Wood[108] quotes the following:—
| Hen-Dung. | |
| Per cent. | |
|---|---|
| Water | 60·88 |
| Organic matter[109] | 19·22 |
| Phosphates | 4·47 |
| Calcium carbonate and sulphate | 7·85 |
| Alkaline salts | 1·09 |
| Silica and sand | 6·69 |
| Dog-Dung. | |
| Water | 31·0 |
| Ca | 43·0 |
| Na, K, Mg | 0·8 |
| PO4 | 3·4 |
| CO2 | 7·5 |
| Organic matter | 14·2 |
| Traces Fe, Cl, Si, loss | 0·1 |
[108] Journ. Soc. Chem. Ind., 1894, p 220.
[109] Containing nitrogen equal to 0·74 per cent. of ammonia.
This was apparently a sample from a dog fed on bones; that from the kennels, which is more commonly used in leather manufacture, contains much less lime; a sample analysed by Wood gave 4·7 per cent. mineral matter, 9·7 per cent. organic, and 85·6 per cent. of water, part of which was no doubt added.
Analysis.—Little or no attention has been paid to the analysis either of dungs for bating purposes, or of the bating liquors, and although the total cost of manure bates is a high one, it is evident that such low- priced and irregular articles will not pay for elaborate analysis. Probably in some cases it would be worth while to make a determination of moisture and organic and mineral constituents by drying and ignition. Where a further investigation is desired, the determination of the soluble matter by filtering and evaporating a portion of the solution to dryness, and that of the nitrogen by Kjeldahl’s method (see [p. 70]), would be advisable, and of course in the future, when the subject is better understood, a bacteriological examination may be useful. If it is desired to estimate the solution of hide-substance in the use of bate or drench liquors, the determination of the nitrogen in a measured quantity by Kjeldahl’s method will afford the best basis of calculation, allowance being made for the nitrogen present in the original bate liquor. Hide-substance contains about 17·8 per cent. of nitrogen. In many cases, simple weighing of the solid residue, left on evaporating the liquor to dryness and drying for several hours at 100° C., with subsequent ignition to determine lime and other mineral matters, will suffice.
The quantity of hen- or pigeon-dung used in bating hides is very variable, but may be stated at from 12 to 60 litres per 1000 kilos of raw hide, in at least 2000 litres of water. The bate is generally used cold, the hides remaining in it 4-8 days, with frequent handling; but some tanners, especially in the United States, prefer bating in a paddle or drum at a temperature of about 35° C., in which case the time must be diminished to a few hours. The dung is best infused with warm water in a separate vessel,[110] and allowed to ferment for at least a week without use, when it will be found to swarm with micrococcus-chains. Only the clear liquor should be run into the bate-pit, the sediment and dirt being thrown away, or used as manure. In this way the danger of stains and flaking is much reduced. Bates may be mended with fresh portions of dung-infusion for several successive packs of hides, but should not be used too long, as they gain in solvent power by the dissolved hide-substance and the increased fermentation, and the method is not without risk.
[110] This seems to have been first suggested by T. Palmer, Eng. Pat. 13,636, 1886.
After bating, the hides are usually “worked” (“scudded,” “fine-haired”) on the beam, to remove dirt and grease, but in America a wash in the wash-wheel is often considered sufficient. Goods are occasionally “stocked” ([p. 116]) from the bates, but this is not to be recommended, as it is likely to drive out much of the partially dissolved hide-substance and produce undue looseness and loss of weight.
It is difficult to give any definite marks of sufficient bating other than the soft and fallen feel of the hides, which is easily recognised by a practised hand. One of the earliest signs of commencing overbating is the occurrence of bluish patches, or a bluish tinge somewhat similar to an iron-stain, which, if slight, generally disappears in a few days after the hides are taken into the liquors. Hen- and pigeon-dung is probably best kept air-dried, though, if very wet, or for convenience for immediate use, it may be kept in paste like dog-dung.