GYPSUM. Sulphate of lime. A mineral found extensively in various parts of the globe. It is a constituent of soils, especially peat soils, and is found in sensible quantities in the clovers, some of the grasses, in turnips, and in the dung of animals subsisting on grass and clover. Its chemical composition is water, twenty-one per cent. lime, thirty-three per cent., and sulphuric acid, forty-six per cent. When calcined at a low heat it is deprived of its water, and is then known as Plaster of Paris. Gypsum is soluble in 450 parts of boiling water, and in 500 parts of cold water; and a ton of pure gypsum when ground will yield twenty-five bushels of land plaster. Its effect is most marked on soils that are light, dry, and open. On strong clays its effect is not so marked; in fact, the value of gypsum upon any soil can only be arrived at by experiment. On grain the usual application is from 200 to 300 pounds per acre; on grass, clover,. peas, beans, Indian corn, and potatoes, from 400 to 500 pounds are often applied, and to the two latter crops, often in combination with ashes. Applied to clover and grass, after mowing, it increases the aftermath, and also the crops the succeeding spring. To grain it is applied at the time of sowing, and to hoed crops it is applied in the hill or drill at the time of planting. A better way, however, would be to scatter it well around the hill at the time of planting. Thus, at the first cultivating, that outside the hill would be covered, the greater quantity of moisture would be absorbed, and the whole more equally distributed where the roots could find it. Gypsum is said to attract ammonia from the atmosphere. This, how ever, is not true except in a sense. Gypsum is soluble in rain-water; rain-water contains car bonate of ammonia. Thus it enters into combi nation with the sulphuric acid of the gypsum, and sulphate of ammonia, and also carbonate of lime is formed; that is, the ammonia gives up its car bonic acid and takes sulphuric acid, and the gypsum vice versa, according to well-known laws of chemical affinity. In the same way it fixes the ammonia of stables and manure piles, while the action of lime would be to render the am monia still more volatile. Gypsum is not a
manure itself. It is only beneficial in connection with manures, or when the soil contains humus, or is otherwise fertile in organic matter, though the fertility may be locked up from insolubility. The term fix is explained as follows: Sup posing the gypsum to meet with a sufficient sup ply of ammonia in the soil, and that it exercises its full influence, 100 pounds of common un burned gypsum will fix or form sulphate with nearly twenty pounds of ammonia, containing sixteen and one-half pounds of nitrogen. One hundred weight, therefore, (112 pounds,) will form as much sulphate as will contain twenty two and one-half pounds of ammonia; and, if introduced without loss into the plants, it will furnish them with eighteen and one-half pounds of nitrogen. The sulphuric acid contained in gypsum, from well-known principles, acts bene ficially in decomposing and bringing into activity the humus and insoluble matter accumulated in loams or peaty soils. Gypsum is decomposed by carbonate and muriate of barytes, the carbonates of strontia, potash, soda, and of ammonia, as well as by oxalic and humic acids, and where any of the four last named occur naturally in the soil, or are applied by artificial means, new com binations take place, which are attended in some cases with beneficial results. For instance, in order that gypsum may be useful as a fertilizer, the soil must alwaps contain more or less humus, even if it be only two or three per cent. If, however, it contains too much free humic acid, it will decompose the gypsum, so that humate of lime will be formed, and the sulphuric acid will be set free, which may then act as a corrosive on the rootlets of the crops. On this account, a soil very rich in humus must never be manured with too much gypsum, because, though the sulphuric acid were to combine with -another base contained in the soil, it would still form therewith a salt easily soluble in water, by which