78 



These substances are removed from it by hydro- 

 cloric acid, by fermenting it, washing it in hot water 

 and by reburnlng. 



The charcoal after being used six or eight hours 

 in the filter is taken out and placed in cisterns of 

 wood or masonry, and there covered with water 

 mixed with a hundredth part of its weight of hydro- 

 rloric acid and it is left to itself for 8 hours at least. 

 The acid then aS tacks all the substances absorbed by 

 .the charcoal, the azote substances, coloring matter, 

 lime and salts and destroys them or renders them 

 soluble. After eight hours the charcoal is drawn off 

 and piled on the floor, or it is left another eight hours 

 to ferment and is then washed in boiling water. 

 The washer used is a semi cylindrical vessel slightly 

 inclined, in which moves an archimedean screw. 

 The charcoal is shovelled into the lower end and it 

 mounts by degrees against a strong current of hot 

 water, which comes down from the upper part. 

 The hot water takes away all the impurities still 

 in it. The charcoal when washed is placed in heaps 

 on the floor to dry, then calcined and used again. 



A factory working '200,000 pounds of beets per 

 day uses 10,000 pounds of animal charcoal, say 5 

 per cent of the weight of the beets. The use of a 

 larger quantity would be preferab e if economical 

 reasons would allow it. To revivify this quantity of 

 charcoal requires 100 pounds of hydrochloric acid. 

 The stock of charcoal ol' such a factory would be 

 from 30,000 to 40.000 pounds. 



