“Quebracho” means “axebreaker,” and is consequently applied to a variety of hard woods. Its specific gravity is 1·27-1·38, and it therefore sinks in water.

Pistacia lentiscus, Ital. Pistacio, Fr. Lentisque. Sicily, Cyprus, Algeria. Small myrtle-like leaves contain from 12-19 per cent. of a catechol-tannin, and are very largely used in the adulteration of sumach. Leather tanned with sumach adulterated with this material darkens and reddens on exposure to light and air, and for this reason its use in many cases is decidedly injurious. In Cyprus and the East it is known as “Skens,” Ital. Schinia, Fr. Poudre de Lentisque, in England, often called Cyprus sumach. (Cp. p. 272.)

P. orientalis, terebinthus, vera, etc., India, Mediterranean. Various aphis galls, 30-40 per cent. tannin. A sample of galls of Pistacia vera, “Gool-i-pista,” India, recently examined in the Author’s laboratory, contained 30 per cent. of a light-coloured tannin.

Schinus molle, “Molle,” Buenos Ayres. Leaves only used; said to contain 19 per cent. tannin.

S. Aroeira, Brazil. Said to contain 14 per cent. tannin.

Rhus coriaria, Sicilian sumach. Ital. Somacco. (Fig. 53.) A shrubby bush, of which leaves and small twigs are used.

Mostly propagated by suckers from older plants, which are planted in rows about two feet apart in early spring, and pruned to 6-8 inches. Bushes begin to bear the year after planting, though the strength is not so good as from more mature plants. Cropping is either by pruning off shoots, or gathering leaves by hand; in the latter case shrubs are pruned in winter. The leaves are dried either in the fields, or on covered threshing floors, where they are afterwards separated from the stems by beating. Some is exported in this state, as “leaf” or “baling” sumach, but most is ground to fine powder under edge-runners. “Ventilated” sumach is winnowed to remove dust and sand, which often contains iron. “Mascolino” is the best sumach from Palermo and district; “feminella” consists of weaker sorts from other parts, and is generally used for mixing.

The different varieties of sumach are classed as follows:—

To prepare these different grades for ultimate consumption, they are ground in mills similar to those employed for crushing olives, that is, in which two large stone wheels follow each other, revolving upon a circular bed, the whole construction being about the same as the Spanish or Mexican arrastre. The sumach thus pulverised is passed through bolting-screens to separate the finer from the coarser particles.

After the sumach leaf has been subjected to the first process of trituration, the coarse remaining portions are re-ground and the product added to that which has been already obtained. The still unpulverised residue known as peduzzo is sifted, and the coarser and ungrindable parts are used as fuel, while the finer are mixed with the partially-ground, small, leaf-bearing branches (gambuzza, gammuzza), and ground again.

Palermo is the principal seat of the sumach trade. The material is generally bought from the small growers by middlemen, who hold it till market conditions are favourable. The quotations are always in tarì of 42·5 centimes per cantar of 79·342 kilos, which are obsolete even in Sicily, and have to be reckoned into lire (francs) and kilos. Consequently 1 tarì per cantar equals 0·53565 lira per 100 kilos.

In 1894, the prices delivered at the mills were about 41-42 tarì for mascolino, 37-38 tarì for femminello, 14-18 tarì for brusca, and 10 tarì for stinco, per cantar; the lira being worth about 9d.[140]

Sumach has been introduced into Australia, and is said to thrive well in the dry plains of the Wimmera district.

Sumach often contains much sand, and sometimes particles of magnetic iron ore, which cause black stains, and may be collected by a magnet, and which dissolve in dilute hydrochloric acid without evolution of hydrogen, to a yellow solution. Metallic iron, which is also attracted by the magnet, dissolves in hydrochloric acid with effervescence to a colourless or green solution.

Good sumach contains at least 25-27 per cent. of tannin. The Author has analysed samples of undoubted genuineness containing as much as 32 per cent. of a tannin, principally gallotannic, with some ellagitannic acid, and a colouring matter (myricetin) identical with that of Myrica nagi (p. 250), which gives yellows with alumina and tin mordants, and is fugitive to light.

Sumach is the best tanning material known for pale colour and soft tannage, and is hence used for moroccos, roans, skivers, etc., and also for brightening leathers of darker tannages, such as mimosa, gambier, the colouring matters of which warm sumach liquors seem able to dissolve.

In the report of the Society of Arts Committee on bookbinding leathers,[141] it is stated on abundant evidence, that sumach-tanned leathers are less affected by light and gas-fumes, and less liable to decay than those of any other known tannage.

Sumach is frequently adulterated with the ground leaves and twigs of Pistacia lentiscus (“schinia” or “skens”), Coriaria myrtifolia (“stinco”), Tamarix africana (“brusca”), Ailantus glandulosa, Vitis vinifera (leaf of the common grape vine) and some other species of the Rhus family, but Pistacia lentiscus is used to a much larger extent than any of the others. Pistacia, coriaria, and tamarix all contain considerable quantities of tannin, though less than genuine sumach, and of a different chemical constitution.

The most satisfactory method of detecting these adulterants is by microscopic examination, none of the chemical methods proposed being very satisfactory; though, as many of the added matters contain catechol tannins, while those of sumach are purely pyrogallol derivatives, the method proposed by Hughes for the detection of quebracho in oakwood by the reaction of concentrated sulphuric acid (p. 296) might render good service, and any sumach infusion which was rendered turbid by bromine-water would at least be open to grave suspicion.

The most important work on the microscopic structure of the tissues of sumach and its adulterants was done by Andreasch, when during the later stages of his last illness he was obliged to winter in Sicily.[142] His work will well repay study, but unfortunately does not admit of useful abstraction here. A very useful investigation was also made in the Author’s laboratory by Messrs. M. C. Lamb and W. H. Harrison,[143] as regards the treatment and examination of the leaf-cuticles, which renders the detection of mixture comparatively easy. For details, the original memoir must be consulted, but if the suspected sumach be gently warmed for a few minutes with strong nitric acid, its more delicate leaf structure is entirely destroyed, and after washing and neutralising with sodium carbonate the strong cuticles of the leaves of the more common adulterants, “schinia” (Pistacia lentiscus), “stinco” (Coriaria myrtifolia), “brusca” (Tamarix africana), and Ailantus glandulosa are uninjured, and easily recognised. Examination is rendered easier by dyeing the cuticles; safranine, acid green, Bismarck brown, and naphthol yellow being suitable for the purpose. Mr. Lamb’s photographs of the cuticles are reproduced on Plates III. and IV., but if possible, it is most satisfactory to compare the suspected sample direct with known specimens of the adulterants.

R. glabra, Southern States, U.S.A. (Fig. 54). Very largely used in the States to take the place of Sicilian sumach. A sample collected by the late Professor Trimble, and analysed in the Leather Industries Laboratory, contained 25 per cent. of tannin and produced a leather of very much darker colour than Sicilian.

R. typhina, “staghorn” or Virginian sumach, contains 10-18 per cent. of tannin. A sample from same source as above contained 13 per cent.

R. cotonoides, U.S.A. The analysis of a sample of this material gave 21 per cent. of tanning matter, and leather tanned with it was almost equal in colour to that from R. glabra.

Other sorts found in States: R. semialata (5 per cent. tannin); R. aromatica (13 per cent. tannin); R. metopium (8 per cent.); R. copallina, R. pumila, R. canadensis; R. toxicodendron is the well-known “poison ivy,” a climbing plant which causes a severe and irritating eruption if touched.

R. glabra and R. copallina are chiefly recommended for extended cultivation in the United States.

In Virginia, the leaves are collected and cured by the country people, and sold and delivered to owners of mills for grinding. Their particular object being to secure the largest possible quantity of product at the lowest cost, little attention is given to the quality obtained, or the manner of collecting. The most intelligent dealers in the raw material urge upon collectors to observe the following particulars:—To ensure a maximum value for tanning purposes, the leaf should be taken when full of sap, before it has turned red, has begun to wither, or has been affected by frost. Either the leaf-bearing stems may be stripped off, or the entire stalk may be cut away, and the leaves upon it allowed to wither before being carried to the drying shed; but care must be observed that they are neither scorched nor bleached by the sun. When wilted, they are carried to a covered place, and spread upon open shelving or racks to dry, avoiding the deposit in any one place of a quantity so great as to endanger the quality of the product by overheating and fermentation. Sumach should be allowed to remain in the drying-house for at least one month before sending to the market; in case of bad weather, a longer period may be required. When ready for packing for shipment, it should be perfectly dry and very brittle, otherwise it is likely to suffer injury in warehouses from heating and fermentation.

Buyers of sumach leaves for grinding depend largely upon colour for the determination of the value; the leaves should, therefore, when ready for market, present a bright-green colour, which is evidence that they have suffered neither from rain after being gathered, nor from heating during the process of drying. Leaves having a mouldy odour or appearance are rejected. The Virginian crop reaches 7000-8000 tons, and is collected at any time between July 1st and the appearance of frost.

There is an important difference in the value of the European and American products. The proportion of tannic acid in the latter is generally lower than that found in the former, which is much preferred by tanners and dyers. By using Sicilian sumach it is possible to make the finest white leathers, while by the employment of the American product, the leather has a disagreeable yellow or dark colour, apparently due to a colouring matter, which exists in larger quantity in the American variety than in the Sicilian.

Experiments upon the presence of colouring matters made by treating an infusion of sumach with a solution of gelatine, gave the following results:—

For the purpose of tanning white and delicately coloured leathers, therefore, the collection should be made in June; while for tanning dark-coloured leathers, and for dyeing and calico-printing in dark colours, where the slightly yellow shade will have no injurious effect, the collection may be made in July. It appears that for all purposes, the sumach collected after the 1st of August is inferior in quality.

Experimental results as regards percentage of tannin obtained by collecting sumach at different seasons showed:—

It is evident, therefore, that in order to secure the maximum amount of tannic acid, the sumach should be collected in July, but the colouring matter of the leaves has an important influence upon the value of the product. The leaves of the upper extremities of the stalks are always richer in tannic acid than those of the base; and the increase of age of the plant is accompanied by a general diminution of this acid.

The mill used for grinding sumach leaves consists of a heavy, solid, circular, wooden bed, 15 feet diameter, with a depression around the edge a few inches deep and 1 foot wide, for the reception of the ground sumach from the bed, and two edge-rollers, weighing about 2500 lb. each, 5-6 feet diameter, and provided with numerous teeth of iron or wood, thickly inserted. In Europe and in some parts of the Southern States, sumach is still ground by stones revolving on a stone bed, and the sifting is often done by hand.

R. cotinus, Venetian sumach. Fr. Arbre à perruques; Ger. Perrukenstrauch (Fig. 55). More important as a dyeing than as a tanning material, its twigs and wood, “young fustic,” containing a large proportion of a colouring matter (fisetin), which with tin and alumina mordants dyes bright yellows; and much resembles, but is not identical with the myricetin present in R. coriaria.[144] Its leaves, known as Turkish or Venetian sumach, contain about 17 per cent. of tannin, and are used for tanning.

R. pentaphylla, “Tezera,” Algeria, is used by the Arabs for tanning goat-skins.

R. Thunbergii, Kliphout, Cape of Good Hope. A sample of the bark analysed in the Author’s laboratory contained 28 per cent. of tanning matter. A valuable tanning material, of reddish colour. The tannin is of the catechol class.

Several other species of Rhus are used in tanning. R. semialata yields Chinese and Japanese galls, containing up to 70 per cent. gallotannic acid. They are caused, not by a fly, but by the attack of an aphis, as are those of the allied Pistacia.[145] The aphides pass their asexual stage inside the gall, which is large and thin-walled. A similar aphis-gall is found on the American sumach. A specimen of the leaves examined at the Yorkshire College yielded only 5 per cent. of tannin.

Mangifera indica, Mango, widely distributed in the Tropics. Bark and leaves rich in tannin, which gives green-blacks with iron.

CORIARIACEÆ.

Coriaria myrtifolia, French sumach (of which there are four kinds—fauvis, douzère, redoul or redon, and pudis). A poisonous shrub of South of France; leaves used for tanning, and as a sumach adulterant under the name of “stinco”; contain about 15 per cent. tannin. (Cp. p. 272.)

Coriaria ruscifolia bark, the tutu of New Zealand, contains 16-17 per cent. of tannin.

Other Coriarias merit examination, and are known to contain much tannin.

RUBIACEÆ.

Rubia, Madder, allied to Galiums, which are almost the only English representatives of the family. The coffee- and cinchona-plants are foreign representatives.

Nauclea, or Uncaria gambir. East Indies. (Fig. 56.) A climbing shrub, source of “gambier,” or “Terra Japonica”; also called “Catechu,” in common with several other solid extracts. Gambier is first described by the Dutch trader Couperus, in 1780; plant introduced in Malacca, 1758; plantations established in Singapore in 1819.

Culture is mainly by Chinamen, and is very rude; it yields rapid return, but under the treatment to which it is subjected a plantation is worn out in ten to fifteen years. Cropping commences three years after planting, and is continued two to four times annually, with little regard to fitness of shrubs, the plant being cropped till it has barely leaves left to support existence. It is found advantageous to combine pepper-culture with that of gambier, the spent leaves form a good protection for the pepper-plant roots, but they have little actual manurial value.

Cropping is done with a knife called a parang, while a larger knife is used for chopping the leaves and twigs before they are put in a boiler, in which they are heated with water till the liquid, which is constantly stirred during the operation with a wooden five-pronged stirrer, becomes syrupy. The leaves are then brought out with a wooden fork, and allowed to drain on a tray, so that the liquor runs back into the boiler. The coarser matter still remaining in the boiler is removed with a strainer like a racquet, and the finer by straining the liquor through a perforated cocoanut shell into small shallow tubs, where it is allowed to cool with constant stirring with a cylindrical wooden bar, which is worked up and down with a rotary motion until the catechin crystallises. When quite cool the pasty mass is turned out of the tub, cut into cubes with sides 1 inch long with a hoop-iron knife, and dried on bamboo trays in racks under sheds, or sometimes smoke-dried with wood fires.

Good cube gambier is an earthy-looking substance and is dark outside, but pale within from crystallisation of catechin. Catechin is not itself a tanning material, but is apparently converted into a tannin by drying at 110°-126° C., when it parts with a molecule of water. It is very probable that a similar change occurs in the tannery. The tannin is a catechol-phloroglucol derivative, less astringent than most of this series, and of pale colour. (See p. 297.)

A commoner quality, called “block-gambier,” instead of being cut into cubes, is run into large oblong blocks of about 250 lb. weight, which are wrapped in matting and exported in a pasty condition. These contain 35-40 per cent. of tannin, as estimated by the hide-powder method, while the best cubes reach 50-65 per cent. Besides the forms named, various others are made, principally for native use in chewing with betel-nut in the form of small biscuits, or in thin discs (“wafer gambier”) by running the pasty mass into bamboos and cutting the cylinder so formed into thin slices. These forms are usually light in colour, and very rich in catechin.

For details of the chemistry and employment of gambier, see pp. 228, 231, 239, etc.

APOCYNACEÆ.

Aspidospermum quebracho. Sp. Quebracho blanco. Brazil. Bark contains aspidospermin, an alkaloid used in medicine, but both bark and wood are poor in tannin.

Quebracho colorado, see Anacardiaceæ, p. 269.

ERICACEÆ, Heath Family.

Arctostaphylos (or Arbutus) uva-ursi, Bearberry. Used in Russia, Finland; twigs and leaves said to contain 14 per cent. tannin. Often adulterated with leaves of Vaccinium vitis-idæ or Cowberry.

Arbutus unedo, Common Arbutus. Leaves, fruit and bark used on Mediterranean coasts.

VACCINIÆ.

Vaccinium Myrtillus, Bilberry. Used in Piedmont.

SAXIFRAGEÆ.

Weimannia glabra L., “Curtidor” bark. Venezuela.

Weimannia macrostachys D.C. Reunion.

Weimannia racemosa, New Zealand Towai or Tawheri bark.

These species contain 10-13 per cent. of iron-blueing tannin, and have been practically used, but are not of much importance.

TAMARISCINIÆ.

Most of the members of this group are poor in tannin, but several species have galls which are rich.

Tamarix africana; Egypt, Algeria. Galls containing 26-56 per cent. tannin. The small twigs are collected in Tunis, and when dried and ground are imported into Sicily to be used for the adulteration of sumach under the name of “Brusca,” and contain about 9 per cent. of tannin. (Cp. p. 272.)

T. articulata, Morocco, yields galls produced by aphides, called in Arabia Takout, and stated by Vogel to contain 43 per cent. of tannin.

Tamarix gallica, used in Spain and Italy.

OXALIDEÆ.

Oxalis gigantea, source of churco bark, Chili. A thin, brittle, dark red bark, mostly about 2 mm. thick, cork and ross entirely absent. The bark is brittle, and the cells thin. It contains about 25 per cent. of an easily extracted, dark red tannin, giving green-blacks with iron. The bark has been incorrectly attributed to Fuchsia macrostemma. (Cp. Von Höhnel, ‘Die Gerberinden,’ p. 125, and this book, p. 284.)

COMBRETACEÆ.

Several families of this genus contain trees rich in tannin, but most important are the Myrobalans (often, but incorrectly, written Myrabolams or Myrabolans), the unripe fruit of various species of Indian Terminalia.

T. Chebula (Fig. 57), a tree 40-50 feet high, and yielding good timber, is the source of all the ordinary varieties, which differ only in the district from which they are obtained, and the state of maturity of the fruit. The nuts contain from 30 to 40 per cent. of tannin. Of the various sorts, probably those known as Bombays are least unripe, while “lean greens” are the most so. The unripe fruit is the richest in tannin. “Bombays” have a smooth skin in coarse wrinkles, and when cut are porous and light coloured. “J’s” (Jubbalpores) and “V’s” (Vingorlas), have finer and shallower wrinkles, and are harder, solider and consequently darker looking, but do not give a darker liquor, while “lean greens” are greener, have less yellow colouring matter, and consequently more nearly approach in character to sumach, which the tannin in many respects resembles, though probably containing more ellagitannic acid in proportion to gallotannic acid than the latter.

The “nuts” should be bright in colour, not worm-eaten, nor “waxy” or soft. If kept in a damp place they rapidly absorb moisture, and fall into the “waxy” condition, in which they are very difficult to grind, sticking to and choking the cutters or beaters of the mill.

Neither the large hard stones nor their kernels contain tannin, but the latter have an oil which gives a peculiar odour to leather. The tannin exists in large and rather thickly-walled cells, and is not very easily extracted; the skin is wrinkled, but the uncrushed nuts swell up to their original plum-like form when placed in water for some time. The bark is almost as rich as the fruit, and the tree also yields galls.

T. Belerica yields Beleric or “Bedda nuts,” which are downy, rounder and larger than ordinary myrobalans, and contain about 12 per cent. of tannin, used as adulterant of ground myrobalans. A sample of solid extract made from the bark of T. Belerica contained 70 per cent. of tannin.

T. tomentosa has downy nuts, containing about 10 per cent. of tannin, bark stated by de Lof to contain 36 per cent. of tannin. A sample of solid extract contained 56 per cent. of tannin. The bark contains about 11 per cent.

There are several other Indian species.

T. Catappa, “Badamier bark” of Mauritius, contains 12 per cent. of tannin.

T. mauritiana, “Jamrosa bark,” said to contain 30 per cent. of tannin.

T. Oliveri, Malay Archipelago, yields “Thann leaves,” from which an extract is made as a cutch substitute. A sample of the extract from Burmah examined recently in the Author’s laboratory, contained 62 per cent. of tannin. The tannin is a catechol derivative, differing from that of Acacia catechu in containing no phloroglucol (p. 297).

A sample of bark from Mandalay contained 31 per cent. of tannin, while the leaves from the same tree contained 14 per cent.

Emblic myrobalans, see p. 293.

RHIZOPHORACEÆ, Mangles or Mangroves.

Rhizophora Mangle, and other allied species, Mangrove or Mangle, Manglier, Paletuvier, Cascalote, grows on tropical coasts all round the world. The barks vary much in strength, from 15 up to 40 per cent. in different species (see Ceriops). Leaves, used in Havana, are said to contain 22 per cent. tannin. According to Eitner, the younger plants contain the highest proportion of tannin. R. Mangle seems to yield a bark inferior to several other species.

All trees growing in swamp, and of the same character of growth as mangrove, are called “Bakau” in the East Indies (Anglice, mangrove) and various species of Ceriops yield the best tanning bark. A tidal mangrove swamp at low water is a tangle of arched roots like inverted branches on which the trees are supported.

The catechol-tannin, which is easily extracted, is of deep red colour and allied to that of the mimosas. In admixture with other materials the red colour has a much smaller effect, and mangrove bark is now largely used in combination with pine, oak and mimosa.

Several other species are also rich in tannin, and used in different parts of the world under the name of mangle, as are also several species of Conocarpus belonging to the Combretaceæ.

Rhizophora mucronata. India and Burmah. Bark varies considerably; David Hooper, Indian Museum, Calcutta, gives 26·9 per cent. of tannin. Dr. Koerner (Deutschen Gerberschule, Freiberg) analysed two samples in 1900, one containing 48 per cent. and the other 21 per cent. of tannin; two samples from the British Imperial Institute recently examined by the Author showed only 4·5 and 6·1 per cent. of tannin respectively.

Ceriops Candolleana, Bakau or Tengah Bark, East Indies. Goran, Bengal. Contains up to 27 per cent. of tannin and yields an extract which promises well as a substitute for cutch, to which, for dyeing purposes it is nearly or quite equal. The solid extract contains up to 65 per cent. tannin, making a good but dark red leather.

Ceriops Roxburghiana, a somewhat larger tree, also growing in the Sunderbans, bark very similar in strength and character to the above.

ONAGRACEÆ, the Œnothera Family.

Fuchsia excorticata, the only deciduous tree of New Zealand. Contains 5 per cent. tannin.

Fuchsia macrostemma, Chili. Yields Tilco or Chilco bark. Churco bark has been incorrectly attributed to this plant, but it is certainly derived from an oxalis, as stated by the Kew authorities. (Cp. von Höhnel, ‘Die Gerberinde,’ p. 125.)

GUNNERACEÆ.

Gunnera scabra (Pangue?), Pauke, Chili. Used occasionally in the tanning of goat-skins.

MYRTACEÆ.

Eucalyptus globulus, and other species of E. common in Australia, and introduced into Algeria and Southern Europe (gum-trees), are more or less rich in catechol-tannins, their sap being the source of Botany Bay or Australian kinos, which contain up to 79 per cent. tannin. Several species of Eucalyptus afford astringent extracts; those from the “red,” “white,” or “flooded” gum (E. rostrata), the “blood-wood” (E. corymbosa), and E. citriodora, being quite suitable for replacing the officinal kind. The gum is chiefly obtained by woodcutters, being found in a viscid state in flattened cavities in the wood, and soon becoming inspissated, hard and brittle. Minor quantities are procured by incising the bark of living trees; a treacly fluid yielding 35 per cent. of solid kino on evaporation is thus obtained. The gum is imported from Australia, but there are no statistics to show in what quantity.[146]

Eucalyptus longifolia bark, the “woolly-butt” of Australia, contains 8·3 per cent. of tannic acid, and 2·8 of gallic. The “peppermint” tree contains 20 per cent. of tannic acid in its bark. The “stringy-bark” (E. obliqua) gives 13¹⁄₂ per cent. of kinotannic acid. The Victorian “iron-bark” (E. leucoxylon) contains 22 per cent. of kinotannic acid, but is available only for inferior leather.

Myrtus communis, and several other myrtle species, contain a considerable amount of tannin in the bark and leaves.

GRANATACEÆ.

Punica Granatum, Pomegranate. Peel of fruit employed in Spain and the East as substitute for sumach, containing up to 25 per cent. of tannin. Bark said to contain 22 per cent. tannin. Balaustines, wild pomegranates, East Indies. Fruit, said to contain 46 per cent. tannin.

ROSACEÆ.

Tormentilla erecta, Potentilla tormentilla. Root variously stated to contain 20-46 per cent. tannin. Red coloured leather, formerly used in Orkneys, Shetland, and Faroe Islands, and in some parts of Germany.

Sorbus or Pyrus Aucuparia, Mountain Ash. Bark said to be stronger than oak.

Many other plants of the family contain tannin, among others the strawberry.

PAPILIONACEÆ.

Butea frondosa.[147] This (with Pterocarpus marsupium)[148] furnishes East Indian kino. The flowers are used in India as a dye, under the name of Tesu. Bark fairly rich in tannin.

Pterocarpus or Drepanocarpus senegalensis is the source of African kino, which contains up to 75 per cent. of tannin.

Cæsalpinia coriaria, Divi-divi. A tree of 20-30 feet, native in Central America, introduced successfully in India, but principally imported from Maracaibo, Paraiba and Rio Hache. The dried pods contain 40-45 per cent. of a pyrogallol-tannin, mainly ellagitannic acid, and would be a most valuable tanning material, but for a liability to fermentation and sudden development of a deep red colouring matter. The causes are not well understood, but apparently the risk can be materially lessened by use of antiseptics. If used in strong liquors it gives a heavy and firm leather, but is principally employed as a partial substitute for gambier on dressing leather. Used in rapid drum-tannage for light leathers, an excellent colour may be obtained. It is said to give an especially firm and glossy flesh. Leather tanned with it, even when of outwardly good colour, has often a blueish-violet shade within, perhaps due to the development of a colouring matter allied to that of logwood. The seeds do not contain tannin, which lies almost free in the husk of the pod. The pods are about 3-4 cm. long, dark outside, and curl up in drying to an S-shape.

C. digyna, Tari or teri pods. Occurs in Prome, Toungoo, Bassin, Mynang and other parts of India and Burmah, where it is used as a drug. The pod-case is said to yield over 50 per cent. of tanning matter. A sample from Burmah, kindly sent by the Imperial Institute, examined by the Author in 1900, contained 24 per cent. of tannin, but after removing the seeds the remaining pod-cases yielded 44 per cent. of tannin on analysis. C. digyna promises to become a valuable tanning material if it proves free from the tendency to ferment which is so troublesome in divi-divi. It has been introduced into England under the name of “white tan,” which yields a leather quite as white as sumach; but the supply seems at present uncertain.

C. cacolaco, Cascalote, Mexico. Pods rich in tannin (up to 55 per cent., Eitner). Pods larger and fleshier than divi, seeds smaller, tannin similar.

The pods of several other Cæsalpinias are used in tanning, sometimes under the name of “Algarobilla,” which is simply a diminutive of Algaroba, the carob, or locust-bean, derived from Arabic al Kharroba, and applied to several small pods. (See Balsamocarpon and Prosopis.)

C. (or Balsamocarpon) brevifolia, Chili, ordinary Algarobilla. Fig. 58. One of the strongest tanning materials known, containing an average of 45 per cent. of a tannin very like that of divi, but less prone to discoloration. The tannin lies loose in a very open skeleton of fibre, and is easily soluble in cold water; the seeds contain no tannin. If not allowed to ferment it produces a very bright-coloured leather.

Algarobilla has been attributed to Prosopis pallida, but this appears incorrect. Several species of P. are known to yield tanning pods; those of P. Stephaniana of the desert of Kaschan, in Persia, are dschigh dschighe, perhaps identical with dchift or jaft. (See p. 263.) Bark of P. spicigera used in Punjab.

C. (or Hæmatoxylon) campechianum, Logwood, Central America. In addition to colouring matter, and a glucoside which it yields on oxidation, this wood contains about 3 per cent. tannin. Its principal use is in dyeing blacks with iron or chrome mordants. (See p. 413.)