TUNGSTEN COMPOUNDS. 77 



been expressed. Thus, Persoz (Ann. Ch. Phys. [4] i. p. 93) 

 comes to the conclusion that the atomic weight of tungsten 

 and the formula of its highest oxide are not 184 and WO ; 

 respectively, as generally adopted, but that the metal is to 

 be considered as belonging to the arsenic group, having an 

 atomic weight of 153, and forming a pentoxide and a 

 pentachloride known as the tungstic series, together with 

 a lower series of compounds which correspond to the 

 lower arsenic compounds*. This supposition of Persoz's, 

 whilst unsupported by sufficient experimental evidence of 

 its own to attract much attention from chemists, and con- 

 tradicted by the important fact of the normal atomic heat 

 of the metal corresponding to the old atomic weight, has 

 never been satisfactorily proved to be incorrect, and has 

 received a certain amount of corroboration from the sub- 

 sequent vapour-density determinations of the chloride of 

 tungsten published by Debray (Compt. Rend. lx. p. 820, 

 1865). In this research Debray shows that the vapour- 

 density of tungstic chloride, taken in mercury and sulphur 

 vapours, is 168*5 (H=i), the normal density for WC1 6 

 (W= 184) being 198*5, whereas that for Persoz* s tungstic 

 chloride, TuCl 5 (Tu=i53), is 165, and therefore closely 

 corresponds to the experimental density. 



In order to clear up these questions, a thorough in- 

 vestigation of the chlorides and oxychlorides of tungsten, 

 together with the corresponding bromine and iodine com- 

 pounds, appeared before all things necessary. 



Preparation of Metallic Tungsten. — Tungstic acid was 

 first prepared by decomposing 2 kilogs. of the commer- 

 cially pure tungstate of soda with hydrochloric acid. The 

 precipitated tungstic acid was repeatedly washed by decan- 



* At a later date (Bull. Soc. Chimique, 1864, ii. p. 188) MM. Persoz (pere 

 et fils) even state that they have succeeded in separating from the crude tung- 

 states several radicals, giving rise to acids possessing different properties and 

 different compositions. 



