1904] SMITH AND EXNER — ATOMIC WEIGHT OF TUNGSTEN. 129 



Svanberg^ and Struve fused molybdenum trioxide with potassium 

 carbonate and determined the loss in weight. Their value is 

 nearly six units too low and the method must be considered inac- 

 curate. This method was tried with tungsten trioxide and gave 

 values ranging from 160 to 180. The disadvantages of the method 

 are that : the union takes place with considerable spattering ; the 

 temperature of fusion is so high that loss by volatility is probable ; 

 the alkaline carbonates when held in fusion slowly lose traces of 

 carbon dioxide ; and the resulting fusion is extremely hygroscopic. 

 " These difficulties may be obviated by combining the oxide and 

 sodium carbonate in aqueous solution, and then expelling the water. 

 Operated in this manner the method possesses promising value ; 

 and has numerous advantages, among which may be mentioned 



that : carbon dioxide has a molecular weight of forty-four, giving 

 a value for comparison nearly as great as in the simple reduction 

 and oxidation method ; the union of sodium carbonate and tung- 

 sten trioxide in aqueous solution takes place at a low temperature, 

 and the highest temperature used in the desiccator is a safe distance 

 below the melting point of sodium carbonate, so that there is little 

 chance for volatilization either of sodium carbonate or tungsten 

 trioxide, and in the device used there is no chance for loss by 

 spattering; large quantities of material maybe combined with as 

 much ease as small; the method itself would serve for a test of the 

 purity of the material ; the presence of chlorides, sulphates, sodium 

 silicate, and potassium carbonate would not affect the result. The 

 presence of alkaline hydroxides would; and to prevent the possi- 

 bility of this, pure sodium carbonate was saturated in solution 

 with carbon dioxide, and the resulting bicarbonate heated in a 

 vacuum at 300° for three hours. 



^^'^J.prakt. Ch., 44,101 (1848). 



PROC. AMER. PHILOS. SOC. XLIII. 176. I. PRINTED MAY 19, 1904. 



