An indirect method of liming has recently been patented by Messrs. Payne and Pullman of Godalming,[79] which is of both scientific and practical interest. From the difficult solubility of lime, and the consequently weak solutions which must be employed, the ordinary process of liming is a slow one. Caustic soda, however, can be used in much stronger solutions without producing injury to the hide, or larger solution of hide substance, and from its great diffusibility, it penetrates very rapidly. Used alone, however, the hide becomes too much swollen for most purposes, and for certain classes of leather at least (e.g. buff and chamois leather) the presence of a portion of lime in the hide appears to be necessary for successful work. If a hide which has been swollen with caustic soda be afterwards treated with a solution of calcium chloride, double decomposition takes place, and caustic lime is formed actually in the interior of the fibre of the hide, while the sodium unites with the chlorine to form common salt. Both solutions may be used in any convenient way, and by the employment of drums, the whole liming process may be accomplished in five or six hours. It is found, however, that perfectly fresh hides treated in this way cannot be unhaired, and the explanation appears to be that in the ordinary liming process, the epidermis is made soluble by the joint action of bacterial ferments and of the alkaline solutions. If sodium sulphide be added to the caustic soda used for unhairing, the goods will unhair without the use of putrefactive means, but the process is difficult to manage without destruction of the hair, and Messrs. Pullman now recommend that all hides or skins for unhairing by their process should be soaked for forty-eight hours in winter, and twenty-four hours in summer in a really putrid stale soak. This necessity constitutes for very many purposes a serious weakness in the method, as putrid soaking is always extremely dangerous to the grain of the hide, and especially so in hot weather. For certain purposes, however, advantage may be taken of the fact that the hide or skin can be fully limed by Pullman’s process and the fibres swollen so as to be prepared for tanning without any loosening of the hair, and the Author has seen deerskins which have been treated in this way, on which the hair was perfectly firm, while they possessed a softness and fulness which could not be attained without liming. [79] Eng. Pat. 2873, 1898.