While the above shows the composition of a single sample of the meal it should be remembered that there may be wide variations from this standard due either to natural composition or to different degrees of the extraction of the oil.
The composition of the ash is given below:
| Phosphoric acid, | P₂O₅ | 31.01 | per cent. |
| Potash, | K₂O | 35.50 | “ |
| Soda, | Na₂O | 0.57 | “ |
| Lime, | CaO | 5.68 | “ |
| Magnesia, | MgO | 15.19 | “ |
| Sulfuric acid, | SO₃ | 3.90 | “ |
| Insoluble, | 0.69 | “ | |
| Carbon dioxid and undetermined, | 7.46 | “ | |
The cakes left after the expression of the oil from flaxseed and other oily seeds are also very rich in nitrogenous matters; but these residues are chiefly used for cattle-feeding and only the undigested portions of them pass into the manure. Cottonseed cake-meal is not so well suited for cattle-feeding as the others mentioned, because of the cholin and betaïn which it contains; often in sufficient quantities to render its use dangerous to young animals. The danger in feeding increases as the total quantity of the two bases and also as the relative quantity of cholin to betaïn, the former base being more poisonous than the latter. In a sample of the mixed bases prepared in this laboratory from cottonseed cake-meal the cholin amounted to 17.5 and the betaïn to 82.5 per cent of the whole.[125]
The nitrogen contained in these bases is also included in the total nitrogen found in the meal. The actual proteid value of the numbers obtained for nitrogen is therefore less than that obtained for the whole of the nitrogen by the quantity present as nitrogenous bases.
In the United States cottonseed cake-meal is used in large quantities as a direct fertilizer but not so extensively for mixing as some of the other sources of nitrogen. Its delicate yellow color serves to distinguish it at once from the other bodies used for similar purposes. No special mention need be made of other oil-cake residues. They are quite similar in their composition and uses, and manner of treatment and analysis to the cottonseed product.
147. Fish Scrap.—Certain species of fish, such as the menhaden, are valued more highly for their oil and refuse than for food purposes. But even where fish in large quantities are prepared for human food, there is a considerable quantity of waste matter which is valuable for fertilizing purposes. The residue of fish from which the fat and oil have been extracted, is dried and ground for fertilizing uses. The fish scrap thus obtained is used extensively, especially on the Atlantic border of the United States, for furnishing the nitrogenous ingredient in mixed fertilizers, and also for direct application to the fields. In fish flesh deprived of oil and water, the content of phosphoric acid is about two and one-half per cent, while the proteid matter may amount to three-quarters of the whole.[126]
The use of fish for fertilizing purposes is not new. As early as 1621 the settlers at Plymouth were taught to fertilize their maize fields by Squanto, an Indian. According to Goode, the value of nitrogen derived from the menhaden alone was two million dollars in 1875.[127] In 1878 it is estimated that 200,000 tons of these fish were captured between Cape Henry and the Bay of Fundy. The use of fish scrap for nitrogenous fertilizing has, since then, become an established industry, and the analyst may well examine his samples for this source of nitrogen when they are manufactured at points on the Atlantic coast, in proximity to great fishing centers.
148. Dried Blood and Tankage.—The blood and débris from abattoirs afford abundant sources of nitrogen in a form easily oxidized by the microorganisms of the soil. Blood is prepared for use by simple drying and grinding. The intestines, scraps, and fragments of flesh resulting from trimming and cutting, are placed in tanks and steamed under pressure to remove the fat. The residue is dried and ground, forming the tankage of commerce. Dried blood is richer in proteid matter than any other substance in common use for fertilizing purposes. When in a perfectly dry state, it may contain as much as fourteen per cent of nitrogen, equivalent to nearly eighty-eight per cent of proteid or albuminoid matter. Tankage is less rich in nitrogen than dried blood, but still contains enough to make it a highly desirable constituent of manures. Naturally, it would vary more in its nitrogen content than dried blood.
149. Horn, Hoof, and Hair.—These bodies, although quite rich in nitrogen, are not well suited to fertilizing purposes on account of the extreme slowness of their decomposition. Their presence, therefore, should be regarded in the nature of a fraud, because by the usual methods of analysis they show a high percentage of nitrogen, and therefore acquire a fictitious value. The relative value of the nitrogen in these bodies as compared with the more desirable forms, is given in [paragraph 5].