134 EXPEtllMENTS ON MOLVBDENA. 



difficult to fuse, the most violent fire must be emploj-ed, to 

 obtain a more compact metallic button. The experiments 

 related put the possibility of this out of doubt. 



IV. Determination of the specijic gravity of molyhdena. 



Specific gravity From the property, which the masses of molybdena I 

 of molybdena. obtained in the metallic state possessed, of imbibing the wa- 

 ter in which they aie inimersed, it is difficult to ascertain 

 their specific gravity with accuracy. In the three trials I 

 made, I suspended the masses by a hair to one of the arms of 

 a very nice pair of scales; and in order to expel the air as 

 much as possible, I boiled them for a quarter of an hour in 

 distilled water. I afterward weighed them at the common 

 temperature. 

 About 8 611. xhe first trial gave a specific gravity of 8'636 ; the second 

 of 8*490; and the third 8'6l5 : we shall not be far from the 

 truth therefore, if we take the mean term of 8"6ll. It is 

 true the result differs much from that given by some authors, 

 who fix the specific gravity at 4*5, or at 6*5. Hielm gives 

 7'5 for the maximum : but it is probable, that the masses, 

 with which these were determined, were not pure, or were 

 full of blebs, which occasioned the specific gravity to appear 

 less than it really is to Hielm, Ruprecht, and Heidinger. 



y. Determination of the proportion of oxigen to metal in 

 the molybdic acid. 



Experiment to Exp. 18. The knowledge of the quantity of metal con- 

 ascertain pro- Gained in the native sulphuret of molybdena affords a conve- 



portii.n of oxi- , ^ .... . r^ , • 



gen in molyb- ment mode of ascertaining this proportion, i-or this pur- 

 dic acid. p^se I took a hundred grains of select scales of molybdena, 



put them into a small retort with acid as before, and distilled 

 to dryness. Joward the end of the operation sulphuric acid 

 was extricated in gray and heavy vapours. To expel this acid 

 entirely, I broke the retort cautiously ; put the pieces into a 

 small glass, which was pl'aced on a sand bath in a crucible; 

 and kept them in a red heat for half an hour. The whole of 

 the sulphuric acid was thus volatilized, and the molybdic 

 acid was left pure in the form of small crystals of a yellow- 

 ish while colour inclining to gray. This residuum weighed 



ninet3^ 



