[75] Gerber, 1895, pp. 157-9, 169-72.
For details of the analytical methods employed, Eitner’s original paper must be consulted, but the [annexed table] (see [next page]) summarises his results. The letters heading the columns have the following meanings.
A. Hide substance precipitated by neutralisation of the lime with carbonic acid.
B. A further precipitate obtained by slight acidification with hydrochloric acid.
C. Soluble peptones precipitated by hypochlorous acid or mercuric nitrate.
It is obvious that none of these figures represent the total dissolved organic matter, and it is to be regretted that this was not determined. It is, however, fairly safe to assume that the table correctly represents the relative solubility in the different liquors. In each case 2 liters of liquor were used for each kilo of green hide. When old liquors were employed, the hide-substance they originally contained was determined, and deducted from the final result.
| Hide Used. | Description of Lime Liquor. | Days Liming. | Hide-substances in Grams per Liter. | Loss per cent. on Dry Pelt. | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| A. | B. | C. | Total. | ||||||||
| 1 | Oxhide | Fresh lime 30 grm. per liter | - | 6 | [76] | 1·068 | 0·324 | 2·370 | 3·762 | 2·35 | |
| 2 | „ | Ditto | 9 | 2·764 | 0·540 | 3·624 | 6·928 | 4·14 | |||
| 3 | „ | Fresh lime 30 grm., 1⁄2 grm. sulphide of sodium per liter | - | 5 | [76] | 0·852 | 0·172 | 1·816 | 2·840 | 1·75 | |
| 4 | „ | Ditto | 8 | 1·240 | 0·514 | 3·846 | 5·600 | 3·36 | |||
| 5 | „ | 5 weeks old lime, through which four packs had passed | - | 2 | 0·180 | 0·212 | 0·988 | 1·380 | 0·87 | ||
| 6 | „ | Ditto | 5 | [76] | 0·868 | 1·318 | 3·356 | 5·542 | 3·46 | ||
| 7 | „ | 5 months old lime, with sodium sulphide | - | 2 | 0·196 | 0·188 | 0·864 | 1·248 | 0·77 | ||
| 8 | „ | Ditto | 5 | [76] | 0·928 | 1·198 | 3·004 | 5·130 | 3·06 | ||
| 9 | Cowhide | Fresh lime as above | - | 5 | [76] | 1·982 | 0·413 | 4·501 | 6·896 | 4·30 | |
| 10 | „ | Ditto | 8 | 3·132 | 0·672 | 5·741 | 9·545 | 5·94 | |||
| 11 | „ | Fresh lime as above, and 1⁄2 grm. sodium sulphide per liter | - | 5 | [76] | 1·012 | 0·403 | 2·315 | 4·730 | 2·96 | |
| 12 | „ | Ditto | 8 | 2·521 | 0·653 | 5·026 | 8·200 | 4·87 | |||
| 13 | „ | Old disused lime | - | 5 | 0·344 | 0·291 | 2·341 | 2·976 | 1·84 | ||
| 14 | „ | Ditto | 8 | [76] | 2·119 | 1·697 | 6·952 | 10·768 | 6·45 | ||
| 15 | „ | Used sulphide of sodium lime 4 weeks old | - | 5 | [76] | .. | 1·600 | 1·047 | 2·527 | 1·58 | |
| 16 | „ | Ditto | 8 | 0·791 | 0·519 | 4·592 | 5·892 | 3·43 | |||
[76] Hides unhaired.
Taking into account the liming necessary for unhairing only, as shown in the table, it will be noted that the percentage of loss is invariably greater in old limes than in new ones, and less in limes sharpened with sulphide of sodium than where lime alone is used. The only exception to this rule is in No. 15, where a sulphide lime 4 weeks old shows the least loss of any in the time required for unhairing; and indeed sulphide limes if kept strengthened with the requisite addition of sulphide, seem to deteriorate very slowly, No. 8, with a lime 5 months old, showing a result which may still be considered good. Another point especially noted by Eitner is the slight action of old limes during the first stages of liming, as compared with their rapid solvent effect as the hair becomes loosened. The loss in any case does not appear to be so great as the advocates of other unhairing processes have often claimed. If we assume that all the dissolved hide-substance might have made leather, the worst loss on oxhide only limed to the point of unhairing amounts to less than 31⁄2 per cent. on the possible total; and it must be remembered that at least a part of this consists of dissolved epidermis matter, which could not by any possible method have been converted into leather. It will be noted in Nos. 2, 4, 10, 12 and 16, what considerable losses are produced by plumping limes after unhairing, but it must be borne in mind that, in the case of dressing-leather, solution of at least a part of the cementing matter is essential to produce the necessary softness and flexibility. Eitner calculates the dry pelt-weight from that of the green hide on the assumption, based on experiment, that 100 parts of the original skin corresponds to 32 parts of dry pure pelt in green oxhide, 25 parts in green calf-skins, and 56 parts in dried calf-skins. In some of the smaller skins, such as kid worked for glove leather, where great softness and stretch is required, the loss is necessarily much greater than in ordinary dressing-leathers, amounting, in the case of kid, to from 20 to 27 per cent.
The parts taken by the purely chemical activity of the lime, and by the action of bacteria and bacterial ferments in the unhairing process must still be regarded as uncertain. The late Professor von Schroeder[77] carried out a series of experiments on liming and sweating which were characterised by his usual care and thoroughness, and which tend to prove that the chemical action is far more important than the bacterial. He had fresh hides well washed in a tannery immediately after slaughter, and fleshed. The butts were then cut into pieces of about 10 cm. (4 inches) square, and salted in brine repeatedly changed, and finally preserved for use in glass jars in saturated salt solution. He found that when washed free from salt, and placed in a moist chamber at a temperature of 16° C., the hair was sufficiently loosened by bacterial action in four to five days. Pieces placed in the moist chamber without previous removal of the salt only showed signs of sweating after about ten weeks’ exposure. Liming experiments were made with similar pieces of salted hide, both after three days’ washing to free them from salt, and unwashed, and in both cases the pieces unhaired freely in three to four days. These experiments were varied by using 6, 18 and 30 grms. of lime per liter of water in which about 200 grms. of hide were placed, but neither in the washed, nor unwashed portions was there any material difference in the time required to loosen the hair. Addition of 1 vol. of used lime-liquor to 3 vols. of water in making up the limes was equally without perceptible influence, and careful bacteriological examination of hide and liquors showed that the former was almost sterilised by the intense salting, and that the lime-liquors were practically free from bacteria.