Journal of Agricultural Research 
Vol. XI, No. 4 
150 
urination of the latter “unless carried out with special precautions, is not 
very exact.” 
HILGARD’S METHOD 
Details of this were published earliest by Loughridge (19), who had been 
a student under Hilgard at the University of Mississippi. Later (14, 
p. 76) it was described by the latter as follows: 
The fine earth is exposed to an atmosphere saturated with moisture for about twelve 
hours at the ordinary temperature (6o° F.) of the cellar in which the box should be 
kept. For this it is sifted in a layer of about 1 mm. thickness upon glazed paper, on 
a wooden table in a small water-tight covered box (12 by 9 by 8 inches) in which there 
is about an inch of water; the interior sides and cover of the box should be lined with 
blotting paper, kept saturated with water, to insure the saturation of the air. . . . 
After eight to twelve hours the earth is transferred as quickly as possible, in the cellar, 
to a weighed drying-tube and weighed. The tube is then placed in a paraffin bath, the 
temperature gradually raised to 200° C. and kept there 20 to 30 minutes (rapidity of 
raising temperature depending upon the amount of moisture in the soil), a current 
of dry air passing continually through the tube. It is then weighed again, and the 
loss in weight gives the hygroscopic moisture in saturated air. 
Some time later, to avoid the decomposition of the organic matter of 
surface soils, Hilgard modified the method to the extent of using an air 
bath, raising the temperature to only no° C, keeping the sample in for 
an hour, weighing, drying again, and continuing the process until a prac¬ 
tically constant weight was obtained. 1 
Under “fine earth” was included the material finer than 0.5 mm. 
resulting from the sample being reduced by a rubber pestle, instead of by 
one of steel or porcelain, to prevent any crushing of soil particles. He 
sometimes digested clayey soils with distilled water until fully disin¬ 
tegrated, after which the muddy water was evaporated with the soil 
slush and the whole thoroughly mixed. As the determination of the 
hygroscopic coefficient was, with Hilgard, almost always incidental to a 
chemical or physical analysis of the soil, this rather tedious preliminary 
preparation of the sample was no serious matter in view of the great 
amount of time and labor involved in the detailed analyses to follow. 
Hilgard studied the effect of differences in temperature upon the amount 
of moisture absorbed by a soil and found that it increased with the tem¬ 
perature, provided that the saturation of the air was maintained. In 
this view he was not confirmed by the work of Knop (16), Schloesing 
(26), Ammon (6), and Von Dobeneck (10), who found a lower absorption 
at higher temperatures. He attributed their findings to their failure to 
provide for the saturation of the air inclosed within the absorption 
vessel. 
More recently Patten and Gallagher (25, p. 31-35) have reported some 
data confirming the view of Knop, etc., but, as Lipman and Sharp have 
pointed out (18, p. 716), their description of their methods makes it evident 
1 Hilgard, E. W. Methods of physical and chemical soil analysis. Cal. Agr. Exp. Sta. Circ. 6, 
p. 17. 1903. 
