1912] BRIGGS & SHANTZ—WILTING COEFFICIENT 27 
THE RELATION OF THE WILTING COEFFICIENT TO THE HYGROSCOPIC 
COEFFICIENT 
When a dry soil is placed in a saturated atmosphere, it will 
absorb water vapor until a condition of approximate equilibrium 
is attained. The moisture content of a soil under such conditions 
is known as the hygroscopic coefficient of that soil. 
The determination of the hygroscopic coefficient, unless carried 
out with special precautions, is not very exact. It is influenced 
by variation in temperature and by any departure from a condition 
of complete saturation of the surrounding air.2 The time element 
is also an important factor, since the soil absorbs water very slowly, 
particularly near the point of equilibrium. In fact, equilibrium 
would not be theoretically obtained until the interstitial spaces 
of the soil were practically filled with water. The method thus 
has certain inherent disadvantages which are not encountered in 
moisture equivalent determinations. 
The hygroscopic moisture determinations given in this paper 
were carried out in a double-walled ice chest kept in a subterranean 
room, where the temperature was approximately 20 C°.% The 
bottom of the chest was covered with water and the zinc walls 
were lined with blotting paper which was kept saturated. 
A comparison of the hygroscopic coefficient and the wilting 
coefficient for a number of soils is given in the accompanying 
table (table III). The soils used are the same as those employed 
in the preceding experiments, being arranged in order of increasing 
moisture equivalents. 
The hygroscopic determinations given in the table are the mean 
of duplicate measurements. The determinations range from o.5 
per cent in sand to 13.2 per cent in clay loam. The corresponding 
wilting coefficients have been discussed in connection with the 
preceding table. 
The ratio of the hygroscopic coefficient to the wilting coefficient 
is given for each soil in the last column of the table. The mean of 
this ratio is 0.68, with a probable error of +o.012. We have, 
9 Hircarp, E. W., Soils. 1906. p. 196. 
%” Determinations by J. W. McLANE. 
