Important: Safety Warning
This page recommends pest-control substances such as arsenic compounds, strychnine, or cyanide — in some cases applied to food crops. These substances are lethal to humans and animals, and their use is now banned or strictly controlled.
This page describes trade processes that use dangerously toxic materials such as cyanide solutions, mercury amalgams, or strong acids. These processes require training, equipment, and precautions far beyond what the text describes.
This information has been left in for historical purposes but should not be acted upon.
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Household and Garden Pests: Fill
In compounding this mixture, first put the copper sulphate on a piece of cheese cloth, tying the ends together so it will not spill, and suspend it from a stick in a bucket of water. Fill the barrel or tank to contain the solution half full of water, carefully measuring the amount used. When the copper sulphate is fully dissolved, pour it into the receptacle. Thoroughly slake the lime and strain the milk of lime into the barrel. Then add sufficient water to make 50 gallons.
Stock Solution. - Weighing the copper and lime at the time of making the mixture is sometimes inconvenient, but as the mixture deteriorates if allowed to stand, it is not feasible to make it up in advance.
It is, however, a good idea to make up stock preparations of sulphate of copper and of lime, and have them ready for mixing when required. The lime should be fresh quicklime and when slaked must be covered with water to keep out the air. Thus a stock mixture can be kept all summer without harm.
To prepare a stock solution of sulphate of copper, suspend some evening 50 pounds of copper sulphate in 25 gallons of water. The next morning, if the water is well stirred, each gallon of water will contain 2 pounds of sulphate. This will form the stock solution of copper sulphate. The undissolved sulphate must, of course, be removed. Put in the spray barrel 2 gallons of this solution, which is equivalent to 4 pounds of copper sulphate. Fill the spray barrel half full of water before adding the lime. This is necessary, because if lime is added to a strong solution of sulphate of copper, the mixture will curdle. Now stir up the water in the lime barrel so as to make a dilute milk of lime, but do not let it get as thick as cream, otherwise lumps will form and clog the spray nozzle. To determine the amount of milk of lime necessary (which will depend upon the strength you desire), get from a drug store a vial of ferrocyanide of potassium (yellow prussiate of potash). Continue to add lime to the mixture as long as drops of the cyanide continue to change from a yellow to a brown color. When the change of color ceases, add another pail of milk of lime to make the necessary amount a sure thing. A little too much lime does not do any harm.