CITRIC-SOLUBLE PHOSPHORIC ACID AND POTASH. 7 
entirely soluble in 2 per cent citric acid. After heating the mixture 
for one hour longer at the same temperature almost 50 per cent of 
the phosphoric acid and more than 15 per cent of the potash were 
volatilized, and upon heating for three hours more the phosphoric 
acid was still further reduced. 
The sample richest in citric soluble phosphoric acid and potash 
(33S B) was submitted to a microscopic examination by Mr. W. H. 
Fry of this bureau. It was found to be isotropic and possessed all 
the external characteristics of a glass. 
This Avas to be expected, however, since the melt was cooled too 
rapidly to allow of its crystallization. 
SOLUBILITY OF THE POTASH OF THE SLAG IN WATER SATURATED 
WITH CARBON DIOXIDE. 
The fact that the phosphoric acid of basic slag is fairly soluble in 
water saturated with carbon dioxide is taken as an added proof of 
its availability under soil conditions. It was thought advisable, 
therefore, to test the solubility of the potash in the slag product 
(33SB) in this same medium, comparing this solubility with that of 
the potash in feldspar. 
Considerable work has been done on the so-called solubility of 
orthoclase in water and in various other solvents. 1 It is recognized, 
however, that this mineral has no definite solubility in water, but the 
dissolved material undergoes practically complete hydrolysis or de- 
composition, the amount of this decomposition being considerably 
affected by the fineness of the mineral, the method of grinding it 
(whether wet or dry), the quantity and temperature of the water 
used, and the length of time the water is allowed to act. 
In Table IV the apparent solubility of feldspar in pure water and 
in water saturated with carbon dioxide as determined by several in- 
vestigators is given. Few of these results are comparable, owing to 
the different conditions under which the experiments were conducted, 
but they are of interest in showing what widely divergent results 
are obtained by varying these conditions. 
1 Roger Brothers, Am. Jour. Sci. and Arts. 2, 401 (1848) ; Daubrer, A., Etudes Synthfi- 
tiques de Geologic Experimentales, pp. 268-275 (1879) ; Clarke, F. W., Jour. Am. Chem. 
Soc, 20, 739 (1898) ; Lemberg Inaugural Dissertation Dorkat (1877) ; Cameron and Bell, 
Bui. 30, Bureau of Soils, IT. S. Dept. of Agriculture (1905) ; Cusbman and Hubbard, Bui. 
28, Office of Public Roads, U. S. Dept. of Agriculture (1907). See also Cameron, Pro- 
ceedings Eightb International Congress of Applied Chemistry, New York, 1912, Vol. XV, 
p. 43 et seq. 
