An unsaturated dicarboxylic acid (HO.CO.CH=CH.CO.OH) of cis conformation, having various uses in the manufacture of artificial resins, the dyeing and finishing of wool, silk, and cotton, and also combined with certain drugs to make salts more soluble than the basic forms. The corresponding isomer having trans conformation, is identical in chemical formula, is called fumaric acid.  [PJC]