764 EXPERIMENT STATION' HF.CoHD. 



of Jlil.uard just iiieiilionod, or tliat ol' T. Hrli](isin«;, may be nscd,' The 

 flay sediiiiciit, liowevur, may contain iine particles of other substances 

 besides chiy, such as quartz, ferric hydrate, etc., and it may be ueces- 

 sary to determine these clicniically and snl)tract the weiii'lit of tliese 

 from tlie total weight of the sediment. 



The humus substances are also deterinincd chemically, especially the 

 colloid humus matter {mnfirre noire) which is physically very impor- 

 tant. This determination is best made by (Irandeau's method.- 



Whcn the constituents themselves are considered in their relation to 

 the properties of the soil, aside from the effect due simply to the size 

 of the ])aiticles, as for instance with reference to the conduction of 

 heat, chemical analysis can not be disi)ensed with, for Riechanical 

 examination can not give the necessary information.^ Under certain 

 circumstances it may be of importance to make an examination of the 

 mineral constituents of the different sediments.^ 



THE AHRANGEMENT OK THE SOIL PARTICLES (STRUCTURE OF THE SOIL). 



Separate fjrahi structure. — If we consider a soil divided up into its 

 individual particles, which are massed together more or less closely, we 



see that the size of the interstitial spaces and consequently the move- 

 ment of water and air in the soil are dependent solely on the size and 

 form of the particles. This arrangement is called (after Hilgard) the 

 "separate grain structure" {Einzelkornstructnr). If the i)articles are 

 spherical and of equal size they can be supposed to be massed together 

 in either of two ways: (1) Each sphere rests in the space between the 

 adjoining" spheres (Fig. 4), or (2) the planes tangents to the spheres at all 

 their i)oints of contact intersect at right angles. The former arrange- 

 ment produces a three sided or four sided regular pyramid while the 

 latter gives rise to a cubical form (Fig. 5). In the first case the 

 arrangement is the most compact possible and the volume of the inter- 

 granular space (volume of pores) amounts to 25.95 per cent of the 

 total volume. In the second case we have the least compact arrange- 

 ment, and the volume of the pores rises to 47.64 per cent of the total 



'E. Rainaun, Foistliche Bodenkunde, Berlin, 1893, p. 50. 



2 Jour. AgT. Prat., 36 (1872), No. U-17. Compt. Keiid., 71, p. 988. 



3F. Walniscbaffe, 1. c, p. 43-85. 



*F. iSteiiuiedc, Aulcitnng zur luiueralogisclieu Bodeiuiualyse, 1889. 



