THE MANUFACTURE OF ACID PHOSPHATE. 3 
apatite (CaF0a 4 P 3 O 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 5 ), but it is seldom found in a pure condition. The occur- 
rence of apatite associated with magnetite in northern New York 1 
has long been known, 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 mam "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 ! 
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;. 
