before it comes to perfection; the colours which it affords are however unfortunately fugitive.

The purple obtained from gold, by means of tin, is found to depend on the deoxygenization of the gold by the solution of tin; a similar effect may be obtained by impregnating silk or cotton with glue, eggs, or other animal substances, together with sugar or orpiment, and applying to them the solution of gold. The nitromuriate of platina affords, in combination with a muriatic solution of tin, a fixed colour like that of arterial blood.

'Respecting the antiquity of calico printing, Dr. Bancroft observes, (p. 346,) that Pliny describes the Egyptians as practising a species of topical dying, or calico printing, which, as far as can be discovered from his general terms, appears to have been similar to that which inany ages after, was found to exist in Hindostan, and other parts of India, and was from thence introduced into this and other countries of Europe. He says the Egyptians began by painting or drawing on white cloths, (doubtless linen or cotton,) with certain drugs, which in themselves possessed no colour, but had the property of attracting or absorbing colouring matters. After which these cloths were immersed in a heated dying liquor, and though they were colourless before, and though this dying liquor was of one uniform colour, yet, when taken out of it soon after, they were found to be wonderfully tinged of different colours, according to the different natures of the several drugs which had been applied to their different parts;' and that these colours, so wonderfully produced from a tincture of only one colour, could not be afterwards discharged by washing.'

The art of calico printing has been much improved and simplified in modern times, especially by the mixture of the acetate of lead with the aluminous mordant, forming an acetate of alumine. A still more economical method, lately invented, is to employ the acetic acid in the form of the pyrolignic, obtained by the destructive distillation of wood, and to substitute lime for lead. The acetate of iron is also now generally prepared from the pyrolignic acid. MM .Thenard and Roard found that the acetate of alumine, when exposed to a warm atmosphere, lost some of its acid, leaving an excess of alumine; but alum, tartar, and the salts of tin are attached to the fibres of the cloths impregnated with them in their entire state, and may be recovered by repeated washings, until they are decomposed by the operation of the colouring substances. The method of employing some of these substances may be understood from the following description of the proces

ses.

When pieces of calico have been printed with iron liquor, whether it be applied to those which either have received, or are intended to receive, the aluminous mordant also, they are to be thoroughly dried by a stove heat, and afterwards passed through the mixture of cow dung and warm water,' which is supposed not only to cleanse them

more effectually, but possibly to communicate to them some animal impregnation subservient to the durability of the colours; they are afterwards, in the language of the calico printers, to be streamed, or extended in running water, and beat, to remove all the loose or uncombined particles of the mordant, and thus fit them to be dyed with either madder, sumach, weld, or quercitron bark; these being the principal and almost the only adjective colouring matters so employed by calico printers, and sufficient (excepting the blue from indigo) to produce, with the aluminous and ferruginous mordants, all the various colours seen and admired on printed calico.

Ex. Gr. If pieces of calico, to which these mordants have been ap plied, both separately and mixed, be put into a dying vessel, with water scarcely blood warm, and in which three, four, or five pounds of madder in powder for each piece have been previously mixed, and they be turned as usual, through the liquor by the winch, gradually, but slowly, raising the heat, so that it may only reach the boiling point at the time when the calicoe will have been sufficiently dyed, the several pieces will be found to have imbibed colour in every part. The figures or places to which the unmixed iron liquor was applied will have been dyed black, and those on which the aluminous mordant was printed will be red, of different shades, if the mordant had been used at different degrees of concentration: and, if both mordants were mixed and applied in different proportions, such applications will have produced various shades of purple, violet, chocolate, and lilac colours, whilst the parts, or grounds intended to be ultimately left white, will manifest a considerable brownnish red discolouration; but as the madder colour producing it is not [there] united to the calico, by the affinity or attraction of any intermediate basis, it will not be able, as in other parts, to resist the action of exterior agents, and may therefore (as is usually done) be removed, and the grounds made white by boiling the pieces in water soured by fermented bran, and by afterwards spreading them for some days(according to the season) upon the grass, where, with the well known treatment, the colours dyed upon a basis will become brighter, whilst that without one will completely disappear.

'Calico printed with the same mordants, and dyed with the quercitron bark, (quercus nigra, Linn.) will acquire fixed and bright yellows of different shades, upon the aluminous bases, and various drab colours upon that of iron. A mixture of these bases will produce olive colours. Along with these it is usual to produce black impressions at the same time by previously applying to the calico a mordant composed of iron liquor and galls, by which figures which, without the galls, would only have manifested a dark drab colour, are made black by dying with the quercitron bark, and if the dying be conducted as I shall hereafter direct, the grounds will be so little discoloured that no exposure upon the grass will be required as is necessary with madder and weld, an advantage which has nearly put an end to the use of weld in calico printing."

-p. 377.

The colouring matter of kermes, derived from the coccus ilicis, our author considers as identical with that of cochineal, although

VOL. XI. NO. XXI.

combined with some of the astringent substances derived from the tree. The scarlet afforded by cochineal was unknown in its highest perfection till the year 1630, when the singular power of the oxyd of tin, in exalting its colours, was discovered in Holland: it was soon after communicated to one of the celebrated MM. Gobelins at Paris, and contributed to the perfection of the colours of their tapestries. The nitrate or nitromuriate of tin, commonly used by the dyers, affords a crimson colour, which is converted to scarlet by the tartar employed in the process. Dr. Bancroft has invented an ingenious method of saving this valuable colour, by substituting a yellow dye, in particular the quercitron bark, for the acid substance which changes the colour of the cochineal, and thus forming a compound instead of a simple scarlet. The colour thus obtained is more durable than the common scarlet, but, as it is said, not quite so brilliant by day-light, although somewhat brighter by candle-light. The solution of tin, called spirit by the dyers, is usually made with one pound of aqua fortis, two ounces of sea salt or sal ammoniac, half a pound of water, and two ounces of grained tin, added by degrees. Dr. Bancroft attempted to substitute for it a muriate of tin, but found the corrosive quality of this combination extremely injurious to the cloth: he however succeeded much better with a muriosulfate.

The process employed in dyeing scarlet on wool requires a mixture of all the materials concerned, before their application to the cloth to apply them in succession, as is either indispensable or highly advantageous in many other cases, would here be impracticable: a fact which renders it necessary to be very cautious in all theoretical reasonings respecting the use of mordants. With silk and cotton, the reverse is true, at least with respect to all dyes except the quercitron.

Since the preparation or manufacture of Morocco leather has been established in this country, cochineal is employed to communicate the beautiful colour of that, which is called red Morocco; though in Persia, Armenia, Barbary, and the Greek islands, a similar colour was originally produced by the use of either kermes or lac. As a basis for the colouring matter of cochineal, goat skins, deprived of their hair by lime water, and properly cleansed, are impregnated, on that which was the hairy side, with a saturated solution of alum, applied repeatedly and equally by a sponge, and, after an interval of three or four days, a decoction of cochineal, which has been strained, is applied also by a sponge, to the same side or surface, a little, but not much, more than blood warm, lest it should crisp the leather. This application is repeated from time to time, until a colour sufficiently full and equal has been produced. Afterwards the skins are soaked in bran liquor, and then tanned by a decoction of either galls or sumach, or of both mixed together. I have found that by substituting a diluted muriosulfate of tin, for

the solution of alum, or by employing a mixture of both upon goat skins in a suitable state of preparation, the colour subsequently produced was considerably improved, at least in vivacity.-II. 167.

Dr. Bancroft appears to have bestowed considerable labour and ingenuity on an attempt to obtain the colouring matter of stick lac in a state of purity, and separate from the resin: but it seems to be extremely difficult to exhibit it in an extractive form, without impairing the beauty of the colour. The separation may be part ly effected by employing water not hotter than 190°, which dis solves the colouring matter, and leaves the resin, with some other impurities undissolved; and in this state the colour is as fine as that of cochineal, and somewhat more durable; but it loses its brilliancy in the process of evaporation. The finest parts are also more easily powdered than the rest, and will pass through a sieve while a great portion of the impurities remains behind.

The peculiar colouring matter of Prussian blue, which Dr. Bancroft cannot readily allow to be an acid, as it has usually been de nominated by chemists, affords, with the quercitron bark, a fine green, and as our author first discovered, a good brown with copper. In order to investigate the nature of the green thus obtain ed, he took a piece of cotton which had been printed in stripes with iron liquor and galls, with iron liquor only, with iron liquor and acetate of alumine, and with this acetate only: he dyed it first with quercitron bark, which made the first stripe black, the second dark drab, the third olive, and the fourth yellow: he then took prussiated potass, acidulated with sulfuric acid, and immersing the cotton in it for a minute, he found the colouring matter of the galls and quercitron bark discharged where the basis of iron had been employed: so that the first stripe was become a dark blue, and the rest paler, as they stood in order : when there was less excess of acid, the colouring matter of the galls remained, and that of the bark only was discharged: when the liquor was perfectly neutral, the colour of the quercitron bark was discharged from the ferruginous basis, but not from the aluminous; so that the second stripe, with iron liquor, had become blue, and the third a fine green, while the yellow remained perfect on the fourth, and the part not printed became white, being freed from the discoloration of the bark. In these cases of change of colour, the displacement of one of the substances by the other is sufficiently proved by the state of the liquor, in which the substance displaced is found dissolved.

Among the vegetable adjective colours, weld, the reseda luteoda, holds the first place, as having been the longest in use: besides this, young fustic, the rhus cotinus, sumach, the rhus coriaria, old fustic, the morus tinctoria, and French berries, the rhamnus tinc toria, are the most generally known of the yellow dyes. But all

these appear to have been in some measure superseded by Dr. Bancroft's discovery of the utility of the quercitron bark: a discovery of which the advantages were secured to him by act of parliament for a term of years, although he failed in his application for an extension of that term in 1798, notwithstanding the advantage which the public had derived from the singularly liberal manner in which he had conducted the monopoly. In less than twelve months after that time, the bark rose to three times the price at which he had constantly supplied it, and at which he would have been bound to supply it for another term of seven years, if the bill had been passed. He has presented us with an immense variety of experiments and of practical directions relating to the use of this substance, and his communications must be of great value to the intelligent manufacturer.

We cannot altogether agree with the author in the decided preference which he appears to entertain for the process of bleaching by the oxymuriatic acid, (II. 176.) which seems at present to have become almost universal, not a little to the advantage of manufacturers and tailors, and to the prejudice of the public in general. Sir Humphry Davy has found that, even when neutralized by an excess of lime, the muriatic acid, formed during the process of bleaching, is injurious to the fibres of the cloth; (Elem. p. 242.) and whatever precautions it may be possible to employ for avoiding this evil, we are persuaded, from continued experience, that they are not commonly adopted by manufacturers, either in bleaching cotton or paper.

Madder, the rubia tinctorum, is a very well known and important vegetable, much employed for dyeing red with an aluminous basis, on common woollen cloths. Its effect, in giving a red colour to the bones of animals that feed on it, was first observed by Lemnius in the 16th century, and is now well known to physiologists. Madder does not appear to be capable of affording a prosubstantive colour; and it is absolutely necessary that the basis should be separately applied to the linen or cotton which is to be dyed with it. Galls are commonly employed by practical dyers as a preparation for the aluminous impregnation, in order to promote the attachment of the alum to the cloth; but they add nothing to the durability of the colour.

The rubia peregrina, or Smyrna madder, is principally used in the complicated process for dyeing the Turkey red on cotton, with the assistance of oil, alum, galls, and some blood, which seems to brighten the colour, besides that of the substances which have passed through the alimentary canal of the sheep, carrying with them some of the gastric fluids, and which, in Dr. Bancroft's opi