VOL. LXXXVI.] PHILOSOPHICAL TRANSACTIONS. 21 



matter into the yellowish acid of molybdaena. When the retort was sufficiently 

 cooled, I cut off the neck, and removed the powder, which weighed Q5 grs. 



I next proceeded to decompose the residuum left by the acid solution in the state 

 of sulphate of lead; and having edulcorated it, I boiled it during an hour with 4 oz. 

 of lixivium of carbonate of soda, then washed the powder, and poured on it nitric 

 acid much diluted. The whole was dissolved, excepting a small portion of white 

 powder, which was washed and dried on a filter by the heat of boiling water, and 

 then weighed T V of a grain. This on examination, proved to be siliceous earth. 

 I then exactly saturated the nitric solution with lixivium of pure or caustic soda, 

 and having washed and dried the precipitate of 4ead, I exposed it in a porcelain cru- 

 cible for a -^ of an hour to a heat rather below red ; after which it weighed 146 grs. 



As I had found by a former experiment that a G 



small portion of iron remained with the lead, I Oxydeoflead 14<S 



dissolved the 146 grs. in diluted nitric acid, and Molybdic acid — 95 



precipitated the lead by sulphuric acid. The so- Oxdeofron / 4 2 l 

 lution was then filtrated, and being saturated with , ... *-A, ? 



pure ammonia, T obtained a small quantity of 



oxyde of iron, which, when dried as before, weighed The loss was therefore : > j£. 24 f J 

 1 gr. ■ 



By this analysis, 250 grs. of the ore yielded 25 ° ° 



as annexed, and lost 3.1, which I am inclined to place principally to the account of 

 the lead, as it is scarcely possible to decompose the sulphate of lead without some 

 loss, occasioned by the action of the alkaline solution. 



§ 12. Experiments on the yellow molybdic acid, obtained by the analysis.— 

 a. When exposed to the blow-pipe on charcoal, it was melted by the exterior flame, 

 and the sides of the charcoal were covered with small long crystals, which had a 

 metallic lustre resembling silver*. 



When the heat was continued, the whole was melted, and for the greater part 

 absorbed by the charcoal, the edges of which became covered with a blue powder. 

 When melted in a spoon of platina, some yellow powder was deposited near the 

 edges, and a brownish yellow shining matter was formed, which became streaked 

 in cooling. With borax it produced a brownish-yellow glass, but when the quan- 

 tity of molybdic acid was small, the colour was sometimes blue when the globule 

 was heated by the interior flame. With soda in the platina spoon it formed a 

 brownish opaque matter. And with phosphate of ammonia and soda it formed a 

 glass, which, in proportion to the quantity of molybdic acid, varied from a greenish 

 blue to a deep blue. 



b. 10 grs. of the yellow molybdic acid were boiled with 6oz. of distilled water. 

 About 3 grs. were dissolved, and the solution when filtrated was of a pale yellow 



* Scheele mentions a similar product obtained when molybdaena was exposed to the blow-pipe. Essays, 

 p. 23o. — Also by sublimation. Essays, p. 238. — And Mem. sur la Molybdene, par M. Pelletier. Journ, 

 de Phys., Dec. 1785, p. 439-— Orig. 



