SOILS — FERTILIZERS. 419 



over most of the unglaciated section and over a part of the glaciated section." 

 Including 5 miscellaneous types, 31 soil types of 14 series are mapped, of which 

 the Miami, Carriugton, and Union silt loams are, in their order, the most 

 extensive. 



How great is the surface of a gram of surface soil? II, P. Ehbenbekg 

 (FUJiUng's Landtv. Ztg., 64 (1915), No. 9-10, pp. 233-243) .—In a further contri- 

 bution to the subject the author reviews data to strengthen his previous con- 

 clusions (E. S. R, 33, p. 216). He introduces further data from tests of 

 siliceous gels which show that the so-called hygroscopic water of colloidal gels 

 in soils consists not only of the films covering the surfaces but of the water 

 held by capillarity between these films in the spongy structure of the gel. On 

 this basis it is concluded that the surface of a .soil containing an appreciable 

 amount of colloidal matter is not proportional to the hygroscopic water. 



A new method of measuring the concentration of the soil solution around 

 the soil particles, G. Bouyoucos and M. M. McCool {Science, n. ser., 42 (1915), 

 No. 1084, pp. 507, 50S). — In experiments with sand, loam, clay, and peat with 

 varying moisture contents to test the freezing point method as a measure for 

 the concentration of the soil solution. It was found that the lowering of the 

 freezing point and consequently the concentration of the soil solution varied 

 directly with the amount of water present. When the soils contained a high 

 moisture content the lowering of the freezing point was rather small and did 

 not vary greatly between the different soils, but when the moisture content of 

 the same soils was reduced considerably the lowering of the freezing point was 

 increased, in some cases very greatly. 



In further experiments to ascertain the sensitiveness of the method to detect 

 differences in concentration in the soil solution and to see whether the concen- 

 tration of the soil solution can be increased by the addition of mineral salts, 

 the freezing point of a complete nutrient stock solution in concentrations of 

 80, 2,000, and 4,000 parts per million was determined alone and in contact with 

 the different soils. It was found that the lowering of the freezing point of the 

 solutions in contact with the soils did not vary greatly from that of the solu- 

 tion alone. 



Soil acidity and methods for its detection, E. Tkuog (Science, n. ser., 4^ 

 (1915), No. 10S4, pp. 505-501). — The author disagrees with the conclusions 

 drawn by Harris (E. S. R., 32, p. 30) regarding the cause of soil acidity, and 

 points out that the basis of the colloid theory of soil acidity, namely, that " the 

 relative affinity of the acids is independent of the nature of the base," holds 

 only when all the reacting substances are in a true solution, "or if there are 

 partially soluble substances formed, then in any series of comparisons the 

 solubility of the corresponding substances must be of the same order. The 

 opportunity for secondary or side reactions must also be eliminated or made 

 comparable." 



In order to overcome these difficulties small amounts of very finely powdered 

 soil were thoroughly shaken with comparatively large amounts of salt solu- 

 tions for a short period, then quickly filtered and the acidity of the filtrate 

 determined. It was found that the soil took up very nearly equivalent amounts 

 of different bases from salts having a common acid ion. " The results of these 

 experiments point strongly to the existence of true acid substances as the cause 

 of soil acidity." 



Soil temperature, an important factor in scientific agriculture, L. B. 

 Pritchard (Jour. Dept. Agr. Victoria, 13 (1915), No. 7, pp. 399-405, figs. 5). — 

 The influence of soil temperature on the physical, chemical, and biological 

 properties of soil is briefly discussed, and the results of observations carried 

 out at the Central Research Station at Werribee, Australia, on the diurnal 



