Imágenes de páginas

which occasioned the discovery of the beautiful Tyrian purple. As Hercules (so runs the fable) walked one day on the sea-shore with the fair object of his love, her pet dog, playing around them, seized an open sea-snail, and dyed his mouth of so beautiful a color that the lady uttered a wish to have a dress of that self. same hue. Hercules, of course, succeeded in granting her desire. It is assumed that this discovery dates from the year 1500 B.C. For nearly all that we know of purple dyeing we are indebted to Aristotle, Pliny, and Vitruvius. Pliny mentions two shell-fish that yield the “purple.” the “buccinum,” so called, on account of its resemblance to a trumpet, and the “purpura.” The coloring substance was said to be contained in a transparent and branching vein at the back of the creature's neck, and while the animal was alive, the fluid had a mucous or creamy consistence. If the fish were small, they were pounded; but if large, containing so much as an ounce of the highly valued fluid, the vein was detached, its contents mixed with five or six times its weight of water, and to the mixture thus formed soda was added. in the proportion of twenty ounces to every hundred pounds. The whole was then put into lead or tin vessels and kept in a moderately warm place for five or six days, the scum being from time to time carefully removed. As soon as the fluid assumed the precise tone of color that was desired, the wool was dyed. The process was very simple. The wool, being thoroughly cleansed from grease and all other impurities, was plunged into the dye for some five or six hours, or even longer if the object was to double dye the material, (dibaphes,) in which case it was highly esteemed and proportionably high in price. Wool thus dyed commanded in the reign of the Emperor Augustus the enormous price of two hundred dollars per pound, nearly its weight in gold ! We learn from Vitruvius that various countries had their peculiar shades of [. At the north, the shade approached to violet, while at the south it ecame the vivid red which we now term a bright scarlet. Pliny also distinguishes two different shades of purple—the tyrium or purpura, a dark crimson like that of coagulated blood; and the amethystinum, the light violet blue of the amethyst. Both authors agree in stating that an excellent purple was obtained from some plants; our own madder, it would seem, being among them. Madder (Rubia tinctorum) was undoubtedly known and cultivated in several ancient countries—Italy and Judea, for instance. Woad, too, (Isatistinctosria,) was well known to the ancients, and served to give to the purple that fine violet tint which was so much prized. The purple-yielding shell-fish were found on all the coasts of the Old World; and in Greece, Italy, Dalmatia, Istria, and Egypt, there were large dyeing houses. Of course they used up an immense number of these minute animals; but the supply was equal to the demand. For instance, Mount Testaceo, near Tarentum, consisted almost entirely of the shells of the Murex brandaris, which we believe to be the shells from which the Roman dyers extracted their coloring matter. According to Tacitus, the Germans had a purple dye which was especially in request for linen. But above all the purple dyes of the ancients, that of Tyre and Sidon was admired, and it was a very important item in the commerce of the merchant princes of Tyre. No color has ever been so long valued and so profusely lauded as the purple. 'In the days of Moses it was the distinctive color of the great and the wealthy; Homer makes AEneas offer a superb purple robe to Bellerophen; Dives, in the New Testament, is “clothed in purple and fine linen;” and it was in a robe of purple that the stern Roman Imperator triumphantly returned to the seven-hilled city, after vanquishing and subjugating some far barbarian foe. Pliny o of “the Tyrian purple” as being a color so representative of dignity and majesty that Roman lictors made way for it with their fasces and their followers. Not only was it the distinctive mark for both young and old of high rank or great wealth, but was still further honored by being the indispensable color of the robes of those who reverently sacrificed to the gods, to obtain their favor or to avert their wrath. Pliny is so much in love with the purple that he deems it no mere idle vanity, but a laudable and natural yearning in men eagerly to desire it. To the great majority of Romans purple was forbidden for a long time by its enormous cost as compared with the moderate fortunes of most of the plebeians; but when wealth flowed into Rome and corrupted the Romans, purple was fast becoming the only wear, and the Caesars, from Julius downwards, prohibited its use by private citizens under pain of death. The Byzantine emperors made it penal even to write with purple ink, the use of which they monopolized for their own imperial signatures; and the very art of dyeing in purple was confined as a privilege and a monoply to favored individuals. As a natural con: sequence, the art decayed, and at length was entirely lost towards the end of the twelfth century, though so recently as the preceding century the Greeks, Saracens, and Jews, had been renowned for their skill as dyers. During the twelfth century the purple was less various in its shades, and very much less in request. But though the fickle tyrant Fashion, for a time, discarded purple in favor of scarlet, procured from the Thermes, the traditionary reverence for the imperial purple was not extinct, for even to this day, throughout the Old World, “purple” is synonymous with imperial power and place. Strangely enough, while purple-dyeing was a disused, if not a forgotten, art in many of the countries to which it had once procured so much profit, it still continued to be considerably practiced in Britain. With that island the ancient Phoenicians are known to have had considerable commerce, the Britons, as we learn from Herodotus, supplying the Phoenicians with tin, and it is probable that it was from the Phoenicians that the Britons learned the art of purpledyeing. The practice of the art existed in England till the close of the fourteenth century; and so late even as 1684 an Irishman is said to have made a large fortune by the peculiar skill with which he gave the purple dye to fine linen and other articles of female apparel. He, like the ancients, obtained his dye from a shell-fish. The Chinese are said to have had a dye resembling the purple; and in the New World, according to Don Antonio d'Ulloe, the people of the provinces of Guayaquil and Guatemala were, from the earliest times, possessed of a beautiful red color, which they obtained from certain sea-snails of a size not greater than a hazelnut. These, on account of their scarcity, were highly prized, and were used only for dyeing choice and costly matters, such as beads, fringes, braidings, &c. It was the popular belief that both the weight of the animal and the color of its juices varied with the hours of the day. The purple dye had at length become so entirely forgotten that what the ancient writers had said of it was regarded as a fable, invented by the Phoenicians to conceal their knowledge of the cochineal insect. A shell-fish yielding such a fluid was no longer known. It was not until the seventeenth century that the first attempt was made to rediscover and to ultilize the long-forgotten secret of antiquity. Then, indeed, men were enabled once more to view the prodigy with their own eyes, for in the West Indies, in Peru, on the coasts of Italy, France, and England, there were found muscles whose vital juices, from being at first colorless, soon took, successively, the shades of yellow, green, blue, and finally a splendid purple. William Cole, of Bristol, in England, was the first who, in the seventeenth century, experimented for the revival of the lost art of dyeing in purple, and he used only the common muscle which is so abundant on the shores of England, and after long trial at length discovered the long-sought-for shell-fish in the Purpura Lapillus. “If, ” says he, “we carefully break the shell we find, near the head of this shell-fish, a white vein lying in a furrow, and within that vein is a white, creamy, and somewhat glutinous fluid, which is the much-desired dyestuff.” His description precisely coincides with that of Aristotle and of Pliny.

In 1709 Jussien made similar researches on the French coast—researches which, in the following year, were continued by Reaumur, who delighted to make theory and speculation the obedient handmaidens of every day utility. Somewhat later the soft-shelled molluscs of the Mediterranean shores were carefully examined by Italiani naturalists, and so well has their pains-taking example been followed up that we are now acquainted with a goodly number of molluscs that yield the purple dyestuff. For the most part they belong to the families of the Murer and the Buccinum, of Linnaeus; and it is thought that the Marez trunculus, of Linnaeus, (one of the most abounding of the Mediterranean seasnails,) and the Purpura and Purpura putula, of Lamarck, are identical with Pliny's Buccinum. The Purpura Lapillus is quite common on the European shores, and is believed to have been the most important among the purple seasnails of antiquity. Lesson thinks that the Janthina fragilis is the true buccinum of antiquity. It is a native of the Mediterranean. In stormy weather it is thrown upon the coast of the French department of Ande in such vast numbers as actually to cover the strand. Lesson attributes to Narbonne (the Narbo Martins of the ancients) great skill and celebrity in the art of purple dyeing in the times of ancient Rome. Other writers say that though the Garlish purple was very splendid, it yet was very evanescent. The janthina undoubtedly affords a bright and beautiful purple, and when taken out of the water yields the fluid to the average amount of about an ounce. But the fluid is furnished by a gland entirely different from that spoken of by the old writers, a fact which it is difficult to reconcile with the ancient statement. Moreover, the modern purple is very evanescent, while the ancient was valued no less for its durability than for its beauty. Thus, in Plutarch's Life of Alexander the Great, we read that the Greeks found in the treasury of Darius purple stuffs to the value of five thousand talents, and that, though some of them were nearly two centuries old, the color had not at all faded. Lesson says that the coloring fluid yielded by the janthina passes through the same changes of light and shade as the vegetable colors do. With alkalies, it becomes blue; with acids, red. Some writers include Aplysia depulans and Scalaria clathrus among the purple sea-snails, but this is doubtful. It is true that the aplysia sometimes voluntarily, always when alarmed, does emit a beautiful purple fluid, and, in the latter case, in such quantities as to color the water for several yards around. Probably the purple fluid, in the case of the shell-fish, is analogous to the ink of the cuttlefish, the concealing and protecting provision of the otherwise defenceless creature. The fluid is colored at the moment of its ejection, but the tint is of slight duration. The fluid of the Scalaria clathrus is still more evanescent—time and exposure to light discharging it entirely. Of the Planorbis corneus Wallis says: “If you put salt, ginger, or pepper into its mouth it yields a purple fluid, but the color is so evanescent that we know of no mordant that can fix it.” At present we are acquainted with a great number of purple-yielding shellfish, but we cannot identify any of them with the purple sea-snails of the ancients, the descriptions left us by the old writers being too general and vague. In our own time Bancroft has industriously experimented with the dyeing fluid of purple sea-snails, and he asserts that they yield a fluid which surpasses everything else in animal nature, alike for the brilliancy and the permanency of its purple, and for the facility and simplicity of its use. Within the fish. or when separated from it, the fluid has a creamy appearance, or, as Reaumur phrases it, resembles a well-developed pus. The textures to which it is applied become first of a light, then of a darker green, next blue, and acquire finally a rich deep purple tint, inclining to crimson. According to Bancroft, the gradual prismatic changes of the colors are as beautiful as they are remarkable. Even the most powerful chemical agencies, whether mineral acids or the most corrosive alkali, can only subject this purple to one change—wash the fabric in strong soapsuds and the purple becomes a magnificent and permanent crimson. Dyed with this singular fluid the fabric passes through all the prismatic changes of color of which we have spoken, in a very few minutes; and if exposed to heat as well as light, the changes are so rapidly effected that the eye can scarcely appreciate the passing of one hue into another; but if, on the contrary, light be completely excluded, the first pale, yellowish green will remain unchanged for years. Bancroft proved this with some linen thus dyed, and kept for nine years in the dark. As to the causes of the changes of color they are not clearly understood. Berthollet thinks that the coloring matter absorbs oxygen. Bancroft attributes the effect to light. He justifies his opinion by reference to the coloring of prints, flowers, &c., which coloring is known to take place, not from warmth, but from light. It is by the mere exclusion of light that we bleach, for instance, endive and celery. As far as we are at present informed, the chemical nature of this coloring matter is as little known as the modus operandi of its successive changes after being applied to a textile material. Highly as Bancroft and others have praised the purple, it has had its day of popular favor. For dyeing fine muslins, and as a marking fluid, purple is still occasionally used. Even as long ago as the thirteenth century, scarlet, from Kermes, instead of purple, was the adopted color of the Hungarian magnates. Our numerous dyestuffs, and our facile and economical dyeing processes, render us independent of the ancient purple. With the revival of science and art from the decadence into which they had sunk, during what are not unjustly called the dark ages, dyeing, like other arts, started into new, vigorous life. Till the fifteenth century, and still later, Italy bore away the palm in the art of dyeing, for which Florence and Venice were especially renowned. . The discovery of America gave a great impulse to the same art, dyestuffs being furnished which were entirely unknown to the Flora and the Fauna of the Old World. From the Italians the mastery in the art passed to the Flemings; and when the religious persecutions by Spain drove the Flemings into exile, these latter carried their art into France and England. It was a native of the Netherlands, Cornelius Drebbel, by whom, in 1650, the discovery was made that cochineal was capable of yielding a dye far surpassing in beauty the purple of the ancients. Drebbel was at work in his laboratory, when an accident having thrown some aqua rega over the tin fastenings of the window panes, and thence into a bottle full of an aqueous infusion of cochineal, the latter on the instant assumed that magnificent scarlet tint which is now so well known. Drebbel was too acute and too reflecting an observer to neglect such an indication, and from that time cochineal has played an important part in the art of dyeing. Modern chemistry, however, has done more for this art in single years than had previously been accomplished in centuries. Pure and effective mordants and mineral colors have wonderfully changed both the laborious and the economical processes of the art. Colored garments were formerly the external sign of rank or opulence. At the present day, thanks to the labors of men of science, the man who wears the homeliest and cheapest garb, as to quality of fabric, may yet wear it of the most tasteful color: Chemistry, however, is still making and will long continue to make still further improvements in this art, as in others. One of the latest acquisitions thus made by the secluded men of the laboratory is that of the much-valued coloring material known as

Murexine, (MURExidroth.)

This color is extracted from the uretric acid contained in urine. The ancient adepts, or alchemists, carefully analysed that fluid, in which indeed they sought their arcanum, and in the course of their experimenting they produced volatile alkali, and phosphoretic ammoniae natron. The last named salt was probably known to the ancients, and used by them in soldering metals. The uric acid which now is so importantly utilized in urine, or rather in uric calculi, was found by Scheele, in the year 1776, which are, for the most part, composed of that acid, itself a component part of the urine of all carnivorous animals, and perhaps of all animals having a renal secretion;" being in the excrement of birds, snakes, and even in that of caterpillars, snails, &c. Scheele remarked, that a solution of uric acid in acid of saltpetre left, when evaporated, a red sediment, and would stain the skin a fine red color. In 1818, Prout, by the action of ammoniae on a solution of uretric matter in acid of saltpetre, discovered a material which he called “purple acetic ammoniaeum,” on account of its splendid color. He thus describes ''. process of producing it: Pure acetic acid and acid of saltpetre are mixed with an equal volume of water and gently warmed till solution takes place and strong fermentation is produced. The superfluous acid of saltpetre is then diluted with ammoniaeum and the whole reduced by evaporation. During the operation the color gradually changes from purple to red, and through numerous shades of dark red. Greenish granular crystals are precipitated, which consist of purpuric acid and ammoniaeum. This reaction is remarkable, and so positive that chemists have long availed themselves of it to detect the presence of uretric acid in any organic substance, for this characteristic coloring only takes place in the way mentioned and where uretric acid is present. Liebig and Woehler, in 1837, also produced this brilliant colored matter while experimenting on the changes of uretric acid under the influence of oxydating matter. It appeared in the form of small crystals, or short four-sided prisms, which when held up to the sunlight appear of a rich garnet-red color, changing, under a reflected light, to a greenish metallic splendor not unlike that of the wing of a rose-chaffer. Those chemists believing Prout to be mistaken as to the chemical composition of this beautiful . material gave it the name of “murexid,” from murer, the purple snail. It is not formed directly from the uretric acid, which is first converted into aloxan and aloxantine by means of acetic saltpetre. These are two colorless combinations of little durability, but, acted upon by ammoniaeum, they exhibit the purple-red coloring. Prout produced several compositions from purpuric acid and other bases, such as lime, quicksilver, and oxyde of zinc, and all such compositions were remarkably beautiful in color. He also claimed that some of those compositions can be utilized not only in painting, but also in the o of wool and other textiles, but his statement could not immediately be acted upon. In the first place, his description was so vague and general that experiments often failed when based upon it. Then the temperature, not less than the concentration of the fluid, is of great importance in producing the result, which often is very different even when the accurate prescription of Liebig and Woehler is followed. Moreover, in Prout's time the raw material was insufficient for the production of a large and constant supply of this dyestuff. It is true that, as we have stated, the uretric acid is furnished by many species of animals, but it is furnished only in very small quantities. Man, for instance, secretes only about one-third of a drachm of it in twenty-four hours. The excrement of birds is distinguished for its great proportion of uretric acid; it is or W. of the weight of dried pigeon's dung. But that could not be produced in large quantities any more than the excrement of snakes, which consists chiefly of uretric-acidical salts.

* Millions of dollars are annually paid for guano by the farmers on both sides of the Atlantic. yet they, for the most part, suffer the urine of their live stock to sink uselessly into the ground or to pollute and empoison the air, forgetting, if they ever knew, that guano is only more oil. than the manure of the farm-yard or the stable because birds have no urinary passuge, and therefore their fascal excrement contains all the uretric salts.-Translator.

« AnteriorContinuar »