8 
igniting soils for 15 minutes to remove humus, found an increase in 
solubility of phosphoric acid, which, he concluded, was due to the de- 
struction of organic matter with which the phosphoric acid was 
combined. He used as solvents, hydrochloric acid, specific gravity 
1.15, distilled water, and several of the weaker organic acids. Stewart * 
used Schmoeger's method of determining the increase of solubility 
in 12 per cent hydrochloric acid before and after ignition, as an 
indication of the phosphoric acid combined with organic matter. 
Fraps, 2 while finding an increase in the solubility of phosphoric acid 
on ignition, considers that this increase is not wholly due to organic 
phosphorus, but that mineral phosphates in soils are also rendered 
more soluble by ignition, thereby rendering the ignition method an 
unsuitable one for determining organically combined phosphorus. 
On the other hand, Lipman 3 found while working on a series of Cali- 
fornia soils, that heating decreased the solubility of phosphoric acid 
in strong nitric acid. Peterson 4 found that the solubility increased 
rapidly with increase in temperature from 130° up to 200° C, but 
that the solubility of the mineral phosphates in soils was not increased 
by heating below 240° C. 
Valuable work on the solubility of the mineral constituents of 
soils is to be found among the publications of the Bureau of Soils, the 
work being confined largely to the use of water as solvent. In a 
bulletin of that bureau, 5 King gives comparative results of work upon 
fresh and oven-dried soils which show the effect of heating to 110° C. 
to be striking. On the average more nitrates, phosphoric acid, sul- 
phates, bicarbonates, and silica were recovered from the oven-dried 
soils than from the fresh samples, while the average of the chlorin 
determinations showed a decrease. No determination of the basic 
constituents are tabulated, but King states that upon later investi- 
gations he found an increase in potash, lime, and magnesia in oven- 
dried soils. He makes several suggestions as to the cause of this in- 
crease, both from a physical and chemical standpoint, but it is evident 
from his discussions that he considered the cause to be primarily 
physical. A number of other investigators have noted an increase 
in total inorganic matter soluble in water 6 as a result of heating, 
but no separation of the elements was made. 
The special phase to which this paper is devoted is that of the effect 
of heat upon the solubility of the mineral constituents, distilled water 
and fifth-normal nitric acid being used as solvents. 
i Illinois Sta. Bui. 145. 
2 Texas Sta. Bui. 136. 
* Jour. Indus, and Engin. Chem., 4 (1912), No. 9, p. 663. 
* Wisconsin Sta. Research Bui. 19. 
* U. S. Dept. Agr., Bur. Soils Bui. 26, p. 55. 
6 New York Cornell Sta. Bui. 275. 
