vu1 _ 18,_ so 9 INDUS’IXIAL AND ENGINEEM.VG CIfEWIS’I’KY _ _ _ ~ ~ __ .__
934
Tanning 1876-1926’ BY John Arthur Wilson A. F. GALLUX Br SONS
co..
MILWAUEBII, Wlh
LTHOUGJI the taniiing inilustry lias beeii flourishing daruagc froin the long cuutikct wit11 the liiiie liquors necesiiifor many thousands of years, the last fifty years mark k t e d by t.lic crudeness of tlie operatiiin. In she-upper what is practically the beginning of the applicat’ion Icatlier this dsmage shows itself in the form of a marred o f scieiice to tannery ~i~~etliwls. The great “father of leather appearance of the grain surftace and it wns tolerated only ausc the public of 1878 w-as less esrrctiiig in its demands chcmistry,” I’rof. Ji. It. frocter OS England, is still coiltributing to the advaiicement of the science that owcs so regnriling filiencss of appearance tlian tlre putilic~of today. In the modern tannery a cliemist controls the liiniiig mueii tu his genius and iiiitiativc. Soieiice has not yet changed the general principles of tnmiing wliich liare been pruccss. h i f o r m saturation of the liquurs with calcimii h y h x i d e is guaranteed by tlic use of aii ex evolved through all tlie ages of c~i~ilizatiom, but i t 11 a ~ a yone mystery after another, rcvcaliiig mucli of tiie system of nieclianical st,irriug sucli as a rotniting paddle wheel meelsariism of tlie complex processes and Innking Iwssil)ln s1.t in the rat. Sitice it is desired to hydrolyze tlie keratinow fairly rigid control of i~pcrtitioiisthat often failed in the liaiiils proteins, but not tlie collagen, sodium sulfide is added and of artisans of lifelong training. The result for the tanner it. concentration controlled by chemical auaiysis. Sorlium Bas ireeii less troulile witli much fewer losses, less dependcnoe suffide ciiinbines with lieratins, hut not with collagen, and upon higldg skilled workmen and upon costly materials, tlic (xrmlmml formed is mucli nme readily hydrolyzed alluili than t,he original keratiiis. The action is thus iiiorc uniform operation, aiid better leather a t less cost. eilcd up and the hair and epidermis loosened before the Control of Bacterial Action it~ts,ckedtlic collagen appreciably. Pur each type Tlic avcragc tanner of 1876 knew nothing at all ahout of skin tile cliemist has found tliat tliere is an optimum bacteria and coiisequently was bafiied hj- frequent recurrences temperature of liming at d i i e h the damnge to the collagen of damage t u tlic stock in tlie processes preceding tanning. is least when the hair loosening is completed. N’itli proper The finished leather might appear t o be pitt,cd, or to have control the liming can be completed in a single day am1 in wliat is called a loose or pipy grain, or aliow ttio pattern OS only one liquor. Not only is tliere a consideral~lesaving tiie blood vessel system upon the lcatlier surface, or miglit in time and labor, but the skins stiffer practically no damage have its important properties affccted adversely in many and the finished leather is of higher and more uniform quality other ways. Often darnages of this End had their origin tlriin when linied by the best methods in vogue in 1876. in tlie soaking operation, in which the skins are cleansed Bating and softened before liming. The soak vats occasionally J’erliaps the most wllolesome advame made by scieiice became infected with certain kinds of proteolytic bacteria that caused destruction of the skin fibers in various ways in tanning was the substitution of purified trypsin for the and the leather finally obtained was of corresponi~ingly otrnoxiuus dungs used in the o p e r a t i ~ icalled liating. In lowered quality. Sometimes severe losses were sustained 1876, after tlie skins had been limed, unliaired, arid washed, before it was even suapected that the damage had its origin it was practically a uiiirersal rule to suak tliem in vats in the soak vats. In the modern tannery, bacterial nctiun coritaii~ing warm infusious of the dung of dugs or fowls. in soaking is kept under control by regulationof temperature, frequent cliirnging of tlie water, and tlie uhe of antiseptics, such as chlorine, guided by bacteriological exaininatioiss of tlie water from the vats. Where the danger of contamiiation is very great, it is a11 easy matter to reduce the bacterial count of water contaiuing skins from o \ w a million per cubic centimeter to a ricgligiblc quantity, without harming tlic skins, by the application US aboilt :dl to 100 parts per s nil lion of clilurine.
A
Liming
In liming, tu loosen the hair ami epidcrinia of the nkiiis, the tanner of fifty years ago would simply d u m p a pack of skins into a vat of water containing more calcium hydroxide tlian would dissolve. Usually tlie lime liquor was one that liad been used several times before arid contaiued accumulated calcium salts and protein decomposition products. At intervals of one to two days the pack was transferred to vats of freslm Jiquor, finally ending in liinewater freslily prepared. This procedure required from one to three weeks tu loosen the hair, depending upon the temperature of the water, which was usually not controlled. Since no means was provided for agitating the liquors, they were not kept uniformly saturated with lime and the results were correspondingly irregular. The skins also suffered more or less 1 Received
May 10, 1D86,
Modern Method o t Movine. S k i m from Vat to Vat By ineans 01 a crane end hoirf a P?ck of 400 skins can b e moved trot= o m vat to Rnotber in lesa tlian a m i n u b Hormerly creh skin was moved sepnrrfely by hand.
This treatment prior to tanning gave a finished product with a rnucb smoother and finer grain surface than could he obtained by any other treatinent then known. The tanner liad no idea as to what constituent of the dung was responsible for tlre observed effects nor as tu tlie mechanism of the reaction taking place in tlie skin. Tlris made it difiicult
to control bhe operation of hating and consequently m!ir!li lenther was spoiled in this process. The difficulties encountered in hating, or puoring, as it was sometimes called, are vividly pictured in a statement by the pioneer investigator of bating, the late Joseph T. Wood, of Nottingharn, in his book: When learning thc trade as an apprentice cvery fault iu the leathers was attributed to this part of the work, and the troubles and miseries of the “pucr shop” first cviiscd me tu take up the studv. 01 . nueriur. . I was dctcrmined to know the causes underlying the process. Puering is not only a filthy and disxusting
Experimenlal Tannery-A
Part of Modern Chemical I.uborafocy
Wood analyzed the dung lilpi
