VOL. LXXXVI.] PHILOSOPHICAL TRANSACTIONS. ] 1 



excess. 1. Prussiate of pot-ash only changed the colour to pale green. 2. Car- 

 bonate of pot-ash expelled the ammonia, and a white precipitate like starch was 

 formed, which was principally composed of molybdic acid and pot-ash. 



e. To the 2d portion of the solution I added 3 oz. of concentrated nitric acid, 

 and evaporated it nearly to dryness. A bright yellow matter was deposited, which 

 I found to be molybdic acid combined with a portion of lead. There was also a 

 small quantity of liquid, which I diluted with distilled water, and then precipitated 

 some sulphate of lead by sulphuric acid. When this was separated I added prus- 

 siate of pot-ash, and obtained a quantity of Prussian blue. 



§ 8. Molybdate of lead with black Jlux. — 100 grs. of the ore were mixed with 4 

 times the weight of black flux. The mixture was then put into a crucible with 

 a piece of charcoal over it ; a cover was fitted to the crucible, and it was placed in 

 a furnace in which a strong heat was kept up during an hour. When the crucible 

 was cold and was broken, there did not appear any reguline button, but shining me- 

 tallic particles were dispersed throughout the mass. It was then reduced to pow- 

 der, and the largest particles were separated by washing, were dried on paper, 

 and weighed 31 grs. ; on examination they proved to be lead in the metallic state. 

 Other particles were separated by a magnet, and the remainder consisted of a black 

 powder. 



a. Diluted nitric acid was poured on this black powder and dissolved it, ex- 

 cepting a small residuum, which consisted of siliceous earth with a little charcoal. 

 1. The solution was diluted with distilled water, and filtrated. 2. I then first 

 separated a quantity of lead by sulphuric acid, and afterwards obtained some 

 Prussian blue by prussiate of pot-ash. 



b. The alkaline solution which had been formed when the melted mass was 

 washed, was poured on a filter, and distilled water was added till it came away 

 tasteless. The filtrated liquor was without colour : nitric acid was then added 

 till the alkali was saturated. When about half of the requisite quantity of nitric 

 acid was poured in, the liquor became pale blue, and as the quantity was increased 

 it changed to green ; and, lastly, when the nitric acid was added till it was in a 

 small excess, the liquor was of a bright amber colour. 1. This solution, with prus- 

 siate of pot-ash, afforded a brown precipitate of molybdaena. 2. Muriate of tin 

 changed the colour to a beautiful deep blue. 3. But sulphuric acid had no effect. 



c. The amber-coloured solution was evaporated to dryness, and a saline mass of 

 a bright citron-colour remained at the bottom of the vessel. As part of the yellow 

 colouring matter appeared to be only mixed with the salt, I dissolved it in distilled 

 water, and separated a quantity of a citron-coloured powder, which was the mo- 

 lybdic acid. The solution was twice again evaporated, and each time some mo- 

 lybdic acid was separated ; but a part still remained intimately combined with the 

 salt, so as with water always to produce the amber-coloured solution. 



I now proceeded to examine the ore with the acids. As the results which I ob- 

 tained when the ore was digested with nitric acid were the same as those mentioned 



c 2 



