Prep. By digesting half an ounce of subacetate of copper in fine powder with one fluid ounce of acetic acid diluted with half a fluid ounce of water, at a temperature not exceeding 212°, with repeated stirring, till a dry residue is obtained. Then dissolving this in sufficient water to make the solution measure five ounces. In this process the subacetate (2 CuO, C4 H3 O3) is made to assume another equivalent of acetic acid, and is thus converted into the acetate (CuO, C4 H3 O3).

Use. It is used in the Pharmacopoeia for detecting the presence of butyric acid in-valerianate of zinc, the valerianate being often adulterated with the butyrate, to which a few drops of oil of valerian are added to simulate the odour of valerian. The suspected salt is first distilled with sulphuric acid, and the solution of acetate of copper added to the distillate; pure valerianic acid gives, under these circumstances, no precipitate, but if any butyric acid is present, a bluish-white precipitate of butyrate of copper is produced. The butyrate of copper is a sparingly soluble salt, and is represented by the formula (CuO, C8 H7 O3 + 2 HO).