260 THE ATOMIC WEIGHTS. 



Bernoulli 79.480, d= .0560 



Persoz , 79-314, ± .0070 



Roscoe 79.264, ± .0146 



Waddell 79. 339, j^ .0069 



. Pennington and Smith 79-392, ± .0004 



Schneider, 1896 , 79-3II, ± .0018 



Shinn 79- 39 1 , ± .0066 



General mean 79-388, ± .00039 



Here the work of Pennington and Smith vastly outweighs everything 

 else; and if their supposition as to the presence of molybdenum in all 

 the previous investigations is correct, this result is to be accepted. 



The rejection of the figures given by Berzelius and by Bernoulli would 

 exert an unimportant influence upon the final result. There is, there- 

 fore, no practical objection to retaining them in the discussion. 



In 1861 Scheibler* deduced the atomic weight of tungsten from 

 analyses of barium metatungstate, BaO.4WO3.9H2O. In four experi- 

 ments he estimated the barium as sulphate, getting closely concordant 

 results, which were, however, very far too low. These, therefore, are re- 

 jected. But from the percentage of water in the salt a better result was 

 attained. The percentages of water are as follows : 



13-053 

 13-054 

 13-045 

 13.010 

 13.022 



Mean, 13.0368, i .0060 



The work of Zettnow,t published in 1867, was somewhat more com- 

 plicated than an}'' of the foregoing researches. He prepared the pure 

 tungstates of silver and of iron, and from their composition determined 

 the atomic weight of tungsten. 



In the case of the iron salt the method of working was this : The 

 pure, artificial FeWO^ was fused with sodium carbonate, the resulting 

 sodium tungstate was extracted l\y water, and the thoroughly washed, 

 residual ferric oxide was dissolved in hydrochloric acid. This solution 

 was then reduced by zinc, and titrated for iron with potassium perman- 

 ganate. Corrections were applied for the drop in excess of perman- 

 ganate needed to produce distinct reddening, and for the iron contained 

 in the zinc. 11.9-56 grammes of the latter metal contained iron corre- 

 sponding to 0.6 cc. of the standard solution. The permanganate was 

 standardized by comparison Avith pure ammonium-ferrous sulphate, 

 Am2Fe(SOJ.^.6H,p, so that, in point of fact, Zettnow establishes directly 

 only the ratio between that salt and the ferrous tungstate. From Zett 

 now's four experiments in standardizing I find that 1 cc. of his solution 



* Journ. fiir Prakt. Chem., 83, 324. 

 tPoggend. Annalen, 130, 30. 



