SOILS — FERTILIZERS. 515 



crop growth. Several examples of damage to crops attributed to lack of air 

 in the soil are described. 



The results of this study are taken to indicate that one of the conditions 

 for the best growth of crops in the alluvial soil is an ample supply of air for 

 the roots, obtained by adjusting and maintaining the proper relations between 

 the air and water in the soil. Water, when excluding air from the roots, was 

 found to act as if it were a poison to crops. 



Soil colloids, P. Ehrenberg {Die BodenkoUoide. Dresden and Leipsic: 

 Theodor Steinkopff, 1915, pp. XII +563, figs. S).— It is the purpose of this book, 

 which is intended for agricultural chemists, scientifically inclined farmers and 

 teachers, and students gf agriculture, to summarize in usable form the present 

 knowledge and practical applications of the colloid chemistry of soils which, 

 while a relatively new branch, has been constantly growing in importance. 



The book is divided into three main sections. The first section briefly 

 sketches the history and scope of colloid chemistry and points out some of the 

 characteristic properties of colloids in general. The second section describes 

 the diiferent tji^es of soil colloids and their properties, more especially from 

 the technical viewpoint. The third section, to which by far the most space is 

 devoted, is a practical presentation of the behavior of the different soil colloids 

 under the influence of the different natural and cultural agencies. 



The adsorptive power of peat moors, P. Rohland (KoUoid Ztsclir., 16 

 (1915), No. 5-6, pp. 146-l.'f8). — Experiments are reported in which it was found 

 that the adsorptive power of peat moor soil is similar to, but considerably less 

 than, that of clays and clay soils. The peat soil also contained colloids capable 

 of adsorbing analin, vegetable, and animal dyes of complex composition, but 

 did not adsorb dyes of simple composition. Adsorption of ions was not observed 

 with peat soil. 



The formation of humic bodies from org'anic substances, W. B. Bottomley 

 {Biochcm. Jour., 9 {1915), No. 2, pp. 260-268) .—An investigation of the rela- 

 tionship between carbohydrates and the so-called " humic acid " and " humin " 

 substances from soil is reported. For the purpose of this investigation humic 

 acid was assumed to consist of " substances thrown down as brown colloidal 

 precipitates by mineral acids from the water or alkaline extracts of humus," and 

 humin of " substances insoluble in water and alkalis, but rendered soluble by 

 fusing with caustic soda or potash, from the solution of which humic acid can 

 again be precipitated." 



It vx-as found that sugars on boiling with hydrochloric acid yielded a mixture 

 of humic acid and humin bodies, varying in proportion with the different sugars 

 used. The composition of " natural " humic acid from soil or peat, after purifi- 

 cation by alcohol, was found to approximate very closely that of " artificial " 

 (sugar) humic acid. Humic acid and humin were also produced from sugars 

 by the action of various organic acids, lactic, acetic, propionic, butyric, etc. 

 The action of heat alone on sugars produced humic acid and humin bodies, 

 these substances being stages in the process of carbonization. Humic bodies 

 were not obtainable from proteins free from carbohydrates. " The two groups 

 of Inmiic bodies, humic acid and humin, obtained artificially from carbohy- 

 drates, indicate a basis for the natural processes of humus formation." 



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



Amino-acid nitrog'en of soil and the chemical groups of amino acids in the 

 hydrolyzed soil and their humic acids, R. S. Potter and R. S. Snyder (Jour. 

 Amer. Cliem. Soc, 37 {1915), No. 9, pp. 2219-22,37).— Studies, at the Iowa Ex- 

 periment Station, of soils receiving six different treatments and of peat soil 

 are reported, the purpose of which was to correlate " the amounts of the various 

 chemical groups [E. S. R., 26, p. 22] (1) in the soil with its humic acid, (2) in 



