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 popularly known as "saltpetre" or "nitre". Owing to its high price it is very little used by farmers and gardeners. It is not only rich in nitrogen, but also in potash, and should therefore be regarded more as a potassic manure. When of 85-per-cent purity it contains 14 per cent of nitrogen and 40 per cent of potash.
This resembles nitrate of soda somewhat in appearance but is rather coarser in the crystals. It is a compound of ammonia and sulphuric acid, and is obtained from the ammonia liquor of gasworks, ironworks, etc. In a pure state it contains 258 per cent of ammonia, equal to 21.2 per cent of nitrogen. A pinch of unadulterated sulphate of ammonia will vaporize completely on a red-hot surface. The commercial product, however, of about 95-per-cent purity contains 245 per cent of ammonia, equal to 20.2 per cent of nitrogen. It may be used in the same way as nitrate of soda, but is more lasting in its effects. It should not be mixed with nitrate of soda, basic slag, or with lime or chalk, as these would liberate the ammonia and cause it to be lost.
The production of sulphate of ammonia has increased from 42,000 tons in 1872 to 289,000 tons in 1906, and more than one-half the quantity is obtained from gasworks.
Sulphate of ammonia is neither an acid nor an alkaline manure; it is a neutral substance, and when added to the soil causes a loss of calcareous or chalky food (see p. 161).
This manure has recently come into prominence as a nitrogenous fertilizer. It is obtained from calcium carbide, so much used for acetylene gas. When this is heated to 1000° C. the nitrogen from the atmosphere combines with it and forms about 60 per cent of calcium cyanamide. This contains 20 per cent of nitrogen, the remainder being 24 per cent quicklime, 10 per cent carbon, and 15 per cent of various mineral oxides. In appearance nitrolim resembles basic slag, being a dark-grey finely powdered substance. In action it is somewhat similar to sulphate of ammonia, and is much slower in its action than nitrate of soda.