REEI has its origin in the decomposition of the elements of the rocks and soils under the action of air and water, and the rain-water washes out the soluble carbonates of lime, and alkaline chlorides, and sulphates, and carbonates, which are formed into carbonate of.lime, carbonate of soda, sulphate of lime, chloride of soda, sulphate of soda, sulphate of magnesia, which effloresce on the surface of the ground.
Reh is thus not a special salt, or mixture of salts, but a very variable compound. It is really the most easily soluble salt in the earth water, re maining in solution after the decomposition of carbonate of lime, and on evaporation. The ingredients and their relative proportions are found to vary in different places, exactly as the well waters at different spots differ in saline contents, and in the same area there is a close relation between the two.
Deterioration of the land irrigated from the Ganges and Jumna canals attracted serious at tention in the villages along the Western Jumna canal, and its branches, about Delili, Paniput, Rohtak, and Kurnool. In 1857, Mr. Sherer, joint magistrate of Aligarh, examined the tracts of country deteriorated, and the picture presented by him of the suffering in some of the villages was truly deplorable. Out of 580 canal villages, 59 or nearly 10 per cent. had been injured in degrees ranging from severely to partially, 6 per cent. being severely injured. The maximum appeared to be reached in Paniput, where 46 villages, or 19 per cent., were injured. Reh effloresces in several parts of the Panjab, where there are no canals at all ; in these places it appears in land irrigated from wells where the water is very far from the surface. The efflor escing salt consists of sulphate of soda, with a variable proportion of chloride of sodium or common salt. As far as experience goes, lauds near canals, like the Hasli, in the Lahore district, constructed at, but not below, the ordinary level of the watershed, are usually found to be free from reh efflorescence. Generally speaking, the farmers assert that fully impregnated reh land is incurable and valueless. In gardens and small plots, it has been found useful to dig out the soil to the depth of 2 feet or so entirely, and putting in fresh soil. Sluicing and irrigation has been
recommended. Nitrate of lime is recommended as a probable chemical antidote for the salts of the reh. It has been known that the best remedy for reh is the saline efflorescence of old mortar on walls, or which appears on ground containing carbonate of lime and animal 'natter. In this substance nitrate of lime is found, and this salt would act by producing the insoluble carbonate of lime, and the sparingly soluble sulphate of lime, and the deliquescent nitrate of soda, instead of the efflorescent sulphate and carbonate of soda, which are the principal constituents of reh. Nitrate of lime is prepared by distilling shora or saltpetre with kali safed, and neutralizing the acid liquor that passes over with chunam. The native cultivators, in some parts, have long been accustomed to employ cliikna kullur, or earth which looks damp ; this earth is found where anitnal remains are deposited, and usually contains nitrate of lime. The reh composed principally of sulphate of soda and chloride of sodium, with, in some places, carbonate of soda ; the sulphate and carbonato of soda are very efflorescent salts, and inelt partly in their water of crystallization at a temperature of about 98°, while they are rather sparingly soluble when tho temperature falls below 60°. Hence during the hot weather the reh melts and percolates tho ground; to some considerable depth ; but as the weather becomes cooler, crystals fonn in this soil and form a capillary network, upon which it travels till it arrives at the surface, where the salt gives off its water of crystallization, and falls into a dry powder by efflorescence. If to rt solution of these salts, nitrate of lime be added, no change is produced by it on the chloride of sodium, but the sulphate and carbonate of soda are converted into nitrate of soda, a deliquescing salt, while the lime is changed either into the insoluble carbonate of lime, or the sparingly soluble sulphate of lime, neither of which are efilorescent or in any way injurious to vegetation.—Powell's Handbook, pp. 95, 112 ; Records Gott of India, No. 42 of 1864, Note on Reh, etc.