1814.] On the Cause of' Chemical Proportions. 245 



After having in vain endeavoured to form sulphuret of tungsten 

 by distilling a mixture of acid and sulphur, [ mixed tungstic acid 

 with sulphuret of mercury, and heated the mixture in a glass 

 retort. But the retort was not capable of enduring the heat neces- 

 sary to separate the sulphuret of mercury from the sulphuret of 

 tungsten, as the two appeared to be chemically combined. I at last 

 Succeeded in forming sulphuret of tungsten by the following pro- 

 cess. I mixed yellow oxide of tungsten (obtained from crystal- 

 lized tungstate of ammonia) with four times its weight of very pure 

 sulphuret of mercury, in a Hessian crucible. I covered the sur- 

 face of the mixture \Xith charcoal. This crucible I inclosed in 

 larger one, surrounding it wiih charcoal in a coarse powder. Ovei 

 the whole 1 placed a cover, which did not prevent the escape of 

 gaseous matter. I exposed this crucible to the greatest heat which 

 I could raise in an ordinary furnace, for half an hour. " I then 

 allowed it to cool. 



The sulphuret of tungsten thus obtained is a greyish black 

 powder, which, when rubbed upon a polished liematite, assumes a 

 beautiful metallic lustre. Under the hammer it concretes into 

 metallic masses having some coherence. The metallic surface of 

 this sulphuret has the colour of sulptiuret of copper, but it is some- 

 what more blue. a. 100 parts of this sulphuret exposed to heat in 

 a platinum cup, till it disengaged no more sulphurous acid gas, 

 left for residue 93*5 parts of a brown oxide in the state of powder, 

 which when exposed to a strong heat, became dark green without 

 atiy chatjge iri its weight, b. 100 parts of the same sulphuret 

 heated with nitromuriatic acid, produced with muriate of barytes 

 182 parts of sulphate of barytes. Hence the sulphuret of tungsten 

 is composed of 



Tungsten 75-04 lOO-al 



Sulphur 24-96 .... 3S-2G 



■ I m 



100-00 



But we have seen that this sulphuret produced by combustion 

 9J-5 of tungstic acid ; that is to say, that '24-9G of sulphur are 

 replaced by IJS-4G of oxygen. Hence it follows, that 100 of 

 tungsten should combine with 24-6 of oxygen, to become tungstic 

 acid. 



We find here as well as with molybdenum, that the composition 

 of the sulphinet is not analogous to that of the acid ; but to an 

 oxide whose oxygen is to that of the acid as I toI-L. If according 

 to these data we caUulate the composition of the acid from that of 

 the sulphuret, we find that 100 of tungsten ought to combine with 

 :,'4-!> of oxygen, liut as the analysis of the acid is founded on that 

 of the sulphuret, it is evident that the true point ought to i)e 

 between 'M'H iuul '24'.). Till wc get more exact experiments, 1 

 shall consider 24-75 us the correct number. Hence tungstic acid 

 ii couiposed of 



4 



