I PHILOSOPHICAL TRANSACTIONS. [ANNO 17q6. 



pouring on the powder small quantities of nitric acid diluted with 6 parts of distilled 

 water, after which I edulcorated and dried the residuum. The nitric acid used in 

 this operation contained, as Klaproth has mentioned, calcareous earth, oxyde of 

 iron, and oxyde of lead ; but as prussiate of pot-ash produced a pale green preci- 

 pitate, I suspected that some other metallic substance beside iron and lead was in 

 the solution. I therefore added muriate of tin to a portion of it, which was imme- 

 diately changed from a pale yellow to -a pale blue, and showed that a small quan- 

 tity of molybdic acid was present in the solution. 



§ 3. Molybdate of lead mith water. — I boiled 12 oz. of distilled water on 20 

 grs. of the purified ore in a glass matrass during 3 hours. The ore did not 

 appear to be changed, nor did the water after it had passed the filter afford any 

 trace of matter in solution. I believe therefore that the molybdate of lead is in- 

 soluble in water. 



§4. As Mr. Klaproth had proved the action of the fixed alkalies on the mo- 

 lybdate of lead, in the dry way, I was desirous to know what effects they would 

 produce in the humid way, and therefore made the following experiments. 



Exper. 1. a. I boiled 4 oz. of strong lixivium of caustic pot-ash with 20 grs. of 

 the purified ore, till there remained at the bottom of the matrass a dry mass, which 

 was partly red, yellow, and green. I reduced this to powder, and poured distilled 

 water on it, till the water came away without any taste. The alkaline solution was 

 nitrated, and afterwards saturated with sulphuric acid. The liquor then became 

 turbid, and deposited a small quantity, of a white precipitate, which consisted of lead 

 and some molybdic acid. This was separated by a filter, and prussiate of pot-ash 

 being added to the clear liquor, precipitated a great quantity of molybdaena, in the 

 state of a reddish-brown flocculent precipitate. 



b. I took the residuum of the alkaline solution, which now was chiefly of a red 

 colour, and appeared like. minium, and poured nitric acid very largely diluted on it, 

 till the whole was dissolved. I then precipitated the lead with sulphuric acid, and 

 from the clear liquor which remained, I afterwards, by the means of prussiate of 

 pot-ash, obtained a quantity of Prussian blue. 



Exber. 2. a. 20 grs. of the purified ore were boiled with 4 oz. of a lixivium of 

 carbonate of pot-ash. When all the water was evaporated, there remained a white 

 saline mass, which was reduced to powder, and treated with distilled water as in the 

 former experiment. A large quantity of a heavy white residuum remained on the 

 filter. The clear solution was saturated as before with sulphuric acid, and a white 

 precipitate, similar to that of the former experiment, was obtained. This was se- 

 parated, and a copious precipitate of molybdaena was produced, on the addition of 

 prussiate of pot-ash. 



b. The white residuum was then edulcorated, and when diluted nitric acid was 

 poured on it, it was dissolved with effervescence. From this solution I precipitated 

 the lead by sulphuric acid, and afterwards the iron by prussiate of pot-ash. Am- 

 monia, when digested on the ore, had not any effect. From these experiments 



