| Natural. | Dry Residue. | |
| Urea | 3·010 | 44·70 |
| Lactic acid, lactate of ammonia, and extractive matter | 1·714 | 25·58 |
| Uric acid | 0·100 | 1·49 |
| Mucus | 0·032 | 0·48 |
| Sulphate of potash | 0·371 | 5·54 |
| Sulphate of soda | 0·316 | 4·72 |
| Phosphate of soda | 0·294 | 4·39 |
| Biphosphate of ammonia | 0·165 | 2·46 |
| Chloride of sodium | 0·445 | 6·64 |
| Muriate of ammonia | 0·150 | 2·46 |
| Phosphates of magnesia and lime | 0·100 | 1·49 |
| Silica | 0·003 | 0·05 |
| Water | 93·300 | |
| ——— | ——— | |
| 100·000 | 100·00 |
Among the special organic constituents of the urine are three substances, urea, uric acid, and hippuric acid, which are of much importance in a manurial point of view. The first of these is found in considerable quantity in the urine of all animals, but is especially abundant in the carnivora. Uric acid is found only in these animals, and is the most remarkable constituent of the excrement of birds, serpents, and many of the lower animals. Hippuric acid is most abundant in the herbivora. These substances are all highly nitrogenous. They contain—
| Urea. | Uric Acid. | Hippuric Acid. | |
| Carbon | 20·00 | 36·0 | 60·7 |
| Hydrogen | 6·60 | 2·4 | 5·0 |
| Nitrogen | 46·70 | 33·4 | 8·0 |
| Oxygen | 26·70 | 28·2 | 26·3 |
| ——— | —— | —— | |
| 100·00 | 100·0 | 100·0 |
They are extremely prone to change, and in presence of animal matters readily ferment, and are converted into salts of ammonia. Thus human urine, which, at the time of emission is free from smell of ammonia, and has a slightly acid reaction, becomes highly ammoniacal if it be kept for a few days. This is due to the conversion of urea into carbonate of ammonia; and the same change takes place, though more slowly, with uric and hippuric acids.
It is obvious, from the foregoing analyses, that great differences must exist in the manurial value of the urine of different animals. Not only do they vary greatly in the proportion of solid matters which they contain, but also in the kind and quantity of their nitrogenous constituents. They differ also in regard to their saline ingredients; and while salts of potash and soda form the principal part of the ash of the urine of the ox, sheep, goat, and horse, and phosphoric acid and phosphates are entirely absent, that of the pig contains a considerable quantity of the latter substances, and in this respect more nearly resembles the urine of man. Human urine is also much richer in urea and nitrogenous constituents generally, and has a higher value than any of the others.
It is especially worthy of notice that the urine of the purely herbivorous animals (with the exception of the sheep, which contains a small quantity), are devoid of phosphates and urea; and consequently, when employed alone, they are not general manures—a matter of some importance in relation to the subject of liquid manuring, which will be afterwards discussed.
Dung.—The solid excrement of animals is equally variable in composition. That of the domestic animals which had the ordinary winter food was found to have the following composition:—
| Horse. | Cow. | Sheep. | Swine. | |
| Per-centage of water in the fresh excrement | 77·25 | 82·45 | 56·47 | 77·13 |
| Ash in the dry excrement | 13·36 | 15·23 | 13·49 | 37·17 |
100 parts of ash contained—
| Horse. | Cow. | Sheep. | Swine. | |
| Silica | 62·40 | 62·54 | 50·11 | 13·19 |
| Potash | 11·30 | 2·91 | 8·32 | 3·60 |
| Soda | 1·98 | 0·98 | 3·28 | 3·44 |
| Chloride of sodium | 0·03 | 0·23 | 0·14 | 0·89 |
| Phosphate of iron | 2·73 | 8·93 | 3·98 | 10·55 |
| Lime | 4·63 | 5·71 | 18·15 | 2·63 |
| Magnesia | 3·84 | 11·47 | 5·45 | 2·24 |
| Phosphoric Acid | 8·93 | 4·75 | 7·52 | 0·41 |
| Sulphuric acid | 1·83 | 1·77 | 2·69 | 0·90 |
| Carbonic acid | ... | trace | trace | 0·60 |
| Oxide of manganese | 2·13 | ... | ... | ... |
| Sand | ... | ... | ... | 61·37 |
| —— | —— | —— | —— | |
| 99·80 | 99·29 | 99·64 | 99·82 |