Preparation
Bordeaux mixture can be prepared using differing proportions of the components. In preparing it, the CuSO4 and the lime are dissolved separately in water and then mixed. Calcium oxide (burnt lime) and calcium hydroxide (hydrated lime) give the same end result, since an excess of water is used in the preparation.
The conventional method of describing the mixture's composition is to give the weight of CuSO4, the weight of hydrated lime and the volume of water, in that order. The percentage of the weight of CuSO4 to the weight of water employed determines the concentration of the mixture. Thus a 1% Bordeaux mixture, which is typical, would have the formula 1:1:100, with the first "1" representing 1 kg CuSO4 (pentahydrated), the second representing 1 kg hydrated lime, and the 100 representing 100 litres (100 kg) water. As CuSO4 contains 25% copper, the copper content of a 1% Bordeaux mixture would be 0.25%. The quantity of lime used can be lower than that of the CuSO4. One kg of CuSO4 actually requires only 0.225 kg of chemically pure hydrated lime to precipitate all the copper. Good proprietary brands of hydrated lime are now freely available, but, as even these deteriorate on storage (by absorbing carbon dioxide from the air), a ratio of less than 2:1 is seldom used, which corresponds to a 1:0.5:100 mixture.
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