78 PROF. H. E. ROSCOE ON CERTAIN 



tation, the mass being heated by steam, and the rapid 

 settling of the precipitate being brought about by the 

 plentiful addition of sal-ammoniac. After complete wash- 

 ing, the acid, drained on a Bunsen's filter, was mixed with 

 excess of strong ammonia, which converted it completely 

 into white ammonium salt. This was then dissolved in 

 water, and the solution filtered and concentrated, when 

 several crops of needle-shaped crystals were obtained. 

 Care must be taken in the last crystallization to prevent 

 (by the addition of strong ammonia) the formation of flat 

 scales of a double tungstate of sodium and ammonium, 

 which yields, on heating, an impure greenish acid. 



The crystals of ammonium tungstate were then converted 

 into tungstic anhydride by strong ignition in access of air. 

 This oxide possesses a bright canary-yellow colour, and be- 

 comes dark orange on heating. A very slight admixture of 

 sodium-salt imparts to the oxide a greenish tint, which no 

 amount of oxidation can remove ; it also becomes greenish 

 on exposure to light. 



The metal was prepared by igniting the tungstic anhy- 

 dride, contained either in a platinum or in a porcelain 

 tube, to bright redness in a current of dry and purified 

 hydrogen. The metal powder thus prepared possessed a 

 light grey bright metallic lustre ; on oxidation it gained 

 26-1 per cent., that required by W=i84 to WO ? being 

 26*09 P er cent. 



Three determinations of the specific gravity of the metal, 

 prepared on two different occasions, gave : — 



Preparation A, specific gravity in water at 1 2 0, o 19-261 



» „ „ i8°-o 19213 



Preparation B, „ „ 9°*5 18*950 



or mean specific gravity, referred to water at 4 , 19*129. 

 This number is considerably higher than that found by 

 previous observers. 



