Page:Experimental researches in chemistry and.djvu/32

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1818.]
17
Oxide of Silver in Ammonia.

occurred with the same solution a fourth and fifth time. The liberation of the azote, therefore, does not belong exclusively to the formation of fulminating silver, but seems rather to depend on the production of protoxide.

I endeavoured to form fulminating silver by using the protoxide described in the first part of this paper, but could not succeed: I got nothing but a black powder from it, which appeared to be the same oxide in another form. I endeavoured also to form fulminating silver from those portions of oxide given off by the further boiling of solutions which had previously yielded the detonating compound, but failed; I presume from its being also a protoxide. When the fulminating compound is dissolved in the acids, it gives off a gas which I believe to be oxygen, but I could not work with quantities sufficient to ascertain this point. Perhaps to these reasons for supposing fulminating silver to be a compound rather of the peroxide than the protoxide, may be added the easy solubility of the protoxide in ammonia, and the difficult solubility of the detonating compound.

The oxide which is obtained by boiling solution of silver in ammonia, I have supposed to be a protoxide similar to the one obtained by spontaneous evaporation. This opinion is founded on the liberation of azote during its formation in consequence of the decomposition of ammonia by oxygen, and on its apparent incapability of forming fulminating compounds: the idea is supported by the following circumstance. A tube, in which solutions of silver in ammonia had been repeatedly boiled, became coated on the inside with the oxide, so as to be perfectly opake; on pouring dilute nitric acid into it to remove the oxide, the tube became lined with brilliant metallic silver, which, however, was soon dissolved by the continued action of the acid. I attribute this phenomenon to the reduction of one part of the oxide by another, which was thus rendered soluble in the acid.

When a portion of the ammoniacal solution is evaporated to dryness in a platinum capsule, it leaves a film of oxide, which, when decomposed by heat, gives a perfectly continuous and smooth coat of silver to the vessel. I have also covered other metals, as iron and copper, with silver in the same way, and found that the burnisher might he applied without any injury