64 CHEMICAL MANURES. 



tion of sodium bisulphate, carbonate and phosphate of Ume, dis- 

 solve whilst the silica, and iron, and alumina compounds remain 

 insoluble, and may be separated by filtiation along with the gypsum. 

 By evaporating the solution a yellow^ salt is obtained, the composi- 

 tion of which corresponds to the formula QNa^^SO^ + CaH^P^,Og + H.^0, 

 which may be employed as such, as a manure, or mixed with 

 gypsum, horn meal, peat ; it may also be used in stables, to fix 



ammonia. 



6. 'In making superphosphates, Martin proposes to use the acid 

 sulphate from manufacture of nitric acid. The acid sulphate from 

 the cylinders is dissolved in water, so as to get a solution of 45^ to 

 50° B. The precipitate consists of bisulphate, which it is easy to 

 convert into sulphate by recrystallization, whilst the strongly acid 

 solution is used to dissolve raw phosphates. All the phosphoric 

 acid is dissolved, and the resultant superphosphates have less 

 tendency to retrograde than those made with sulphuric acid of 50° 



to 53° B. 



7. Thonnar and Huxton s Belgian patent No. 96,109, and Bol- 

 lancVs Belgian patent 196,190, to eliminate the oxides of iron and 

 alumina, may also be mentione i. 



8. Schitcht proposed to make superphosphates from ferruginous 

 ^' phosphate thus : As soluble oxides of iron induce retrogradation 



of the phosphoric acid in superphosphates, whilst protoxides are 

 inactive, and as sulphate of ammonia possesses the property of 

 forming with protoxides of iron readily oxidizable in the air double 

 salts very stable in air, Schucht, on such data, proposed to dissolve 

 phosphates in presence of sulphate of ammonia, then to effect the 

 ] eduction and so obtain very stable superphosphates of ammonia. 

 With this end in view, the finely ground superphosphates are mixed 

 with sulphate of ammonia. One part Fe^g requires 175 per cent 

 of that salt to form the double salt FeSO^ + (MHJoSO^ + 6H.p. 

 Reduction can only be effected by weak sulphurous acid which is 

 injected under pressure into the diluted mixture of superphosphate 

 heated to 80° to 100° C. Schucht thinks that the small amount of 

 sulphurous acid in the product will quickly oxidize and become in- 

 nocuous to plant life. The author is not aware if this method has 

 ever been used ; in any case, Schucht makes no mention of it in 

 his book. Besides, a phosphate containing 3 to 4 per cent of 

 sesquioxide of iron and alumina will on'y cause an inversion of 

 050 per cent in stored superphosphate, a loss say of Id. a cwt. 

 That is why the above process scarcely merits attention, except 

 perhaps in those cases where the purchaser also pays for nitrogen. 

 Otherwise the process would hardly be worth the trouble. 



9. Carr's process dealing with phosphates rich in oxides of iron 

 and alumina is analogous. It consists in calcining the phosphate, 

 grinding it fine and then mixing 1000 parts with 400 parts of sul- 



