90 



CHEMICAL MANUEES. 



drum is carefully inspected, the screws of the frames tightened, and 

 those of the manhole doors, because, in spite of the use of double 



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 IpHlliili'i ' S i ^ :il 





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screws, they are liable to become loose under the trituration to which 

 they are exposed. Care must be taken to keep the sieves in perfect 



