362 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 54 



Next in order is the work done by Eoscoe.' This chemist used a 

 porcelain boat and tube, and made six weighings, after successive reduc- 

 tions and oxidations, with the same sample of 7.884 grammes of trioxide. 

 These weighings give me the following five percentages which, for the 

 sake of uniformity with foregoing series, I have classified under the 

 usual, separate headings: 



Reduction Series. 



79.196 



79.285 

 79.308 



Mean, 79.263 



Oxidation Series. 



79.230 

 79.299 



Mean, 79.2645 

 Mean of all, 79.264, ± .0146 



Hence W = 183.482. 



In Waddell's experiments " especial precautions were taken to pro- 

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

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



1.4006 grm. WO3 gave 1.1115 W. 79.359 per cent. 



.9900 " .7855 " 79.343 



1.1479 " .9110 " 79.362 



.9894 " .7847 " 79.311 



4.5639 " 3.6201 " 79.320 



Mean, 79.339, ± .0069 



Hence W = 184.332. 



The investigation by Pennington and Smith '' 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 M0O3.2IICI. The residual WO3, was then reduced in pure 

 h3'drogen, and the tungsten so obtained was oxidized in porcelain cru- 

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

 finally cooled in vacuum desiccators over sulphuric acid. Tlie o.xida- 



1 Ann. Chem. Pharm., 162, 368. 1872. 

 - Amer. Chem. Journ. , 8, 280. 1886. 



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



