79 
of lime they contain ; — they are also peculiarly suitable for 
manuring potatoes and barley, as they fall to powder under 
the action of the atmosphere and yield up their silica and 
lime to enrich the land. 
“ A Study of certain Tungsten Compounds,” by Professor 
Henry E. Roscoe, Ph.D., F.R.S., &c. 
The constitution of the Tungsten compounds, the 
equivalent of the metal and even its elementary nature, are 
subjects upon which, for many years, serious doubts have 
been expressed. Thus Persoz, who at one time proposed to 
regard the so-called tungsten as containing two elements, at 
a subsequent date explained this by the assumption that 
the equivalent of tungsten and the formula of it highest 
oxide are not 184 and W0 3 respectively, but that the 
metal is one belonging to the arsenic group, having an 
atomic weight of 153, and forming a pentoxide and a penta- 
chloride known as the tungstic compounds, together with a 
lower series which correspond to the lower arsenic com- 
pounds. This latter supposition, whilst unsupported by 
sufficient experimental evidence of its own to attract much 
attention from chemists, and contradicted by the important 
fact of the normal atomic heat of the metal corresponding 
to its old atomic weight, has never been satisfactorily proved 
to be incorrect, and has received a certain amount of cor- 
roboration from the subsequent vapour density determina- 
tions of the Chloride of Tungsten published by Debray. In 
this research Debray shows that the vapour density of 
tungstic chloride taken in mercury- and sulphur-vapours, is 
168 - 5 (H = l), the normal density for WC1 6 (W=184) being 
198’5; whereas that for Persoz’s tungstic chloride, TuC 1 5 
(Tu = 153), is 165, closely corresponding to the experimental 
density. 
In order to clear up these questions a thorough investiga- 
tion of the chlorides and oxychlorides of tungsten, together 
