Dr. Lindley's communication was ill.u.s.trated with specimens of coloring matters yielded by various lichens collected in the neighbourhood of Edinburgh, &c.

BARKS FOR TANNING.

Let us now take a brief review of the sources from whence tanning materials may be obtained, which will also enable us to form a fair estimate of the prospect of future supplies. Only one medal was awarded, at the Great Exhibition, for tanning substances, viz., to Messrs. Curtis, Brothers (United Kingdom, No. 126), but honorable mention was made of the following compet.i.tors:--One from Tunis, one from Van Diemen's Land, one from New Zealand, one from Belgium, one from the Cape of Good Hope, one from Canada, and one from the United Kingdom.

The substance from which pure tannin is most frequently obtained for chemical purposes is nutgalls, for tannin const.i.tutes above 40 per cent, of their weight. It may be procured also from several other sources, such as oak, horse chestnut, sumach, and cinchona barks, catechu, kino, &c.

The basis of the skins of animals is composed of a substance to which the name of gelatine is given. One of the properties of this substance is, that when combined with tannin, it forms the compound of tannate of gelatine, or leather, a substance which is so useful to mankind.

From time immemorial, the substance employed to furnish the tannin to the hides of animals, in order to convert them into leather, has been oak bark. But as the purpose for which oaks are grown is their timber, and not their bark, the supply of oak bark cannot be calculated upon, and this is, perhaps, one of the causes why tanning as an art is in such a backward state.

The consumption of tannin required in the leather manufacture may be estimated from the fact that more than 672,000 cwts. of raw hides were imported in 1851, besides the hides of the cattle, &c., consumed in the United Kingdom. On the Continent and in the United States the consumption of bark for this purpose is also considerable.

The imports of bark for the use of tanners and dyers has amounted yearly to the very large quant.i.ty of 380,674 cwt., besides what we obtain at home. Oak bark contains usually the largest proportion of tannin, and according to Davy's experiments eight-and-a-half pounds of oak bark are equivalent for tanning purposes to two-and-a-quarter of galls, three of sumach, seven-and-a-half of Leicester willow, eleven of Spanish chesnut, eighteen of elm, and twenty-one of common willow bark. Tannin obtained from these sources, however, differs materially in some of its characters. The tannin of nutgalls, which is that generally employed for chemical purposes, is sometimes called gallo-tannic acid, to distinguish it from other species.

Notwithstanding the number of different substances which have from time to time been introduced for the use of tanners, it is, nevertheless, pretty generally acknowledged that there is nothing superior, or even equal, to good oak bark, and that all attempts to hurry the process beyond a certain point by the use of concentrated solutions of tan, &c., are for the most part failures, as the manufacture of good leather, to a great extent, depends on the process being conducted in a slow and gradual, but--at the same time--thorough and complete matter.

Oak bark is, however, by no means the only astringent bark well suited to the use of the tanner, and in various parts of the world other similar substances are used with very great success. All these tanning materials, though they may not be considered by the English tanner equal to the best oak bark, are, nevertheless, of great value to him; they may be employed in conjunction with oak bark, or even as a subst.i.tute in times of scarcity, or when the price of oak bark is high; in fact the very existence of such substances tends to keep down and equalise the price of bark, and to prevent it from undergoing those great fluctuations in value which would necessarily occur were it the only tanning material available to our manufacture--("Prof.

Solly in Jury Reports of Great Exhibition.")

There are a vast number of bark and other substances useful for tanning purposes, which are found in the tropics, that are comparatively unknown or little regarded in Europe; but which might be readily obtained in large quant.i.ties and at a trifling cost. The bark of many species of _Acacia_ furnishes the tanning principle in a great degree, particularly that of _A. arabica_, which, under the name of Babul wood, is largely used about Scinde, Biliary, Gruzerat, and other parts of India; where it is regarded as a powerful tonic. The fruit of _A. vera_, termed Egyptian and Senegal "bablah," has been employed in tanning and dyeing. Numerous species of this tribe are found abundant in New South Wales and the Cape Colony, and these, particularly the wattle bark of Australia, are in common use for tanning, from their astringent properties. The bark and rind of the fruit of the pomegranate (_Pumica Granata_) have similar properties.

The bark of _Avicenna tomentosa_ is in great use in the Brazils for tanning. So are the curved pods of _Caesalpinia Coriari_, in the East and West Indies, under the name of Divi-divi. _Coriaria myrtifolia_ is not only used in tanning leather, but also for staining black. It is worth 9 to 10 per ton. _Pterocarpus marsupium_ furnishes about Tellicherry the concrete exudation called kino, a powerful astringent used for tanning.

The plants of the mangrove tribe, _Rhizophora Mangle_, and other allied species, have frequently an astringent bark, which is in many cases used for tanning and dyeing black. This tree is very common in most tropical countries, where it forms dense thickets on the muddy banks of rivers and the sea sh.o.r.es. The bark of _Bauhinia variegata_, is made use of in Scinde and other parts of Asia. The bitter astringent bark and the galls of several of the Tamarisk tribe are also well suited for the purpose.

_Mesembryanthemum nodiflorum_, one of the numerous indigenous species of the Cape, is used in making morocco leather.

The extract procured from the bark of the _Butea_, that of the _Buchanania latifolia_, the _Scyzgium_ (_Calyptranthes_), _Jambolana_, &c., are likely to be of consequence to the tanners, and could be produced in India in large quant.i.ties. Specimens of these, and of the bark of the Saul tree, of _Nychanthes arbortrista, Terminalia angustifolia_, and of the gaub fruit (_Diospyros glutinosa_), were shown by the East India Company. The bark of the hemlock tree is extensively employed for tanning in New Brunswick.

The bark of yellow hercules (_Xanthoxylum ochroxylon_), and the pods of _Acacia tortuosa_ are used for tanning in the West Indies.

In the instructions given by the Admiralty to Sir James Boss, when proceeding on his Antarctic Expedition, his attention was particularly called to the astringent substances adapted for tanning, and to the various extracts of barks, &c., imported into England from our Australian settlements, and which are employed by the tanner. Little sterling information has as yet been obtained as to the qualities of the astringent gums, barks, and dyes, yielded in such abundance by the trees of those colonies, and the proportion of tannin they contained.

In 1846, 563 tons of bark for tanning were exported from Port Phillip.

A large quant.i.ty of tannin is extracted from various species of Eucalyptus, the gigantic gum trees in Australia and Van Diemen's Land (of which quarter all the species are natives), and sent to the English market; it is said to be twice as powerful in its operations as oak bark. Some of these trees attain a height of 200 feet. Their bark separates remarkably into layers. A sort of kino gum, an astringent resinous-like substance, is also extracted from _E.

resinifera_, the brown gum-tree of New Holland, which is sold in the medicine bazaars of India. It exudes in the form of red juice from incisions in the bark. A single tree will often yield 60 gallons. In Brazil they use the bark of _Luhea panicata_, an evergreen climber, for tanning leather; and in Peru the bark of some species of _Weinmaunia_ serve the same purpose. Among other powerful astringents I may notice the root of a species of Sea Lavender (_Statice Caroliniana_), _Myrica cerifera_, and _Heuchera Americana_, all natives of North America. Also the petals of _Hibiscus Rosa-sinensis_, a native of Asia.

The sea-side grape (_Coccolaba uvifera_) yields an astringent substance, known as Jamaica kino.

The bark of the _Ca.s.sia auriculata_, and the milky juice of the _Asclepias gigantea_, are used for tanning in India.

The red astringent gum obtained from _Butea frondosa_, a middling size tree, common in Bengal and the mountainous parts of India, is used by the natives for tanning. English tanners, however, object to its use on account of the color which it communicates to the leather.

The barks of the _Mora excelsa_, Benth; Courida (_Avicenna nutida_), cashew (_Anicardium occidentale_), guava and hog-plum (_Spondius lutea_, Linn.), have all been successfully used for tanning in Demerara and the West India Islands, where they are very abundant.

Specimens were sent from British Guiana.

The root of the Palmetto palm (_Chaemaerops Palmetto_) is stated to be valuable for the purposes of tanning. The leaves of _Nerium Oleander_ contain tannic acid. The bark of a species of Malphigia is much used by the Brazilians.

The panke (_Gunnera scabra_) is a fine plant, growing in Chili, on the sandstone cliffs, which somewhat resembles the rhubarb on a gigantic scale. The inhabitants eat the stalks, which are subacid, tan leather with the roots, and also prepare a black dye from them. The leaf is nearly circular, but deeply indented on its margin. Mr. Darwin measured one which was nearly eight feet in diameter, and therefore no less than twenty-four in circ.u.mference. The stalk is rather more than a yard high, and each plant sends out four or five of these enormous leaves, presenting together a very n.o.ble appearance.

The barks replete with the tanning principle should be stripped with hatchets and bills from the trunk and branches of trees in spring, when their sap flows most freely. The average quant.i.ty of oak bark obtained from our forests is estimated at 150,000 tons annually, of which Ireland and Scotland furnish but a very small quant.i.ty.

The following table, given by Dr. Ure, shows the quant.i.ty of extractive matter and tannin yielded by different substances:--

In 480 parts In 100 parts by Davy. by Cadet.

Sicilian sumach 78 -- Malaga ditto 79 -- Souchong tea 48 -- Green tea 41 -- Bombay catechu 261 -- Bengal ditto 231 -- Nutgalls 127 46 Bark of pomegranate -- 32 " Virginian sumach -- 10 " Carolina ditto -- 5

Catechu and Gambier are very valuable for tanning, and are alluded to under the heads GAMBIER and ARECA PALM.

CATECHU is obtained from the _Acacia Catechu_, an arboreous tree growing from fifteen to twenty feet high, with a brown and scabrous bark. The interior wood is brown, dark red or blackish, and the exterior white, one or two inches thick. It inhabits various parts of the East Indies, of which it is a native, and is also now common in Jamaica. It bears whitish or pale yellow flowers.

The catechu obtained from this tree in Pegu, is celebrated throughout India, and fetches 4 to 5 more per ton than gambier and other astringent extracts. When of good quality, catechu is more powerful as an astringent than kino. Of all the astringent substances we know, catechu appears to contain the largest proportion of tannin, and Mr.

Purkis found that one pound was equivalent to seven or eight of oak bark for tanning leather.

The term catechu, observes Dr. Pereira, is applied to various astringent extracts imported from India and the neighbouring countries. A few years ago the terms catechu, terra j.a.ponica, and cutch were employed synonymously; they are now, however, for the most part used in trade somewhat distinctively, though not uniformly in the same sense. The manufacture of catechu from the _Acacia catechu_ as practised in Canara and Behar, has been described by Mr. Kerr ("Med.

Obs. and Inquiries," vol. v.), and Dr. Hamilton ("Journey through Mysore," &c., vol. iii.), while Professor Royle has explained the process followed in Northern India. According to the last-mentioned gentleman, "the kutt manufacturers move to different parts of the country in different seasons, erect temporary huts in the jungles, and selecting trees fit for their purpose, cut the inner wood into small chips. These they put into small earthen pots, which are arranged in a double row, along a fireplace built of mud; water is then poured in until the whole are covered; after a considerable portion has boiled away, the clear liquor is strained into one of the neighbouring pots, and a fresh supply of the material is put into the first, and the operation repeated until the extract in the general receiver is of sufficient consistence to be poured into clay moulds, which, in the Kheree Pa.s.s and Doon, where I have seen the process, are generally of a quadrangular form. This catechu is usually of a pale red color, and is considered there to be of the best quality. By the manufacturers it is conveyed to Saharunpore and Moradabad, whence it follows the course of commerce down the Ganges, and meets that from Nepaul, so that both may be exported from Calcutta."

GAMBIER.

The Gambier plant (_Uncaria Gambler_, Roxburgh, _Nauclea Gambir_, Hunter), has been described by Rumphius under the name of _Funis uncatus_. It is a stout, scandent, evergreen shrub, which strongly resembles the myrtle. It is generally cultivated in the same plantation with pepper, as the leaves and shoots, after undergoing the process by which their juice is extracted, to furnish a kind of catechu, are found to be an excellent manure for the pepper vines. The leaves and young shoots of the gambier plant are collected as soon as they have attained a sufficient size, and boiled in iron pans until the juice acquires the consistence of treacle. The decoction is poured out into narrow troughs, dried, and afterwards cut up into small cakes, and packed in baskets for exportation. The gambier extract, which is of a yellowish brown color, and has the consistence of hard cheese, is much esteemed by the Malays for mixing with the preparation of betel, which they are in the habit of chewing; and considerable quant.i.ties have lately been imported to this country, where it is used for dyeing colors, and for tanning leather. The demand for gambier here is on the increase; and when better known to our chemists, it will probably be found applicable to many other purposes than those to which it is at present applied.

There were, in 1850, 400 gambier and pepper plantations on the island of Singapore; each measures or occupies on an average an area of 500 fathoms square, and employs eight to ten hands to cultivate and manufacture the gambier and pepper. There are some pepper plantations in addition, and they have been found to answer very well without any gambier being cultivated with them. Gambier cultivation is generally a losing undertaking, but it is adopted to obtain the refuse of the leaves for manuring the pepper vines, and also to employ the people in the plantations; it besides affords the proprietors the means of getting monthly sums to carry on the cultivation of pepper, which affords two crops yearly. There were formerly 600 plantations in Singapore, but the reason already a.s.signed, and the formation of spice plantations contiguous have caused the abandonment of all those near the town. Each plantation must have an equal extent of forest land to that cultivated with gambier and pepper, to enable the manufacture of the gambier being carried on, and each gambier plantation, of 500 fathoms square, contains about 3,500 pepper vines, which yield on an average two catties per vine, or 70 piculs of pepper, and about 170 piculs of gambier annually;--a good plantation will, however, yield sometimes as much as 120 piculs of pepper, and 200 piculs of gambier, and a bad one as little as 40 to 50 piculs of pepper, and 60 to 80 piculs of gambier. Were it not for the enormous commission charged by the agents of these plantations, from whom the cultivators get all the advances, it would prove a profitable cultivation. The rates of commission charged generally are as follows:--Per picul of gambier, fifteen to twenty-five cents; per picul of pepper, thirty to forty cents; and if the price of the former is below one-and-a-half dollars, and the latter below three-and-a-half dollars per picul, a small reduction is made in the rates of commission. On every picul of rice supplied to the planters twenty to twenty-five cents commission is charged; this includes the interest of money advanced, which is never charged. A gambier and pepper plantation is valued or estimated at about 400 dollars on an average. The following is supposed to be a correct estimate, on an average, of the yearly expenditure and returns of a gambier and pepper plantation of 500 fathoms square, viz:--

EXPENDITURE.

drs. c. men. drs. c.

Eight men at 3 dollars and 7 Java rupees per month, wages for headman and labourers respectively 22.70 12 272.40 Five piculs of rice, including commission, say 6.50 12 81.60 Fish, &c. 5 12 60.0 Boat or cart hire to carry rice and produce 1 12 21.0 ------ 435.0

PRODUCE.

170 piculs of gambier, valued at l dollar 45 cents per picul, less 15 cents commission chargeable, nett 221.30 -- --- 70 piculs of pepper, at 4 dollars, less 40 cents per picul commission, nett 287.0 -- 508.0

Yearly profit, 73 dollars, or about 15.

Several gambier and pepper plantations have been abandoned in Singapore, partly from the ground being impoverished, but more particularly from the exhaustion of the forest adjacent to their estates. The exhaustion of the trees by yearly consumption deprives the planters of the necessary fire wood which is used for the boiling down of the gambier. A gambier plantation gets exhausted in fifteen years, either from the want of firewood or the land getting impoverished.

There are about 200 plantations at Joh.o.r.e, and the produce of gambier for the season of 1851 was calculated at 30,000 piculs.

This shrub was, at one period, cultivated with success at Pinang and other places to the eastward, but as Java was the princ.i.p.al market for the produce, and the Dutch had levied a duty of twelve Java rupees per picul on it, the cultivation at the former island did not repay its cost, and it was accordingly abandoned. Prices have been lately advancing, and the Chinese are talking of trying it again. The plant is partial to hilly land or slopes at the skirts of hills. Two hundred plants are usually placed on one orlong of land, being six feet asunder. They are raised from seed, and are topped to eight or ten feet, when the gambier is to be prepared. The Chinese dry the seed slightly, and sow in rainy weather.

The seeds vegetate in forty days, and are planted out in the second or third month afterwards.

At the expiration of fourteen months, the first cutting of the branches, with the leaves on, is made. These are put into a boiler, and when the juice has been extracted, the branches and refuse are thrown away, and the boiling is continued until the liquor has obtained the proper consistence, when it is put into shallow troughs, dried, and cut into slices for sale. The second cutting takes place eight months subsequently to the first. The plant now grows strong and admits of frequent cropping, and it will endure for twenty years. No manure is used, but the plantation is kept clean.

Estimated cost of cultivating ten orlongs, about 13 acres, according to Colonel Low:--

Spanish dollars.