ALUMINA AND SESQUIOXIDE OF IRON. 39 



the acid solution to ebullition, to add sulphite of soda, 

 in order to reduce the sesquioxide of iron to the state 

 of proto-sesquioxide, replace the solution over the 

 lamp, boil for some time and then neutralize with car- 

 bonate of soda, and afterwards boil with excess of 

 caustic soda until the precipitate is black and pul- 

 verulent. 



The tendency to bumping preceding the actual ebul- 

 lition of the fluid, may be guarded against by means 

 of a spiral coil of platinum wire placed in the liquid, 

 or by constant agitation of the latter ; when ebullition 

 has opce set in, there is no further need of these pre- 

 cautions. Remove the liquid now from the gas, allow 

 to deposit, pass the clear fluid through a filter, which 

 must not be over-porous, boil the precipitate again with 

 a fresh quantity of solution of soda, then wash it by 

 decantation and. afterwards on the filter with hot water. 

 Acidify the alkaline filtrate with hydrochloric acid, 

 boil with some chlorate of potassa (to destroy any traces 

 of organic matter), concentrate by evaporation, and 

 precipitate the alumina by sulphide of ammonium or 

 ammonia. The boiling of the precipitated oxides with 

 the solution of soda is best effected in a large silver 

 or platinum dish. The soda must be free from alumina 

 and silica. Or the very dilute solution of both bases 

 may be neutralized with carbonate of soda, mixed 

 with sulphite of soda and heated until no sulphurous 

 acid is given off. All the alumina is precipitated, 

 while the iron remains in solution. The precipitate is 

 ignited. The solution of iron is concentrated, mixed 

 with some chlorate of potassa and hydrochloric acid 

 and heated. After the sulphur has been filtered off 

 the iron is precipitated by ammonia. 



The separation may be obtained by placing the 

 mixed precipitate, ignited in a porcelain boat, which is 

 placed in a tube of the same material heated to red- 

 ness, through which a current of dry hydrogen is 



