Pennington and Smith.] doK) [Nov. 2, 



(0=16), while Ostwakl {Outlines of General Chemistry, translated by- 

 Walker, 1890, p. 30) says, "the mean of the good determinations is 

 W=184 " Waddell {Amer. Chem. Jr., 8, 280) gives as the mean of his 

 determinations 184.5 (0=16). The results presented in this communica- 

 tion show, therefore, a wide difference from those usually looked upon as 

 most correct. 



The evidence in earlier papers of the absence of molybdenum from the 

 tungsten is far from satisfactory. Waddell recognizes this ; hence he 

 employs Rose's method for the removal of molybdenum from his starting- 

 out material. Since the publication of his research other experimenters 

 have declared and proved the insufficiency of this method (Traube, Fried- 

 heim, loc. cit.) for the purpose to which Waddell applied it. For this 

 reason the Rose method was not followed in tliis present investigation, as 

 well as from fear that it might introduce alkali, difficult to eliminate. As 

 a substitute for it the method of Debray was adopted. 



In considering the factors that possibly could have caused a rise in the 

 atomic value other than that occasioned by the complete removal of 

 molybdenum, two suggest themselves. First, the occlusion of hydrogen 

 by the finely divided metallic tungsten, upon cooling in that gas, would 

 produce such a result. Waddell (^loc. cit.) by one experiment is satisfied 

 that such gas occlusion does not occur. Derenbach {Inaug. Dissertation, 

 Wiirzburg, 1892) claims that there is an appreciable retention of hydrogen 

 by the finelj' divided metal. The question is therefore one of importance, 

 and while this communication contains no data on this point, yet if an 

 occlusion equal to that claimed by Derenbach {Dissertation, p. 43) be 

 granted to have occurred in each experiment recorded in this investigation 

 the final result would not be equal to that actually obtained. We must 

 therefore look further for the cause of the rise in the atomic value. The 

 reductions of the trioxide were made in a platinum vessel. An examina- 

 tion of the metallic tungsten for platinum did not show its presence. 



Again, tungsten trioxide volatilizes slightly at elevated temperatures ; 

 its escape would operate to augment the final value of the tungsten con- 

 slant. There is, however, no evidence that loss in this way did occur, 

 for the porcelain lid suspended over the crucible during the long ignition 

 period never showed the presence of trioxide. Even if such a volatiliza- 

 tion had taken place, it is not at all probable that three weighings could 

 have been made with no change in the same. Furthermore, the remark- 

 able concordance of the individual results among themselves precludes 

 the idea that the rise in the found atomic mass is attributable to volatiliza- 

 lion of trioxide. In the end it seems most reasonable to assume that the 

 new value is due to a full and complete elimination of the last traces of 

 molybdenum from the tungsten prior to its oxidation. 



Chemical Laboratory, University of Pennsylvania, 

 November, 1894. 



