SOILS FERTILIZERS. 521 



Importance and action of soil colloids in the determination of soil surfaces 

 by the Eodewald-Mitscherlich method, P. Ehrenberg {Ztschr. Angew. Chem., 

 23 {1910), No. 39, p. 18^1; Chem. Ztg., 34 {1910), No. 113, p. 1006; abs. in Jour. 

 Soc. Chem. Indus., 29 {1910), No 20, p. 1217).-~lt is pointed out that air drying 

 of a soil, as is done in the Rodewald-Mitscherlich method (E. S. R., 15, p. 847), 

 appreciably reduces the soil surface, especially when the percentage of humus 

 is high, and consequently lowers the hygroscopicity. The author therefore pro- 

 poses to determine the vapor tension over 10 per cent sulphuric acid on the un- 

 dried soil. Many other agencies besides drying affect the surface area, and 

 soils of almost the same surface area have very different physical properties. 



Contributions to physical soil investigation, P. Ehrenberg and H. Pick 

 {Ztschr. Forst ii,. Jagdiv., 43 {1911), No. 1, pp. 35~Jf7). — This article is based 

 upon the investigations noted above. 



Significance of the osmotic pressure and electrolytic conductivity for the 

 study of the soil, J. Konig, J. Hasenbaumer, and H. Metering {Landw. Vers. 

 Stat., Ilf {1910), No. 1^2, pp. 1-56, pi. 1, figs. 5; abs. in Jour. Chem. Soc. [Lon- 

 don], 98, 1910, No. 578, II, p. 1104; Zentbl. Agr. Chem., J,0 {1911), No. 2, pp. 

 73-75). — Investigations on osmotic pressure and electrolytic conductivity in 

 their relation to vegetation are reported. The apparatus used in determining 

 the osmotic pressure consisted of filter candles, a glass cylinder, and a thermo- 

 regulator. The observations on the electrolytic conductivity were made by the 

 Kohlrausch method, using a Wheatstone-Kirchhoff bridge, rheostat, and ther- 

 moregulator. The results were studied in their relation to the kind of soil 

 and its absorptive capacity, the action of different fertilizers, and the effects of 

 different crops. 



The determination of the osmotic power of the plant to take up water gives 

 good results when the temperature is kept constant. The variations by this 

 method are much less than in earlier investigations, a much more gradual and 

 regular rise and fall in the water-absorptive power being observed. A tempera- 

 ture of from 18 to 20° C. is best, 18° being taken in this case to correspond to 

 that of the electrolytic conductivity. The temperature of 25° formerly used is 

 not recommended because at this temperature a strong diosmose of the salts 

 takes place and considerable quantities of gum are dissolved from cells of the 

 apparatus. The degree of diosmose of salts in the study of the osmotic power 

 of the plant depends upon the nature of the salt and probably upon the charac- 

 ter, i. e., the uniformity of the semipermeable membrane. For substances that 

 are not, or are only slightly, diosmotic this method may be used advantageously 

 in determining the molecular weight. With strongly diosmotic materials the 

 determination of the isotonic pressure by a solution of no, or one of slight, 

 diosmotic power may be used for that purpose. 



The determination of the electrolytic conductivity of the soil, in general, gives 

 results that stand in close relationship to the osmotic power. An absolute 

 agreement, however, is not to be expected, since the soils vary in their physical 

 and chemical relations. Ordinary fertilizing increases the osmotic properties 

 as well as the electrolytic conductivity of all soils, whereas the growth of vege- 

 tation decreased both of them. The osmotic property, therefore, as well as the 

 electrolytic conductivity is an expression of the degree of solubility of the plant 

 food of the soil, the method of determining the electrolytic conductivity being 

 the simpler and more rapid, whereas that of determining the osmotic property 

 seems to be the most certain and accurate when good osmometers are used. 

 The electrolytic conductivity increased with the decrease in size of the soil 

 particles. 



