A Beautiful Dye From Coal Tar.

Scientific American 5, 28.1.1860

The attention of calico-printers and of woolen and cotton manufacturers throughout the world having been for some time directed to n new, beautiful, and perman­ent violet dye which is obtained from coal tar, we pre­sume many of our readers will be interested in the fol­lowing article which we translate from Le Gaz, of Nov. 15, 1859, and which contains a brief description from the largest French manufacturers of their mode of producing this new and valuable dye. Is there not an opening for a profitable enterprise in its manufacture from the refuse of our own coal oil and gas-works?

Among the sub-products which are obtained in the manufacture of illuminating gas, there is one, coal tar, which enjoys the privilege of endowing, from time to time, the industrial world with some new substance which signalizes its advent by a marked step in the progress of the arts. We borrow from our colleague, Doctor Quesneville, an article full of interesting details, which he has just published, on the application of nitro-benzine to the dyeing of cloths.

The attention of the industrial world has been for sometime fixed on benzine and nitro-benzine, and on the numerous applications which aniline has received in the printing of fabrics, and in the dyeing of silk, woolen, and cotton.

The violet tints have generally been made with archil, but in consequence of the small stability of that coloring principle, violets thus made change under the influence of light alone, and they are altered by the feeblest acids. Aniline ie now replacing arthil; it constitutes the base of a fast violet color, which does not fade in the light, and which is acted upon by neither acids nor alkalies. It is to this great stability that it owes all its importance. It gives every variety of shade front the most delicate lilac to the deepest violet. Tho apparition of this fixed violet has produced a veritable revolution in dyeing, but its introduction has been obstructed to the present time, by the difficulty of procuring it. Messrs. F. Laurent and Casthelaz, manufacturers of chemical products, of Paris, have for some time been endeavoring to overcome these difficulties, and having succeeded in making important improvements in the mode of manufacture, they have erected apparatus at their works at Aubervilliers for the production of benzine, nitro-benzine, and aniline on a large scale, and will be able henceforth to furnish a sup­ply of these articles. We have the pleasure of publishing the following account, which Messrs. Laurent & Casthe­laz have addressed to us on their method of manufacture.

Charcoal has not yet been transformed into diamond, but we have succeeded in extracting from mineral coal a product equal in value to that of gold, of a magnificent tint, and of an extraordinary power of coloration; it is called aniline violet. This substance is designated, by persons who do not keep themselves informed in regard to the progress of science, as the violet of coal or of char­coal. Coal is indeed the primary source of it, but it is only after a long series of operations that this precious color is reached.

1. Distillation of Coal.—Coal must be submitted to distillation; this operation is the base of the manufacture of illuminating gas, and the products to which it gives birth are: First, Coke, a fixed product, which remains in the retort. Second, Coal tar, a semi-liquid product, which passes over in distillation. Third, Ammonical waters, and the sal-ammoniacs. Fourth, Illuminating gas. Gas and coke are the principal, ammonia and coal tar the secondary products; during, a long time, indeed, coal tar was of scarcely any use, anti was burned under the retorts; now it is gathered with care and distilled, and it is this product which particularly interests us in re­lation to aniline.

2. Distillation of Coal tar.—The presence of aniline has been discovered in coal-tar, but in so small quanti­ties had mingled with so many foreign substances, ammonia, benzine, taluine, phenic-acid, bucoline, naphthaline, brai, &c., that to directly extract it a treatment would be required too long and too expensive. The coal tar is therefore submitted to distillation, and furnishes the following products: First, Dry brai, a product not fixed, which remains in the retort. Second, The volatile oils of coal. We shall occupy ourselves onion witch these latter.

3. The Distillation of Coal Oils.—The volatile oils of coal are very complex products; they contain, in fact, nearly all the products which we have mentioned as constituent parts of coal tar, with the exception of the brai. Submitted to distillation they pass over at divers temperatures, and are thus separated, giving us oils of various densities mid properties. First, Heavy oils. Second, Light oils. The heavy coal oils are but little employed. In consequence of the property which they possess of preserving wood from the attacks of insects, they are used for injecting railroad ties. The light coal oils are mixtures in variable proportions of benzine, toluine, phenic acid, med other substances of less interest. According to their density they serve for the manufac­ture of phenic acid, of picric acid or of benzine.

4. Distillation of Light Coal Oils. This operation is the base of the preparation of benzine. It is necessary to submit the oils employed to either two or three distillations, according to their purity; bringing them to a density of 27° or 28° Beaumé. The benzines vary much according to the nature of the coals from which they are made, and according to the temperatures at which they are distilled. These diferences are seen both in their odor and volatility, and according to their quali­ty they are applied to various purposes. First, Benzine serves for the dissolving of caoutchouc adn gutta-percha. Second, It enters into the composition of certain var­nishes in consequence of its dissolving action on resinous guns. Third, It dissolves fatty substances. and there­fore serves for removing grease-spots from cloths. Fourth, It is employed for lighting, in which case it is burned in lamps specially adapted to it, either pure, or mixed with other liquids less carbonized. Filth, It is employed as an agent for carbonizing illuminating gas. By passing gas through benzine it takes up tho particles of carbon, and thus acquires a much more considerable illuminating power. Sixth, It is used in the preparation of nitro-benzine. We have cited only the principal uses of ben­zine, but these will suffice to show the importance of this product.

5. Transformation of Benzine into Nitro-Benzine.‑Benzine submitted to the action of concentrated nitric acid, or to a mixture of nitric and sulphuric acids, and distilled, gives a reddish liquid which is the crude nitro­ benzine. Submitting this product to one or two distil­lations, we obtain a pale yellow liquid, of an agreeable odor, resembling that of bitter almonds, of a density much superior to that of water, marking 20° to 22° of the hydrometer. This is distilled nitro-benzine.

6. Transformation of Nitro-benzine into Aniline.—Nitrobenzine, pure and distilled, being submitted to the action of nascent hydrogen, transforms itself into aniline, which in its turn may be purified by one or two distilla­tions. It presents itself, then, under the form of an olea­ginous liquid, white when first obtained, but soon becom­ing yellow, rose tinted, and then red. It constitutes a volatile salifiable base.

7. Transformation of Aniline into Aniline Violet. - Finally, the white aniline, under the influence of oxydiz­ing agents, is transformed into aniline violet. This sub­stance is sold in several states, as a liquid more or less concentrated, as a paste and as a powder. The follow­ing are the comparative prices of the products of which we have spoken:—Coal, 1/4c. per lb.; coal tar, 3/4c. do.; heavy coal oil, 2½c. a 3 3/4c. do.; light coal oil, 6 3/4c. a 10 1/4c.; benzine, 10½c. a 13c.; crude nitro-benzine, 57c. a 61c.; rectified nitro-benzine, 82c. a 96c.; ordinary aniline, $3.27 a $4.90; liquid aniline violet, 28c. a 41c.; carmine aniline violet, 32c. a $1.92; pure aniline violet in powder, $245 a $326.88.

The price of aniline is certainly high, but a small quantity suffices to give much coloration; the value of the violet anilines is always proportioned to the quantity of coloring matter which they contain. The importance of this dye is nor generally recognized : this importance is due to the fixity, the unalterability, and the beauty of all the violet tints which it produces.