DEYING AND ENRICHMENT OF PHOSPHATES. 63 



the present state of the manure trade, and they will continue to be 

 so as long as high grade phosphates, with a low oxide of iron and 

 alumina content, are available, which only require to be rendered 

 soluble to produce excellent superphosphates. The following are 

 the chief patents taken out for this purpose : — 



1. Dumonceau and Nicolas (French patents Nos. 201,427 and 

 5101,461) seek to fortify low grade phosphates, consisting of phos- 

 phate of lime and carbonate of lime, by the use of sulphur. The 

 principle of the two methods is as follows : Phosphatic chalk is 

 calcined so as to obtain a mixture of phosphate of lime and quick- 

 lime, which is mixed with water and sulphur in iron pans. The 

 insoluble phosphate of lime is separated from the soluble sulphides 

 formed. The strength is thus fortified 20 to 30 per cent. A 

 current of carbonic acid is injected into the solution, and sulphur 

 and sulphuretted hydrogen separated, the latter being converted 

 into sulphur by sulphurous acid. 



2. Simpson replaces sulphur by sulphuretted hydrogen (German 

 patent 58,925), and after calcination of the raw phosphates, injects 

 it into water, holding the phosphates in suspension. The calcium 

 sulphides are afterwards treated by carbonic acid, or by sulphate 

 ■of soda, to transform them into gypsum and sulphurous compounds ; 

 the latter treated by carbonic acid yield sulphuretted hydrogen 

 and soda. 



3. Brochon (French patent 215,577) extracts phosphates rich 

 in carbonate of lime by carbonic acid under pressure after crushing 

 and stirring up with water. The liquid containing the acid carbon- 

 ate of lime is separated from the insoluble phosphate and treated 

 for the recovery of the carbonic acid. But carbonate of lime is 

 only feebly soluble in carbonated water even under pressure (1 cubic 

 metre of water only dissolves 3 kg. (or 100 gallons, 3 lb.) under 

 a pressure of 4 atmospheres at 5^ C). The process is thus too costly. 



4. Winsinger, to prepare bicalcic phosphate free from oxide 

 of iron, completely soluble in citrate of ammonia (German patent 

 No. 51,739), extracts all the phosphoric acid of the phosphate of 

 lime by sulphuric acid, converts half the solution into monocalcic 

 phosphate, by carbonate of lime and milk of lime, which precipi- 

 tate iron ; he adds this precipitate to the other half, and obtains by 

 .addition of sodium sulphate, sodium carbonate and quicklime, 

 phosphate of lime insoluble in water free from oxide of iron, which 

 he finally adds to the solution of monocalcic phosphate. A bicalcic 

 phosphate is thus obtained, and gypsum and caustic soda as bye-pro- 

 ducts. This process is rather complicated. 



5. 0. lahne (German patent 57,295) prepares phosphate of 

 lime free from oxide of iron, alumina and silica, by acting on 

 phosphates rich in oxide of iron and alumina, by sodium bisulphate. 

 'The raw phosphates (coprolites, etc.) treated with an aqueous solu- 



