Human fæces contain about 75 per cent of water; and their dry residue was found by Way to have the following composition:—
| Organic matter | 88·52 |
| Insoluble siliceous matters | 1·48 |
| Oxide of iron | 0·54 |
| Lime | 1·72 |
| Magnesia | 1·55 |
| Phosphoric acid | 4·27 |
| Sulphuric acid | 0·24 |
| Potash | 1·19 |
| Soda | 0·31 |
| Chloride of sodium | 0·18 |
| ——— | |
| 100·00 |
In a sample analyzed by myself there were found—
| Organic matter | 86·75 |
| Phosphates | 8·19 |
| Alkaline salts, containing 1·18 of phosphoric acid | 2·53 |
| Insoluble matters | 2·53 |
| ——— | |
| 100·00 | |
| Nitrogen | 4·59 |
| Equal to ammonia | 5·57 |
It is to be observed that the urine and dung of animals differ conspicuously in the composition of their ash, the former being characterized by the abundance of alkaline salts, while the latter contains these substances in small proportion, but is rich in earthy matters, and especially in phosphoric acid. Salts of potash, for example, form nine-tenths of the inorganic part of the urine of the ox, while less than three per cent of that alkali is found in its dung. Phosphoric acid, on the other hand, is not met with in the urine, but forms about ten per cent of the dung. Silica is the most abundant constituent of the dung, but a large proportion of that found on analysis has been swallowed in the shape of grains of sand and particles of soil mechanically mixed with the food, although part is also derived from the straw and grains, which contain that substance in great abundance. The difference in the quantity of nitrogen they contain is also very marked, and is distinctly shown by the following analyses by Boussingault, which give the quantity of carbon, hydrogen, nitrogen, oxygen, and ash in the dung and urine of the horse and the cow in their natural state, and after drying at 212°.
| HORSE. | COW. | |||||||
| Natural. | Dry. | Natural. | Dry. | |||||
| Urine. | Dung. | Urine. | Dung. | Urine. | Dung. | Urine. | Dung. | |
| Carbon | 4·46 | 9·56 | 36·0 | 38·7 | 3·18 | 4·02 | 27·2 | 42·8 |
| Hydrogen | 0·47 | 1·26 | 3·8 | 5·1 | 0·30 | 0·49 | 2·6 | 5·2 |
| Nitrogen | 1·55 | 0·54 | 12·5 | 2·2 | 0·44 | 0·22 | 3·8 | 2·3 |
| Oxygen | 1·40 | 9·31 | 11·3 | 37·7 | 3·09 | 3·54 | 26·4 | 37·7 |
| Ash | 4·51 | 4·02 | 36·4 | 16·3 | 4·68 | 1·13 | 40·0 | 12·0 |
| Water | 87·61 | 75·31 | 0·0 | 0·0 | 88·31 | 90·60 | 0·0 | 0·0 |
| 100·00 | 100·00 | 100·0 | 100·0 | 100·00 | 100·00 | 100·0 | 100·0 | |
Hence, weight for weight, the urine of the horse, in its natural state, contains three times as much nitrogen as its dung; that of the cow twice as much; and the difference, especially in the horse, is still more conspicuous when they are dry.
It is obvious that the quality of farm-yard manure must depend—1. On the kind of animal from which it is produced; 2. On the quantity of straw which has been used as litter; 3. On the nature of the food with which the animals have been supplied; 4. On the extent to which its valuable constituents have been rendered available by the treatment to which it has been subjected; and 5. On the care which has been taken to prevent the escape of the urine, or of the ammonia produced by its decomposition.
The composition of farm-yard manure has engaged the attention of several chemists; but there are still many points on which our information regarding it is less complete than might be desired. Its investigation is surrounded with peculiar difficulties, not merely on account of its complexity, but because its properties render it exceedingly difficult to obtain a sample which fairly represents its average composition. In the case of long dung, these difficulties are so great that it is scarcely possible to overcome them; and hence, discrepancies are occasionally to be met with in the analyses of the most careful experimenters. The most minute and careful analyses yet made are those of Voelcker, who has compared the composition of fresh and rotten dung, and studied the changes which the former undergoes when preserved in different ways. He employed in his experiments both fresh and rotten dung, and subjected them to different methods of treatment. His analyses are given in the accompanying table, in which column 1 gives the composition of fresh long dung, composed of cow and pig dung. 2. Is dung of the same kind, after having lain in a heap against a wall, but otherwise unprotected from the weather for three months and eleven days in winter, during which time little rain fell. 3. The same manure, kept for the same time under a shed. 4. Well rotten dung, which had been kept in the manure heap upwards of six months. 5. The same, after having lain against a wall for two months and nine days longer.
| 1 | 2 | 3 | |
| Water | 66·17 | 69·86 | 67·32 |
| Soluble organic matters | 2·48 | 3·86 | 2·63 |
| Soluble inorganic matters· | |||
| Silica | 0·237 | 0·279 | 0·239 |
| Phosphate of lime | 0·299 | 0·300 | 0·331 |
| Lime | 0·066 | 0·048 | 0·056 |
| Magnesia | 0·011 | 0·019 | 0·004 |
| Potash | 0·573 | 1·096 | 0·676 |
| Soda | 0·051 | 0·187 | 0·192 |
| Chloride of sodium | 0·030 | 0·106 | 0·058 |
| Sulphuric acid | 0·055 | 0·160 | 0·119 |
| Carbonic acid and loss | 0·218 | 0·775 | 0·445 |
| —— 1·54 | ... 2·97 | —— 2·12 | |
| Insoluble organic matters | 25·76 | 18·44 | 20·46 |
| Insoluble inorganic matters— | |||
| Soluble silica | 0·967 | 0·712 | 1·893 |
| Insoluble silica | 0·561 | 0·857 | 1·075 |
| Oxide of iron, alumina, and phosphates | 0·596 | 0·810 | 1·135 |