ELISHA MITCHELL SCIENTIFIC SOCIETY. 37 



EXPERIMENT II. 



The formula used was : Lbs. 



Rock (60" seive) .1 500 



Sulphuric acid 46'"B 1200 



Temperature of acid I22°F. (so^C). 



Temperature in pan i6o°F. (7i°C). 

 Sampled from pan, bottled, corked and cooled. 



Calculated. Found, 



per cent. per cent. 



Phosphoric acid, soluble in water 8.73 8.81 



Phosphoric acid insoluble in water 5,87 5.01 



Phosphoric acid reverted 1.69 



Phosphoric acid insol. am. cit. 65" 3.32 



Phosphoric acid total 14.60 13.82 



Moisture 21.73 22.45 



From Experiments I and II it will thus be seen that it is possible 

 to calculate within one per cent, of the actual analysis. If care be 

 taken to use uniform qualities of rock and acid, and to mix thor- 

 oughly, hut not too much, I believe that the difference can be 

 brought within still narrower limits. 



It may be of interest to some to have a compact working formula 

 for calculating the probable yield of a given mixture, and I have 

 prepared one. It is in fact the one I use constantly. With the 

 higher grades of Charleston rock it may be relied upon to within 

 1 per cent. 



Let a = amount of acid used. 



m = " " " needed for complete decomposition. 



c = coefficient of solubility, 

 w = total weight of mixture. 

 then 



looX— ^ — ' =per cent, phosphoric acid insoluble in water. 

 w 

 and 



100 X — = per cent, phosphoric acid soluble in water. 

 w 



To derive m, let x= per cent. H2SO4 in 53°B acid 



y= " " " " strength of acid used. 



z = No. of pounds 53°B acid needed for complete decomposi- 

 tion of I pound. 

 Phosphoric acid in bone phosphate=4.36 (constant.) 



p=pounds of phosphoric acid in mixture. 



