294 



SILICATES. 



has passed long enough, which may be known by its 

 producing no more protochloride of iron, it is stopped, 

 the hydrogen again passed to expel the vapor of hy- 

 drochloric acid, and the tube left to cool before taking 

 the boat from it. This is placed again in the case or 

 tube and weighed ; the weight it has gained gives the 

 weight of the alumina. 



Fig. 48. 



The separation of the alumina would be complete 

 if the mass was perfectly pure, which is not the case, 

 if the material which comes from the nitrates is not 

 sufficiently washed. 



In this case, the material which has been treated 

 with nitric acid, then with hydrochloric acid, may 

 contain lime left with^the alumina. The lime is found 

 as chloride of calcium. The alumina is moistened 

 with a small quantity of water, which is decanted, 



