128 CHEMICAL MANUEES. 



of cold air under pressure, which lowers the temperature to 20" C. 

 The superphosphate is then sifted ; it quits the sieve in a very fine 

 state, ready to be dispatched. The cold air treatment not only 

 prevents the substance from aggregating into lumps, but it at the 

 same time prevents retrogradation, as will be seen later on. The 

 plant dries [it is claimed] 10 tons of superphosphate per hour. It 

 requires few repairs. Fuel is well utilized, for on burning ordinary 

 coke, only 1 cwt. per 5 tons of superphosphate is used to remove 

 5 per cent of moisture. 



It is right to add that to work regularly, this machine requires 

 to be manned bv workmen familiar with this class of work ; it 

 increases the output of the factory, and superphosphate can be 

 dispatched from the heap.^ The cooling of the superphosphate was 

 the object of the German patent No. 112,151 of 14 April, 1899, of 

 which the following is the translation. The processes employed up 

 to now for drying superphosphates have the drawback of leaving 

 these products at a high temperature, so that if run on to a heap 

 thev onlv cool very slowlv. Now, heat is very iniurious to the 

 superphosphate in the heap, and it then acquires a great tendency 

 to form lumps. Under the pressure to which it is subjected by its 

 own weight, it becomes compressed more strongly the longer the 

 warehousing is prolonged, and it is then necessary to pulverize it 

 once more before dispatching it. To this drawback a graver one 

 has to be added, stored superphosphate has a great tendency to 

 retrograde, the phosphoric acid rendered soluble then returning to 

 the insoluble condition, because heat favours retrogi^adation and 

 the dried superphosphates preserve their heat when in high heaps, 

 and only cool slowly. The object of the present invention is to 

 avoid retrogradation of the soluble phosphoric acid in superphos- 

 phates which have to be stored. For this purpose the heat is 

 removed from the dried, hot, pulverized superphosphate by a 

 current of cold air. The conveyance of the superphosphate thus 

 finished, to the store, is done in tilting trucks or by aerial conveyor. 

 This latter system is the best and the most economical in the manu- 

 facture of superphosphates, where it is indispensable to utilize as 

 much as possible the covered space to store the goods. This is 

 what a manufacturer who uses the Lutjens process says : "I could 

 not be better satisfied with the scraping machine. The super- 

 phosphate obtained by this process is exceedingly fine, free from 

 lumps, and so dry that it may be dispatched a few days after it is 

 cooled. It responds to all exigencies. Before dispatching it I pass 

 it through a sieve of 6 mm. (a quarter inch sieve), and I get no 



^ With say three screens on to a heap, one man with a pick is occupied in 

 "getting "the superphosphate for the other six men — two men to each screen 

 — a left-handed man mated with a right-handed man, but most men accustomed 

 to this class of work are ambidextrous. — Tr. 



