This section is from the book "Commercial Gardening Vol3", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Sulphide of potassium, or "liver of sulphur", is an excellent fungicide for use against the superficial mildews, as Apple-tree mildew, Rose mildew, Hop mildew, etc. It is of especial use in checking the spread of a disease in greenhouses, etc, but it must be borne in mind that the solution discolours white paint. It is readily soluble in water, and may be used in the proportions of 2 to 3 oz. to 3 gall, of water, depending on the relative hardness of the foliage. One ounce to 3 gall, of water is, as a rule, strong enough for plants grown under glass.