1901.] SMITH AND EXXER — ATOMIC WEIGHT OF TUX'GSTEX'. 125 



his work to volatilization of substance, both in the experiments of 

 reduction of trioxide and in those in which the metal had been 

 oxidized. Hardin adopted the method of purification pursued by 

 Pennington and Smith, and therefore believed that the material 

 with which he operated was pure ; hence the errors were the 

 result of imperfections in the method employed. 



Pennington and Smith, cognizant of the presence of molybdenum 

 in the tungsten compounds, confirmed by numerous observations of 

 others, were induced to undertake a solution of the difficulty 

 surrounding the atomic weight of tungsten because they noticed in 

 Schneider's communication, that when he reduced tungsten trioxide 

 in a current of hydrogen '' ein weissliches Sublimat " appeared on 

 the anterior portion of the reduction tube, which sublimate 

 Schneider thought was tungsten chloride, but which Pennington 

 and Smith, in the light of the discovery of molybdenum in all 

 tungstates, believed was due to the latter element. They accord- 

 ingly purified a portion of tungsten trioxide by the plan recom- 

 mended by Schneider and, after eliminating any possible molyb- 

 denum content, made tungsten metal and oxidized it. They gave 

 as a result of their labors probably the most concordant series of 

 figures ever published for the constant in question. The other 

 striking feature of this series was their high value, namely 184.^21. 

 This was much higher than that generally considered to be the cor- 

 rect value. Its rise was supposed to be due to the complete 

 removal of molybdenum. Let it be noted that Pennington and 

 Smith used tungsten metal from trioxide reduced in a crucible of 

 platinum, and further that they used the second method only. 



The work of Smith and Desi, who used the third method, appar- 

 ently confirmed the conclusions of Pennington and Smith. It may 

 be said that the early work of Schneider, leading to the value 184, 

 had been practically confirmed by subsequent investigators, so that 

 the constant 184 had been looked upon for a period of forty-five 

 years as the accepted atomic weight of tungsten. The experiments 

 of Pennington, Sftiith and Desi could not fail to be regarded with 

 some question notwithstanding the evident care exercised by them 

 in preparing suitable material for their respective studies, and the 

 conscientiousness to detail exhibited in the experimental work. 

 Schneider was still living on the appearance of the communi- 

 cations just referred to and in letters to one of us, as well as in a 

 public print, naturally took exception, in the most courteous man- 



