The standard formula for use on fruit is usually a 5-5-50 or a 3-3-50 mixture, that is, 5 pounds quick-lime, 5 pounds copper-sulfate crystals, and 50 gallons of water; or if a weaker solution is desired, 3 pounds quick-lime and 3 pounds copper-sulfate to 50 gallons of water. In general, it is best to prepare stock solutions of the lime and of the copper-sulfate from which the bordeaux mixture may be prepared later as needed. To prepare stock solutions, proceed as follows: dissolve the required amount of copper-sulfate in water in the proportion of one pound to one gallon several hours before the solution is needed, suspending the copper-sulfate crystals in a sack near the top of the water. A solution of copper-sulfate is heavier than water. As soon, then, as the crystals begin to dissolve the copper solution will sink, bringing water again in contact with the crystals. In this way the crystals will dissolve much sooner than if placed in the bottom of the receptacle of water. In case large quantities of stock solution are needed, two pounds of copper - sulfate may be dissolved to one gallon of water.
Slake the required amount of lime in a tub or trough. Add the water slowly at first, so that the lime crumbles into a fine powder. If small quantities of lime are used, hot water is preferred. When completely slaked or entirely powdered, add more water. When the lime has slaked sufficiently, add water to bring the mixture to the proportion of one pound of lime to one gallon of water. These stock mixtures should not be allowed to dry out and should be kept covered.
To make the bordeaux, use five gallons of stock solution of copper-sulfate for every fifty gallons of bordeaux required. Pour this into the tank. Add water until the tank is about two-thirds full. From the stock lime mixture take five gallons of the thoroughly stirred lime-milk for each fifty gallons of the mixture required. Dilute this a little by adding water, and strain into the tank. Stir the mixture and add water to make the required multiple of fifty gallons. Experiment stations often recommend the dilution of the copper-sulfate solution and the lime mixture each to one half the required amount before pouring together. This is not necessary, and is often impracticable for commercial work. It is preferable to dilute the copper-sulfate solution. One should never pour together the strong stock mixtures and dilute afterwards. Bordeaux mixture of other strengths as recommended is made in the same way, except that the amounts of copper - sulfate and lime are varied according to the requirements.