22 PHILOSOPHICAL TRANSACTIONS. [ANNO 1790. 



colour. It had scarcely any perceptible flavour, but turned litmus paper red. When 

 prussiate of pot-ash was added to a portion of the solution, no apparent change 

 was effected; I therefore added a small quantity of nitric acid, which produced a 

 copious brown precipitate of molybdaena. The sulphuric and muriatic acids had the 

 same effect, when poured into the solution, either before or after the addition of 

 prussiate of pot-ash. With muriate of tin it changed to a beautiful deep blue. 



Lead was precipitated from solution of nitrate of lead, in the form of a pale 

 yellow precipitate, which was a regenerated molybdate of lead. Nitrate of barytes 

 rendered the solution slightly turbid, but I did not find that the precipitate which 

 subsided was soluble in cold water, as Scheele has mentioned*. The solution did 

 not precipitate lime from nitric acid. 



c. 10 grs. of the yellow molybdic acid were dissolved when digested with 1 oz. of 

 concentrated sulphuric acid. The solution as it cooled became blue.-f- Prussiate 

 of pot-ash produced a^reddish-brown precipitate. Muriate of tin had no effect. 

 When a portion of the solution was distilled to dryness, the yellow molybdic acid 

 was left in its original state.J The remainder of the solution was saturated with 

 lixivium of soda, by which the blue colour was heightened, and some white floc- 

 culent matter was precipitated. Prussiate of pot-ash added to part of this saturated 

 solution did not precipitate the molybdaena, till the alkali was again supersaturated 

 with an acid. Muriate of tin poured into the solution saturated with alkali, changed 

 it to a deep blue ; but when the alkali was again saturated with an acid the muriate 

 of tin ceased to have any effect. The white flocculent matter which was precipitated 

 when the solution was saturated with soda, was edulcorated and heated with nitric 

 acid, by which it was converted into a yellow powder, similar to the molybdic acid 

 which had been dissolved. 



d. 10 grs. of the yellow molybdic acid, when digested in a strong heat with 1 oz. 

 of concentrated muriatic acid, formed a pale yellowish-green solution. Prussiate of 

 pot-ash precipitated the molybdaena. Muriate of tin had not any effect. A portion 

 of the solution being distilled to dryness, left a greyish-blue residuum. § I then 

 saturated the remaining part of the solution with lixivium of pot-ash, by which the 

 blue colour became more apparent and a much larger quantity of white flocculent 

 matter was precipitated than when soda was employed. Prussiate of pot-ash did not 

 affect this solution, till the alkali was again saturated with an acid. Muriate of tin 

 was precipitated by the solution saturated with alkali, highly coloured with blue ; 

 but when the alkali was again saturated with an acid, the muriate of tin had no 



* Essays, p. 234. — Scheele does not mention the quantity of water which he employed. — Orig. 



+ Scheele observes that sulphuric acid dissolves a considerable quantity of molybdic acid, and that the 

 solution as it cools becomes blue and thick ; but when heated, the colour disappears, and returns again 

 as the liquor cools. Essays, p. 235. — Orig. 



\ M. Pelletier says, that a small portion of molybdaena is raised by sulphuric acid when distilled with 

 it ; but I did not find it so with the molybdic acid. — Mem. sur la Molybdene, Journ. de Phyi . 

 Dec. 1785.— Orig. 



if Scheele has made the same observation. Essays, p. 235. — Orig. 



