SOILS — FEBTTLIZERS. 513 



J,^ (1913), No. 12, pp. 7V3, li)Jf). — The aiuhur discusses various views on Ibis 

 subject and reacbes tbe conclusion tbat it should be taught as an individual 

 science from two standpoints, viz, the scientific and the technological. 



Soil analysis, G. Gomez (Bol. Dir. Gen. Agr. [Mexico'^, Rev. A^r., 2 {1912), 

 No. 7, pp. 5U3-607). — The author points out tbe importance of phj'sical and 

 chemical analysis in soil chissitication and judgment, and in determining the 

 fertilizer need of soils. He proposes a simple notation which facilitates com- 

 parison of tbe results of physical and chemical analysis. 



Chemical composition of soils, V. I. Vernadskii (Pochvovwdienie (P^d-o- 

 loyie), 15 (lUlS), No. 2-3, pp. 1-21).— The author, in the first part of his article, 

 draws attention to the important part played by gases in the physical, chemical, 

 and biological activity of soils, and also to their geological importance. He 

 considers the colloidal soil constituents to be the seat of activity of soil gases, 

 states that these gases or their solutions participate in all the processes of re- 

 duction, oxidation, and hydrate formation which occur in the soil, and re- 

 views particularly the activities of nitrogen, hydrogen, oxygen, carbon dioxid, 

 and methane in this respect. The character, properties, and quantitative re- 

 lations in the soil of gases are said to be strongly inOuenced by meteorological 

 and biochemical factors. 



In conclusion the importance is emphasized of considering not only the solid 

 and liquid soil constituents, but also the soil gases in soil analysis. 



In the second part of the article attention is drawn to the elements rubidium, 

 csesium, and thallium, and to their similarity to potassium. Cifisium and 

 thallium are disregarded as occurring only in traces, but th e rubidi um is 

 thought to affect seriously the accuracy of potassium determinations in the 

 ordinary methods of chemical soil analysis, owing to the significant quantities 

 of the former element found in soils and plants and also to the difficulty of dis- 

 tinguishing it from potassium by the ordinary methods. 



Colloidal chemistry and its importance in soils, geology, and mineralogy, 

 H. NiKLAS (Intcniat. Mitt. Bodcnk., 3 (1913), No. 5, pp. 883-403, pi. i).— The 

 author reviews the elements of colloidal chemistry and points out some of its 

 important relations to soils, geology, and mineralogy. 



Most soil gels are considered to be reversible, and most soil colloids are con- 

 sidered to be negatively charged, which is said to explain their power for 

 absorbing the positively charged bases of basic salts. Such absorption results 

 in gel formation and better soil structure, as is shown by a series of photographs 

 illustrating typical colloidal reactions, precipitation, and absorption. The 

 absence of €4ectrolytes, or the presence of so-called physiologically basic salts, 

 such as sodium nitrate, is said to cause the formation of soils, which results in a 

 compact, poorly aerated soil structure. In such cases fall plowing is suggested, 

 as it allows the winter frost to form gels in the soil, thus loosening the struc- 

 ture. Heat and dryness are also said to coagulate the soil colloids and improve 

 the structure, but too heavy rains form sols of the reversible gels and also 

 by washing out the soil salts cause a return of the compact, badly aerated 

 structure. 



Soil formation by weathering is thought to be based on colloid chemistry, 

 especially the formation of laterite, red soil, ortstein, and clay from feldspar. 

 Colloidal humus is considered to be active in soil formation. The beneficial 

 effect of lime salts on soil structure is attributed to the higher gel forming 

 power of bases of higher valence, and it is stated that the more the effect of 

 the positive ion exceeds that of the negative ion the more beneficial is the effect 

 on the soil structure. The beneficial effect of stall and green manure on the 

 soil structure is attributed to the addition of new colloids, which not only form; 

 gels but also dissolve lime. 



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