ELISHA MITCHELL SCIENTIFIC SOCIETY. 21 



REVERSION OF PHOSPHORIC ACID BY HEAT, 



TOGETHER WITH SOME OBSERVATIONS 



ON THE FINE GRINDING OF 



ANALYTICAL SAMPLES. 



W. B. PHILLIPS, Ph. D. 



When manufactured Phosphates are analyzed immediately after 

 preparation, the percentage of Phosphoric acid soluble in water is 

 generally found to be higher than at any subsequent time. A por- 

 tion of it becomes insoluble in water, but is soluble in some of the 

 organic salts of Ammonia; i. e., in the oxalate, and citrate. To 

 this Phosphoric acid the term Reverted is applied, signifying, as is 

 well known. Phosphoric acid which, though at one time soluble in 

 water, has become insoluble in that liquid, and occupies an inter- 

 mediate position between the original tri-calcium-phosphate of the 

 crude material, and the tetra-hydrogen-calcium-phosphate of the 

 manufactured product. 



The change from Soluble to Reverted begins almost at the very 

 moment of manufacture, and continues for an indefinite period, vary- 

 ing among other things with the raw material used, the quantity of 

 acid employed, &c., &c. 



It might be supposed that as this reversion begins when the pro- 

 duct begins to dry, it was connected intimately with the process of 

 drying. But it has been shown by Post (Chem. Industr. 1882, p. 

 217,) that it goes on even in samples enclosed in hermetically 

 sealed bottles, and hence is not dependent on the loss of moisture, 

 under ordinary conditions of temperature. 



The limits of this paper will not allow me to enter at all into the 

 discussion of the various causes of reversion. Among the more 

 prominent ones are the presence of unattacked oxides of Calcium, 

 Iron, and Aluminum, and Calcium Sulphate and Carbonate. 



The object of this paper is to direct attention anew to the fact 

 that a temperature of 100° c maintained for varying lengths of time 

 on the manufactured phosphates causes a very rapid reversion. 



The material used was a saj'.ple of an "Acid Phosphate" pre- 

 pared under my personal supervision at the works of the Navassa 

 Guano Company. It was prepared as follows : 



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