This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The mixture is made in the following: proportions: -
2 lb. sulphate of copper, 98 per cent purity. 2 1/2 lb. washing soda, 98 ,, „
10 gal. of clean water.
For large areas it is recommended to make up four times the above quantities in a 40-gal. paraffin barrel in the following way: "Thoroughly wash out the barrel and pour into it 35 gal. of clean water. The 8 lb. of sulphate of copper should then be put into a canvas bag, or tied up in a piece of canvas cloth, and put into and moved about in the water in the barrel until the crystals are dissolved. This operation can be more quickly accomplished if the crystals of sulphate of copper have been previously ground.
"Having prepared the solution of sulphate of copper, next dissolve the 10 lb. of washing soda in 5 gal. of water in a separate vessel. Then pour the washing soda solution slowly into the copper sulphate solution in the barrel, stirring continuously. The mixture should then be ready for use".
In case the mixture is not quite properly made, owing to differences in strength of the materials, it may be tested with a piece of blue litmus paper, which can be obtained from almost any chemist cheaply. If the blue litmus paper turns red, more washing soda should be dissolved and added in small quantities, with continual stirring, until the litmus paper retains its blue colour.