AGRICULTURE: ALWAY AND McDOLE 
257 
concentration. Now this is exactly what we should expect if the sur- 
face layer of these solutions consists of a single layer of group mole- 
cules of water. Milner shows that the deficiency of salt is 4.1 X IQ-^i 
gram molecules of salt per square centimeter for a normal solution 
(c =0.001). Hence we may place = -4.1 X lO-^. 
This result can be explained if we assume that there is a layer 4.1 X 
10-^ cm. thick on the surface which contains no salt. This then should 
represent the length of the water group molecule. It is interesting to 
note that practically this same value is obtained with solutions of all 
the different inorganic salts. 
Taking the molecular weight of water in the surface to be 18, we 
find the cross-section of the water molecule to be 7.3 X lO-^^ sq. cm. 
It is beheved that this method of studying the structure of liquid 
surfaces will prove to be of very general application. The writer is 
undertaking experiments to measure the cross-sections of molecules ad- 
sorbed on water surfaces from vapors. Thus, benzol vapor greatly low- 
ers the surface tension of water, and in this way some knowledge may 
be obtained as to the shape of the benzol molecules under different 
conditions. Of course other Hquids than water may also be used. 
There is a great deal of available data on surface tension of solutions 
in the literature which can serve this same purpose. I hope to refer 
to as many of these cases as possible, in a paper on the constitution 
of liquids which will soon be submitted for publication in the Journal 
of the American Chemical Society. 
1 Langmuir, I., /. Amer. Chem. Soc, Easton, Pa., 38, 1916, (2221). 
2 Pockels, A., Nature, London, 43, 1891, (437-439). 
3 Lord Rayleigh, Phil. Mag., London, 48, 1899, (331-337). 
* Devaux, H,, Washington, Smithsonian Inst., Ann. Rep., 1913, (261-273). 
« Marcelin, A., Paris, Ann. Physique, 1, 1914, (19-34). ^ 
« Hardy, W. B., London, Proc. R. Soc, (A), 86, 1912, (610-635). 
" Milner, S. R., Phil. Mag., London, 13, 1907, (96-110). 
« Szyszkowski, B. v., Zs. physik. Chem., Leipzig, 64, 1908, (385-414). 
9 Donnon, F. G., and Barker, J. T., London, Proc. R. Soc, (A), 85, 1911, (557-573). 
THE IMPORTANCE OF THE WATER CONTAINED IN THE DEEPER 
PORTIONS OF THE SUBSOIL 
By F. J. Alway and G. R. McDole 
MINNESOTA AGRICULTURAL EXPERIMENT STATION 
Communicated by R. Pearl, February 10, 1917 
The most extreme views are entertained as to the importance of the 
water contained in the deeper portions of the subsoil — that below the 
depth penetrated by the roots of crop plants. Thus while McGee^ 
