23 
nitric acid as shown in a number of instances, This is probably due 
to precipitation subsequent to extraction in the nitric acid extracts. 
Part of the increase in the solubility of sulphates in the heated 
soils of this series was probably due to absorption of the products of 
combustion of the gas used in heating the oven. It was found that 
by passing the products of combustion through water a precipitate 
of barium sulphate was obtainable upon the addition of barium 
chlorid. King 1 found an enormous increase in the solubility of 
sulphates upon heating in an oven at 110° C. using both gasoline and 
kerosene as a source of heat, thus largely eliminating this factor. 
In spite of the possibility of an introduction of error due to this 
cause it is probable that the results tabulated here disclose correctly 
the effect of heat upon the sulphates. In addition to the already- 
mentioned reasons, namely, destruction of organic matter, soil films, 
etc., it is necessary to take into consideration the chemical effect of 
heat upon the various mineral sulphur compounds. Calcium sulphate 
is known to exist in four forms, two being anhydrous, one of which is 
more soluble than the other. Sulphur also exists in soils as sulphids 
generally combined with iron, or as sulphates in combination with iron, 
lime, or magnesia, also combined with organic matter in many essential 
forms. The effect of heat would be most marked upon the latter in 
that it would undergo considerable decomposition at 250°, the sulphur 
being oxidized to sulphur dioxid or trioxid, which upon treatment 
with water as a solvent would tend to form sulphuric acid or sulphates 
to the extent of the bases in solution. On the other hand, it is evident 
that large amounts of sulphur will be lost through volatilization upon 
ignition. Soil Xo. 428, a highly organic soil, illustrates this effect 
best in that the increase from air dried to oven dried (100° C.) is 
1,600 parts per million, while the decrease from the sample heated 
from 250° C. to ignition is 1,900 parts per million. It is evident 
from these data that upon igniting the soils the sulphur set free from 
the destruction of the organic matter is oxidized and volatilized so 
that it is lost before combination with the bases takes place. 
BICARBONATES. 
The following table shows the bicarbonate content of the water 
extracts : 
Solubility of bicarbonates in water. 
(Parts per million of dry soil.) 
Treatment of soil. 
Soil 
No. 
74. 
Soil 
No. 
164. 
Soil 
No. 
9. 
Soil 
No. 
292. 
Soil 
No. 
290. 
Soil 
No. 
405. 
Soil 
No. 
416. 
Soil 
No. 
417. 
Soil 
No. 
406. 
Soil 
No. 
428. 
SoU 
No. 
426. 
370.1 
44S.O 
1,309.2 
314.2 
106.4 
137.4 
91.3 
45.1 
113.5 
419.4 
338.9 
230.9 
158.5 
283.7 
363.5 
252.1 
132.9 
202.7 
327.7 
70.9 
161.4 
297.5 
157.3 
174.6 
35.4 
221.4 
1533 
73.8 
73.6 
2X6.0 
143.0 
53.9 
52.5 
136.4 
68.2 
118.5 
73.1 
204.3 
582.8 
133. 1 
70.5 
Dried at 100° C 
Dried at 2.'*)° C 
Ignited 
102.7 
SflS. 4 
MD.fi 
(7. S. Dopt. Iff., Bur. SoiLs Bui. 26 p. 56 
