 

 be expected. 



It must be stated, however, that also for this phenomenon, no defi- 

 nite and proved exi»lanation can be offered. The following hypothesis, 

 however, would seem worth considering. 



Tt is assumed that a portion of the water found in the soil is inactive 

 or unavailable and does not take part in dissolving the salts in the 

 soil. How this portion of the water is rendered inactive and in 

 what form it exists, cannot be asserted with certainty. There are 

 two possible ways in which it might exist: (1), as loosely chemically 

 combined water, and (2), as adsorbed water. In the first case the 

 water might react with some of the components of the soil to form 

 hydrolysed substances or hydrates. There is a great amount of evi 

 dence which goes to bear out this view. It is suggested by Muntz and 

 Gaudechon, (14), that a part of the heat generated u[)on moistening 

 dry soils is probably due to chemical combination between the water 

 and some soil components. Clays, for instance, are believed to possess 



(") Ann. Scl. Agron. (3). 4, 393-443, 1909. 



