But a much more important property of salt is its solvent action on the plant-food present in the soil. Its action in decomposing the minerals containing lime, magnesia, potash, &c., is similar to the action of gypsum. By acting upon the double silicates it liberates these necessary plant-foods. It is not only on the basic substances upon which it acts, but also on the phosphoric and silicic acids, which it sets free. Its power of dissolving ammonia from the soil is considerable. Experiments with a weak solution of salt on a soil by Peters and Eichhorn to test its solvent power, showed that the salt solution dissolved more than twice as much potash and nearly thirty times as much ammonia as an equal quantity of pure water did. When applied to the soil, it seems chiefly to liberate lime and magnesia. The exact nature of the chemical action taking place is a point of some dubiety. According to some, it is changed into nitrate of soda; according to others, into carbonate of soda. The latter theory seems to be the more probable one. Its action on the lime and magnesia compounds is to convert them into chlorides; and this chemical reaction explains the action that salt has in increasing the water-retaining and water-absorbing power of the soil; for the chlorides of magnesia and lime are salts which have a great power of attracting water from the air. Again, the very fact that salt acts as an antiseptic may serve to explain its beneficial action in certain cases where it prevents rankness of growth. No doubt this was its function when applied along with Peruvian guano. This it might do by preventing too rapid fermentation (nitrification) of the manure, or by actually weakening the plant. Its action when applied with farmyard manure may also be similar. But while its effect in many cases may be towards retarding fermentation, on the other hand its action, when applied along with lime to compost-heaps, is towards promoting more rapid decomposition. Probably a reaction takes place between the lime and the salt, the result of which is the formation of caustic soda. Such are some of the ways in which salt may act. It must at once be seen how its action in one case will be favourable and in another case unfavourable. There must be fertilising matter present in the soil if it is to act favourably. Again, it will only be under such circumstances, where rankness of growth is likely to ensue, that its antiseptic properties will act favourably and not unfavourably. _Best used in small Quantities along with Manures._