156 



NATURE AND PROPERTIES OF SOILS 



trol the hygroscopicity. The following figures from Briggs 

 and Sehantz,^ by whom the hygroscopic coefficient was deter- 

 mined by exposing air-dry soil at 20° C. to a saturated atmo- 

 sphere and then drying at 110° C, illustrate this point. The 

 organic matter was not a serious disturbing factor. 



iABLE -A..X.i-X. 



HYGROSCOPIC CAPACITY OP VARIOUS SOILS EXPRESSED IN PER- 

 CENTAGE BASED ON DRY SOIL-^ 



Soils 



Coarse sand 



Fine sand 



Sandy loam . . . 

 Fine sandy loam 



Loam , 



Clay loam 



Clay 



Percentage 



Hygroscopic 



01" Clay 



COEPFICIENT 



1.6 



.5 



3.9 



1.5 



7.5 



3.5 



12.9 



6.6 



14.4 



9.6 



22.0 



11.4 



32.5 



13.2 



^ Briggs, L. J., and Schantz, H. L., The Wilting Coefficient for Dif- 

 ferent Plants and Its Indirect BeterTMnation; U. S. Dept. Agr., Bur. 

 Plant Ind., Bui. 230, p. Q^, Feb., 1912. See also, Loughridge, R. H., 

 Investigations in Soils Physics; Calif. Agr. Exp. Sta., Rep. of Work of 

 the Agr. Exp. Stations of Calif, for 1892-3-4, pp. 76-77. Ammon, Georg., 

 Untersuchungen uber das Condensationsvermogen der JBodenaonstituenten 

 fur Gase; Porsch. a. d. Gebiete d. Agri.-Physik., Band II, Seite 1-46, 1879. 

 Bobeneek, A. P., von, Untersuchungen iiber das Ahsorptionsvermogen 

 und die Eygroshopisitat der Bodenlconstituenten ; Forscli. a. d. Gebiete 

 d. Agri-Physik., Band XV, Seite 163-228, 1892. 



* During the many years of soil investigation, especially where the 

 problems had to deal either directly or indirectly with moisture, five 

 methods of water expression have been evolved, their use depending on 

 the nature of the work and on the points to be expressed. They may be 

 listed under two general heads: 



A. Percentage expression 



1. Percentage on a dry basis 



2. Percentage on a wet basis 



B, Yolume expression 



1. Cubic inches to the cubic foot of soil 



2. Percentage by volume 



3. Surface inches 



A soil carrying 25 per cent, of water on the dry soil basis contains 20 

 per cent, on the moist basis (soil plus water). The former method is 



