110 BULLETIN 1059, U. S. DEPARTMENT OF AGRICULTURE.. 
vapor from escaping, their results are not indicative of those to be 
expected when vapor pressures are maintained in true equilibrium 
with solutions of reasonable osmotic pressure. As has been stated, 
a solution showing 12 atmospheres pressure will be in equilibrium with 
vapor 99 per cent saturated, and even this degree of saturation, it is 
believed, would be extremely difficult to maintain except in a fully 
sealed vessel. 
On the other hand, Patten and Gallagher (136) have carried out 
experiments, both on absorption of vapor and evaporation from soils, 
in "desiccators" which are assumed to be similar to the bell jars 
mentioned hereafter, and which, while usually not strictly vapor 
proof, approach much nearer to the ideal condition. Patten and 
Gallagher, both in their review of earlier work and in their own 
experiments, have established a number of salient points which assist 
in the proper conception of the relation between vapor (or, to a cer- 
tain extent, gas) molecules and solid particles, such as those of the 
soil. Schubler 17 and Davy 17 are quoted as having shown that, in 
general, the finer the texture of the soil and the greater its content 
of humus, the higher is the absorption capacity of soil for water 
vapor. These results, while actually referring to the initial rate of 
absorption, are fairly indicative of the forces with which various 
soils attract water vapor. Von Dobeneck 17 obtained similar results, 
though concluding that large grains absorbed more vapor per unit 
of surface than small ones. Each soil particle reacts upon vapor 
molecules independently, and each has a specific relation to different 
kinds of gases. Several investigators have decided that the absorp- 
tion of vapor decreases with an increase in temperature, even though 
the absolute vapor pressure increases proportionately. Patten and 
Gallagher have carefully proven this. Hilgard's contrary finding 
may be explained on the basis that he was dealing almost, wholly 
with rate of absorption, and higher absolute vapor pressure should 
more quickly bring about equilibrium. Mason and Richards 17 found 
that cotton fiber containing water resembles a solution in exhibiting 
a definite partial vapor pressure. 
Patten and Galleghers most important results have to do with the 
rates of absorption of vapor, and with evaporation, in the presence 
of various vapor pressures controlled by sulphuric acid solutions 
and vessels of water, within desiccators. The rate of absorption by 
dry soils increases, and the rate of evaporation from wet soils de- 
creases quite regularly as the partial vapor pressure in the desiccator 
is increased. It is, however, evident in all of the results that as the 
vapor pressure approaches saturation the amount of absorption in- 
creases in greater proportion than does the vapor pressure. A num- 
ber of the graphs are strongly suggestive of the idea that, if com- 
17 For complete citations see Bureau of Soils. Department of Agriculture, Bulletin 51. 
