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 hun-dred 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 Sacc, 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?

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 splen did 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 solutions 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

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.

METHOD OF PRESERVING LEPIDOPTERA.

PREPARED FOR THE SMITHSONIAN INSTITUTION BY TITIAN R. PEALE.

THE difficulties in the preservation of zoological collections generally arise from two causes, namely, moisture and destructive insects.

To guard against the effects of moisture requires so little ingenuity that I shall merely allude incidentally to the necessity of drying the specimens well at first, and then keeping them in dry places.

The greatest of all difficulties to guard against, particularly in this country, is the voracity of the destructive insects belonging to the entomological families of Dermestida and Tineida. These are the worst enemies of the zoological curator, as well as the fur-trader and careful housewife.

Tinea tapetzella, the clothes moth, which troubles the housewife and the clothier, does not disturb the entomologist; consequently the whole of this family may here be passed by in silence.

Dermestes lardarius (the bacon beetle) and Anthrenus musæorum (museum beetle) and their congeners are the great depredators. In the time of the Pharaohs of Egypt they destroyed the mummies which were intended to last through all time, and now in our day they destroy the specimens with which we hope to enlighten posterity. As they have been known for centuries, numerous poisons and various devices have been resorted to in order to destroy them, but they remain as numerous as ever, being naturalized and abundantly propagated wherever man has made his resting-place on the earth.

In early life I was a devoted student of nature, an industrious collector of specimens, and a somewhat expert taxidermist. It is, however, needless to record the fact that I lost my specimens, like others, almost as fast as they were collected, and, as a last resource, I was compelled to undertake a careful study of the habits of the enemies with which I had to contend, in order to learn the means of subduing them. I early found that substances containing albumen or gelatine stand but little chance of escaping the ravages of the Dermestidæ, and must be destroyed, sooner or later, by their attacks, whether moist or dry, unless chemically changed in character, or kept by some mechanical arrangement beyond the reach of the insect. I say chemically altered, because, as in the case of gelatine soaked in corrosive sublimate, the coagulation of the material, which is a chemical change, so alters the matter as to render it no longer a proper food for the insect. The means of protecting, therefore, must be adapted to the kind of specimens to be preserved. Our present object is principally to describe a successful experiment in preserving Lepidoptera, and to this subject we shall chiefly confine our remarks.

The vapor of camphor, and the essential oils generally, are sickening or fatal to the perfect insects of the family Dermestidæ, but have little or no effect upon their eggs or larvæ; consequently, although these perfumes in close cases are useful to keep out the parent insects, they will not destroy the progeny after a lodgement has once been attained. The several species of this family, unlike most other insects, have no fixed period or season for depositing their eggs, and consequently require to be vigilantly guarded against at all times. They are about one year in attaining their full growth, in which time they cast their skins four or five times. Their feet, though armed with claws, are unfit to climb on a hard smooth substance like that of clean polished glass. They spin no silk, and therefore cannot, like many caterpillars, construct a fibrous ladder to climb

up the same surface. Upon these simple facts I based plans for the preservation of Lepidoptera as long ago as 1828, and since then no specimen which I have wished to preserve has been touched by Dermestes.

For collecting insects I have generally found the case described by LeValliant, during his travels in South Africa, the most convenient. This principally consists of a box filled with perpendicular slides covered with cork, to which the specimens are pinned, and a horizontal drawer at the bottom to receive any specimens which may be disengaged from the slides during transportation, and thus preventing it from damaging those which remain on the slide. The spaces between the slides being all open below, a single bag of camphor placed in the drawer will diffuse its vapor through all the compartments, and thus prevent the attack of ants, roaches, and other large insects which prey, especially in tropical countries, on the fresh specimens. By placing the specimens on the perpendicular slides, tile-fashion, I have found that double the number could be accommodated, while additional security was gained by this arrangement from the danger of the loosening of the pins by the jolting of the box.

In the preparation for the cabinet I begin by pinning the specimens to be preserved in the order in which they are finally to be preserved on the bottom of a shallow box, lined with a thin layer of cork, or, better, of balsa-wood, which is easier penetrated by the point of the pin. This box must be of precisely the same length and breadth as those which are to form the permanent cases of the cabinet. When the specimens have been ar

ranged in the order to suit the taste, and so that one may not overlap the other, the box, with its contents, is transferred to an oven, which I also invented in 1828 for this special object, but which has since been used, generally by chemists and others, for a variety of purposes. It is surrounded and heated by boiling water, the temperature of which is sufficient to kill the eggs and the larvæ of the Dermestes, but is not sufficient to injure the specimens of butterflies, moths, &c. The specimens are kept in this oven several hours, or during the night. (See Fig. 1.)

Fig. 1.

After the specimens have been sufficiently baked I lay a clean pane of plate glass immediately over the specimens, which, resting on the perpendicular sides of the box, does not touch them. On the upper side of this glass plate, face down, and directly over the pin securing each specimen, I attach, with fish-glue, (isinglass,) a circular piece of paper, about a quarter of an inch in diameter, containing a printed number. The size of the glass plates which I use, and find most convenient, is eight and a half by ten and a half inches. It is commonly imported, and used for cheap mirrors. It must be cleaned with dilute nitric acid, or the surface will be liable to become foggy in damp changes of weather.

Next small cylinders of cork of the same diameter as the papers containing the numbers, and just large enough to support the specimens, are cemented to the glass plate directly on the top of each of the paper numbers. The cement used for this purpose is composed of about equal parts of resin, beeswax, and chrome green, melted, for convenience, over a nursery lamp placed on the table beside me. The pieces of cork are dipped into the composition, and while the portion of the latter which adheres is still liquid, they are attached to the glass in their proper positions.

The next operation is to attach the plate glass to a wooden frame, thus forming a shallow box, of which the glass plate will be the bottom, having the numbers and cork supports on the inner side. This frame is made of strips of