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.
This is another name for a more or less impure chloride of potassium. It is manufactured from carnallite, which is found in enormous quantities in the German potash deposits. It contains from 70 to 98 per cent of pure potassium chloride, and its chief impurity is common salt, which may vary from a mere trace to 20 per cent. Small quantities of magnesium chloride and magnesium sulphate are also present. The standard commercial muriate of potash usually contains 80 per cent of pure potassium chloride, which is equivalent to 505 per cent of potash. One ton of "muriate" thus contains as much potash as 4 tons of kainit. In practice it may be used in the same way as kainit, but only one-fourth of the quantity is needed - about 56 to 112 lb. per acre.