SUPERPHOSPHATES. 153 



Since 1890 the increase has been maintained, as is seen by 

 the following return of the production in the United States 

 alone": 



1895. 1896. 1897. 1898. 1899. 



Tons... 1,098,668 862,671 1,014,322 1,231,758 1,710,000 



Large quantities now come from Algeria, the output in 1898 

 being over 223,000 tons.f 



The following table gives the average composition of a 

 number of mineral phosphates : 



Calcium 

 Tricalcium phosphate. fluoride. 



Coprolites ... ... 5060% 



Belgian phosphate ... 33% 



Florida, pebbles ... ... 6065% 



South Carolina ... ... 58% 1 2% 



Lalm or Nassau (Germany) 30 75% 



Canadian ... ... 8095% 



Redonda Phosphate (Leeward Islands) consists largely of 

 aluminium phosphate and is therefore, in its raw state, not of 

 much value. Lalm phosphate also contains a considerable 

 quantity of ferric oxide and alumina, which lowers its value. 



Mineral Superphosphates. It is for the manufacture of 

 these substances that the mineral phosphates are chiefly used, 

 for in their raw state the latter are too insoluble to be of much 

 value as fertilisers. In an extremely fine state of division, 

 however, they become more available and are sometimes used. 



Superphosphate is made by treating the mineral with 

 sulphuric acid, when a replacement of phosphoric acid by sul- 

 phuric acid takes place, calcium sulphate and free phosphoric 

 acid being formed 



Ca 3 P,0 H + 3H 2 S0 4 - 3CaS0 4 + 2H 8 P0 4 . 



The sulphuric acid also acts upon calcium carbonate, cal- 

 cium chloride or fluoride, and oxides of iron and aluminium, 

 if these be present, evolving carbon dioxide, hydrochloric or 

 hydrofluoric acid 



CaC0 3 + H,SO 4 CaS0 4 + H,0 + C0. 2 



CaCl. 2 + H. 2 S0 4 CaS0 4 + 2HCl 



* Jour. Soc. Chem. Ind. 1899, 190, and I'.XH i, s;. t J. S.C.I. 1899, 315. 



