Per cent. | ||
| Water | 29 | ·7 |
| Fat | 42 | ·0 |
| Fatty acids combined with lime | 6 | ·6 |
| Albuminous matter soluble in water | 3 | ·8 |
| Hair and insoluble albuminous bodies | 14 | ·4 |
| Ash (containing 57 per cent. CaO) | 3 | ·5 |
The fat had a—
| Melting-point | 40–44° |
| Saponification number | about 121 |
| Iodine number | 31·6 |
| Hehner value | 91·9 |
| Acid value | 9·3 |
Dr. Fahrion found, in a sample of the fat extracted with ether:—
| Per cent. | Iodine number. | |
| Unsaponifiable | 47·6 | 27·3 |
| Fatty acids (sol. in petrol ether) | 39·3 | 30·2 |
| Oxy acids (sol. in ether) | 13·5 | 13·4 |
The figures obtained for the fat therefore agree closely with those for wool fat.
Action of the Bird-Dung Bate.—The depleting action of the pigeon- and hen-dung bate is very similar to that of the puer, or dog-dung bate; but the bating process with these materials, as we have seen (p. [18]), is carried out at a lower temperature, and is consequently more prolonged. The principal difference between the two bates appears to be a chemical one, due to the fact that bird dung contains all the urinary products which are present only to a small extent in the dung of mammals. In birds uric acid is the chief stage in nitrogenous katabolism, the mechanism of its formation being a process of synthesis in the liver (Halliburton). Urea is also present in considerable amount, and does not appear to be so easily decomposed as the urea in animal urine.[41] As we shall show in the next chapter, urea, and probably also urates, greatly facilitate the permeability of gelatine, and to this fact may be ascribed the more gradual action of bird-dung bates. If we attempt to bate hides with dog-dung, the grain of the hide is found to be attacked and destroyed before the bate has penetrated to the interior of the hide. On the other hand, a bird-dung bate may be used at a temperature of 38° to 40° C. for the puering of skins destined for light leather, but its action is not so favourable as that of the puers.
Composition of Bird Excreta.
— | Pigeon | Hen | Duck | Goose | |||
| Moisture | 58·32 | 56·08 | 60·88 | 46·65 | 77·08 | ||
| Organic matter† | 28·25 | 19·56 | 19·22 | 36·12 | 13·44 | ||
| Phosphates | 2·69 | 2·54 | 4·47 | 3·15 | 0·89 | ||
| Carbonate and sulphate of calcium |  | 1·75 | 3·08 | 7·85 | 3·01 |  | 2·94 |
| Alkaline salts | 1·99 | 0·82 | 1·09 | 0·32 | |||
| Silica and sand | 7·00 | 17·92 | 6·69 | 10·75 | 5·65 | ||
— | 100·00 | 100·00 | 100·00 | 100·00 | 100·00 | ||
| † Containing nitrogen equal to ammonia | | 1·75 | 1·21 | 0·74 | 0·85 | 0·67 | |