Bone-dust, besides nitrogen, contains about 23 per cent of phosphoric acid.
“That does not give me,” said the Deacon, “any idea of its value.”
“Let us put it in another shape, then,” said I. “One ton of good bone-dust contains about as much nitrogen as 8½ tons of fresh stable-manure, and as much phosphoric acid as 110 tons of fresh stable-manure. But one ton of manure contains more potash than 5 tons of bone-dust.”
Bone-dust, like barnyard-manure, does not immediately yield up its nitrogen and phosphoric acid to plants. The bone phosphate of lime is insoluble in water, and but very slightly soluble in water containing carbonic acid. The gelatine of the bones would soon decompose in a moist, porous, warm soil, provided it was not protected by the oil and by the hard matter of the bones. Steaming, by removing the oil, removes one of the hindrances to decomposition. Reducing the bones as fine as possible is another means of increasing their availability.
Another good method of increasing the availability of bone-dust is to mix it with barnyard-manure, and let both ferment together in a heap. I am inclined to think this the best, simplest, and most economical method of rendering bone-dust available. The bone-dust causes the heap of manure to ferment more readily, and the fermentation of the manure softens the bones. Both the manure and the bones are improved and rendered richer and more available by the process.
Another method of increasing the availability of bone-dust is by mixing it with sulphuric acid.
The phosphate of lime in bones is insoluble in water, though rain water containing carbonic acid, and the water in soils, slowly dissolve it. By treating the bones with sulphuric acid, the phosphate of lime is decomposed and rendered soluble. Consequently, bone-dust treated with sulphuric acid will act much more rapidly than ordinary bone-dust. The sulphuric acid does not make it any richer in phosphoric acid or nitrogen. It simply renders them more available.