THE MANUFACTURE OF ACID PHOSPHATE. 6 



apatite (CaFCa 4 P 3 12 ) . The latter variety is by far the most com- 

 mon, but there are intermediate compounds containing both chlorine 

 and fluorine. Pure fluor-apatite contains 42.3 per cent phosphoric 

 acid (P 2 O s ), but it is seldom found in a pure condition. The occur- 

 rence of apatite associated with magnetite in northern New York x 

 has long been known r but attempts to separate the apatite commer- 

 cially have proved unsuccessful. 



In Norway and Canada, however, there are large deposits of apa- 

 tite which were at one time extensively worked, but the discovery 

 of cheaper and more accessible sources of phosphoric acid (particu- 

 larly in the United States) has caused a serious curtailment in the 

 mining of this mineral. 



The main objections to apatite as a source of phosphoric acid are, 

 first, the expense of mining and picking the rock and, second, the 

 large percentage of fluorine, which yields obnoxious gases when the 

 rock is treated with sulphuric acid. The superphosphate now man- 

 ufactured from apatite is but a small percentage of the total material 

 marketed. 



The vast bulk of acid phosphate produced both in this country 

 and abroad is made from the amorphous phosphates of lime, of which 

 there are enormous deposits in the States of Florida, Tennessee, Utah, 

 Idaho, Wyoming, and Montana, and in northern Africa, and smaller 

 deposits in the States of South Carolina, Arkansas, and Kentucky in 1 

 this country, and in France, Germany, England, and Belgium. 



Ocean and Pleasant Islands of the Gilbert group, as well as some 

 of the Society Islands in the southern Pacific and Christmas Island 

 in the Indian Ocean, contain large quantities of very high grade 

 phosphate rock; in fact, these phosphates are as rich as any amor- 

 phous phosphates known. It is only in recent years, however, that 

 the deposits have been developed to any extent, and owing to the 

 lack of harbors the rock must be loaded at sea, which makes their 

 exploitation somewhat difficult. 



The character of the American deposits, the methods of mining 

 and preparing the rock for the market, the cost of production, annual 

 output, and other details of this industry have been described in 

 bulletins of this department, 2 and so need not be repeated here. 



In Table I is given a list of the more important phosphatic sub- 

 stances (with their approximate composition) used in the manu- 

 facture of acid phosphate. 



i Blake, W. P., Trans. Am. Inst. Min. Engrs., 21, pp. 157-160 (1892-93). 



2 Buls. 41, 69, 76, and 81, Bureau of Soils, U. S. Dept. Agr.; Bui. 14, U. S. Dept. Agr. (1913). 



