As regards the relative effect of dog- and hen- or pigeon-dung bates, the chief of the published experiments are those made by W. J. Salomon at the Vienna Versuchsanstalt für Lederindustrie,[106] in which he determined the relative solvent power of equal quantities as being, for dog-dung 2¹⁄₂, for pigeon-dung 2, and for hen-dung 1. It is obvious that these figures, though interesting, must be taken with some reserve, as the composition even of pure dungs is by no means constant, depending on the feeding of the animals, and adulteration is common. The writer has heard stories of a certain dealer who used to fabricate his product from clay by the aid of a popgun, though he does not vouch for the statement! It is generally held that the action of bird-dung is more penetrating, but less softening and loosening than that of dog-dung, which is thus generally used for descriptions of leather where great softness and stretch are required. It is to be remembered in this connection that bird-dung bates are generally used cold, and hence are much slower in their action, which allows them time to penetrate thicker hides more uniformly. Few analyses of the dungs used in leather manufacture have been published, and these mostly with a view to manurial value. Schulze[107] gives the result of forty analyses of pigeon-dung as follows:-- Min. Max. Mean. per cent. per cent. per cent. Water 3·80 40·00 21·00 Nitrogen 1·47 5·04 2·53 Phosphoric acid 1·00 2·77 1·79 Potash 0·71 2·57 1·46 One sample contained 43·3 per cent. of sand! [106] Tech. Quart., 1892, v. p. 81. [107] Der Landwirt, 1895, li. p. 301. 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.