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.RS., &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 WO3 respectively, but that the 

 metal is one belonging to the arsenic group, having an 

 atomic weight of lo3, 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 WCIq (W==184) being 

 198*5; whereas that for Persoz's tungstic chloride, TuCls 

 (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 oxy chlorides of tungsten, together 



