Postgraduate Department of Chemistry, Sambalpur University, Burla (Sambalpur) Manuscript received 18 September 1971; revised 25 March 1973; accepted 21 June 1973 A springly soluble copper(II)-tartrate, CuC4H4O6 has been prepared. It behaves as a mono-­basic add in aqueous solution due to the reaction, CuC4H4O6 + H2O \(\rightleftharpoons\)CuC4H4O6\((\bar{OH})\)+H+ for which the equilibrium constant is 2.57 x10-6. The water soluble sodium, potassium and ammonium compounds of composition M Cu C4H4O6(OH) or M Cu C4H3O6.H2O have also been prepared.