The materials used to accomplish these chemical and physical alterations in the nature of hides and skins are found in all three kingdoms of nature. They are likewise found among the products of chemical industry.

The mineral kingdom, for example, furnishes salt and alum, used for producing tawed or white leather.

In many countries animal fats, and notably in the Americas the brains of deers, have been employed to make chamois or wash leather. Among chemical products such inorganic compounds as the salts of copper, iron, cerium, titanium, and notably of chromium, and organic aldehydes, especially formaldehyde, have all been used for tanning.

The most important tanning materials are those derived from the vegetable kingdom. They include a great variety of woods, barks, leaves, fruits, etc., containing in varying amounts the so-called tannins or tannic acids. These latter differ widely in chemical constitution and properties. They all possess in common the power of precipitating gelatin from its solution as an insoluble compound. They are also all derivatives of the aromatic series, containing either pyrocatechol, CH(OH)2, pyrogallol, C,H,(OH), or, somewhat rarely, phloroglucinol, the isomeride of the latter. The result of their action upon the hides of cattle is the production of the brownish, yellowish-brown, or reddish-brown leather of commerce.

This paper will describe such occurrences of the tannins in the flora of Latin America as are actually or potentially of importance among the world's sources of tanning materials.

It is manifestly impossible to include in any such list all tanninyielding plants. A tabulation of that character would embrace a large part of the vegetable kingdom as represented in the indigenous growths of Latin America.

For the sake of convenience these substances may be classified under the following heads: Woods, barks, leaves, excrescences, roots and bulbs, fruits and seeds.

TANNINS FROM WOODS.

The number of woods yielding tannin in sufficient abundance to warrant an industrial exploitation is exceedingly limited throughout the world. The woods of the oak and the chestnut form almost the only examples in the Northern Hemisphere.

The past few decades have witnessed the rapid extension of the use in tanning of the quebracho wood of Argentina. It may now be regarded as the most important tannin asset of the world. Its dominating position is revealed in the import statistics of the United States. During the fiscal year ending June 30, 1914, the tanning materials brought into the United States were valued at $3,864,000. Quebracho wood and extract constituted 87 per cent of the total. Quebracho, in fact, formed 38 per cent of all the tanning material used in the United States.

It will thus be easily realized that, while the number of plants and trees in Latin America yielding notable amounts of tannin is limited, one of these plays the leading rôle in the world's leather industry.

QUEBRACHO.

The name" quebracho " is derived from the Portuguese " quebrar," break, and "hacha,” ax. Its literal meaning is "ax breaker." Formerly the term was applied to every hardwood tree in South America that dulled the chopper's tools. It is now used commercially in connection with but three trees, the true quebracho, the white quebracho, and the red quebracho. The latter two are of no importance as sources of tannin. Much confusion has resulted from the indiscriminate use of the name for totally different varieties of wood.

The true quebracho, Loxopterygium or Quebrachia lorentzii Griseb., belongs to the family of the Awacardiaceæ, or cashew family, and to the genus Quebrachia.

It is found in Argentina, Bolivia, Brazil, Paraguay, and Uruguay. The more specific habitat is a district extending eastward some 500 miles from the Andes Mountains, and reaching northward from near the mouth of the Parana River for a distance of about 600 miles. The area of this district is, roughly, 300,000 square miles. The territory in which the tree is industrially exploited includes the northern portion of Argentina and the Province of Chaco in Paraguay.

At the present rate of consumption, it is estimated that the annual cut of quebracho is much less than the sum total of annual growth. The total available supply is estimated at 168,000,000 tons. Less than 1,000,000 tons are cut annually at present.

The quebracho is never found in pure stands. It is scattered through open forests containing, as a rule, a large variety of species. It is rare to encounter more than five quebracho trees per acre.

In consequence of this scattered occurrence, it is necessary to cut annually over about 500,000 acres of forest land in order to secure the quantity required to meet the demands of the world's markets. The value of the quebracho forest land is quite variable. In Argentina, when near a railroad, it commands $2 or more per acre. Paraguay the average price is $1.50 per acre, although there are cases where the rate is as low as 15 to 25 cents per acre.

In

The favorable location for the quebracho tree is on slightly elevated ridges lying between watercourses. A sandy soil, with moderate atmosphere but abundant soil moisture, seems also conducive to growth.

Where conditions are very favorable, trees are encountered ranging in height from 50 to 75 feet and varying in diameter from 2 to 4 feet. Ordinarily the trees are 18 to 36 feet in height and 18 to 40 inches in diameter. The best wood is found in the virgin forests along the Parana River and the Picole Majo River.

Thus far, the tree seems to be immune against the attacks of insects. When first felled, the sapwood is of a light yellow color. On exposure to the sun it assumes a light-red tint. The hardwood, when freshly cut, is of a dark, cherry-red color. This deepens with age.

Quebracho wood ranks among the heaviest and hardest woods known. It is the most durable wood found in Argentina. Highly tempered tools are needed to work it, even when in the green state. After complete seasoning it is exceedingly resistant to cutting tools. The specific gravity ranges from 1.27 to 1.38. Ordinarily, I cubic foot weighs 78 pounds.

As the quebracho wood is fine-grained and takes a beautiful polish, it possesses a pronounced commercial value and is employed locally for a great variety of uses-for cabinetmaking, house construction, etc. It does not appear, however, that for such purposes it ranks above other hardwoods occurring in Argentina.

Apart from its chief use as a source of tannin, it has been in abundant demand in Argentina for many years as a satisfactory material for railroad ties. Nine such ties weigh 1 ton. These ties remain on a roadbed indefinitely in a state of perfect preservation. It has been assumed that the large amount of tannin present acts as a preservative and causes the durability. Ties now in use for 25 years are absolutely sound.

Throughout the region of occurrence, the quebracho ties are gradually replacing the iron or steel ties hitherto used in railroad construction. The standard ties on the Argentina broad-gauge railway are 9 feet long, 10 by 13 inches cross section. They cost $2 to $2.50 each. On account of the hardness of the wood spikes can not be driven into it. Holes are therefore bored and bolts are employed to fasten the rails.

The chief drawback to the use of quebracho wood for this purpose is the almost total lack of resilience. There is also a marked tendency to crack when exposed to frost. The necessity of boring holes for the bolts used makes an additional expense.

Experiments have been started in the United States to test the desirability of quebracho ties for our railways. The quebracho timberland of Argentina yields, on an average, 18 ties per acre. American white oak or pine forests yield from 40 to 60 ties per acre.

TANNIN VALUE OF QUEBRACHO.

The tannin content of the different parts of the quebracho tree varies somewhat with the region where it grows. Numerous analyses give, ordinarily, the following results:

Heartwood
Sapwood

Bark

Per cent of tannin.

20-24

3- 4

6-8

One analysis from the Gran Chaco district shows an unusually high tannin content:

Jean (Bull. Soc. Chem., 1880, 33, 6) found that the tannin of quebracho was distinctly different from that of oak bark or chestnut wood. In 1903, Procter (Leather Manufacture, 269) showed that a red phlobophane was present in the tannin, and that it contained catechol and phloroglucinol nuclei.

In 1906, Strauss and Geschwender (Zeitschr. f. angew. Chem., 19, 1121) isolated the pure tannin, free from phlobophanes. It 48022°-18- -2

formed a light, flaky mass, easily becoming sticky when exposed to the air on account of its hygroscopic character. They consider it as identical with maletto tannin, found in the bark of various species of eucalyptus, notably Eucalyptus occidentalis, and with the tannin extracted from cinchona bark. It received the formula of C43 H50 020Nierenstein (Collegium, 1905, 65, and Ber. d. deut. ch. Gesell., 1907, 40, 4575) regards the quebracho tannin as consisting of a mixture of three distinct tannins. From quebracho phlobophane, on distillation with zinc dust, he obtained anthracene. Incidentally, this reaction is worthy of more extended study, as offering a source of hydrocarbon for use in the manufacture of alizarin.

It is definitely established that a considerable amount of the tannin extracted from quebracho is but sparingly soluble in cold water, and is partly deposited when hot aqueous solutions are allowed to cool.

There is still much to be done in clearing up the exact chemical nature of the tannin content of quebracho, and it is to be hoped that the problem may be solved in a final manner. It is highly probable that a more exhaustive study may pave the way for removing the difficulties attendant upon the use of quebracho extract alone for tanning purposes.

In this connection, it may be noted that quebracho wood contains a fine yellow dye, fisetin, identical with the dyestuff present in young fustic. It is present as a glucoside combined with tannic acid. The colors obtained from fisetin are, unfortunately, somewhat fugitive to light. Mention may also be made of the “quebracho resin," which collects as a thickened juice in crevices of the tree.

UTILIZATION OF QUEBRACHO FOR TANNING.

It is worthy of note that, as a rule, the sapwood of the quebracho tree and its bark are completely neglected as sources of tannin, and are allowed to go to waste. When we consider that chestnut wood contains but 3 to 6 per cent of tannin, that oak wood contains but 2 to 3 per cent, that the tannin content of oak bark is often as low as 8 per cent, and yet know that. all three are profitably employed on a relatively large scale as sources of tanning extracts, it is a matter of surprise that these two constituent portions of quebracho logs should be entirely neglected, when once in the possession of extract factories.

There would appear, also, to be a distinct field for experimentation on the characteristics of the tannins formed in the sapwood and in the bark of the quebracho tree. It is not impossible that they may be free, to some extent, from certain disadvantages attending the use of the tannin obtained from the heartwood. Almost invariably, the tannin present in the heartwood is extracted by boiling with water, and the concentrated extract is used for tanning purposes. The special field of usefulness for quebracho in the production of current forms of leather has now been quite clearly defined.

In regard to color, quebracho alone does not seem to impart any distinctive tint. However, when alum and salt are added to the bath, finer results are obtained than when gambier is employed. The resultant leather is of a handsome, pale, straw-colored grain on the exterior surface, while the flesh side remains almost white.