TWENTY grams of hexuronic acid, prepared by Svirbely and Szent-Gyorgyi, were shaken in 500 c.c. of acetone in the presence of 50 grams of anhydrous copper sulphate for twenty-four hours. After filtration, the fluid was evaporated in vacuo to one third of its volume. On addition of a double volume of petroleum ether the monoacetone derivative of hexuronic acid crystallises out in well-formed large, colourless prisms or long needles. These were dissolved in acetone and recrystallised by the addition of petroleum ether. Seventy per cent of the theoretical yield was obtained.