SILICATES. 291 



smell of ammonia is distinctly perceived, the process is 

 continued ; if it is not, a drop of ammonia is added 

 with a glass rod, the mixture stirred, and notice is 

 taken if the smell of ammonia remains and if a pre- 

 cipitate is formed; generally there is no precipitate, 

 and it is then certain that all the alumina has been 

 precipitated by the calcination. It is left to digest on 

 the sand-bath until it is also certain that the nitrate of 

 ammonia has penetrated the whole mass, then a little 

 water is added, and the liquid decanted, to prevent 

 accident, on a filter. 



Water is again placed in the capsule, boiled, de- 

 canted, and washed a dozen times in order to be sure 

 that the boiling water penetrated the entire mass ; 

 when the decanted liquid leaves no residue if evapo- 

 rated on platinum foil, the washing is discontinued. 



The material submitted to analysis is then divided 

 into two portions first, the portion soluble in nitrate 

 of ammonia, and secondly, the insoluble portion left in 

 the capsule. 



The insoluble portion in the capsule is treated with 

 nitric acid, whic his left to digest slightly heated; nitric 

 acid dissolves the alumina and the peroxide of iron. 



If manganese is not present, the silica which remains 

 is white; if present, it is black. The silica is washed, 

 and the washings evaporated in a platinum crucible 

 and ignited. 



The mixture of alumina and oxide of iron is weighed. 



If the silica contains peroxide of manganese, it is 

 washed with dilute sulphuric acid, adding a crystal of 

 oxalic acid. The oxalic acid decomposes the binoxide 

 of manganese and converts it into peroxide, which 

 dissolves in sulphuric acid; the sulphate of mangan- 

 ese is washed; the sulphate mixed with sulphuric 

 acid in a platinum crucible is heated to 300 to 400, 

 and the sulphate of manganese weighed ; the silica re- 

 mains in a state of purity after all these treatments 



