Many other saline substances have been tried as manures; but in most instances on too limited a scale to permit any definite conclusions as to their value. The experiments have also been too frequently performed without the precautions necessary to exclude fallacy, so that the results already arrived at must not be accepted as established facts, but rather as indications of the direction in which further investigation would be valuable. There is little doubt that many of these substances might be usefully employed, if the conditions necessary for their successful application were eliminated; and no subject is at present more deserving of elucidation by careful and well-devised field experiments.
Phosphate of Lime.—The use of bones in their natural state as a manure has been already adverted to, and it was stated, that though their value depended mainly on the phosphates, the animal matters and other substances contained in them were not without effect. The action of phosphates is greatly promoted by solution in sulphuric acid, and the application of the acid has brought into use many varieties of phosphates of purely mineral origin, or which have been deprived of their organic matters by artificial processes. Of these, the spent animal charcoal of the sugar-refiners, usually containing about 70 per cent of phosphates, and South American bone ash, are the most important. The latter is now imported in very large quantity, and has the composition shewn in the following analyses:—
| I. | II. | III. | |
| Water | 6·10 | 6·28 | 3·03 |
| Charcoal | 5·05 | 2·19 | 2·02 |
| Phosphates | 79·20 | 71·10 | 88·55 |
| Carbonate of lime | 4·05 | 3·55 | 5·60 |
| Alkaline salts | 0·15 | traces | ... |
| Sand | 5·45 | 16·90 | 0·80 |
| ——— | ——— | ——— | |
| 100·00 | 100·00 | 100·00 |
Bone ash has hitherto been almost entirely consumed as a raw material for the manufacture of superphosphates; but as it is sold at from £4: 10s. to £5: 10s. per ton when containing 70 per cent of phosphates, it is, in reality, a very cheap source of these substances, and merits the attention of the farmer as an application in its ordinary state.
Of strictly mineral phosphates, a considerable variety is now in use, but they are employed exclusively in the manufacture of superphosphates, as in their natural state they are so hard and insoluble, that the plant is incapable of availing itself of them.
Coprolites.—This name was originally applied by Dr. Buckland to substances found in many geological strata, and which he believed to be the dung of fossil animals. It has since been given to phosphatic concretions found chiefly in the greensand in Suffolk and Cambridgeshire, which are certainly not the same as those described by Dr. Buckland, but consist of fragments of bones, ammonites, and other fossils. Coprolites are now collected in very large quantities, and about 43,000 tons are annually employed. They are extremely hard, and require powerful machinery to reduce them to powder, and hence their price is considerable, being about £2: 10s. per ton. Their composition varies somewhat according to the care taken in selecting them, and the locality from which they have been obtained. A general idea of their composition may be derived from the subjoined analyses:—
| Water | 1·95 | 1·90 |
| Organic matter | 2·59 | 6·85 |
| Phosphate of lime | 55·21} | 61·15 |
| Phosphate of iron | 3·84} | |
| Carbonate of lime | 26·70 | 16·20 |
| Sulphate of lime | 1·97 | " |
| Alkaline salts | 1·85 | 3·21 |
| Sand | 5·89 | 11·65 |
| ——— | ——— | |
| 100·00 | 100·00 |
Within the last two or three years, coprolites have been found in great abundance in France, but they are of inferior quality, and rarely contain more than 40 per cent of phosphates.
Apatite, or mineral phosphate of lime, is found in large deposits in different places. It is particularly abundant in Spain, and occurs also in America and Norway. From the latter country it has been imported to some extent; and during the last year considerable quantities have been brought from Spain, and the importations will undoubtedly increase very largely as the means of transport improve in that country. Spanish apatite contains—
| Water | 0·80 |
| Phosphate of lime | 93·30 |
| Carbonate of lime | 0·50 |
| Chlorine, etc. | traces |
| Sand | 4·70 |
| ——— | |
| 99·30 |