The dog dung, which is usually obtained from hunting kennels, and of which the composition is given in Chapter II., is simply diluted with water in the paddle;[13] five buckets, weighing about 165 lb., are required for the above quantity of goods.[14] [13] When the puer is dirty it should be diluted with water and strained through a bag, or the diluted puer may be put into a tub and the heavy grit and dirt allowed to fall to the bottom of the vessel. Puer from hunting kennels is usually clean enough to use without this process. [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 1_s._ 6_d._ per bushel (one bushel equals eight gallons). The amount used depends on the state of the goods, the prevailing weather, and, further, on the quality of the puer.[15] When the temperature is maintained at 40° C., ordinary limed goods, which have been washed, come down in from one to three hours.[16] [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.