violent raving which appears in every page against 'shaved heads," that his own head might reap advantage from the razor, and that his faculties have been disturbed by the same fatal curiosity which drove a laybrother of the order of St. Francis and several others quite mad.' Near Ribeira Grande, we are told there is an aperture in the side of a mountain, from whence a light vapour issues, which, if corked up, would an earthquake, or cause an generate explosion that would blow up the mountain. To this aperture our knight errant placed his ear; when his trusty squire, who attended with a long pole to spur on the ass of his master, interrupted him by an exclamation which sufficiently shewed the perilous nature of enterprize in which he was engaged.

I learned from him that of the numerous persons who put their ear to the aperture, from a curiosity similar to mine, they all became mad, instantly mad, and were never again restored to the light of reason, or the rational government of themselves.'-p. 154.

And the rationale of this phenomenon is clear and conclusive.

The mania is caused by the chemical action of the sulphuric and vitriolic acid of the vapour, which, by penetrating into the minutest pores of the brain subject to their action, operate as a solvent, or produce irritation by sheathing themselves in the pores of the body, in which they become mixed.'

Lest, however, this solution should not be sufficiently obvious, we are indulged with the choice of a substitute.

That as the vapour is composed of combustible bodies like metals, or the compound ones, as phosphorated hydrogen, sulphurated hydrogen, and the metallic phosphurets generated in the fiery abyss, from which the vapour ascends, it may become so impregnated with oxygen, as to possess that peculiar acid, which, if communicated to the brain, might act as a solvent or irritant till madness ensues.'-p. 157.

A tremendous epistle follows, of volcanic eruptions destroying primitive plains covered with aromatic plants; of earthquakes from the effervescence of marine and mineral contents,' the effects of which are sudden blasts, violent explosions, and a rumbling in the bowels of the earth;' when this 'fermentation of vapours gets vent by an eruption of water and wind,' it' upsets mountains from their bases.' But his theory of volcanoes, and earthquakes, and dews, which the editor assures us is quite original, is too sublime for our comprehension. The prospect brightens towards the close, and we are told, that though St. Michael's is hell within, it is paradise without. It is a paradise, however, which, if we believe the captain, cannot boast of many saintly souls.' Page is heaped upon page, descriptive of the intrigues of amorous and sentimental nuns and libidinous priests; inventions of the most dull and clumsy order which might just as well have been produced in the laboratory of the Minerva Press as on the island of

St. Michael's, and which, indeed, are scarcely worthy of the lumber garret of that fashionable staple of fiction. In one of the imaginary convents erected by the captain,' we are entertained by a concert of music performed exclusively by nuns who played on french horns, fiddles, and flutes.' p. 189.

The manners and customs of the inhabitants of St. Michael's are so unlike the manners and customs of the Portugueze, either at home or in any of their colonies, that we shall not notice them. To each of the rest of the islands the author assigns a short letter. At Terceira he just stops to read the Captain General a lecture; gives the same dimensions to Graciosa and St. George, though the former is only two and a half, and the latter twelve leagues long Mccalls the channel between St. George and Pico a short ferry,' though it is full four leagues across; goes to Santa Cruz in St. George's, where no such place exists; finds that wine is the staple produce of Fayal, which never exported a single pipe of its own growth; and swells the population of the islands to half a million, which is about three times the actual number,-but we shall pursue him no farther, being perfectly satisfied that he never set his foot on any of them, with the exception perhaps of St. Michael's. The book is evidently the compilation of one of those gentlemen who write travels by the fireside, and perform their voyages up four pair of stairs. From the miserable attempts at science, and the slip-slop jargon of chemical nomenclature, we suspect that the materials were furnished by some surgeon's mate who had obtained a few days leave of absence from his captain to make the tour of the island. We suspect, too, from the strangeness of the language, that the work has been got up by a foreigner, probably by the editor Mr. J.Haydn: thus we have 'Fermozean beauties carnationed by the refrigerent element,'-but we will spare our readers the disgust to which it has been our lot to submit to in wading through the most contemptible trash (to use the author's own expressions) that was ever imposed on the public.'

ART. XIV. Experimental Researches concerning the Philosophy of permanent Colours, and the best Means of producing them by Dyeing, Calico Printing, &c. By Edward Bancroft, M. D. F.R.S. 2 vols. 8vo. pp. 1124. London. 1813.

THE

HE art of dyeing is one of the most useful and the most erwonderful of all known arts; and,' according to Mr. Chaptal, whom Dr. Bancroft quotes, if any art can inspire mankind with a noble pride, it is this art, which not only imitates, but even exceeds nature, in the richness, splendour, and permanency, of the

colours that it affords.' We are bound to suppose that there is. some foundation for the opinion thus enounced by a philosopher so respectable as Mr. Berthollet: but we should find ourselves a little at a loss to demonstrate, with mathematical precision, what other utility the art of dyeing possesses, than that of affording employment and emolument to a great number of individuals, whose business it is to render it subservient to the innocent gratification of the taste and luxury of others, without any direct advantage of such a kind as can properly be denominated utility; at least in the same sense that the production and preparation of food are understood to possess utility. We recollect, however, but one instance, in the history of all ages and all nations, of an individual who carried his ideas of the propriety of pursuing utility only, to the exclusion of the mere gratification of the eye, so far as to refuse to use or wear any article of furniture or clothing which had ever been submitted to the dyer's art: his coat was white, his hat was drab, and his shoes were brown, as nature had left the raw materials; but he found no followers, even among the sectaries whose principles he had in this manner practically caricatured; and the consent of mankind, so universally and unequivocally expressed, must be allowed to be imperative, in rendering a compliance with custom and taste, in these respects, almost as indispensable as a submission to the irresistible dictates. of hunger, thirst, and cold..

The first volume of Dr. Bancroft's elaborate and valuable work was published in 1794; but it now appears with so many alterations and additions, as to possess a considerable share of novelty and interest. In the introduction, the author defines the sense in which he applies the terms characteristic of the different kinds of colouring substances; substantive colours being such as afford a permanent tint by simple application without mixture, and adjective such as require a mixture with some other substance to fix them; this substance, serving as a bond of union, is called a mordant, though it is sometimes difficult to ascertain which of two substances that are mixed is the more properly considered as the colour, and which as the mordant. If the substances thus employed are mixed before their application to the materials to be dyed, the compound is called by Dr. Bancroft a prosubstantive. colour; but it happens more commonly, that the colours are more effectually fixed, by applying the substances concerned in succession, as if the particles wedged each other in, after their penetration into the pores of the materials. There is, however, a complete fallacy in Dr. Bancroft's reasoning on the effect of heat in opening the pores, so that the colouring particles may be compressed when they cool again (p. 90); since these particles are at least as much contracted by the effect of cold as the substances which

they penetrate, and often much more. That the colouring particles are only partially distributed in or upon the surface of the substance coloured, is evident from the mixture of two tints, when the materials producing them are applied in succession; and a fugitive colour, constituting one of those tints, is not found to be in any degree fixed by applying a more permanent colour upon it; so that a compound green thus constituted will generally fade into a blue. In many cases it might be supposed that the absorption of oxygen contributed to wedge the particles more firmly into their situations; but it sometimes happens, on the other hand, that oxygen appears rather to be extricated than absorbed, while the colour is acquiring its lustre by exposure to the light, as Dr. Bancroft has found with respect to the Tyrian purple.

Of the mordants employed for fixing colours, one of the most extensively useful, and the most unequivocally entitled to the denomination, is alum, which is attracted by the fibres of many animal and vegetable substances, and, remaining attached to them, serves to unite them to the colouring matter, by leaving its earth as a common bond of union. The name alumen is found in Pliny, and Beckmann suspects that it may be of Egyptian origin; it is true that, according to Kircher's vocabulary, the Egyptian word, synonymous with alum, is oben, but we find alom, signifying cheese, which may possibly have had some connection with the coagulating power of this highly astringent substance. Dr. Bancroft observes, that alum, and its use in dyeing, must have been known to the ancients long before the time of Pliny, since they never employed tin, and either alum or tin is absolutely necessary for obtaining a scarlet from kermes.

Dr. Bancroft proceeds to trace the art of dyeing from the ancients, whom he proves to have been acquainted with many of the most important processes, through the middle ages, when it was but imperfectly preserved in Italy, to the latest improvements, as described in the works of Macquer, Keir, Henry, Berthollet, Chaptal, Vitalis, Scheffer, Poerner, and Dambourney, as well as to those which he has himself introduced, both in theory and in practice. He divides the body of his work into four parts; the first, after some general discussions respecting colour, and substances to be coloured, is devoted to the subject of substantive colours, whether animal, as the Tyrian purple, vegetable, as indigo, or mineral, as iron; the second to the adjective colours of animal origin, as kermes and cochineal, lac, and Prussian blue; the third to vegetable adjective colours, as weld, quercitron, madder, Brasil wood, and logwood; and the fourth to compound colours of various kinds, and particularly the mixtures which produce black dyes, and inks of all descriptions.

It has been a common opinion, that the general cause of the destruction of colour, by exposure to the air, is the combination of the colouring substance with oxygen; but Dr. Bancroft observes that the nitric acid imparts oxygen much more readily than the oxymuriatic, though it has incomparably less effect on colours, and that the action of either of these acids is no direct test of the effect of exposure to the air. Thus a red dyed with madder, on an aluminous basis, was much more rapidly destroyed by the oxymuriatic acid, than a purple obtained from logwood and tin, though the sun and air would have acted on these colours in a manner totally different. A black dye also, which was little affected by the oxymuriatic acid, was totally destroyed by the nitrous, although this acid had incomparably less effect than the former on a Turkey red. The colouring matter of the buccinum was exposed in its recent state to the sun's rays (p. 151), immersed in oxymuriatic acid; and became purple more rapidly than when simply moistened with water; although afterwards, when placed in the dark, the acid had completely bleached the coloured substance in a few hours. Dr. Bancroft is of opinion that this singular substance, which is found in several testaceous animals, and bas at first the appearance of a limpid mucilage, emits some phosphoric acid together with oxygen, while it acquires its colour, and that this is the cause of the offensive smell, which has always been observed to accompany the change.

The colour of indigo is also dependent on the different degrees of its oxygenization: the recent juice is nearly colourless; the absorption of a small portion of oxygen renders it green, and that of a larger blue; in the latter state it is insoluble in water, and with the assistance of agitation, collects into flocculi, the separation being commonly promoted by the addition of lime water, or some other alkali, as a precipitant. It is found not only in the indigo-ferae, but also in the isatis, or woad, and in some other vegetables: it is capable of distillation or sublimation by a moderate heat, and affords, when burnt, a fine purple smoke. This smoke is noticed by Pliny as observable in an Indian colour, which is thus identified with indigo. In its blue state it is incapable of attaching itself to animal or vegetable fibres; and the process of fermentation in the dyer's vat serves to restore its green colour and its solubility, apparently, as Dr. Bancroft has shown, by the abstraction of oxygen. The materials employed for this purpose are generally a decoction of woad, madder, and bran, to which lime and indigo are added. When the fermentation has been continued a sufficient time, the internal parts of the liquor are green and the surface only blue. Sometimes bran and madder only are used with indigo, a little potash being added to promote the solution. Another mode of deoxygenizing the indigo