568 
AGRONOMY: L. T. SHARP 
hydrate is a stabilizing agent in a fairly wide range of concentrations. 
Sodium carbonate, on the other hand, failed to stabilize at any concen- 
tration. Both substances are precipitating agents at concentrations 
greater than rg- normal. Our studies with the hydrogen electrode include 
systems of soil suspended in various concentrations of these substances. 
In case sodium hydroxide or carbonate is added to a soil the bases 
combine directly with the silicates forming addition-compounds, as has 
been also pointed out by Sullivan (loc. cit.^^). Water or carbonic acid 
is the end-product, hence the washing process so essential for the appear- 
ance of diffusion in soils after the use of neutral salts is not so necessary 
in the case of alkaline salts. 
Briefly stated the experiments upon which the above summary is 
based have enabled us to throw upon the subject of salts in relation with 
soil colloids a light which has never before, particularly by soil chemists, 
been cast upon it. Not only is the way opened for an extensive experi- 
mental field in the physical chemistry of the soil, but there are indi- 
cations that the principles involved, part of which are for the first time 
gathered together and correlated by us, will be of profound practical 
significance in the important subjects both of 'alkali' and of fertilizer 
salt applications to soils. Many of the perplexing aspects of the physi- 
cal effects of continued nitrate of soda and other fertilizer appUcations 
to soils, as well as those following the leaching out of alkali, will, we hope, 
be largely cleared up by the investigations soon to be reported at length. 
My thanks are due to Dr. Chas. B. Lipman for many helpful sugges- 
tions and for his critical reading of the manuscript. 
^London, J. Chem. Soc, 71, 568 (1897). 
^London, Proc. R. Soc, 66, 115 (1899). 
»/. prakL Chem., Leipzig, Ser. 2, 25, 445 (1882). 
*J. Amer. Chem. Soc, 35, No. 4 (1913). 
' Free has already discussed flocculation as a matter of degree — Philadelphia, J. Frank. 
Inst., 1910. 
® Forsch. auf dem Gehiete der Agrik. Physik, Vol. 2, 1879, p. 251. 
' /. prakt. Chem., Ser. 2, 23, 388 (1881). 
8 Physical Properties of Soil, Cambridge Univ. Press, 1900, p. 30. 
^ Loc. cit. 
" The Soil, 1910, p. 252; also London, J. Chem. Soc, 85, 964 (1904). 
" Cited from U. S. Dept. Agric. Of. Exp. Sta. Rec, 29, No. 8, 719 (1908). 
« Hawaiian Agric. Exp. Sta., Bull. No. 35, 1914. 
" U. S. Dept. Agric. Bur. Soils, Bull. No. 45. 
Bodenkunde fiir Land-und Forstivirte, p. 51. 
" After reviewing this subject Sullivan draws the following conclusion — " So far as the 
evidence goes, then, the action of silicates, clay, and other constituents of the earth's crust 
on solutions of such salts as do not dissolve in water with alkaline reaction consists in an 
equivalent exchange of bases." U. S. Geol. Sur., Bull. No. 312, p. 27 (1907). 
^' For a discussion of the presence of free acid in salt solutions in contact with soils the 
reader is referred to the work of Parker, /. Agric. Res., 1, 179 (1913). 
