Aniline dye

“ Down to the middle of the 19th century natural dyestuffs alone, with but few exceptions, were at the command of the dyer. But already in the year 1834 the German chemist Runge noticed that one of the products obtained by distilling coal-tar, namely, aniline, gave a bright blue coloration under the influence of bleaching powder. No useful colouring matter, however, was obtained from this product, and it was reserved for the English chemist Sir W.H. Perkin to prepare the first aniline dye, namely, the purple colouring matter Mauve (1856) . ”

“ The poorest aniline dye eats into the rug, and the color fades.
Wool Drying after Dyeing
Madder ranks high among those plants which yield a permanent dye. It belongs to the genus Rubia; the root employed is that of the Rubia tinctorum. This is largely cultivated in certain districts of India, but the best comes from near Smyrna, and from other parts of Asiatic Turkey. The plant grows wild throughout a large section of Central Asia and Russia. With both the European and the Indian madders the roots of the plants are the only parts that yield the dye. ”

“ Thus aniline dyes, though so greatly praised for their beauty, are not the unmixed good which some pretend them to be.
As regards dyes, light colours are more healthy than dark, since they contain less colouring matter, and fast dyes are safer than those which fade rapidly. Indigo-black is a very "fast" dye, and is therefore better than blacks obtained from logwood. ”

“ Artificial Colors
In a pinch of aniline dye there is all of the color which a cherry-tree can produce in one season. The cherry juice or the cherry jelly is refreshing and invigorating, while the aniline dye, whether harmful or harmless, is without food value, lifeless and dead. ”

“ The chemical composition and constitution of aniline black has not yet been worked out. It is not by any means an easy colour to dye, but still with careful attention [Pg 206] to carrying out the various operations in detail excellent results can be attained.
Aniline black is the fastest black which is known, it resists when well dyed exposure to air and light, is quite fast to washing and soaping. Its disadvantages are that there is, with some methods of working, a tendency to tender the cotton fibre, making it tear easily ”

“ The aniline dye is dissolved in the alcohol and the copper sulphate in the water. The wood is first coated with the copper sulphate solution, and after this coating has been given plenty of time to dry the aniline salt tincture is applied. Shortly the copper salt absorbed by the wood will react on the aniline hydrochloride, developing a deep, rich black which acids or alkalies are powerless to destroy. Coat with shellac and give a French polish, thus bringing the ebony finish up to a durable and unsurpassed luster. ”

“ This he puts in the nitro group and makes nitro-benzene, C6H5NO2. He treats this with hydrogen, which displaces the oxygen and gives C6H5NH2 or aniline, which is the basis of so many of these compounds that they are all commonly called "the aniline dyes." But aniline itself is not a dye. It is a colorless or brownish oil.
It is not necessary to follow our chemist any farther now that we have seen how he works, but before we pass on we will just look at one of his products, not one of the most complicated but still complicated enough. ”

“ The aniline dye industries have grown out of the discoveries of many chemists. The basic work was done by Faraday, Laurent, and Runge, who isolated valuable hydrocarbons from coal gas tar. Hoffmann discovered aniline and Perkin obtained mauve in 1856 by the oxidation of aniline with chromic acid. ”

“ This dye is prepared by heating a mixture of magenta, acetate of sodium, and aniline in iron pots, provided with stirrers, &c., in an oil bath, to 370° Fahr. (190° C.) , and the excess of aniline distilled over. When a good blue has been obtained the heat is removed, and the thick treacly fluid purified. This is effected for the commoner varieties by treating the crude product with hydrochloric acid, to dissolve all the excess of aniline, and the various red and purple impurities ”

“ The blood of the slaughtered animals, which formerly was allowed to run away, has been found to contain a most valuable aniline dye, and for this purpose it is now collected and taken to the blood-houses, where in order to obtain this dye it is necessary to place the blood in shallow tins, where it is warmed by steam-pipes, the liquid is then drawn off, which is the albumen from which the dye is extracted, the residuum left in the trays is of the consistency of jelly, and is sold for manure. ”

“ One objection to the use of aniline dyes is that by removing some of the natural oil of the wool they are apt to make it brittle, so that it is less able to stand wear. Another is that in time some of the dyes, which have been applied collectively to produce a single colour, will fade or even disappear, so that the final colour may be a most undesirable shade not in harmony with those that surround it. If the fibres are brittle and become harsher to the touch when wet with water, it is an indication that aniline dyes have been used. ”

“ Aniline dye manufacturers in this country are making a tremendous, and, they believe, an encouraging effort to supply the want of dyes, so greatly needed since the cessation of German exportation of that product.
Some idea of the way in which the domestic industry has been called upon to meet the demand of the textile mills was given by one of the largest American concerns in the dye business, who said that his company has daily to reject orders for some thirty to eighty thousand pounds of dyes because of their inability to manufacture them fast enough. ”

“ The discovery of other brilliant aniline dyestuffs followed in rapid succession, and the dyer was in the course of a few years furnished with Magenta, Aniline Blue, Hofmann’s Violet, Iodine Green, Bismarck Brown, Aniline Black, &c. Investigation has shown that the products of the distillation of coal-tar are very numerous, and some of them are found to be specially suitable for the preparation of colouring matters. Such, for example, are benzene, naphthalene and anthracene, from each of which distinct series of colouring matters are derived. ”

“ For many years, almost the only method of dyeing cotton goods with the aniline colors consisted in a preliminary steeping in sumac or tannic acid, followed by a passage in some suitable compound of tin, and subsequent dyeing in the coloring matter. Sumac and tin have been used for two hundred years or more as the dyer's basis for a considerable number of shades of color from old dye-stuffs; there never has been the least suspicion that there was anything hurtful in colors so dyed. Sumac or tannic acid, in combination with alumina, may be held to be equally inoffensive ”

“ To-day the black, offensive and unpromising substance, with magical metamorphosis, has been transformed by the chemist into the most beautiful dyes, excelling the hues and shades of the rainbow, the most delightful perfumes and flavoring extracts, the most useful medicines, the most powerful antiseptics, and a product which is the very sweetest substance known. The aniline dyes represent one of the great developments in this field. ”

“ This change is due, together with certain other causes, to an oxidation brought about by atmospheric oxygen. By employing oxidizing agents, this oxidation can be accelerated and carried further, and eventually the Aniline Black is obtained. Among the substances which may be used to bring about the conversion of aniline to the insoluble black dye are manganese dioxide, lead peroxide, hydrogen peroxide, chromic acid, ferric salts, potassium [147] permanganate, chloric acid and chlorates in the presence of certain metallic salts, particularly those of vanadium and copper. ”

“ If greater fastness is required, and more especially if it is a case of replacing aniline black, Diaminogene diazotised and developed is a good dye-stuff. It is extensively used for dyeing umbrella cloths and linings. ”

“ Mr Nicholson obtains another violet from aniline red, by heating it in a suitable apparatus to a temperature between 200° and 215° C. The resulting mass is exhausted with acetic acid, and the deep-violet solution diluted with enough alcohol to give the dye a convenient strength. Aniline violet, although it resists the action of light to a very considerable extent, has been shown by Chevreul to be inferior in this particular than either madder, cochineal, or indigo. ”

“ It makes no difference whether the cudbear is put in before or after the indigo. Three ounces of aniline purple dissolved in alcohol, 1/2 pint, can be used instead of the cudbear. Wood spirit is cheaper than alcohol, and is much used by dyers for the purpose of dissolving aniline colors. It produces a very pretty shade, but should never be used on mixed goods which have to be bleached.
Dark-blue Dye.—This dye is suitable for thibets and lastings. Boil 100 pounds of the fabric for 1 1/2 hours in a solution of alum, 25 pounds; tartar, 4 pounds; mordant, 6 pounds; extract of indigo, 6 pounds ”

“ The colour is fully developed in them, and to dye a fabric they only require fixing in their unchanged state upon that fabric. Such dyes are termed monogenetic, because they can only generate or yield different shades of but one colour. Indigo is such a dye, and so are Magenta, Aniline Black, Aniline Violet, picric acid, Ultramarine Blue, and so on. ”

“ At the present time every colour, and all tints and shades of colours, are produced from aniline ; and, while the processes employed and the combinations formed are very numerous, the names under which the dye-stuffs
are sold must be said to be endless. Of the processes by which aniline may be prepared, that only is available in manufacturing which was devised by Zinin, when he prepared it, under the name of benzidarn, from nitrobenzol. ”

“ By a similar process, using a dye-bath containing the aniline salt and oxidizing mixture, cotton fibre is easily dyed. The black cannot be used for silk or wool, as the oxidizing materials attack these fibres, but for cotton dyeing and calico printing this colouring-matter has come seriously into competition with the black dyes obtained from logwood and madder. The use of aniline for this purpose, first rendered practicable by Lightfoot, is among the most important of the many wonderful applications of coal-tar products in the tinctorial industry. ”

“ The disadvantages of the aniline dyes are several: they have a tendency to make the fibres of the textile fabric brittle, and when it is wet the colours will frequently run. Some dyes also fade more readily than others, so that if a colour be the product of two or more dyes, the resultant tint may be totally unlike the original. On the other hand, not all vegetable dyes are fast; but as they fade they mellow into more pleasing shades. Efforts have been made to encourage the use of old vegetable dyes ”

“ Great care has to be taken in dyeing the threads of the weft, which are much finer than those of the warp. Vegetable dyes, such as cochineal, madder, indigo, etc., must be used, for permanent colours can never be obtained with aniline dyes. The old Spanish dyes were considered the best. In this country, one sometimes gets the fine colours in an old Mexican serape or a prized Navajo blanket. The wool that is used to mend old tapestries in the American museums is coloured with dyes made by Miss Charlotte Pendleton in her workshop near Washington, which I have visited. ”

“ The dyeing is sometimes done by brushing on a table, grain-side upwards, but more usually the skins are folded closely down the back, flesh-side inwards, so as to protect it as much as possible from the influence of the colour, and then passed through the dye-bath, which is now generally of aniline colours. ”

“ Any of this class of black may be so topped with aniline black if thought necessary A very fast black is thus got.
Black.—Make the dye-bath with 15 lb. Sulfaniline black G, 60 lb. salt, 10 lb. soda, and 5 lb. sulphide of sodium. Work [Pg 125] at a little under the boil, then lift, rinse well and pass into a hot bath of 3 lb. bichromate of potash, 3 lb. sulphate of copper, and 4 lb. acetic acid for half an hour, then lift, rinse well and dry. ”

“ Woodward (fig. 13) made the pioneer use in America of the newly discovered aniline dyes in staining tissue, so that certain parts become more visible under the microscope. The idea of staining specimens so as to cause particular features to stand out more clearly was as old as Van Leeuwenhock himself, but the unstable nature and the limited range of colors of most of the vegetable and animal dyes available had limited the use of the idea until the discovery, by the English youth, William Henry Perkin, of aniline dyes made from coal tar. ”

“ You can manufacture it yourself, of course, by making a saturated solution of one of the aniline dyes (mauveine is the most powerful) , and adding a few drops of glycerine, but, so far as my own experience goes, the home-made article is never really satisfactory, and does not give nearly the number of copies yielded by that which is specially supplied. Always procure violet ink in preference to black or red. It is far more powerful, and gives better and more numerous impressions. ”

“ On the whole, the employment of powerful aniline dyes is an advance as compared with the use of the vicious and often highly poisonous mineral colours which Hassall met with so frequently in the middle of the 19th century. Mineral colours, with very few exceptions, are no longer used in food. Oxide of iron or ochre is still very often found in potted meats, fish sauces and chocolates; dioxide of manganese is admixed with cheap chocolates. All lump sugar of commerce is dyed. ”