216 EXPERIMENT STATION EECORD. 



in the humus soil and least in the sandy soil. The differences between sandy 

 and clay soils as regards adsorption of coloring matter were A'ery great. The 

 increase in adsorption of coloring matter with variations in its concentration 

 were least in the sandy soil. The hygroscopiclty was greatest in clay and least 

 in the sandy soil. 



The degree of swelling of mineral acid soils was generally greater than that 

 of neutral soil rich in humus. This difference was greatest on treatment with 

 sodium carbonate and caustic soda solutions. On the other hand, the volume 

 of swelling of some of the acid soils was less than that of neutral soils poor in 

 humus. 



The variations in the volume of swelling on treatment with reagents, ac- 

 cording to the type of reagent, were much greater with mineral acid soils 

 than with neutral soils. This is taken to indicate that the mineral acid soils 

 contain considerable quantities of colloidal substances showing movable, un- 

 stable forms. 



The hygroscopicities of the different mineral acid soils were not markedly 

 different from those of neutral soils, but the relation of the volume of swelling 

 to hygroscopiclty for mineral acid soils was generally greater than for neutral 

 soils, excepting in the case of acid soil rich in humus. 



The adsorptive power of mineral acid soil for coloring matter was generally 

 greater than that of neutral soil. The relations of adsorptive power to hygro- 

 scopicity for mineral acid soils were generally greater than for neutral soils 

 excepting in the case of acid soil rich in humus. The ammonia absorbing 

 power of acid soil was generally greater than that of neutral soil, but there 

 was little difference between the smallest values of the former and the greatest 

 values of the latter. The increase of the coefficient of ammonia absorption was 

 not greater for acid soil rich in humus and for neutral soil than for mineral 

 acid soil. 



How great is the surface of a gram of surface soil? P. Ehrenberg {Fiihling's 

 Landiv. Ztg., 63 (191J,), No. 23, pp. 725-735) .—The author briefly reviews the 

 work of others on the subject, and points out that while the i*esults obtained by 

 most investigators as to the surface of a gram of soil correspond closely those 

 obtained by Mitscherlich on the basis of hygroscopiclty are quite different. 



From computations based on the assumption that the thickness of the surface 

 film of hygroscopic water in soils is equal to the diameter of a molecule of 

 water, it is concluded that the results obtained by Mitscherlich are, on this basis, 

 double what they should be. Other data are reviewed which would indicate 

 that the thickness of the .surface film of hygroscopic water more neai'ly ap- 

 proaches the sum of the diameters of ten molecules, and it is stated that if 

 computed on this basis the results obtained by Mitscherlich would correspond 

 approximately to those obtained by other investigators. 



It is further stated that according to his studies there are always many un- 

 known factors present affecting the determination of the absolute surface of a 

 soil, and that the results obtained can, therefore, give only an approximate in- 

 dication of the actual facts. 



Investigations on the influence of plant roots on the structure of the soil, 

 M. Berkmann (Untersuchungen Wber den Einfliiss der Pflanzenicurzeln auf die 

 Struktur des Bodens. Diss. E. Tech. Hochsch. Miinchen, 1913, pp. 55, figs. 6) . — 

 This article has been noted from another source (E. S. R., 80, p. 120). 



The gases of swamp rice soils. — II, Their utilization for the aeration of 

 the roots of the crop, W. H. Harrison and P. A. Subeamania Aiyeb (Mem. 

 Dept. Agr. India, Chem. Ser., Jf (1914), No. 1, pp. 17, pi. 1, figs. 2). — In continua- 

 tion of previous work (E. S. R., 30, p. 515) a series of experiments made to de- 



