CHEMISTRY AND LEATHER

Hokitika Guardian, 27 August 1929, Page 2

CHEMISTRY AND LEATHER

PROCESSES EXPLAINED

INSTRUCTIVE ADDRESS. At a meeting of the chemical section of the Philosopnical Society held recent Mr Philip White, leather research chemist gave an interesting address on the subject of “Chemistry and Leather” before a good attendance ol members.

The manufacture of leather, he said, was one of the oldest trades in existence yet the earlier chemists dkl no. apply themselves to the difficult pro blein off tanning. Professor Proctor ,0 Leeds who died only recently lias been called “the Father o>f Leather Chemistry as he spent his whole life investigating chemical problems of the tannei come of these fundamental problems, even, were little nearer solution than they were twenty years ago.. The study cf leather manufacture embraced the sciences of biochemistry, bacteriology my.ology, ezyme action, as well as phical organic, and inorganic chemistry so that the future leather trades chemist may be a specialist in one of these branches alone. h.he skin as it lefft the butcher may be said to consist of three separate layers said Mr White. First the peidermis (including the hair or wool) then the true skin, or cerium, and finally the body. The skin contained a complex series of-glands, duets, and muscles, which automatically regulated the atmospheric conditions. The epidermis was mainly protective, but the corium, or true skin, consisted of bundles o' fibres twisted round much in the same manner as rope was bound. It was the tanner’s erait to make this fibrous state of the skin persist throughout to the finished .leather. From the chemical viewpoint, the skin was built up of proteins (chiefly) and fats'. The study of proteins was extremely complex and difficult, and despite the labours of Emil Fischer, and others, their knowledge of fundamental constituents of all living matter was still in the very early stages. It was only by the breaking down of the proteins, with the study off thejr degradation products, that any light at all had been thrown on the structure of even the simplest protein. From the tanner’s viewpoint, the chief proteins were the keratins (of the hair and epidermis), ■collagen of the true skin, and elastin which was in ; a lawyer- just under the epidermis. '» f J> i • As the keratins were easily soluble in alkalis, the first stage.in tanning was to “ lime ” the skins or hides. Stronger alkalis- and' sulphides were often added to hasten the process 5 therefore soaking inj. or painting, with' some form of alakli had replaced the old method of removing wool by sweating in the fellniongeries.. It was soon discovered, that a “mellow” limeliquor acted more rapidly than a fresh-ly-made one, and a study of .the constituents of the “ mellow ” liquors had shown that the methylamine (a degradation product of th.e skin), “sharpened ” such liquor. The use of this chemical in the lime-liquors was therefore being thoroughly investigated. The protein of the true skin (collagen) had properties somewhat similar to glue (which substance was, in fact, one of its degradation products. It swelled up with water (“plumped”), but the water could not he squeezed out of it as from a sponge. The “/pickling ” process of the tanner and ffellmonger took advantage of that, but salt and acid were added to the “ pickle,” the former having the effect of keeping the swelling or “plumping” down. Thousands of our sheepskins were exported each season in this state.

Mr White then gave a brief outline of the process of tanning as follows: The hide arrives in the tanyard, and is thoroughly washed, after which the hair is removed by “liming,” as just explained. .The flesh is removed, and the sink is now known as a “ pelt.” Tne skin is then “delimed,” by means of a soaking in a cheap commercial acid, but when a soift, pliable leather is desired, a treatment is given at this stage with an euzyme which takes out of the skin the protein previously described, known as elastin. Tlie older," filthy methods of doing this have been replaced by modern ones, depending on the acti?n of “artificial bates.” which were introduced by Wood, of Leeds. Tn either case, the skin is now in a “delimed” state,. soft, and is ready for the actual tanning' process. It may be stored indefinitely in a nick led condition. For' certain classes of leather, various bark tans are still regarded as most suitable, but th : s lengthy process has to a considerable extent been replaced by the shorter chrome-tannage- Moreover, Sliasny, of Leeds has synthetised artificial tannins of the same nature 'as bark tans, and those are also coming into favour. Whichever method o'f tanning is adopted, the “pelts” are put into pits for the required period (up to three months in some cases,) along with a water solution of the tan and acid: They are occasionally transported from pit to pit, and each time enter a more concentrated acid and tanning solution The nature of the chemical combination between the proteins of the skin and the tannins is a very fundamental property of leather manufacture, which has had unceasing, investigation but which still presents enormous difficulties. The leather is finally dried, “stufed” with grease, and oiled( if required) split, rolled, dyed, etc. In ifact, the final stages of finishing the leather are mainly mechanical, and were but briefly mentioned. The speaker was asked several questions, one of which was for an opinion

regarding the merits of New Zealand leather. In reply Mr White stated that laboratory and practical wearing tests carried out up to the present time indicated that the New Zealand leather was, if anything rather superior to the imported article. The lecture was illustrated by lantern slides, and the speaker was heartily thanked by the members for his instructive address.