J90 



EXPERIMRNTS ON MOLYBDENA. 



Experiments 07i the blue oxide of molyhdena, 



Ssperiments Exp. 23. Fifty grains of metallic raolybdena powdered 

 Oil tins. were put into a porcelain crucible, placed in a sloping di- 



rection on the fire, and heated till the surface acquired a 

 blue colour. On first heating the powder became of a 

 brownish yellow, which soon changed to a copper brown. 

 This colour remained some minutes, till the crucible ac- 

 quired a greater heat. The metal burned in a part where 

 the crucible scarcely began to be of a dull red. Imme- 

 diately on this I drew back the crucible, and kept it for a 

 quarter of an hour exposed to a moderate heat, constantly 

 stirring the powder. The brown colour thus changed com- 

 pletely to a grayish blue, and the powder carefully collected 

 and weighed had gained an addition of five grains, or one 

 tenth. Having poured on it an ounce of water, and shaken 

 it a few minutes, a very small portion only was dissolved. 

 On keeping the mixture for two hours at a heat of 30° 

 [86° F.] the solution assumed a deep sapphire blue colour; 

 and a bitter metallic taste. Having decanted the solution, 

 and poured a fresh quantity of water on the residuum, I 

 proceeded as before, and obtained a very pale blue solution.^ 

 The residuum I boiled with two ounces of distilled water in 

 a china cup till half the fluid was wasted; and when the 

 powder had subsided, I had a fine deep sapphire blue solu- 

 tion. The same thing took place on repeating this process. 

 Not so soluble Thus the oxide formed in this experiment did not comport 

 cediU^ex'^eri- '^^^^^ ^'^^ ^^'^* obtained in the preceding [Exp. 22.) where 

 meat. the blue oxide obtained by the calcination of metallic mo- 



lybdena dissolved in water completely. In this present case 

 the blue oxide appears to have penetrated the rest of the 

 mass, and prevented tlie whole from being oxided to this 

 point, by which it bad become itself less soluble. 

 Residuum. The residuum when dried weighed twenty grains, and wns 



of a dark gray inclining to brown, which led me to believe 

 it Yvas a mixture of brown oxide and metal. I then put it 

 Heated again. a«;ain into the cup, and roasted it cautiously ; and in fact, 

 as soon as I began to heat it, its colour changed to brown 

 inclining to blue, till by degrees it became entirely blu'e. 

 After having boiled it three different times with two ounces 



of 



