[Book VI, 



CHAP. XX. 



MOLYBDENA. 



j?ort Account of this Semi metal. May le reduced to an Acid. A 

 fcarce Mineral. 



THIS is a mineral fubftance, which has till 

 lately been confounded with plumbago, but is 

 now found to be a combination of a particular me- 

 tallic fubftance with fulphur. It is of a blackifh colour, 

 and confifts of mining lamina?, which have a degree 

 of flexibility, fo as to be very difficultly reduced to 

 powder. 



Molybdena reduced to its metallic form refembles 

 lead in colour and fpecific gravity, but is very brittle, 

 eafily calcined and volatilized, and will not mix with 

 lead when in fufion. 



It differs from all other femi-metallic fubftances by 

 being nearly infufible in our furnaces ; it is probably 

 the impoflibility of reducing it to the form of a round 

 button, which induced Klaproth to fuppofe that Jie 

 had never brought it to its metallic date. By Mr. 

 Pelletier's account, however, it was evidently reduced, 

 and Mr. Hielm produced a flill purer and more 

 perfect regulus. In a red heat it calcines. When 

 in its reguline (late it gives no colour to borax. 

 Molybdena, in this ftate, is called by Mr. Kirwan 

 molybdenite. 



Molybdena is capable of being oxygenated fo far 

 as to become an acid, in which ftate it is a concrete 

 body, white and pulvcrulcntj refembling chalk. This 



acid, 



