EXPERIMENTS ON MOLYBpENA. g^l 



the roasting continued a quarter of an hour longer, gave t}i£ 

 same results, 



X. Action of hidrothianates of alkaline svlphurets, and of 

 •pure hidrothian acidf on molybdic acid, 



Exp. 41. I dissolved molybdate of ammonia in twenty Solution of 

 times its weight of water, and added sulphuric acid, till the ™o'yt> 'ena in 



'" ; . n -> • ^ T 11 T 1 ■ 1 sulphuric ICld 



precipitate formed was entirely redissolved. 1 then poured treated wiih 

 m hidrothianate of amniotiiacal sulphiiret, and a reddish hiilroguretted 

 brown precipitate was formed, which was more or less con- ammonia. 

 siderable, and the supernatant liquor was more or less blue, 

 according as the quantity of sulphuric acid and of water 

 employed to dissolve it v/as greater or less. I found too, that 

 on adding a small quantity of hidrothianate of ammoniacal 

 sulphuret to the solution of molybdate of ammonia, the 

 sulphuric acid produced no precipitate, but merely rendered 

 the solution b)ue; while a precipitate took place, if there 

 were a larger quantity of hidrothianate of ammoniacal ?ul- 

 phuret: thus in one case all the hidrothianate of sulphur is 

 employed in disoxiding the molybdic acid. 



Exp. 42. Five grains of sublimed molybdic acid dissolved Molybdicacid. 

 in ten drops of concentrated sulphuric acid were put into 

 five ounces of water. Hidrothianate of sulphuret of am- 

 monia occasioned in this a chocolate coloured precipitate, 

 which was almost black when dried. An excess of acid did 

 not decompose it, or produce a blue colour: thus it was 

 similar to the native sulphuret of molybdena. 



Exp. 43. Molybdate of ammonia was dissolved in twelve Molybdate of 



times its weight of vyater, sulphuric acid added in excess, ^"^'^°"'* ^"!* 



" . ' ^ .-.'_,. sulphuret and 



and solution of sulphuret of potash poured in. This occa- hidroguretted 



sioned a light reddish brown precipitate, and the liquor be- »ulphuret of 

 came blue. Sulphuric acid being added to a solution of 

 molybdate of ammonia merely to saturation, hidrothianate 

 of sulphuret of potash occasioned a flesh coloured red pre- 

 cipitate inclining to a copper colour. In a solution to which 

 no sulphuric acid had been added, no precipitate was occa- 

 sioned by the hidrothianate, the liquid merely becoming a 

 little milky, which might be expected from the property I 

 have already observed the sulphuret of potash possesses of 

 dissolving molybdena. The acid added afterward produced 



