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 was 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 Synthe- 

 tiques de Geologie 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) ; Cushman and Hubbard, Bui. 

 28, Office of Public Roads, U. S. Dept. of Agriculture (1907). See also Cameron, Pro- 

 ceedings Eighth International Congress of Applied Chemistry, New York, 1912, Vol. XV, 

 p. 43 et seq. 



