Von Schroeder has found that a strength of 6 grams of calcium oxide (CaO) per liter was sufficient, but, in practice, much more is generally added. It is also noteworthy that a perfectly fresh milk of lime must be made much stronger than one which has been used. This is partially due to the fact that some bacterial action takes place in an old lime and that ammonia is formed which assists unhairing, in addition to the effect of the lime itself, and partially because the lime in old liquors remains in suspension for a much longer time, and is thus more evenly distributed. A method of liming, sometimes known as the “Buffalo method,” has been largely adopted for sole-leather in America, and is now used in many Continental yards. It consists in a very short liming and the subsequent use of warm water. The limes are also often sharpened by the addition of a little sodium sulphide or of some other sulphide. Thus, in one large yard in the States, the hides for sole-leather (salted “packers”) are limed for 10 hours only with 2 lb. lime and 2¹⁄₂ oz. of sulphide of sodium per side, and after lying overnight in water of a temperature of 35-45° C., are easily unhaired. A Continental firm lime two days in weak fresh limes with a little tank-waste, and then treat with water at 32° C. for 6-8 hours, when the hides are unhaired and returned to the warm water for two hours before scudding. All sorts of combinations between liming and hot water treatment can be employed. The longer and stronger the liming, the lower temperature or shorter time in the water will suffice. The method is much to be recommended for firm sole-leather, but it does not saponify grease or swell the fibres thoroughly, and usually vitriol is used for the latter purpose in a later stage. The hide goes into the liquors practically free of lime, and the loss of hide-substance is much less than in the ordinary method of liming.