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Valonia is the acorn-cup of the Quercus cegilops, which grows in the isles of the Grecian Archipelago and on the coasts of Asia Minor. It is especially employed for tanning leather and adulterating garancine.

Divi-divi is the pod of the Cœsalpina coriara, and is chiefly imported from South America.

Myrobalans, which is largely used for tanning leather and producing blacks on wools, is the dried nut of the Terminalia chebula, and is imported chiefly from Calcutta.

Dr. Stenhouse bas shown that the tannin matter of valonia, divi-divi, myrobalans, and oak bark are not identical with those of gall-nuts and sumach. They do not yield gallic acid when boiled with dilute sulphuric acid, but sugar and some other organic principle.

From the above facts, it must be obvious to all who use tannin matters, whether dyers or tanners, that these substances not only vary in value, according to the variety of plant from which they have been obtained and the country whence they are imported, but there are sources of détérioration which cannot be detected by the eye. Thus, for example, if a new sumach be mixed with a comparatively old one, it is impossible to detect the fraud. The only method, therefore, of ascertaining the value of a sample is to détermine chemically the amount of tannic acid it contains. This may be done by the foliowing process:—A weighéd quantity (say 100 grains) of the substance to be tested is boiled with dis-tilled water, and the décoction run off into a beaker, with-ont filtering. This process is repeated four or five times. A test solution is prepared by dissolving one drachm of gélatine in four ounces of water, and adding 15 grains of powdered alum to the solution. 155 grains of this solution represent five grains of pure tannic acid. The test fluid is carefully dropped into the beaker until, on the falling of a drop upon the surface, the characteristic ring of tannate of gélatine is no longer produced. The quantity of test fluid used is then ascer-tained, and from this the amount of tannic acid is calcu-lated.

Before passing from this class of tannin substances, there is one that I must mention, which bas been used

from the most ancient times, in Egypt, Arabia, and other



Eastern countries, to dye wool, horse-hair, leather, &c. with boiling water the residue from catechu, which has It is the leaves of the Lawsonia inermis, which appears yielded its mimotannic acid to ether. The water on to be the gopher wood of Scripture and the hennis of cooling deposits a brown crystalline precipitate, which

the Egyptians. The leaves are mixed with water, to form a paste of an orange-brown colour. This paste also is employed by the Asiatic ladies to dye the nails of their hands and feet, as well as their ears and hair.

Catechu, gambier, and gumkino are the most valuable of the tannin substances, which give a green colouration with persalts of iron. They are most extensively used to produce a great number of shades, varying from light drabs to dark brown, in cheap dyed cotton goods, such as fustians and corduroys. They are used in calico printing chiefly to produce browns, in silk dyeing to weight the silk, and in tanning to produce a low class of leather, easily distinguishable from that proporly tanned with bark and other matters belonging to the first class, because when used for making shoes it communicates to the stockings a peculiar orange yellow hue.

For a long time there was much doubt as to the genus of plants from which catechu, gambier, and kino, which resemble each other very closely in their properties, were derived. M. Guibourt, a few years ago, solved the problem. He found that real catechu, cutch, or Terra japonica was the berry of the Arica palm. called Areca catechu, and the Acacia catechu, whilst gambier is extracted from the leaves of the Uncaria gambir, belonging to the

family Bubiacece, and kino is obtained principally from the Butea frondosa, a leguminous plant.

Catechu is found in commerce principally in two states, the best in lumps varying in weight from 80 to 901bs., of a dull purple colour, and covered with leaves ; the second, in masses, more or less covered with sand.

Gambier is imported into this country in the form of small cubes, having a yellowish brown colour.

Good catechu should not leave, on incinération, more than 4 or 5 per cent, of ash. Its aqueous solution should give, with alcohol or gélatine, an abundant white precipitate, with lime and baryta a brown precipitate, with salts of lead and tin a yellow precipitate varying in shade with the salts employed, and with bichromate of potash a brown precipitate. It should also take a decided brown hue with alkalis, and assume a greenish colour with salts of iron.

Catechu, besides naturally varying widely in quality, is freely adulterated with minerai substances, starch, tannin matters, and blood.

I have just stated the amount of ash a good catechu should yield. To ascertain the presence of starch, the sample should be first treated with alcohol, and the insoluble residue boiled with water, which will give a fine blue coloration on the addition of iodine if starch be présent. The presence of any ordinary tannin matter in the catechu will modify the green coloration which the latter substance gives with the persalts of iron. Blood may be detected if présent by treating the catechu with alcohol, and, after drying the insoluble residue, heating it in a tube, when ammoniacal vapours will be given off, as well as vapours of a most offensive odour.

Catechu is composed of three distinct substances, first, a tannin matter called mimo-tannic acid ; second, catechine, or catechinic acid; and lastly, a brown colouring matter due to the oxidation of the catechine.

Mimo-tannic acid is prepared by treating pulverised catechu by ether in a displacement apparatus. The ethereal solution leaves on évaporation a yellow porous mass of this acid. Bombay catechu yields about 55*5

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per cent, of mimo-tannic acid ; that from Bengal, 48'2 per cent., while gambier yields from 36 to 40 per cent.

Catechine, or catechinic acid, is obtained by treating

is re-dissolved in water and yields with sub-acetate

of lead, and the precipitate washed. The lead com-pound is then suspended in water, and decom-posed by sulphuretted hydrogen, when pure catechine remains in solution. Its formula is C10H10 04. It rapidly becomes coloured brown in the presence of air, and an alkali, being, it is said, converted into japonic acid, whilst, with alkaline carbonates, it yields rubinic acid. It is also converted into japonic acid under the oxidising influence of salts of copper and of bichromate of potash.

If dyers, instead of employing catechu as imported, were to grind it, and wash with cold water, they would obtain an extract which would yield very pure shades of green drabs, while the insoluble residue of catechine would give a great variety of shades of brown. To increase the permanency of catechine colours, the goods dyed with them should be passed through a solution of bichromate of potash, as is usually done for catechu browns.

Dr. Stenhouse has shown that the tannin matters giving a green coloration with persalts of iron, such as catechu and elder and larch barks, do not contain a glucoside. The only exception he has found to this rule is willow bark.





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LONDON; W. TROVNÇE, PRINTER, CURSITOR-STREET, CHANCERY-LANE, E.C,

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