VOL. LXXXVI.] PHILOSOPHICAL TRANSACTIONS. g 



it appears, that the molybdate of lead is decomposed by the fixed alkalies in the 

 humid way, and that the component parts of the ore are lead and iron mineralized 

 by the molybdic acid *. 



§ 5. Molybdate of lead with sulphur. — A mixture, composed of 50 grs. of the 

 ore and 150 grs. of sulphur, was put into a small glass retorts, to which a receiver 

 was luted. The fire was then gradually raised till all the sulphur was driven over, 

 and the bottom of the retort began to melt. The residuum was a black, loose pow- 

 der, which was greasy to the touch, and soiled the fingers like molybdaena. This 

 black powder was digested in a strong heat with nitric acid, diluted with 3 parts of 

 water. Nitrous fumes were discharged during the digestion, and the powder was 

 dissolved, excepting a residuum of molybdic acid, which was of a greenish-yellow 

 colour. The solution was diluted with an equal quantity of distilled water, and was 

 filtrated. Sulphuric acid was then added till all the lead was precipitated ; after 

 which I obtained a brown precipitate by prussiate of pot-ash -j~. 



^ 6. Molybdate of lead with carbonate of ammonia. — A mixture, composed of 

 50 grs. of the ore and 220 grs. of dry carbonate of ammonia, was put into a glass 

 retort, and was sublimed with a gentle heat. The molybdate of lead remained 

 in the retort without having suffered any apparent alteration. The ammonia 

 however had raised a small portion ; for when it was dissolved in distilled water, 

 and was saturated with an acid, prussiate of pot-ash produced a brown cloud. 



§ 7. Molybdate of lead sublimed with muriate of ammonia. — Exper. 1. A 

 mixture of 50 grs. of the molybdate of lead and 240 grs. of muriate of ammonia 

 was sublimed. The sublimate was partly yellow, green, and blue ; there was also 

 some muriatic acid, and the residuum was a black powder ^. a. The sublimate 

 was mixed with an equal weight of sulphur and distilled. The residuum of this 

 was a black powder, resembling the mineral called molybdaena, and when distilled 

 with nitric acid, afforded a citron-coloured oxyde. 



b. A quantity of distilled water was boiled on the residuum of the first sublima- 

 tion, by which a part was dissolved, and communicated a blue colour to the water. 

 1. Prussiate of pot-ash added to some of this blue liquor, produced a precipitate 

 of Prussian blue. 2. Sulphuric acid added to another portion deepened the blue 

 colour. 3. Lixivium of carbonate of soda precipitated some ochry matter. 4. And 

 nitrate of silver was decomposed, and muriate of silver was precipitated. 



c. Nitric acid diluted with 6 parts of water was then poured on the undissolved 

 powder, and was digested on it in a sand-heat. The powder was nearly dissolved, 



* The alkalies, whether caustic or combined with carbonic acid, do not act in the humid way on mo- 

 lybdaena when mineralized by sulphur. Scheele's Essays, p. 230 ; and Mem. sur la Molybdene, par 

 M. Pelletier, Journal de Phys. Dec. 1785, p. 437. — Orig. 



+ As the quantity of molybdic acid in the ore is much greater than that of iron, it is scarcely possible 

 to discover the latter when they are precipitated together by prussiate of pot-ash. — Orig. 



+ M. Sage has observed, that molybdaena with muriate of ammonia affords a blue sublimate. Journ. 

 de Phys. 1788, p. 389.— Orig. 



VOL. XVIII. C 



