G18 EXPERIMENT STATIOX RECORD. 



The author proposes and explains a system of classifying such soils by their 

 varying degrees of plasticity. For this purpose the ordinarily accepted classifi- 

 cations of soil particles do not go far enough into the microscopic and ultra- 

 microscopic particles, but he approves of the proposed international classification 

 (E. S. R., 31, p. 417). Ordinarily it is necessary for a rational classification to 

 take account only of particles 2 mm., 0.2 mm., 0.02 mm., and 0.002 mm. and less 

 in diameter. The author's apparatus and methods for mechanical analysis of 

 soils, especially for the separation of the very fine microscopic and ultramicro-zT^ 

 scopic particles, are described. ^ C?»V(«y 



0.i)2^m.] 



Soils containing more than 50 per cent of coarse sand (2 to ^SiHfxo.m..') are con 

 sidered dry sandy soils fit only for forestry. Soils containing more than 50 per 

 cent of fine s:ind (0.2 to 0.02 mm.) or silt (0.02 to 0.002 mm.) may be classwl as 

 loamy clay, normal loam, or loamy sand. Soils containing more than 50 per cent 

 of colloid particles (0.002 mm. or less) are very heavy, highly plastic clay soils. 

 The importance and value of determining the degree of plasticity in the latter 

 class of soils are especially emphasized, and simple methods of determining the 

 limits of (1) fluidity, (2) "rolling out," and (3) sticky plasticity are described. 



Two natural classes of clay soils based on such determinations are di.stin- 

 guished, (1) highly plastic (sticky) clays containing more than 50 per cent of 

 colloid particles, and (2) less plastic soils containing more than 50 per cent of 

 fine sand or silt. The determination of plasticity of clays is preferred to 

 mechanical analysis because it is very simple and much more rapid. Further 

 study of the colloid substances which determine the plasticity of soils is in 

 progress. 



The course of denitrifi.cation in soils of different water content, O. Lem- 

 MERMANN aud J. L. WicHEKS {Ceuthl. BaJd. [etc.], 2. AM., 4I {1914), ^0. 18-23, 

 pp. 608-625, fig. 1). — The authors review work of others bearing on the subject 

 and report comparative studies of thi'ee soils of different water-holding capaci- 

 ties with reference to the intensity of the denitrification process. With the 

 same relative water content with reference to the total water capacity entirely 

 different results as regards nitrate reduction were obtained with the three 

 soils. The most nitrates were destroyed in all three soils when the water 

 content corresponded to the total water capacity. The formation of elementary 

 nitrogen decreased with decreasing water content, but was not always the least 

 with the least water content. This is thought to be due to the influence of 

 other bacteriological processes on the denitrification pi-ocess. 



The chemistry of soils: Evolution of purins, G. Chardet {Rev. G^n. Chim., 

 n {1914), ^^0. 10, pp. 154, 155; ahs. in Chrm. Zcnthl., 1914, II - A'o. 10, p. 655).— 

 In continuation of a previous article (E. S. E„ 31, p. 515) the author briefly 

 discusses certain theoretical considerations involved in the breaking down of 

 nucleo-proteids with simultaneous formation of purin bodies. It is concluded 

 that the purin bases occur in tlie soils either as nucleic acids derived from 

 vegetable alkaloids or formed from the nucleo-proteids of dead micro-organisms. 

 They occur in very small amounts in soils and it is not likely that they exert 

 any considerable influence on plant gi'owth. 



The effect of deciduous and evergreen trees on the soil and its vegetation, 

 A. Koch {Ccnthl. Bakt. [etc.], 2. Aht., 41 {1914), A'o. lS-23, pp. 545-572. /)/.<(. 

 4). — The author reviews the work of others bearing on the subject, and reports 

 studies of the humu.s of pine and beech forest soils and of the volatile oils and 

 other products of conifers with reference to the germination of seeds, the 

 growth of plants, and the life and activity of yeasts and soil and other bacteria. 



Buckwheat and cabbage plants and beech and pine seedlings grew much 

 better in the beech humus than in the pine humus. Both kinds of humus were 



