Superphosphates made from bones alone are generally distinguished by a large quantity of ammonia, and a rather low per centage of biphosphate of lime. This is owing to the difficulty experienced in making the acid react in a satisfactory manner on bones, the phosphates being protected from its action by the large quantity of animal matter which, when moistened, swells up, fills the pores, and prevents the ready access of the acid to the interior of the fragments. Superphosphates from bone-ash, on the other hand, contain a mere trifle of ammonia, and when well made a very large quantity of biphosphate of lime. Their quality differs very greatly, and depends, of course, on that of the bone-ash employed, which can rarely be obtained of quality sufficient to yield more than 30 or 35 per cent of soluble phosphates. Coprolites are seldom used alone for the manufacture of superphosphates, but are generally mixed with bone-ash and bone dust. Mixtures containing salts of ammonia, flesh, blood, etc., are also largely manufactured, and some are now produced containing as much as four or five per cent of ammonia, and the consumption of such articles is largely increasing.
The analyses above given are all those of good superphosphates, in which abundance of acid has been used so as to convert a large proportion of insoluble into soluble phosphates; but there are many samples of very inferior quality to be met with in the market, in which the proportion of acid has been reduced, and the quantity of phosphates made soluble is consequently much lower than it ought to be. The following analyses illustrate the composition of such manures, which are all very inferior and generally worth much less than the price asked for them.
| Water | 21·60 | 5·37 | 7·19 |
| Organic matter and ammoniacal salts, | 11·62 | 13·91 | 8·80 |
| Biphosphate of lime | 2·98 | 2·02 | 6·42 |
| Equivalent to soluble phosphates | (4·65) | (3·15) | (10·02) |
| Insoluble phosphates | 25·70 | 15·80 | 14·03 |
| Sulphate of lime | 23·66 | 47·52 | 51·93 |
| Alkaline salts | 10·70 | 3·73 | 3·43 |
| Sand | 3·80 | 11·65 | 8·20 |
| ——— | ——— | ——— | |
| 100·00 | 100·00 | 100·00 | |
| Ammonia, | 1·32 | 0·59 | 0·33 |
The deliberate adulteration of superphosphate, that is, the addition to it of sand or similar worthless materials, I believe to be but little practised. The most common fraud consists in selling as pure dissolved bones, articles made in part, and sometimes almost entirely, from coprolites. Occasionally refuse matters are used, but less with the intention of actually diminishing the value of the manure as for the purpose of acting as driers. It is said that sulphate of lime is sometimes employed for this purpose, but this is rarely done, because that substance is always a necessary constituent of superphosphate in very large quantities; and as farmers look upon it with great suspicion, all the efforts of the manufacturers are directed towards reducing its quantity as much as possible. It is very commonly supposed by farmers that the sulphate of lime found in so large quantity in all superphosphates, and often amounting to as much as fifty per cent, has been added to the materials in the process of manufacture, but this is a mistake; it is a necessary and inevitable product of the chemical action by which the phosphates are rendered soluble, although its quantity depends on the materials from which the manure is made. When pure bones are used its quantity is small, and it does not greatly exceed twice that of the biphosphate of lime; but in a manure made from coprolites, or other substances containing a large proportion of carbonate of lime, which must in the process of manufacture be converted into sulphate, it may be four or five times as much.
Although there is no manure which varies more in quality, or requires greater vigilance on the part of the purchaser, in order to obtain a good article, there is no doubt that superphosphates, owing to the process of manufacture being better understood, and to increased competition, have considerably improved in quality. Six or eight years since a manure containing thirty per cent of phosphates, of which twelve or fifteen had been converted into biphosphate, was considered a fair sample, but now the proportion rendered soluble is greatly increased; and where bone ash alone is employed, as much as thirty and even forty per cent of soluble phosphates is occasionally found. This, of course, is an exceptional case, and great attention and care in the selection of materials are necessary to obtain so large a proportion. The analyses already given will shew the farmer what he has to expect in good superphosphates, but it is very necessary that he should take care to obtain from the manufacturer a manure equal to the guarantee; and he ought to bear in mind that, owing to the difficulty of getting materials of constant composition, variations often take place to a considerable extent in manures which are supposed to be made in exactly the same manner.
Phospho-Peruvian Guano.—Under this name a kind of superphosphate, which is understood to be made by dissolving a native "rock guano," has recently attracted considerable attention, and is used to a large extent. Its composition is—
| Water | 9·54 |
| Organic matter | 21·38 |
| Biphosphate of lime, equivalent to 25·22 soluble phosphates | 16·81 |
| Insoluble phosphates | 10·88 |
| Sulphate of lime | 37·21 |
| Alkaline salts, containing 1·32 of phosphoric acid, and equivalent to 2·86 soluble phosphates | 2·22 |
| Sand | 1·81 |
| ——— | |
| 100·00 | |
| Ammonia, | 3·50 |
It is chiefly distinguished by the large proportion of valuable ingredients it contains, and the care taken to secure uniformity of composition.
A variety of substances are sold under the name of nitrophosphate, potato manure, cereal manure, etc. etc., which are all superphosphates, differing only in the proportion of their ingredients, and in the addition of small quantities of alkaline salts, sulphate of magnesia, and other substances, but they present little difference from ordinary superphosphates in their effects.
The use of superphosphate has greatly extended of late years, and its consumption has increased in a greatly more rapid ratio than that of guano or any other manure. Ten or twelve years since it was comparatively little known, but it has now come to be used in many cases in which Peruvian guano was formerly employed. It produces a better effect than that manure on light soils, although in general a mixture of the two answers better than either separately. When Peruvian guano is to be applied along with it, the farmer will naturally select a superphosphate made from bone ash, and containing the largest obtainable quantity of soluble phosphates; but when it is to be used alone, it is advisable to take one made from bones, or at all events one containing a considerable quantity of nitrogenous matter or ammonia. The kind to be selected must, however, be greatly dependent on the particular soil, and the situation in which it is to be used.