THE WATER OF SOILS. 20; 



subjoined, together with the maximum height reached by each. 

 The diagram is very eloquently illustrative of the great differ- 

 ences in the capillary properties of granular sediments of the 

 various grades ; and it would seem that it ought to be possible 

 to deduce from it by a somewhat complex formula the rate 

 and height of ascent of water in any soil of known physical 

 composition. In nature, however, the presence of clay and 

 the greater or less degree of flocculation of mixed sediments 

 will always vitiate to a very great extent the results deducible 

 from such calculations ; hence the data conveyed by the observ- 

 ations of Loughridge must be considered applicable only to 

 granular sediments free from clay and entirely deflocculated. 



It is curious that in this case the " clay " showed a rise 

 markedly below that of the finest granular sediment, despite 

 the extreme fineness of its particles. This proves plainly that 

 the physical nature of colloid clay is unlike that of the granular 

 sediments ; as has been repeatedly mentioned above. 



Maximum and Minimum of Water-holding Power. It is 

 clear that at the base of the columns of soils just considered, 

 the maximum of water-absorption of which the soil is capable 

 will have been brought about; while at the top of the same 

 column, the minimum of possible liquid absorption (continu- 

 ous films of water) will exist. The same minimum moisture- 

 condition will be produced when a limited quantity of water is 

 placed with a large mass of soil ; the moisture will spread to 

 certain limits, until the surface films of water have all acquired 

 uniform tension ; and will then cease to extend, except by 

 evaporation and hygroscopic absorption. 1 It is clear that the 

 same condition will be brought about in the course of time at 

 the top of a soil column in which water has percolated from 

 above; and hence the minimum mentioned, aside from evapora- 

 tion, represents approximately the usual condition of the soil 



1 Ad. Mayer ( Agriculturchemie 2, p. 141) designates this minimum content of 

 liquid water as the " absolute " water capacity of the same ; but it is not obvious 

 wherein this factor is better entitled to this name than would be the maximum 

 (see Wollny's Forsch., 1892, p. i.). M. Whitney (Rep. Proceedings Ass'n Agr. Coll. 

 & Kxp't St'ns, Nov. 190.}) gives as a new observation the fact that in soils ap- 

 proaching the drought condition water " does not obey the ordinary physical laws 

 as we recognize them in capillarity." This evidently refers simply to the well- 

 known phenomenon mentioned above. 



