258 THE ATOMIC WEIGHTS. 



In Wadd ell's experiments* especial precautions were taken to pro- 

 cure tungstic oxide free from silica and molybdenum. Such oxide, 

 elaborately purified, was reduced in hydrogen, with the following results : 



1.4006 grm. WO 3 gave 1.1115 W. 79-359 per cent. 



.9900 " .7855 " 79-343 " 



1.1479 -9" " 79-362 " 



.9894 .7847 " 79-3 11 



4.5639 3.6201 " 79.320 " 



79-339, .0069 



The investigation by Pennington and Smith f started from the sup- 

 position that the tungsten compounds studied by their predecessors had 

 not been completely freed from molybdenum. Accordingly, tungstic 

 oxide, carefully freed from all other impurities, was heated in a stream 

 of gaseous hydrochloric acid, so as to volatilize all molybdenum as the 

 compound Mo0 3 .2HCl. The residual WO 3 , was then reduced in pure 

 hydrogen, and the tungsten so obtained was oxidized in porcelain 

 crucibles. Care was taken to exclude reducing gases, and the trioxide 

 was finally cooled in vacuum desiccators over sulphuric acid. The oxida- 

 tion data are as follows, with the usual percentage column added. The 

 weights are reduced to a vacuum : 



Tungsten. . Oxygen Gained. Percentage. 



.862871 .223952 79-394 



.650700 .168900 79.392 



.597654 .155*43 79-390 



.666820 .173103 79.391 



.428228 .111168 79.390 



.671920 .174406 79.392 



-590220 .153193 79-394 



.568654 .147588 79-394 



1.080973 .280600 79.392 



Mean, 79.392, dr .0004 



With O = 16, this series gives W = 184.92. 



The very high value for tungsten found by Pennington and Smith, 

 nearly a unit higher than that which was commonly accepted, seems to 

 have at once attracted the attention of Schneider,^ who criticised the 

 paper somewhat fully, and gave some new determinations of his own. 

 The tungsten trioxide employed in this new investigation was heated in 

 gaseous hydrochloric acid, and the absence of molybdenum was proved. 

 The data obtained, both by reduction and by oxidation, are as follows: 



*Am. Chem. Journ., 8, 280. 1886. 



tRead before the Amer. Philos. Soc., Nov. 2, 1894. 



J Jourii. fur Prakt. Chem. (2), 53, 288. 1896. 



