A Text-book of Tanning (eBook)

A treatise on the conversion of skins into leather, both practical and theoretical

H. R. Procter (Autor)

eBook Download: EPUB

2019 | 1. Auflage
2471 Seiten
Good Press (Verlag)
978-7-6646-0537-6 (ISBN)

Infos

H. R. Procter's 'A Text-book of Tanning' is a comprehensive guide that delves into the intricate process of leather tanning. Procter's meticulous attention to detail and clear explanations make this book an invaluable resource for anyone interested in the chemical and mechanical aspects of tanning. Written in a straightforward and accessible style, the book provides a thorough exploration of the history, techniques, and chemical processes involved in the tanning industry. Procter's work stands out for its practical approach and wealth of information, making it an essential read for students and professionals in the field. This book is a significant contribution to the literature on tanning, offering a wealth of knowledge and insight for those looking to deepen their understanding of this age-old craft.

Textauszug

[C] Dingler's Polyt. Journal, vol. 220, p. 167.

Hide Albumen.—The fresh hide, besides this coriin (which, very possibly, is only evolved by the action of the lime), contains a portion of actual albumen, viz. that of the blood serum and of the lymph, which is not only contained in the abundant blood-vessels, but saturates the fibrous connective tissue, of which it forms the nourishment. This albumen is mostly removed by the liming and working on the beam, which is preparatory to tanning. Probably for sole-leather, the albumen itself would be rather advantageous if left in the hide, as it combines with tannin, and would assist in giving firmness and weight to the leather. It is, however, for reasons which will be seen hereafter, absolutely necessary to get rid of any lime which may be in combination with it. The blood also must be thoroughly cleansed from the hide before tanning, as its colouring matter contains iron, and, in combination with the tannin, would give a bad colour.

The reactions of blood and lymph albumen are very similar to those of ordinary white of egg. It is precipitated by strong mineral acids, especially nitric, and also by boiling. The precipitate produced by strong hydrochloric acid redissolves by the aid of heat to a blue or purple solution. Tribasic phosphoric, tartaric, acetic, and most other organic acids, do not precipitate moderately dilute solutions of albumen, but convert it into a sort of jelly, which, like gelatin, does not coagulate, but liquefies on heating. It is precipitated by neutral salts of the alkali metals. Blood-albumen slightly acidified (with acetic acid) is precipitated by potassium ferrocyanide. It is not precipitated by dilute infusions of oak bark, but is rendered uncoagulable by heat, hence it cannot be employed to remove tannins from their solutions.

Elastic Fibres.—The elastic or yellow fibres of the hide are of a very stable character. They are not completely dissolved even by prolonged boiling, and acetic acid and hot solutions of caustic alkalies scarcely attack them. Probably they do not combine with tannin, and are very little changed in the tanning process.

Hair, Epidermis, and Glands.—These are, as has been seen, all derived from the epithelial layer, and hence, as might be inferred, have much in common in their chemical constitution. They are all classed by chemists under one name, "keratin," or horny tissue, and their ultimate analysis shows that in elementary composition they nearly agree. It is evident, however, that the horny tissues are rather a class than a single compound.

The keratins are gradually loosened by prolonged soaking in water, and, by continued boiling in a Papin's digester, are dissolved to an extract which does not gelatinise on cooling. Keratin is dissolved by caustic alkalies; the epidermis and the softer horny tissues are easily attacked, while hair and horn require strong solutions and the aid of heat to effect complete solution. The caustic alkaline earths act in the same manner as dilute alkaline solutions; hence lime easily attacks the epidermis, and loosens the hair, but does not readily destroy the latter. Alkaline sulphides, on the other hand, seem to attack the harder tissues with at least the same facility as the soft ones, the hair being often completely disintegrated, while the epidermis is still almost intact; hence their applicability to unhairing by destruction of the hair. Keratins are dissolved by fuming hydrochloric acid, with the production of a blue or violet coloration, like the albuminoids. They also resemble albumen, in the fact that their solution in sulphuric acid is precipitated by potassium ferrocyanide. By fusion with potash, or prolonged boiling with dilute sulphuric acid, keratin is decomposed, yielding leucin, tyrosin, ammonia, &c. The alkaline solution of keratin (hair, horns, &c.) is precipitated by acids, and, mixed with oil and baryta sulphate, is employed under Dr. Putz's patent as a filling material for leather, for which purpose it acts in the same way as the egg-yolks and meal used in kid-leather manufacture. Eitner attempted to use it for the same purpose with bark-tanned leather, but without much success. Putz has also proposed to precipitate the material after working its solution into the pores of the leather.

CHAPTER III.

Table of Contents

COMMERCIAL TANNING MATERIALS.

Algarobilla.—The seed-pods of Prosopis pallida and P. Algarrobo are known as algarobilla, the two kinds being distinguished as negro and blanco. The trees are abundant in mountainous parts of South America, notably Chili and the Argentine Republic. The pods contain up to 50 per cent. of a bright-yellow tannin, somewhat resembling that of myrobalans. The friable tannin is readily soluble in cold water, and is so loosely held in the fibrous network of the pod, that great loss is sustained by careless handling. The commerce in algarobilla does not figure in the official trade returns; but J. Gordon & Co., Liverpool, obligingly state that they imported 50 tons, at an average value of 18l. 10s. a ton, in 1880. Widow Duranty & Son, also of Liverpool, are good enough to add that they received 160 tons in 1881, the first that had reached them for a long time. Havre imported 50 tons in 1881. The name algarrobo is also applied to Balsamocarpon brevifolium in Chili, and to Hymenæa Courbaril in Panama.

Chestnut-extract.—The wood of the chestnut (Castanea vesca) contains 14–20 per cent. of a dull-brown tannin. It is quite different from the bark and bark-extract of the American chestnut-oak (Quercus sessiliflora). Its extract is used largely to modify the colour produced by hemlock-extract, and for tanning and dyeing. The pulverised wood is also extensively employed in France. The imports are included in barks and extracts, p. 39.

Cork-bark. See Oak-barks.

Cutch, Catechu, or Terra Japonica (Fr., Cachou; Ger., Catechu).—The term kát, kut, or "cutch," is applied to the dried extract, containing 45–55 per cent. of dark-coloured mimo-tannic acid, prepared chiefly from 2 trees:—(1) Acacia Catechu [Mimosa Catechu, M. sundra], a tree of 30–40 ft., common in most parts of India and Burma, growing also in the hotter and drier districts of Ceylon, and abundant in tropical East Africa—the Soudan, Sennar, Abyssinia, the Noer country and Mozambique, though the utilisation of its tannin is restricted to India; (2) A. [M.] Suma, a large tree inhabiting South India (Mysore), Bengal, and Gujerat.

The process for preparing cutch varies slightly in different districts. The trees are reckoned to be of proper age when their trunks are about 1 ft. diam. They are then cut down, and the whole of the woody part, with the exception of the smaller branches and the bark, is reduced to chips: some accounts state that only the darker heart-wood is thus used. The chips are placed with water in earthen jars, arranged in a series over a mud fire-place, usually in the open air. Here the water is made to boil, the liquor as it becomes thick and strong being decanted into another vessel, in which the evaporation is continued until the extract is sufficiently inspissated, when it is poured into moulds made of clay, or of leaves pinned together in the shape of cups, or in some districts on to a mat covered with the ashes of burnt cow-dung, the drying in each case being completed by exposure to the sun and air. The product is a dark-brown extract, which is the usual form in which cutch is known in Europe.

In Kumaon, North India, a slight modification of the process affords a drug of very different appearance. Instead of evaporating the decoction to the condition of an extract, the inspissation is stopped at a certain point, and the liquor is allowed to cool, coagulate, and crystallise over twigs and leaves thrown into the pots for the purpose. By this method is obtained from each pot about 2 lb. of kath or catechu, of an ashy-whitish appearance. In Burma, the manufacture and export of cutch form one of the most important items of forest revenue. The quantity of cutch exported from the province in 1869–70 was 10,782 tons, valued at 193,602l., of which nearly half was the produce of manufactories situated in British territory. The article is imported in mats, bags, and boxes, often enveloped in the large leaf of Dipterocarpus tuberculatus. It is brought down from Berar and Nepal to Calcutta. That of Pegu has a high reputation.

Our imports of cutch in 1880 were 5155 tons, value 173,040l., from the British East Indies; 539 tons, 15,572l., from other countries; total, 5694 tons, 188,612l. Our exports in the same year were:—892 tons, 28,527l., to Germany; 676 tons, 24,562l., to the United States; 478 tons, 15,505l., to France; 303 tons, 10,537l., to Holland; 177 tons, 5859l., to Russia; 141 tons, 4835l., to Belgium; 245 tons, 8719l., to other countries; total, 2912 tons, 98,544l. The approximate London market value of Pegu cutch is 21–42s. a cwt.

An astringent extract prepared from the areca nut (Areca Catechu) is said to contribute to commercial cutch; if so, it is a totally distinct product from those just described.

Divi-divi, or Libi-dibi.—These names are applied to the seed-pods of Cæsalpinia coriaria, a tree of 20–30 ft., indigenous to several of the West Indies, Mexico, Venezuela, and North Brazil, and naturalised in Madras and...

Produkt-Details

• Erscheint lt. Verlag: 27.11.2019
• Sprache: englisch
• Themenwelt: Technik ► Bauwesen
• ISBN-10: 7-6646-0537-7 / 7664605377
• ISBN-13: 978-7-6646-0537-6 / 9787664605376