40 



ALUMINA AND SESQUIOXIDE OF IRON. 



passed, and which it is necessary to maintain until it 

 is completely cool. Then there should be substituted 

 in place of the current of hydrogen, a current of hy- 

 drochloric acid gas, which transforms the iron into 

 volatile chloride and leaves the alumina, which is 

 weighed. A complete description of this process of 

 separation of iron and alumina may be found in the 

 article on silicates. The apparatus is arranged as fol- 

 lows: L is a gas furnace upon which is placed a salt 

 bath I. In the bottle H there is placed some fresh 

 chloride of sodium, on which is poured concentrated 

 hydrochloric acid. 



Fig. 3. 



Then the bottle H is placed in cold water and sul- 

 phuric acid gradually poured upon it, taking care that 

 the mixture does not become heated, and stopping 

 when vapors of hydrochloric acid begin to form. It 



