The ageing of bordeaux mixture

Abstract

Bordeaux mixture (5:5:50) prepared at room temperature (24° C.) contains a high initial concentration of copper in the aqueous phase (4 to 7 mg. copper/litre). On keeping the mixture at 24° C. the copper content of the solution decreases, and in a few days, attains a steady value of 0·47 mg. copper per litre. The changes in copper concentration of the aqueous phase are due to the ageing of the precipitate. Experiments conducted at 0° and at 70° C. show that an increase in temperature markedly promotes ageing. In the initial stages of formation of Bordeaux mixture, the aqueous phase is supersaturated with calcium sulphate, but the supersaturation does not influence in any way the ageing of the precipitated Bordeaux mixture. If, soon after its formation, the Bordeaux mixture is washed with water saturated with lime and with calcium sulphate, the rate of ageing of the solid is slightly reduced.