928 
Journal of Agricultural Research 
Vol. XXVIII, No. 9 
noting the rise in temperature. The water equivalent thus included the heating 
effect of the stirrer and loss due to radiation during the 5-minute period required 
for determinations. The water equivalent of the calorimeter was found to be 
16.8 gm. of water. The specific heat of the soil or the colloid was taken as 0.2 
in each case. 3 
A 5 to 15 gm. sample of soil or air-dried colloid was ground to pass a 50-mesh 
sieve, dried for 18 hours at 110° C., cooled, weighed, and placed in a desiccator 
in the thermostat, where it was brought to a temperature of 25°. Seventy-five 
grams of water were placed in the calorimeter and allowed to come to a temperature 
of 25° ±0.05°. When necessary a current was passed through the wire for 
a few seconds in order to reach more quickly the temperature desired. After 
reaching a temperature of 25°, the calorimeter was allowed to stand in the 
thermostat for at least 30 minutes before making a determination. It was found 
that under these conditions the temperature of the water would not vary more 
than 0.02° over a period of 5 minutes. Having thus reached constant tempera¬ 
ture, the sample was added through a copper funnel inserted in a hole in the 
fiber cap. At the end of 5 minutes, the thermometer reading was taken. The 
temperature at the end of this time was usually at or near its highest point where 
it remained with slight recession for several minutes. 
Duplicate determinations as a rule showed a maximum variation of about 0.5 
'Calories per gram. This variation was just as great for materials of low heat of 
wetting as for those with high values. It is thus seen that for the average soil 
-colloid the result is accurate within about 5 per cent; while for those of very low 
heat value the percentage may run considerably higher. 
HEAT OF WETTING OF COLLOIDAL MATERIAL AND OF SOILS 
The colloidal materials studied were prepared by the use of a super centrifuge 
as described in a previous publication of this bureau (4) * The particular samples 
used were selected from a list of some 50 which had previously been investigated 
for adsorptive capacities and chemical composition. They covered very nearly 
the variations in adsorptive capacity and chemical composition encountered in 
"the 50 samples. It was therefore presumed that they would cover fairly well 
"the range of heat of wetting values to be expected in the colloidal material from 
normal soils. The soils from which these colloids were extracted were some of 
the important soil types and differed widely in texture and other characteristics. 
The heats of wetting in water of the colloidal materials and corresponding soils 
Are shown in Table I. 
Table I .—Heat of wetting of colloidal material and corresponding soil 
Type of soil or colloidal material 
Heat liber¬ 
ated per 
gram of 
colloidal 
material 
Heat liber¬ 
ated per 
gram of 
soil 
-Cecil clay loam subsoil_ 
Calories 
4.5 
Calories 
1.6 
Chester loam soil_ 
7.2 
1.1 
Marshall loam soil......... 
14.2 
4.3 
Miami silty clay loam subsoil______ 
11.8 
6.4 
Norfolk fine sandy loam subsoil______ 
6.0 
1.5 
Sassafras silt loam subsoil_ _ 
9.8 
2.2 
Sharkey clay soil_ 
16.3 
9.6 
Wabash silt loam soil_ 
17.6 
5.2 
* Patten (11) found the specific heats of several soils, including sands, a muck and a clay, varied between 
0.16 and 0.21. Mitscherlich (7) gives values for sands and clays ranging from 0.13 to 0.27. The heats of 
wetting of the samples tested would have been affected less than 1.6 per cent by a variation of 0.1 in the spe¬ 
cific heat of the sample. 
