This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Copper sulphate (98 per cent) ... ... ... 2 lb.
Washing soda (pure) ... ...... .. 2 1/2 lb.
Water ...... .......... 10 gal.
Dissolve copper sulphate in 9 gal. of water in a wooden vessel, and the washing soda in 1 gal. water. Pour the dissolved soda into the copper solution, and stir constantly. If blue litmus paper turns red in the solution add more soda while stirring, until the litmus remains blue. This mixture is found superior to Bordeaux mixture for spraying Potatoes, and is more easily prepared and applied.