Harpenden, July 21.
A paper by R. Warington, read before the Chemical Section of the British Association at Montreal.
ANILINE DYES IN DRESS MATERIALS.
By Professor CHARLES O'NEILL.
Twenty-eight years ago Mr. Perkin discovered the first of the aniline dyes. It was the shade of purple called mauve, and the chief agent in its production was bichromate of potash. This salt is not actively poisonous, and no one thought of attributing injurious properties to materials dyed with the aniline mauve. Next in chronological order came magenta red. It was first made from aniline by the agency of mercurial salts, and afterward by that form of arsenic known to chemists as arsenic acid. The fact that this at one time fashionable color was prepared by means of an arsenical compound was spread through the country in a very impressive manner by the great trial as to whether the patent was valid or not, all turning upon the expression in the specification of "dry arsenic acid," and the disputes of scientists whether this expression meant arsenic acid with or without water. The public mind had been for some time previously exercised and alarmed by accounts of sickness and debility caused by arsenical paper-hangings; it was, therefore, easy for pseudo scientists to create an opinion that the magenta dye must be also poisonous, and that persons wearing materials dyed with this color were liable to absorb arsenic and suffer from its action. Ever since there have been, at intervals, statements more or less circumstantial, that individuals have suffered from wearing materials dyed with some of the artificial dyes. At the present time these statements are emphasized by the exhibition at the Healtheries of models of skin diseases said to be actually produced by the wearing of dyed garments. Whether it be true or not that any form of skin disease has been produced by the wearing of dyed articles of clothing is simply a question of evidence, and there is evidence enough to show that individuals have experienced ill effects who have worn clothing dyed with artificial colors. But, as far as we know, there is an entire want of any evidence that will satisfactorily show that the inconvenience suffered by wearers of these dyed goods has been owing to the dyeing material. Years must elapse before chemists or physicians can hope to become thoroughly informed of the physiological action produced by the cutaneous absorption of the thousands of new products which the ingenuity and industry of technological chemists have made available for the manufacture of colors; they are also new to science, most of them very complex in their constitution, and so dissimilar to previously studied compounds used by the dyer, that it may be said we have nearly everything to learn concerning their action upon the human economy. With respect to dyed woolen and silk goods it is almost entirely a question as to the innocence or otherwise of the coloring matter itself, which in nine cases out of ten is an organic body containing no mineral matter of any sort, and not requiring the assistance of any mordant to enable it to dye. Considerations of arsenic, or antimony, or mercury existing in the dyed stuffs are absolutely excluded. In a few cases the dyestuff is a zinc compound, and zinc in small traces may possibly be fixed by the material, but this metal is not known to be actively noxious. Textiles made from fibers of animal origin do not require, and as a rule do not tolerate, the addition of any metal in dyeing with the artificial colors, and if the manufacture of the color require the use of a metal, such as arsenic, which by unskillfulness or carelessness is left in it when delivered to the dyer, the tendency of the animal fiber is to reject it.
But the case with regard to textiles made from vegetables fibers is quite different; upon materials made from cotton, flax, jute, or other fiber of the vegetable kingdom, the new aniline colors cannot be fixed without the assistance of other bodies acting the part of mordants. Some of these bodies are actively poisonous in their nature, and introduce a possible element of danger to the wearer of the dyed article. 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; now it is a fact that the great bulk of cotton goods are dyed with the aniline colors by the agency of these harmless chemicals. But of late years the dyers of certain goods, and the calico printers generally, have found an advantage in the use of tartar emetic, and other compounds of antimony, to fix aniline colors; besides this, some colors are fixed in calico printing by means of an arsenical alumina mordant; it need not be mentioned that antimony, as well as arsenic, is, when administered internally, an active poison in even small quantities, and that externally both are injurious under certain conditions. An alarmist would require nothing further than this statement to feel himself justified in attributing everything bad to fabrics so colored; but the practical dyer or calico printer knows that though he employs these poisonous bodies in his business, and that some portion of them does actually accompany the dyed material in its finished state, not only is the quantity excessively small, but that it is in such a state of combination as to be completely inert and innoxious. In the case of tartar emetic, it is the tannate of antimony which remains upon the cloth, a compound of considerable stability, and almost perfectly insoluble in water; in the case of a few colors fixed by the arsenical alumina mordant, the arsenic is in an insoluble state of combination with the alumina, in fact, the poisons are in the presence of their antidotes, and not even the most scrupulous manufacturer has any fear that he is turning out goods which can be hurtful to the wearer. Persons quite unacquainted with the process of dyeing are apt to think that goods are dyed by simply immersing them in a colored liquid and then drying them with all the color on them and all that the color contains; they do not know that in all usual cases of dyeing a careful washing in a plentiful supply of water is the final process in the dye-house, and that nothing remains upon the cloth which can be washed out by water, the color being retained by a sort of attraction or affinity between it and the fiber, or mordant on the fiber. Dyeing is not like painting or even the printing or staining of paper for hangings, where the vehicle and color in its entirety is applied and remains. It follows, therefore, that many chemicals used in dyeing have only a transitory use, and are washed away completely—such as oil of vitriol, much used in woolen dyeing—and that of others only a very minute quantity is finally left on the cloth, as is the case in antimony and arsenic in cotton dyeing and printing.