20 
magnesia and lime, more particularly the latter. The data in the 
tables show a decrease in solubility of lime and an increase in that of 
potash upon ignition in a majority of the samples. In addition to the 
above-mentioned factors a decrease in solubility after ignition would 
be produced by the conversion of the bicarbonates into normal car- 
bonates, the former of which are more soluble than the latter. This 
would, of course, be most striking in the water extracts. 
POTASH. 
' The following table shows the relative effects of heat upon the solu- 
bility of potash: 
Solubifity of potash in water and fifth-normal nitric acid. 
Calculated on basis of dry soil.] 
Soil No. 
Soluble in water (parts per 
million). 
Soluble . in fifth-normal nitric acid (per 
cent). 
Air dry. 
Dried at 
100° c. 
Dried at 
250° C. 
Ignited. 
Air dry. 
Dried at 
100° C. 
Dried at 
250° C 
Ignited. ; 
74 
128.2 
64.3 
117.8 
77.2 
87.1 
96.6 
"98.2 
60.3 
36.5 
£44.8 
43.8 
119.8 
117.4 
82.3 
192.7 
76.3 
92.4 
55.1 
96.2 
100.8 
49.2 
202.8 
58.7 
107.4 
339.3 
40.1 
301.9 
118.0 
90.6 
45.9 
78.3 
77.4 
19.4' 
353.5 
56.4 
64.4 
217.5 
132.5 
260.6 
• 83.8 
.77.4 
43.6 
147.6 
140,6 
. 78.2 
220.7 
182.9 
59.0 
0.053 
.027 
.073 
.061 
.177 
. 056 . 
.055 
• .061 
.014 
.0:38 
.025 
.032 
0.066 
'.032 
.081 
. 155 
.142 
.084 
.056 
.0,54 
.013 
.051 
.024 
.032 
0.050 
.026 
.064 
.202 
.054 
.095 
.038 
.038 
.032 
.029 
.030 
.033 
0.068 
i 4 
.071 
.113 

|92 
.134 
290 . . .' 
.094 
405 
.090 
416 
.062 
417 ' 
.072 
406 
.022 
428 
.041 
426 
.070 
448 
.053 
. The figures ■show that the effect of heat upon potash is slightly 
different from -the effects on lime and magnesia. The ignited soils 
appear to contain this element in the most soluble form, while the 
samples dried in air and at 100° C. contain it in the least soluble 
form. In the air-dried samples potash is also more soluble in the 
cultivated than in the uncultivated soil, and the greatest solubility 
of this element is also found in the highly organic soils. 
Soils in general possess fixing power for potash and for phos- 
phoric acid in particular. The fixing of potash is generally believed 
to be due to hydrated silicates and organic matter. Cameron and 
Bell 1 on continuously extracting a soil with water until no more 
potash dissolved, then grinding the sample and reextracting, found 
an additional amount of potash to be removed. This they attributed 
to a colloidal aluminum silicate upon the surface of the particles, 
thus protecting them from the action of the water as well as absorb- 
ing the potash. Dehydration and decomposition would therefore 
materially overcome the fixing power, and the potash replaced by 
lime or magnesia would not be refixed during a short period. 
' U. S. Dept. Agr., Bur. Soils Bui. 30, p. 26. 
