16 EXPERIMENT STATION RECORD. [Vol. 35 



March, 1915. It describes the methods and apparatus adopted and results (in 

 detail) obtained in a systematic study of the pollution of the air in and 

 around various English cities as indicated by measurement and chemical 

 examination of the rain water and deposits collected in special gages devised 

 for the purpose. The data include rainfall in millimeters, and tar, ash, total 

 solids, soluble sulphates, chlorin, and ammonia expressed in metric tons per 

 square kilometer. 



SOILS— FERTILIZERS. 



A guide to the mineralogical analysis of soil, F. Seemann (Leiffaden tier 

 Mincralogischeri BodcnanuJiiHe. Vienna : Wilhelm Braumiiller, IOI4, pp. IX+110, 

 pis. S, flgs. 39). — This book represents the author's experience as a teacher of 

 mineralogical soil analysis, in which an effort is made to correct some of the 

 faults of earlier methods. 



The volume is divided into the following main parts: Collecting of sample; 

 investigation of the most important physical properties of the soil ; mechanical 

 soil analysis; and mineralogical examination of soil constituents, embracing (1) 

 methods and (2) character of the soil-forming minerals. Seven tables for the 

 determination of minerals in the soil are included. 



The data of geochemistry, F. W. Clarke (U. S. Geol. Survey Bui. 616 

 (1916), pp. 821). — This is the third edition, revised and enlarged, of this work 

 (E. S. R., 26, p. 517). 



The plasticity of clay and its relation to mode of origin, N. B. Davis 

 {Trans. Amcr. Inst. Mining Engin., 51 {1916), pp. ^51-^80, figs. 4). — Plasticity 

 is defined, especially with reference to clay, and theories of plasticity as devel- 

 oped by others, based on (1) structure of clay particles, (2) presence of 

 hydrous aluminum silicates, (3) molecular attraction between particles, and 

 (4) presence of collodial gelatinous matter, are reviewed and discussed. The 

 theory of suspension and emulsion colloids is reviewed and experiments on 

 the plasticity of four excessively plastic clays are reported. A further study 

 deals with the formation of residual and transported clays. 



It is concluded that " plasticity in clays is due to the gelatinous state of 

 matter, a state common to them because of their mode of origin. This gelat- 

 inous matter may be silicic acid gel, alumina gel, iron oxid gels, silicate gels, 

 or organic gels. Two or more of these are usually present, and their effect will 

 be further modified by adsorbed salts and the relative proportions of large and 

 small grains, and to a limited extent by the shape of the grains. The particular 

 kind and amount of gelatinous matter present, the size and shape of grain, and 

 the relative proportions of large and small grains, are important factors in 

 determining the other related physical properties of tensile strength and air 

 shrinkage." 



On osmosis in soils, C. J. Lynde and .T. V. Dupr6 {Proc. and Trans. Roy. 

 Sac. Canada, S. ser., 9 {1915), Sect. Ill, pp. 69-80, figs. 2; Jour. Amcr. Soc. 

 Agron., 7 {1915), No. 6, pp. 283-292, figs. 2).— Further experiments on the sub- 

 ject with a moist clay subsoil (E. S. 11., 33, p. 420), for the purpose of testing 

 phenomena observed in previous experiments, are reported. The general 

 conclusion is drawn that " whatever the cause, water moves through clay sub- 

 soil from a weak soil solution toward a strong one. The results agree with 

 the theory that this movement is caused by osmosis." 



Salts, soil colloids, and soils, I>. T. Sharp {Proc. Nat. Acad. ScL, 1 {1915), 

 No. 12, pp. 563-568). — This is a general discussiim of the results of investiga- 

 tions, to be re|)orted iii detail later, on the subject of salts in relation to soil 

 colloids. The experiments are based largely on the striking change in physical 



