EXPERIMENTS ON MOLYBOENA. IpJ 



of water till half was evaporated, 1 obtained a blue solu- 

 tion. Still I had a residuum of fifteen trains, which was Still a resi- 



7 . duuna. 



of a copper brown inclining to blue. This I set aside for 



the present, and made a trial with a large quantity of metal, 

 in order to find a readier method of obtaining the blue 

 oxide, 



Exp. 24. I reduced two hundred grains of metallic mo- Exp. 24. 

 lybdena to as fine a powder as possible, and treated this as 

 in the preceding experiment. A copper brown oxide was 

 formed, which became blue on continuing the heat. When 

 it was nearly of an indigo blue, with a tint of gray, and be- 

 gan to burn in different places, I withdrew it from the fire, 

 put it into two ounces of water, and boiled it till half was 

 evaporated. A blue solution was thus obtained, and the re- 

 siduum was treated three times in the same way. The last 

 residuum had entirely lost its blueness, and acquired, a cop- 

 per colour : however, I boiled it thrice more, and the solu- 

 tion was still blue. This is an evident proof, that simple Boiling 

 boiling in water changes the brown oxide into blue oxide, brown oxide to 

 and consequently that the latter is more oxided. t'lue. 



I now attempted actually to convert the brown oxide that Attempts t» 

 remained into blue oxide by continued ebullition in water, effect this cons- 

 and for this purpose I put it into a large vessel with sixteen "^ 

 ounces of distilled water, which I boiled till it was reduced 

 to two. The solution was blue it is true, but not to such a 

 degree as I expected from so long boiling. I therefore tried 

 whether the brown residuum would not be more easily 

 changed into blue oxide, if I merely moistened it and af- 

 terward dried it repeatedly. This I did ten times ; and 

 each time I poured an ounce of water on the residuum, 

 which I boiled for five minutes. The solution was still 

 blue, and in this way I reduced the brown oxide to eleven 

 grains. 



This mode of prepai-ing the blue oxide is very trouble- Trials to pro- 

 some, I was sensible of the defect, and 1 sought by several txide wi^thiess 

 methods to find a better. I had observed, that, when a so- trouble 

 lution of molybdena in sulphuric acid is decomposed by an With sulpKuiic 

 alkaline sulphuret, and that aftenvard a little sulphuric acid ^^^'^' 

 is added, the precipitate, that was formed in the first in- 

 itance, is decotoposed, and a blue solution is produced. 



But 



