178 Miscellaneous Intelligence. 



The preparation of a pure tungstic acid, when it has once contain- 

 ed a fixed alkali, is known to be difficult. When an acid con- 

 taining a little potash or soda is used for the preparation of the 

 brown oxide by hydrogen, this oxide is never obtained, but always 

 metallic tungsten, and in this way the metal may be readily pro- 

 cured. It should be washed with pure potash, to dissolve the 

 difficultly soluble tungstate with which it is mixed. Tungsten 

 then appears as a white metallic powder, very heavy, which, 

 heated in the air, takes fire, 100 parts absorbing 25 parts of oxy- 

 gen to become tungstic acid. 



Oxide of Tungsten and Soda. — Neutral tungstate of soda, heated 

 in hydrogen, suffers no change ; but acid tungstate of soda so 

 treated soon acquires on the surface the colour and lustre of cop- 

 per, which ultimately propagates through the mass. On cooling, 

 the colour becomes gold yellow, and then water added dissolves 

 neutral tungstate of soda, and leaves a heavy crystalline powder, 

 of the colour and almost the lustre of gold. To purify the powder 

 it should be first boiled in water, then in concentrated muriatic 

 acid, then in solution of pure potash, and ultimately again in water. 

 The acid tungstate of soda is prepared by adding tungstic acid to 

 the neutral salt in a state of fusion, until no more is dissolved. 



This metallic-looking substance is a compound of oxide of tung- 

 sten and soda. It is crystallized in regular cubes, which are 

 larger as the operation has been more slowly conducted. Cavities 

 frequently occur in the reduced saline mass, lined with very bril- 

 liant small cubes. It has a perfect metallic lustre, even when 

 rubbed on paper ; its colour is very like that of gold, and, when 

 suspended, as in fine powder in water, and seen before the sun, like 

 gold it is transparent, and of a green colour. No acid, or mix- 

 ture of acid, except concentrated fluoric acid, will affect it, nor 

 do solutions of pure alkalis change it. Heated in the air, it 

 changes colour, softens, appears to fuse, and forms a transparent 

 mass, which, on cooling, becomes a white enamel, soluble in wa- 

 ter, and from which an acid precipitates tungstic acid. The de- 

 composition, however, is never perfect throughout, even in oxygen 

 gas, though combustion then occurs. In a vacuum the compound 

 endures heat without any change. The fusible substance appears 

 to be a tungstate of soda, but it seemed difficult to decide whether 

 the elements of the compound were in the state of metals or 

 oxides. 



It was found that, at a high temperature, the substance was 

 affected by chlorine ; highly heated in that gas, a chloride of 

 tungsten volatilized, and a green mass remained, which, with 

 water, gave chloride of sodium and a green powder, the latter a 

 mixture of a little oxide of tungsten with tungstic acid ; the tung- 

 stic acid was in greater quantity than the oxide and chloride to- 

 gether. Hence the compound contained oxygen, which at first 



