(5 



DR JOHN WADDELL ON 



W0 3 , and that it is reduced to metallic tungsten by ignition in a stream of 

 hydrogen, the weight of oxygen lost, compared with that of the tungsten left 

 behind, gives all the data required for determining the atomic weight of the 

 latter. As a mean of three experiments made with the precipitate described, 

 I obtained the number 184-5. The tenth and eleventh precipitates were united, 

 and treated in the same way as the third fractionation. It was difficult to 

 wash, and the tungstic acid had a greenish tinge, and altogether did not appear 

 so pure as what had been before obtained. During the reduction there was a 

 slight volatilisation. The atomic weight, estimated in this sample, was 183*7. 

 The seventh precipitate was subjected to similar treatment. Its appearance 

 and behaviour were quite satisfactory, and the atomic weight calculated was 

 184. I made a number of other determinations which need not be described. 

 Some of them were made with tungstic acid not freed from molybdenum by 

 sulphuretted hydrogen. In a number of cases a slight volatilisation was 

 observed, and in these the atomic weight estimated was low. So uniformly 

 was the volatilisation noticed when the number obtained was below 184, that 

 there is every reason to believe that where no volatilisation was observed none 

 actually occurred. 



The uniformity in result was greatly in favour of purity in the tungstic acid; 

 but as silica is with difficulty precipitated from a silicate by means of hydro- 

 chloric acid, and as tungstic acid exhibits the same characteristics, I thought 

 it advisable, if possible, to prove the absence of silica independently. This I 

 did by Marignac's method of separation, which consists in fusing with hydrogen 

 potassium sulphate. Tungstic acid forms a tungstate under these circum- 

 stances, while silica remains unaltered, and is left undissolved when the fused 

 mass is treated with water. As no residue was left after solution, the absence 

 of silica was established. 



Subjoined is a table of the estimations described above : — 



Fraction. 



wo 3 . 



W left. 



3 lost. 



Atom weight. 



Remarks. 



III. 



VII 



X. 



1-4006 

 •9900 



1-1479 

 •9894 



4-5639 



11115 



•7855 



•9110 



•7847 



3-6201 



•2891 

 •2045 

 •2369 

 •2047 

 •9438 



184-55 

 184-37 

 184-59 

 184-00 

 183-69 



No volatilisation. 



» 



»> 



Slight volatilisation. 



Of the above determinations, those denoted III. are the most trustworthy, from 

 the fact that there are three concordant estimations. The mean of these is 

 184 - 5, which is the atomic weight of tungsten calculated from oxygen equal 16. 



This reduced to = 15*90 gives W = 18404. 



I made a couple of determinations of the specific gravity of two specimens 



