Page:Experimental researches in chemistry and.djvu/31

16 which gave rise to the idea of its being a combined protoxide, might be explained by the further formation of a portion of oxide similar to that already described.

The method of obtaining this compound has been to precipitate oxide of silver from the nitrate by alkalies, or better, by lime·water, to wash and dry it well, and then to leave it in contact with liquid ammonia for ten or twelve hours; the greater part is dissolved, but a black powder remains, which is fulminating silver; if the solution be heated, note is given off} and a further quantity of fulminating silver is obtained (Annales de Chimie, tome i.).

I find that fulminating silver may he formed from any precipitated oxide of silver, whether moist or dry, recent or old. Boil the oxide carefully in a tube with a mixed solution of potash and ammonia for a few moments; the potash absorbs, all the carbonic acid that may have been united to the oxide, and to a certain degree prevents its solution in the ammonia; a black powder, similar to that procured by the other process, results.

In order to gain some evidence respecting the nature of the oxide combined with the ammonia in fislminating silver, I endeavoured to ascertain the mode of formation of that compound. It appears to be formed in every case where common oxide of silver is dissolved in ammonia, and the entire solution of all solid matter is no evidence of its nomexistenee, for the compound is itself soluble in ammonia, though not so much so as the oxide. When there is an excess of oxide, unless it predominate in a great degree, the undissolved portion will be found to contain fulminating silver, and when the whole is dissolved, by heating the solution, it is thrown down.

To ascertain whether the liberation of azote depended upon the formation of the fulminating compound, I boiled, for a few moments, a solution of the oxide in ammonia; the solution became highly coloured, azote was given 06] and a black curdy precipitate formed, which left the liquid colourless; separatml by a filter, the precipitate proved to be fiilminating silver. The solution was again heated, it again blackened, gave of azote, and again a precipitate formed; this was not fuhninating silver, but merely oxide: filtered and again heated, it gave off note, and more of the oxide was formed; and this