174 MENACCAXITE. 



II. The finely-powdered mineral is fused with at 

 least 6 parts of bisulphate of potassa in a platinum 

 crucible, until it is completely dissolved ; the fused 

 mass, when cool, is powdered and dissolved in cold 

 water. 



This solution has the peculiarity, when long boiled, 

 of depositing the whole of the titanic acid, which is 

 not, however, quite free from iron. 



In order to obtain it perfectly free from the latter 

 metal, the sesquioxide of iron and titanic acid are 

 precipitated by ammonia, the clear solution decanted 

 from the precipitate, and the latter treated with an 

 excess of sulphide of ammonium, which converts all 

 the iron into black sulphide. After standing for 

 several hours, the mixture is diluted with water, the 

 clear liquor decanted, and the precipitate washed once 

 or twice by decantation. 



It is afterwards mixed with sulphurous acid, when 

 it immediately becomes white, since the sulphide of 

 iron dissolves in the form of dithionate of protoxide of 

 iron. The titanic acid is filtered off, washed and 

 ignited, a fragment of carbonate of ammonia being 

 held in the crucible to expel any sulphuric acid. 



A little more titanic acid separates from the filtrate 

 on standing for some time, and on gently heating. 

 The iron, when converted into sesquichloride by 

 chlorine, or by heating with hydrochloric acid and 

 chlorate of potassa, may be precipitated from the 

 solution of ammonia. 



III. The most accurate method of separation of 

 sesquioxide of iron from titanic acid consists in 

 decomposing the diluted solution from No. II. by 

 hyposulphite of soda. The titanic acid alone is pre- 

 cipitated, which is then ignited. 



