220 EXPERIMENT STATION RECORD. 



is not dei^endent upon tlae surface area alone but is affected also by adhesion 

 to tlie soil of the liquid used. 



He holds that theoretically the hygroscopicity of a soil is a better measure 

 of the outer surface than the heat of wetting but that to the present time no 

 method of accurately determining the outer surface has been worked out. 

 Hygroscopicity has not been shown to be a measure of the productivity of the 

 soil, and in just as small a degree can the absorption of carbon tetrachlorid by 

 the soil be taken as a measure of the ease of tilth. Nor is the difference be- 

 tween the hygroscopicity and absorption of carbon tetrachlorid an indication 

 of the extent of decomposition and of the quantity of humus, because humus 

 alone does not determine the relation between hygroscopicity and absorption 

 for carbon tetrachlorid. The influence of drying in determining the hygro- 

 scopicity may be eliminated with some soils, but this can not be done in de- 

 termining the absorption of soils for organic fluids. 



The author expresses the opinion tliat the study of the mechanical analysis 

 of soils by sieve and sedimentation should be vigorously prosecuted, and points 

 out that it is entirely possible to classify mineral soils on the basis of their 

 content of finer particles of an hydraulic value of <0.2 mm., using the micro- 

 scope to determine the more important minerals, their degree of weathering, 

 and their form. He believes that an adequate classification of fine soils would 

 be oue of two groups on the basis of current velocities of 0.02 and 7 mm., re- 

 si^ectively. A division into three groups (current velocity for the third not 

 given) should be the utmost required. 



The importance of soil colloids in the determination of hygroscopicity in 

 cultivated and forest soils, P. Bhrenberg and H. Pick (In Festschrift Van 

 BemmeJen, 1911, pp. 194-205; abs. in Geol. Zentbl, 16 {1911), A"o. 5, p. 228; 

 Wasser u. Abwasser, Jf {1911), No. 9, pp. 373, 37)). — It is pointed out, as in 

 previous papers (E. S. R., 24, p. 521), that drying soils previous to deter- 

 mining the hygroscopicity results in a lowering of the hygroscopicity due to 

 the effect of the drying of soil colloids, particularly humus. 



The plasticity of clays, A. Atterberg {Intcniat. Mitt. Bodenk., 1 {1911), 

 No. 1, pp. 10-43, figs. 3). — This is substantially the same article as that pre- 

 viously noted (E. S. R., 25, p. 319). 



The measurement of soil evaporation under arid conditions, C. II. Lee 

 {Engin. News, 66 {1911), No. 15, pp. 428-432, figs. 7).— This article reports 

 the results of experiments to determine the annual evaporation from soils for 

 varying depths of the water level. The observations were conducted in Owens 

 Valley, Cal., the geologic structure of which " is also typical of that of the 

 Great Basin, being a deep synclinal trough partially filled with alluvial debris 

 from the adjacent mountain ranges." The conditions of the experiment were 

 those of an arid climate, a clay soil with vigorous growth of salt and fresih 

 water grasses, and a permanent ground M^ater surface from 3 to 8 ft. below the 

 ground surface. 



" The experimental equipment consists of two galvanized iron tanks, 6^ ft. 

 in depth, connected at the bottom by an IS-ft. length of galvanized pipe. The 

 smaller tank is 2 ft. 4^e in. in diameter and is furnished with a tight fitting 

 cover. The larger tank is 7 ft. 51 in. in diameter and has a system of branching 

 perforated pipes at the bottom connected with the pipe from the smaller tank. 

 The two tanks and all connections are water tight, and water poured into the 

 smaller, or reservoir tank, passes through into the larger, or soil tank, and 

 escapes through the perforations. 



" These two tanks were placed in excavations of a proper size to receive them, 

 the soil tank filled with the excavated soil, and the reservoir tank filled with 

 water. A 6-in. layer of screened gravel, too coarse to enter the ^-hi. per- 



