When nitric acid is made to act on yellow prusside of potassium, in the proportion of one equivalent of acid for every equivalent of potassium present in the salt, the following reactions are observed. The salt dissolves in the acid with a dark red, almost black colour, a very little nitric oxide is evolved, which soon ceases, and is followed by a copious evolution of cyanogen mixed with nitrogen. The continued action of the acid causes the liquid to cease the usual reactions of red prusside of potassium; the addition of sulphate of iron now produces a slate-coloured instead of blue precipitate. On allowing the solution to cool, abundance of nitrate of potash crystallizes out, mixed with a little prussian blue, and about 5 percent, of the original weight of the salt, of a white granular substance, which is scarcely soluble in cold, and only very slightly so in boiling water. This white substance, on examination, proves to be the remarkable body oxamide , the production of which in an oxidising medium is highly singular. The dark red supernatant liquor, being neutralized with an alkaline carbonate, and boiled, deposits a green precipitate and yields a clear ruby-red solution. This solution furnishes the new class of salts, which is the subject of this paper. It may be evaporated to crystallization, and yields the nitroprusside of the base used in the neutralization.