The Romance of Modern Chemistry

CHEMISTRY AND AGRICULTURE Mention should also be made of another modern electrical method of capturing the nitrogen of the atmosphere for agricultural purposes. This method results in the production of a compound known as calcium cyanamide, which readily yields up its nitrogen for the use of crops. For certain soils and particular crops it is not necessary to manure with nitrate so much as phosphate. One of the simplest ways of supplying this constituent is to grind bones and scatter the bone dust in the soil. Phosphate of lime, of which there is a considerable proportion in bones, is an insoluble substance, and as the plant prefers to have its food in dissolved form, the effect of bone dust is not obvious at once. Such a phosphate manure, however, may be made more readily available by treating the bones or other substances containing phosphate of lime with sulphuric acid ; this brings some at least of the phosphate into a soluble condition, and the product—“super- phosphate,” as it is called—is extensively employed as an ingredient of artificial manures. It does not sound very probable that any product connected with a blast furnace could assist the growth of plants, but here again it is the unexpected that happens. The slag produced in presence of lime when molten pig- iron containing phosphorus is subjected to a blast of air, and so purified, is relatively rich in that element It is accordingly used to a large extent as a phosphate manure, for which purpose it must be very finely ground. By such artificial additions to the soil as the foregoing we are able to stimulate the growth of the plant. But we must not run away with the idea that we are masters of the situation. Although the processes which go on during the growth of a plant seem to be purely 225 p