EXPERIMENT STATION BULLETINS. 603 



be above 1°C at the minimum water content while that of sands and 

 very light sandy loams lies as a rule close to 0.4° C. Since, however, 

 water appears to influence greatly the lowering of the freezing point it 

 cannot always be said that these values of the depression represent 

 absolute relative amounts of salts between the different soils, and 

 especially between the related types of soil. A true comparison of the 

 relative salt content of soils can be ascertained only when the free water 

 content of the various soils is exactly at the equivalent point. 



In all the soils, with the exception of quartz sand and of some ex- 

 treme types of sand, the ratio of the freezing point loAvering is not 

 directly inversely proportional to the ratio of the percentage of water 

 as might be expected (approximately), but the former is many times 

 greater than the latter. Thus, in the case of one of the clay loams the 

 ratio between the lowering of the freezing point and water con- 

 tent is 27.56 and 2.37, respectively. Upon investigating this relation 

 more thoroughly by determining the depression of various soils at a 

 large number of moisture contents it was found that this relation follows 

 a mathematical law and indeed the geometric law, that is, the freezing 

 point depression increases in a geometric progression while the per- 

 centage of water decreases in an arithmetic progression. In the case of 

 quartz sand, however, the depression increases directly inversely pro- 

 portionally to the water content. 



The unusual rapid increase in the depression with the diminution in 

 the percentage of water content and the extraordinary high lowering of 

 the freezing point at the low water content created at first some doubts 

 as to whether these freezing-point lowerings are really caused by con-, 

 centration of the soil solution and not by some physical factors. If 

 they are caused by some physical factors they do not represent concen- 

 tration of solution. Two physical factors which might produce such 

 results it was thought, are (1) the supposed pressure with which the 

 water films are held by the soil particles, and (2) the influence of the 

 soil particles themselves upon the depression. These and other possible 

 physical factors have been thoroughly-considered but it has not become 

 apparent that the depressions of the freezing point as obtained are in- 

 fluenced by any physical agent. On the contrary all evidences, both 

 direct and indirect, point overwhelmingly to the fact that the values of 

 the freezing point lowering at the different moisture contents are 

 caused by and represent actual concentration of solution. 



In explaining that the high depression of the freez,ing point at the low 

 moisture content or the increase of the depression with the decrease in 

 the percentage of water, may represent concentration of solution, the 

 following suggestion is offered: It is assumed that the soil solution 

 contains salts or their ions, produced by the reaction of the dissolved 

 components of the soil minerals, hydrolysis of the minerals, application 

 of fertilizers, decomposition of organic matter, etc. These salts have, 

 as a rule, a high solubilit}' and would require a large amount of them 

 to form a saturated solution. They are formed slowly and since the fre- 

 quent and excessive rains, especially in the humid regions, tend to leach 

 them away, only a relatively small amount of them is present at any one 

 time. At a high moisture content these salts are diluted and the lowering 

 of the freezing point is small. As the moisture content, however, is reduced 



