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XXXVIII. On Tungsten. By F. Wohler*. 



T>EFORE describing some combinations of tungsten, which 

 ■^ in my opinion have not hitherto been known, I will indicate 

 one of the processes I employed to procure pure tungstic acid. I 

 had noticed that on heating a mixture of tungstate of potash and 

 of hydrochlorate of ammonia, the tungstic acid is reduced into 

 oxide by the hydrogen of the ammonia, which separates on the 

 mass being dissolved in water. This property 1 have applied in 

 the preparation of tungstic acid in the following manner : The 

 mixture of pulverized wolfram and carbonate of potash being 

 melted together, the tungstate of potash is dissolved in water, 

 and a sufficient quantity of hydrochlorate of ammonia added ; 

 the mass is then evaporated to dryness, and ignited and fused in 

 a Hessian crucible till the sal ammoniac be entirely decom- 

 posed or evaporated. On dissolving the melted mass in hot 

 water, a black and heavy powder is obtained, which is the ox- 

 ide of tungsten. This is boiled with a weak solution of pure 

 potash, for the purpose of carrying ofFa small portion of super- 

 tnngstate of potash difficult of solution. When it is desired 

 to have tungstic acid, this oxide is to be heated in an open 

 crucible : it takes fire and burns vividly, changing into a yel- 

 low powder. 



Oxide of Tufigste?i. 



This oxide was discovered by M. Berzelius, who obtained 

 it by heating tungstic acid in hydrogen gas. The acid at 

 first turns perfectly blue, then gradually dark brown. As I 

 employed for this experiment the crystalline tungstic acid, 

 such as is obtained by the decomposition of crystallized tung- 

 state of ammonia, I obtained a crystalline oxide of a lustre 

 almost metallic, which after burnishing preserved this lustre, 

 and had a dark copper- col our. It may also be obtained under 

 the same form, but with a perfect metallic lustre, and of the 

 most beautiful copper-colour, by bringing into contact a mix- 

 ture of tungstic acid and zinc filings with diluted muriatic 

 acid. The hydrogen at first turns the tungstic acid blue, and 

 afterwards reduces it to brilliant laminae of a copper-colour. 

 The oxide thus obtained is only preserved imder water ; for 

 by contact with atmos})heric air it instantly turns blue, and 

 soon changes completely into a yellow acid. 



On comparing the character of this oxide of tungsten with 

 the black powder obtained by the treatment of tungstate of 

 potash with sal ammoniac, — which, as I have said, is oxide of 



• From Annulet dc Chimie et de P/ij/siijiic, torn. xxix. p- 43. 



tungsten, 



