MANUFACTURE OF SUPERPHOSPHATE. 



109 



doors each of which empties into a house of its own. Each " den " 

 has a capacity of 50 to 100 tons, according to the size of the factory. 

 Attempts have been made to find methods of rendering phos- 

 phate sokible more rapidly and more completely than by the pro- 

 cesses actually used. To accomplish this the phosphate is reduced 

 to a very line state, i.e. to pass through a No. 100 sieve. A paste 

 is made of it by drenching it with w^ater or with acid of 10° to 20° B. 

 and finally adding the rest of the acid at 60° B. But this process 

 was soon abandoned, for the action was too violent and the metal of 

 the mixer was attacked bv the acid. 



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Fig. 2.3. — Toxic Gas Condensers (Benker and Hartmann's System). 



Attempts have been made to render phosphates soluble by 

 mixtures of hydrochloric and sulphuric acids without any great 

 advantage. The superphosphate contained 0'30 per cent of hydro- 

 chloric acid which rotted the bags, besides the mixture of sulphuric 

 acid and hydrochloric acid attacks the metal. 



Evacuation of the Toxic Fumes. — The gases formed in the 

 superphosphate " dens " cannot be allowed to escape into the atmos- 

 phere without being purified, in consequence of their bad smell and 

 corrosive action. They are generally passed through a wash tower 

 bv means of a fan. Benker and Hartmann make very simple 



