130 CHEMICAL MANUEES. 



These results show that superphosphate dried at 160° C. and 

 shghtly calcined, produce the same effects as ordinary super- 

 phosphates. On the other hand, the action of commercial meta- 

 phosphate is comparatively feeble in the sandy clay experiments. 

 In an experiment on sandy soil the dried and calcined super- 

 phosphate had a less effect than superphosphate simply dried at 

 leO'^ C. (320° F.). 



Drying SiqjerpJiosjjJiates in the Cold. — Cold drying processes 

 consist essentially in mixing dry substances intended to combine 

 with a portion of its phosphoric acid with the superphosphate. 

 Eumpler advises the use of bone black and degelatinized bones. 

 These substances possess a great absorbent power and may be used 

 with success for the drying of high strength superphosphates. As- 

 regards the use of bone dust, 1 per cent may be added to the super- 

 phosphate, according to its percentage of free acid. The bone dust 

 should pass through a 70 mesh sieve. The phosphate taken from 

 the " den " is spread out, the bone dust sprinkled over it, the mass, 

 turned over and passed through an inclined screen. After twenty- 

 four hours the bone dust is almost all dissolved, and the super- 

 phosphate may be dispatched. It is clear, however, that this work 

 done by hand can only partially attain the object in view. Dr. 

 Klippert has the merit of applying this principle by means of an 

 improved equipment, the construction of which is kept secret. 



Drying of the Superjjhosphate by Dusting and Mixing in the 

 Georges Crusher -Sifter. — In France an analogous process to that just 

 described is adopted. This process consists in mixing 3 per cent 

 of raw Gafsa superphosphate well dried and in the condition of fine 

 powder. For this purpose the superphosphate from the "den " is 

 spread by an aerial conveyor on a platform (Fig. 34) ; a workman 

 dusts the product with Gafsa superphosphate and charges it into the 

 grinding sifter shown in the figure. In this machine a shaft with 

 blades driven at a suitable speed triturates the mass and mixes it 

 intimately, whilst the sieve turns it in a contrary direction. The 

 fine material falls from the sieve into the bin of an aerial conveyor 

 which conveys it to the warehouse, where it remains until the time 

 for delivery. Before being dispatched the superphosphate i& 

 crushed and sifted through the Coster crusher. When the super- 

 phosphate is suitably prepared, the treatment indicated suffices to 

 obtain it dry. A great number of factories have installed this pro- 

 cess, which enables them to dispense with a drying machine. It is 

 necessary to add that it is only applicable to superphosphates for 

 home consumption, as superphosphates intended for exportation, 

 especially those for the East, ought to be dried artificially in the 

 drying machine. In the Lutjens process, 1 per cent of degelatin- 

 ized bones is also added, or Algerian phosphate, so as to dry the 

 product and avoid the formation of lumps. The choice between 



