Chapter XVIII: Vegetable Tanning Materials (2)

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:--

Virginia, mixed, collected in June, gave A nearly
white
precipitate.
„ „ „ July, „ A decidedly
yellowish-
white
precipitate.
„ _R. copallina_ „ August, „ A dirty-
yellow
precipitate.
„ _R. glabra_ „ „ „ A very dirty-
white
precipitate.
Fredericksburg, mixed „ „ „ A dirty-
yellow
precipitate.
Sicilian „ „ „ A slightly
yellowish-
white
precipitate.

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:--

Per Cent. of
Tannic Acid.
Virginia, mixed, collected in June, gave 22·75
„ „ „ July, „ 27·38
„ _R. glabra_ „ August, „ 23·56
„ _R. copallina_ „ „ „ 16·99
Sicilian, _R. coriaria_ „ „ „ 24·27

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.

[144] Perkin and Allen, Trans. Chem. Soc. 1896, 1299.

_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.

[145] See Flückiger and Hanbury, ‘Pharmacographia.’

_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]

[146] Compare Journ. Soc. Chem. Ind., 1902, p. 159.

_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.

[147] ‘Dictionary of Economic Products,’ I.B., p. 944; Hummel and
Cavallo, Proc. Chem. Soc. 1894, p. ii.

[148] Agricult. Ledger, 1901, No. 11, Gov. Printing Office, Calcutta.

_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.)

--Algarobilla (_Cæsalpinia brevifolia_).]

[149] ‘New Commercial Drugs and Plants,’ No. 5, T. Christy.

_C. echinata_ yields “Brazil-wood.” (See p. 413.)

_C. Sappan_, Sappan-wood, India.

_Cassia auriculata_, _Turwar_ or _Tanghadi_ bark, Southern India. Used for tanning so-called “Persian” sheep- and goat-skins, contains about 17 per cent. of a catechol tannin. Leather tanned with it is of a pale yellow colour, but rapidly reddens in sunlight. Cp. p. 235.

_C. fistula_, India. Husk of pod, 17 per cent. tannin. The pulp of pod is used as an aperient.

_C. elongata_ and _lanceolata_. Senna leaves. Upper Egypt.

_C. Sophora_, “_Bali-babilan_.”

MIMOSEÆ, a Tribe of Leguminosæ.

_Acacia arabica_, “Babool,” “Babul,” India, Egypt. Fig. 59. Bark contains about 12-20 per cent. of catechol tannin; one of the principal Indian tanning materials, used for kips and heavier leathers. Pods, used in India for bating, contain about same amount of tannin as bark, but of a different kind, that of the bark being a catechol-tannin, with a good deal of red colouring matter, while the pods contain a paler tannin allied to divi, which is not precipitated by lime-water. In Egypt the pods are called _bablah_, a name which is also applied to pods of _A. cineraria_ and _A. vera_, and others. They are used for dyeing glove-leathers.

_A. nilotica_, Egypt. Pods called _neb-neb_ or _bablah_.

_A. catechu_, India. The wood yields cutch or “dark catechu.” A lighter coloured variety called _kath_, containing much crystallised catechin, is also made in India, and principally used for chewing with betel. _A. catechu_ is a tree 30-40 feet high, common in India and Burma, and also in tropical East Africa, where, however, it is not utilised. In Southern India, _A. suma_ is also used for the same purpose.

Trees of about 1 foot diameter are cut down, and the wood (some state the heart-wood only) is reduced to chips, and boiled with water in earthen jars over a mud-fireplace. As the liquor becomes thick and strong, it is decanted into another vessel, and the evaporation continued till the extract will set on cooling, when it is poured into moulds made of leaves or clay, the drying being completed by exposure to the sun and air. “Kath,” or pale cutch, is made in Northern India, by stopping the evaporation at an earlier point, and allowing the liquor to cool, and crystallise over twigs and leaves thrown into pots for the purpose. It contains a large proportion of catechin, apparently identical with that of gambier, but its tannin is much redder. Good cutch contains about 60 per cent. tanning matter, but is principally used for dyeing browns and blacks with chrome and iron mordants. It contains quercetin, a yellow colouring matter (p. 263).

_A. leucophlea_, India and Java “_Pilang_.” Pods and bark equal to _A. arabica_.

Australia abounds in acacias (mimosas), many of which are used in tanning, but vary greatly in strength, not only according to species, but probably also by situation and growth. Probably the best information is to be found in a pamphlet on ‘Wattles and Wattle-Bark,’ by J. H. Maiden, F.L.S., published by the Department of Public Instruction at Sydney, 1890. His analyses were made by the Löwenthal process, and can only be roughly compared with those by the hide-powder method. The analyses given are by the I.A.L.T.C. method, and mostly on samples furnished by Mr. Maiden.

A peculiarity largely developed in the mimosa family is the tendency for the true leaves to be suppressed, and their place taken by the flattened and expanded midrib (phyllode). Thus leaves of two very distinct forms are common in the genus, and some acacias, as _A. heterophylla_, may have both forms on the same branch. Compare _A. pycnantha_ and _A. decurrens_.

The Australian mimosas have been naturalised in India, and grow freely in the Nilgiri Hills, but the bark does not appear to be utilised.

The most important species are as follows:--

_A. pycnantha._ (Fig. 61.) “Broad-leaved” or “Golden Wattle,” South Australia. One of the strongest tanning barks known. A sample marked “special,” analysed in the Yorkshire College, contained 50 per cent. of tannin; another sample marked “ordinary” contained 40 per cent.

_A. longifolia_, the Golden Wattle of New South Wales, only contains half as much tannin as _A. pycnantha_.

_A. mollissima_, with its two varieties _A. decurrens_ (Fig. 62) and _A. dealbata_, are among the most important of the Wattle family commercially. Two samples of the former marked “Green Wattle” showed 36-39 per cent. of tanning matter; another sample marked “Sydney Green Wattle,” contained 41 per cent. A sample of _A. decurrens_, the second variety, was much weaker, showing only 12 per cent. on analysis.

_A. penninervis_ (Hickory bark) is said to be particularly hardy, but its strength seems to vary. A sample from Bateman’s Bay contained 38 per cent. of tanning matter.

_A. binervata_, another “Black Wattle” contains up to 30 per cent. tanning matter, as does also the “Weeping Willow,” _A. saligna_. The latter is poisonous, and is said to be used for killing fish.

_A. prominens_, the bark of which resembles that of the Golden Wattle, _A. longifolia_, in appearance contains only 14 per cent. tannin.

The cultivation of wattles in Australia has been somewhat neglected, but would render possible the utilisation of many acres of land lying waste, or which have already been exhausted and rendered unfit for the growth of cereals. It requires so little attention as to make it very profitable, and wattle-growing and sheep-grazing can be combined satisfactorily after the first year, when the young trees in the plantation have reached the height of 3-4 feet. In Natal the Australian wattles, especially _A. mollissima_, have been acclimatised and cultivated with success, and large quantities of excellent bark are now exported to England. African wattle-barks usually contain about 30 per cent. of tannin.

Wattles grow in almost any soil, even the poorest, but their growth is most rapid on loose, sandy patches, or where the surface has been broken for agricultural purposes. When the soil is hard and firm, plough-furrows should be made at a regular distance of 6-8 feet apart, and the seeds dropped into these. The seed should be sown in May, having been previously soaked in hot water, a little below boiling temperature, in which they may be allowed to remain for a few hours. It should be dropped at an average distance of 1 foot apart along the furrow, in which case, about 7200 seeds would suffice for one acre of land. The seed should not be covered with more than about ¹⁄₄ inch of soil.

On loose sandy soil, it might even be unnecessary to break up the ground in any way; the furrows may be dispensed with, and the seed sown broadcast after the land has been harrowed. After the plants have come up, they should be thinned so that they stand 6-8 feet apart. When the young trees have attained the height of 3-4 feet, the lower branches should be pruned off, and every effort afterwards made to keep the stem straight and clear, in order to facilitate the stripping, and induce an increased yield of bark. It is advisable that the black and broad-leaved kinds should be grown separately, as the black wattle, being of much larger and quicker growth, would oppress the slower-growing broad-leaved one. Care should be taken to replace every tree stripped by re-sowing, in order that there should be as little variation in the yield as possible. In Victoria, the months of September-December are those in which the sap rises without intermission, and the bark is charged with tannin. Analysis proves that the bark from trees growing on limestone is greatly inferior in tannin to that obtained from other formations, differing 10-25 per cent.

The following are South American mimosas:--

_A. cavenia_, Espinillo. Bark, contains 6 per cent., pods, 18-21 per cent., or more of tannin.

_A. cebil_, Red Cebil. Bark, contains 10-15 per cent.; leaves, 6-7 per cent. tannin. Argentine Republic.

_A. Guarensis_, Algarobilla of Argentine Republic. Bark, pods and flowers said to be used for tanning.

_A. timbo_, Buenos Ayres.

_A. curupi_, Curupy bark.

_A. angico_, or _Piptadenia macrocarpa_, Brazil, yields “angica bark,” a sample of which contained 20 per cent. of tanning matter when analysed recently in the Author’s laboratory.

“White Bark,” South America, probably an acacia, bark internally very similar to angica, if not identical.

_A. horrida_, “_Doornbosch_,” Cape of Good Hope, contains 8 per cent. of tannin.

_Inga feuillei_, “_Paypay_,” Peru. Pods said to contain 12-15 per cent. of tannin (doubtful). Several other species of _Inga_ known to contain tannin.

_Elephantorrhiza Burchellii_, _Elandsboschjes_, _Tugwar_, or _Tulwah_, South Africa; a papilionaceous plant. The air-dry root contains 12 per cent. of tannin, and a great deal of red colouring matter. The roots are several feet long, and about 2 inches in diameter, growing by the sides of rivers.

The following additions may be made to the above list:--

EUPHORBIACEÆ.

_Cleistanthus collinus_, “_Kodarsi_,” Deccan. Bark stated to contain 33 per cent. of tannin.

_Phyllanthus emblica_, India, yields emblic myrobalans, which in immature condition contain considerable tannin. Leaves (18 per cent.) and bark used for tanning.

_Phyllanthus distichus_ and _nepalensis_ both yield tanning barks.

COMBRETACEÆ.

_Anogeissus latifolia_, India. Bark and leaves rich in tannin.

GUTTIFERÆ.

_Garcinia mangostana_, India. The rind of the mangosteen fruit contains much tannin.