[14] The quantities of puer used vary considerably in different works. At Trent Bridge, 10 to 15 lb. of wet puer from hunting kennels are used per 100 lb. of wet pelt. In a German works, 15 kilos of fairly dry dog dung are used per 100 kilos of pelt (Blösse). In an American works, two buckets (one bushel) wet dog dung were used to puer 10 dozens of 8 lb. calf skins. This is equal to about 62 lb. of puer to 100 lb. of skin, which seems an excessive quantity. In an Italian works, two kilos dry dung were used to 20 skins of sheep, equivalent to about four kilos per 100. In an English tannery, 100 hides for harness leather required four bushels by measure of pigeon dung, costing 1s. 6d. per bushel (one bushel equals eight gallons).
[15] A German firm, who supply dry dog and pigeon dung for bating purposes, recommend that the material should be spread in a warm room at 30° C., and moistened up to 80 per cent. of its weight with an infusion of oat straw, and continuously turned over until completely softened. Other materials may be used for the fermenting fluid in place of the oat straw infusion, such as broth made from waste fleshings, whey, or even a simple inorganic solution, such as is used for cultivating bacteria, consisting of—
2 parts potassium phosphate.
1 part magnesium sulphate.
1 part calcium nitrate.
1·5 part calcium chloride.
100 parts water.
This procedure is neither more nor less than an application of the principles of bacterial cultivation and propagation, shown to be practically useful in the bating process by Professor H. Becker, of Frankfort, and by the Author in various publications (see Chapter [VII].).
[16] There is considerable variation in the length of time required to bring down the skins. Lamb states that half an hour is frequently sufficient, but at Trent Bridge 2–3 hours are generally required. The causes of the variation are not altogether clear, but depend partly on the previous history of the goods (fellmongering, liming, etc.), and partly on the water used.
[17] The original Turney scudding machine, was invented in 1871, and patented in that year. The specifications are numbered 1351, and 3310, 1871. It was also patented in America. Specification No. 131,480, dated September 17, 1872. Improvements in apparatus for cleaning and scouring hides and skins.
[18] Limed sheep grains, or Pelts, which have been limed for splitting, contain from 3 per cent. to 6 per cent. CaO on the dry skin (see [footnote], p. 7), and about 80 per cent. of water. In a typical case of a fully limed grain, the lime was found to be distributed as follows:—
| Free uncombined lime (CaO) | 1·7 | per cent. on the dry skin |
| CaO combined with skin | 2·5 | " |
| CaO as carbonate, or other salts | 1·4 | " |
── | ||
5·6 |
Thus, 75 per cent. of the total lime in the skin was in the caustic state. If the skin be cut during the progress of the bating operation, and a solution of phenolphthalein applied to the cut surface, the course of bating may be followed, and it will be found that the caustic lime disappears from the skin in a very short period of time, accompanied by the sudden collapse of the fibres. We shall treat of this more fully in Chapter [III]. After puering, the lime (CaO) contained in the skin, amounts to 0·5 to 0·9 per cent., calculated on the dry skin. This lime is in a perfectly neutral state, and is more or less in combination with the fibre of the skin. The exact state in which the lime exists in the skin after puering is not known, and would form a very interesting subject for research.
[19] Schmidt, and Strassburger, Die Fæces des Menchen (Hirschwald, Berlin), 1901.