EXPERIMENTS ON MOLTBDENA. 2^5 



CTi its surface, and on the wet sides of the vessel ; Ijut tliis 

 disappeared after a few minutes. The fine blue colour of 

 the solution changed to a black, and a precipitate of the 

 same colour fell down. The liquor having been filtered, 

 and set on the fire, became again of a fine blue by boilin"^ 

 The water with which the precipitate was several times 

 •washed was also blue, but the colour had little intensity. 

 The precipitate, having been dried, was of a blueish black, 

 and exhibited the following results, 1. Boiled in mo- 

 derately concentrated muriatic acid, it yielded a browniiih 

 yellow solution. 2. Thrown into a crucible at a dull red 

 heat, it burned with a fine blue flame; which in a crucible 

 at a bright red heat was quickly over, bat there was a very 

 considerjible extrication of sulphurous acid after the flame 

 had ceased. The residuum left after the combustion with 

 flame was of a blackish brown, insoluble in water, and re- 

 ducible to molyudic acid by increasing the heat. Put into 

 water and shaken it gave a light blue tinge after some time. 

 The residuum separated by the filter had lost its brown hue, 

 and appeared almost entirely black. These experiments in- 

 dicate, that the molybdic acid had been at first disoxigenized, 

 and that afterward it entered into combination in the brown- 

 ish black precipitate, which appeared to contain a little blue 

 oxide; a circumstance that seems peculiar in this case, and 

 merits investigation ; but which in other respects comported 

 itself as in experiment 45. 



From all the experiments repeated under the Qih and 10th General re- 

 heads it follows: Itit, That potash exerts scarcely any action marks on the 

 on sulphuret of molybdena in the humid way; that this ^s^' '' ^ ^° ' 

 action is luore considerable in the dry way ; and that in dis- 

 solving afterward in water a greater or less combiaation of 

 sulphuretted hidrogen with sulphur takes place. 



Sdly. That the sulphuret of potasjh comports itself in sulphurct of 

 the saiue manner. From compounds formed in the dry way l'"'*^^* 

 acids precipitate a matter, which is a sulphuret of molyb- 

 dena containing a small portion of sulphuretted hidrogen, 

 and which comports itself with acids nearly as native sul- 

 phuret of molybdena. 



3dly. The hidroguretted alkaline sulphurets precipitate bidrotru'etted 

 from the solution of molybdic acid a matter of a colour si- ^j^^^J^'^f ®"^" 



milar 



