It may be prepared by the addition of potassium nitrite to an acetic acid solution of cobalt chloride.
This salt may be used for the separation of cobalt and nickel, since the latter metal does not form a similar double nitrite, but it is necessary that the alkaline earth metals should be absent, for in their presence nickel forms complex nitrites containing the alkaline earth metal and the alkali metal.
This acid gives with silver nitrite the corresponding nitromalonic acid, which readily yielded the third nitromethane, CHaHb(N02),Hd, also identical with the first.
It is also formed by the action of concentrated sulphuric acid on sodium nitrite in the presence of mercury.
News, 23, p. 206) by reducing a solution of potassium nitrite with sodium amalgam, and subsequent precipitation as silver salt.