88 



Calculated. Found. 



Tungsten W=184 48-94 49-18 



Bromine Bra >= 160 42-55 42*05 



Oxygen 0,= 32 8-51 



376 100-00 



Iodide of Tungsten, W I2. 



On passing iodine vapour together with carbonic acid 

 over metallic tungsten heated to redness a very small quan- 

 tity of soft scaly crystals having a greenish metallic lustre 

 is found to sublime. The same substance is formed (but 

 also in small quantities) when iodine vapour is passed over 

 the heated brown oxide or a mixture of metal and oxide. 

 The product was analyzed by passing air over the heated 

 iodide when it is ready converted into tungstic acid, iodine 

 being liberated. The iodide is infusible and cannot be re- 

 distilled without decomposition and it is not immediately 

 acted on by water. 



Analysis gave : Calculated. Found. 



Tungsten W=184 42-01 42-95 



Iodine I2 = 254 57*99 56-64 



438 100-00 99-59 



Atomic Weight of Tungsten. 



1. By reduction of Tungsten Trioxide. 



The difficulty of obtaining perfectly pure tungstic acid 

 and the effect which impurity produces on the atomic 

 weight determinations has been pointed out by Dumas. In 

 order to avoid the danger to which all the former determi- 

 nations are subject, consequent upon the partial reduction of 

 the acid to green oxide which cannot again be oxidised, and 

 the production of which seems to be caused by presence of 

 traces of alkali, the tungstic acid used was prepared by 

 decomposing oxy chloride with water and drying and igniting 

 in platinum (contact with glass reduces some WO3). The 

 loss of weight on reduction in hydrogen and gain of weight 

 on oxidation was several times repeated. The oxide was 

 placed in a porcelain boat being heated in a porcelain tube> 



