176 



ESSAY XII. 



entirely driven off. The recipient, besides the sulphur, 

 was filled with a stinking smell of volatile spirit of sulphur. 

 The residuum in the retort resembled a black powder, which, 

 when rubbed between the fingers, stained them of a shining 

 black colour, and showed the very same phenomena, in every 

 other respect, as native molybdaena itself. We have then a 

 kind of earth in molybdaena which has probably to this time 

 been unknown, and which one may properly call acid of 

 molybdsena, as it has all the properties of an acid. But 

 I think I already hear it objected that it may be some 

 metallic earth, combined with an acid hitherto unknown, 

 or else vice versd. I am content to let this opinion rest 

 upon its own merit, as long as it remains unconfirmed by 

 convincing proofs, deduced from unequivocal experiments ; 

 and although in certain circumstances it resembles a metallic 

 earth, I believe with confidence that molybdsena consists of 

 an acid mineralised by sulphur. 



