ON MOLYBD^ENA 167 



I poured upon it the same quantity of the same acid, 

 distilled and abstracted it as before, and repeated the same 

 operation the fourth and fifth time, till at last a powder as 

 white as chalk remained in the retort. This residuum, after 

 being edulcorated with hot water till it was poured off per- 

 fectly tasteless, was dried. At this time it weighed 6 J drms. ; 

 I shall call it terra molybdccnce. The limpid liquor obtained 

 from the edulcoration was evaporated to half an ounce ; it 

 then assumed a fine blue colour, and grew thick ; it contained 

 a little iron, but was, besides, chiefly acid of vitriol. On 

 diluting the acid with water, the colour disappeared ; fixed 

 and volatile caustic alkalies have no effect upon molybdeena in 

 the moist way. 



SECTION IV. 



From the fine experiments of Mr. Quist on molybdiena, 

 we know that this mineral contains sulphur, and is almost 

 entirely volatile in the open fire. A small piece of it 

 exposed upon a silver plate to the blowpipe makes a 

 beautiful appearance, when the white vapours attach them- 

 selves to the plate in the form of small shining scales, in the 

 direction of the flame. This white sublimate becomes blue 

 whenever it is in contact with the blue flame, but disappears 

 and changes again to white whenever the extreme point of 

 the flame is directed against it. This white sublimate is the 

 same earth that is obtained with the acid of nitre (Sec. in.), 

 and shows the same phenomena in the flame of the blow- 

 pipe. 



SECTION V. 



1 oz. of pulverised molybdtena was mixed with 4 oz. 

 of purified nitre, and detonated in a crucible heated 

 thoroughly hot. The mass thus obtained was of a reddish 



