Per cent. CaO 91·95 MgO 1·30 CO₂ and moisture 6·75 ------ 100·00 _Determination of “Available” Lime._--The practical value of lime for the tanner is easily determined by drawing a sample by breaking off small pieces from a number of lumps of the bulk, coarsely pulverising them in a mortar, and then rapidly grinding a portion as fine as possible, and transferring it at once to a stoppered bottle for weighing. A portion of this, not exceeding 1 grm., is shaken into a stoppered liter flask, which is filled up roughly to the mark with hot and well-boiled distilled water, and allowed to stand for some hours with occasional shaking. When cold it is filled exactly to the mark with cold distilled water, well shaken again and allowed to settle, or rapidly filtered, and 25 or 50 c.c. of the clear liquid withdrawn with a pipette and titrated with N/10 hydrochloric or sulphuric acid and phenolphthalein. Each cubic centimeter of N/10 acid equals ·0028 grm. CaO. It is generally a very mistaken economy to make use of an inferior lime for tanning purposes, as any saving in cost is discounted by the larger quantity required, the more frequent cleaning of the pits, and the danger of stains and of burns from imperfect slaking. The action of lime on the hide has already been spoken of to some extent. It is throughout a solvent one. The hardened cells of the epidermis swell up and soften, the mucous or growing layer and the hair-sheaths are loosened and dissolved, so that, on scraping with a blunt knife, both come away more or less completely with the hair (constituting “scud” or “scurf,” Ger. _Gneist_ or _Grund_). The hair itself is very slightly altered, except at its soft and growing root-bulb, but the true skin is vigorously acted on. The fibres swell and absorb water, so that the hides become plump and swollen, and, at the same time, the “cement-substance” of the fibres is dissolved, and they become split-up into finer fibrils: the fibrils themselves become first swollen and transparent, and finally corroded, and even dissolved. A similar swelling of the fibres is produced by both alkalies and acids, and is probably due to weak combinations formed with the fibre-substance, which have greater affinities for water than the unaltered hide.[72] This swelling is useful to the tanner, since it renders the hide easier to “flesh” (i.e. to free from the adhering flesh) on account of the greater firmness which it gives to the true skin. It also assists the tanning, by splitting up the fibre into its individual fibrils, and so exposing a greater surface to the action of the liquors. This is advantageous in dressing-leather which is afterwards tanned in sweet liquors, and which must have the cement-substance of the fibres dissolved and removed for the sake of flexibility; and, in the case of sole-leather, it is necessary for sake