88 
Calculated. 
Found. 
Tungsten 
II 
oo 
.... 48-94 .... 
.. 49-18 
Bromine 
Br„ - 160 .. 
.... 42-55 .... 
.. 42-05 
Oxygen 
0 2 — 32 .. 
.... 8-51 .... 
376 
100-00 
Iodide of Tungsten, W I 2 . 
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 = 1 84 . . . . 
.. 42-01 
. 42-95 
Iodine I, = 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 oxychloride with water and drying and igniting 
in platinum (contact with glass reduces some W0 3 ). 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, 
