722 EXPERIMENT STATION EECOKD. 



content, the lowering of the freezing point of soils is very high and varies 

 considerably with the extreme types of soil, being highest in clay and lowest 

 in sand. 



" In all the soils, with the exception of quartz sand and some extreme types of 

 sandy soil, the ratio of the lowering of the freezing point is not directly inversely 

 proportional to the ratio of the water content . . . but the former is many times 

 greater than the latter. . . . By determining the lowering of the freezing point 

 of various soils at a large number of moisture contents it was found that . . . 

 the lowering of the freezing point increases in a geometric progression while 

 the water content decreases in an arithmetic progression. In the case of quartz 

 sand and some extreme types of sandy soil, however, the depression of the 

 freezing point Increases inversely proportional with the water content. . . . 

 All evidences, both direct and indirect, point to the fact that high depressions 

 of the freezing point are produced by and represent actual concentration. . . . 

 The rate of increase in the lowering of the freezing point with the decrease in 

 moisture content is uniform throughout, from the maximum to the minimum 

 moisture content, etc." 



Further experiments with washed quartz sand, silt loam, clay, .sandy loam, 

 humus loam, peat, and kaolin to determine, by means of the freezing point 

 method, the influence of adding tenth-normal solutions of potassium chlorid, 

 potassium sulphate, magnesium sulphate, ammonium sulphate, calcium nitrate, 

 sodium nitrate, potassium phosphate, calcium phosphate, and sodium phosphate 

 to the soils, showed that " in the case of the neutral salts the concentration of 

 the soil solution was increased from 20 to 100 per cent of their strength 

 employed, while in the case of the soluble phosphates the concentration of the 

 soil solution of all the soils except peat, quartz sand, and kaolin, was extremely 

 little, if any, increased. These results on the whole do not confirm entirely the 

 theories that the application of soluble salts, even in small amounts, may not 

 increase the total concentration of the soil solution." 



Changes in soils brought about by heating-, A. Wilson {Sci. Proc. Roy. 

 Dublin /S'oc, n. so:, IJf {I'.ilo). Xo. .18, pp. 513-520, ^(js. 3). — Laboratory experi- 

 ments are reported in which the depression of freezing points and the electrical 

 conductivities of extracts of soils wliich had been heated for two hours at from 

 60 to 150° C. were determined. 



It was found that heating increased the amount of soluble matter in soil, 

 this being indicated by a considerable increase in electrical conductivity, a 

 marked depression of the freezing point, and a wide range of coloration of 

 extracts from soil heated at different temperatures. " In each of the extracts 

 about half the depression of freezing point was due to electrolytes. The 

 increase in the amount of water absorbed by the heated soil indicates a change 

 in the texture of the soil brought about by heating. . . . 



"The results of these experiments show that at any rate part of the in- 

 creased productivity of heated soil may be due to the increase in soluble matter 

 induced by heating, and to the change in soil texture, which has a remarkable 

 effect on the retention of water by the soil." 



A list of references to literature bearing on Ihe subject is appended. 



Soil fertiUty, J.E.Rush {Science, n. ser., 42 {1915), Xo. lOSS, pp. 6S.2-634).— 

 It is stated that "the problem of soil fertility is a composite one which needs 

 for its solution a knowledge of the interrelated subjects physics, chemistry, 

 and bacteriology." The presence of the proper bacteria in the soil is. however, 

 considered to be the final deciding factor in soil fertility. 



Maintaining fertility in the Wisconsin drift soil area in Iowa, W. H. 

 Stevemson, p. E. Bkown, and L. W. Fobman {Iowa Sta. Duh 161 {1915), pp. 



