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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 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

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produced volatile alkali, and phosphoretic ammoniæ 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 ammoniæ on a solution of uretric matter in acid of saltpetre, discovered a material which he called "purple acetic ammoniæum," on account of its splendid color. He thus describes the 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 ammoniæum 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 ammoniæum. 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 colored material gave it the name of "murexid," from murex, 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 ammoniæum, 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 dyeing 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 part 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 valuable than the manure of the farm-yard or the stable because birds have no urinary passage, and therefore their fæcal excrement contains all the uretric salts.—Translator.

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If even the chemists were insufficiently supplied with the raw material, still less could it be procured for the purposes of industry. In Prout's time, the cost of a pound of uretric acid was from thirty-two dollars to forty-two dollars and forty cents; it can now be bought for from two dollars to two dollars and fourteen cents, though it is not in a chemically pure state. This great reduction, which enables the manufacturer and artisan to be plentifully supplied with murexid, is owing to the introduction of

annum.

GUANO.

This substance is imported from Peru into various parts of North America and Europe, at the rate of between one and two hundred thousand tons per Guano is found in vast quantities in Peru and on many of the cliffs and islands in that part of America between the 13th and 21st degrees of south latitude. It is the excrement of sea-birds, and contains as much as four per cent. of uretric acid. In those regions the sandy soil could be but unprofitably cultivated without the aid of guano. It is known that as early as the twelfth century manuring with guano was practiced there. Under the Incas, guano was considered so valuable that killing the young birds on the guano islands was punishable by death.

Each of those islands had its superintendent, and each island was assigned to a particular province. From 6,000 to 7,000 tons were annually used in Peru alone; and when Alexander von Humboldt was exploring America, there were as many as fifty small coasting vessels employed exclusively in the transport of guano. Humboldt took some samples to Europe, where they were analyzed by Klaproth, Foureray, and Vauquelin. The celebrated traveller and writer also published what he had learned as to the importance of guano to agriculture, but for some time his words remained unheeded. In Germany, Liebig's call upon the cultivators of the soil failed to stir them into activity, and it is even now insufficiently used, even by England, whose severely worked land more than almost any in Europe requires such a return of the elements of which years of grain-growing have deprived it.

Liebig and Woehler were the first chemists to experiment on guano. In the course of their inquiries on the subject of uretric acid they had often been embarrassed by want of material; they therefore requested William Kind, an apothecary of Bremen, to procure them some, and in due season received a hundred pounds weight from Valparaiso. So much have agriculturists been enlightened since that time, that, in several European countries, guano is an article of considerable yearly importation, and the raw material of uretric acid is never wanting. And such is the potency of modern chemistry that guano, so highly offensive to the nostrils in its raw state, is made to yield some of the most delicate of the perfumes which are used by the fair and the fashionable. A greater contrast than that presented in this case by the raw material and the article it is compelled to yield can scarcely be imagined.

The first attempts to render the murexid available for dyeing purposes were made by Sace, in Alsace, that high school of the art of dyeing; and he succeeded in giving to wool an amaranth color far more beautiful than that obtained from cochineal. This induced Schunberger to try a new course of experiments, in which, if he did not entirely succeed, he at least ascertained that white textures could be thus dyed both handsomely and durably. Sace maintained on this occasion that the coloring matter of the cochineal, the kermes, &c., has some connexion with murexid. He claimed to have discovered that birds, and especially those of brilliant plumage, the parrots, for instance, while they are moulting, secrete scarcely a distinguishable trace of uretric acid, but secrete a considerable quantity as soon as they recover their full plumage. What, then, becomes of the uretric acid when it is no longer excreted from the body?

26 s

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May it not be metamorphosed into some other substance which, like the alloxan, is capable of dyeing the feathers? These questions are only suggested, and we are not as yet able to supply the answers; but this hypothesis, if adopted with regard to birds, must also be extended to reptiles, insects, &c.

The murexid is now a favorite dyeing material, strongly competing even with cochineal. Germany, as usual, was the last to adopt it. In a new and little known process mistakes are quite natural. When this new dyestuff first made its appearance as an article of trade, under the names of purple carmine, purple murexide, or paste murexide, it was in the form of a dirty-brown pulp. Though it sold as high as $4 80 to $6 the pound, it was a very inferior quality, and in many cases contained not more than from four to five per cent. of the murexid. Of course, this inferiority arose from imperfect preparation.

To extract uretric acid from guano, the latter must be moistened with diluted acid of salt, and warmed. The calcareous salts and everything soluble in water or acids is removed, while the uretric acid, with a not inconsiderable quantity of sand and other adulterations, remains. The well-washed residue is then put, in small quantities, into acid of saltpetre of 1.45 specific gravity, and the vessel must be kept cold. Only when the fermentation subsides should more uretric acid be added. By this procedure alloxan and alloxantine are obtained. But it must not be forgotten, that, as it is impossible to hit upon the exactly correct quantity of the acid of saltpetre, we should always have a surplus of the acid at hand. It must be remembered, too, that very noxious fumes escape during the evaporation of the solution. The above-mentioned chemical products of uric acid suffer a further decomposition, and form combinations destitute of murexid. To avoid this, it is necessary that to the solution of uric acid and acid of saltpetre there should, during the evaporation, be an addition of ammonæum. Murexid may be formed without that addition, but always at the expense of the alloxan and alloxantine; for if the ammonæum be absent during the evaporation, the alloxan and alloxantine are required to supply its place in the chemical production of murexid during the evaporation; and, moreover, the decomposition just spoken of continues, and we run the risk of having the murexid destroyed as fast as formed.

The murexid must not be suffered to crystallize; the solution is to be evaporated only to the consistency of a pulp. In the whole process there should be the utmost care observed that only the purest and best murexid be produced. The high price of the pure article would be more than compensated by its greater efficacy in dyeing. All textile fabrics, silk, wool, cotton, and flax, may be dyed with murexid, which is also used in cotton printing. Truly splendid colors are obtained by using the oxmuriate of mercury as the adhesive medium. We are obliged, however, to confess with regret that the murexid red cannot compare with the ancient purple as to durability. Samples on which we experimented with the usual re-agents lost their colors, however beautiful. We do not speak of such re-agents as the corroding alkalies and potent mineral acids which would affect, and in our experiments did affect, black no less than murexid red. But this latter faded under the application of even weak vegetable acids, such as vinegar, lemon-juice, &c., and even perspiration left visible traces upon the delicate tincture. Here, no doubt, are considerable defects; but it is to be remembered that the whole art of dyeing with murexid is as yet'in its infancy. Even the ancient purple was not indestructible, and in the present day the public demand is not for indestructibility, but for cheapness. If the color please the eye and the price per yard be low, little is thought about the durability of the article. Time and the progress of chemical science will doubtless remedy the defects spoken of, since there can be no question but that this color is sus ceptible of great improvement. If the murexid be precipitated from its solu tions by metallic salts, as, for instance, oxymuriate of mercury, or salts of lead or zinc, very beautiful lac colors are obtained, which can be used for the paint

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ing or printing of paper-hangings; and quite a new field is opened to the dyer and printer of textile fabrics by the affinity of this coloring material for various metallic salts. Not only several beautiful shades of red can be produced with it, but also yellow, blue and violet.

And thus it is that our sober and utilitarian day steals one by one its glories from hoar antiquity. What the mightiest and haughtiest magnates of the olden day claimed as their exclusive privilege has now become common property to the humblest as well as to the highest. A striking proof, this common property in beautiful colors, of the superiority of the present age in its utilitarian tendencies to that antiquity which we so highly, and, in a purely asthetic point of view, so justly, glorify. The animals which supplied the ancients with their costly purple are perfectly known to us and easily obtainable, but we cast them aside, because we can more readily obtain our objects by other means. Whether the murexid be the very "purple" of the ancients is a question fairly open to discussion; but that it is so is by no means improbable. We know that uric acid is a constituent of the common snail, and, it is not unreasonable to suppose, of the purple snail also, though the fact be not experimentally proved. Putrefied urine, added to the fluid of snails, furnishes ammonia; so that the ingredients for the formation of murexid are certainly present.

Should the murexid red be still supposed inferior to that resplendent purple which the old writers so eloquently extol, let it not be forgotten that the skill of the dyer was of old limited almost to that one really splendid color, and that our modern wealth of gorgeous colors and delicate tints was then not dreamed of. Could we place our murexid, however, side by side with the true Roman purple, the former probably would not lose by the comparison. The glories of antiquity, like the prestige of our modern great men, might lose not a little of their illusion were we placed in closer contact with them.