12 arbonate of lime, or by cementation r, in a peculiar kind of furnace con- s of utensils, &c. in cast-iron (called also acquire some valuable informachemistry; as it will teach them how inds of metals; how to apportion the Icareous matter; and how to reduce they often receive in exchange; many are annually sent away as ballast for knowledge which would enable them 1 saleable iron. COTTON, and the CALICO manufactures eat importance to these kingdoms. hese sources of national wealth, the be paid to the beauty, the variety, eir several colours. Now of all the endent upon chemistry than those of NTING. Every process is chemical; imparted but in consequence of the tween the cloth and the dye, or the ch is employed as a bond of union then evident how valuable a cheto that youth who is designed for d how necessary is that portion of hable him in a scientific manner to rials, and to determine the kind y for each process. After all, his if he do not take into the acry, the changes which take place in oxygen; a knowledge of which, es of oxidizement which the seires no small share of chemical absolutely necessary, to enable calico-printer to produce in all cases, permanent colours of the shade, which he intends. Moreover, these artists must be indebted to chemistry for any valuable knowledge which they may acquire of the nature of the articles they use in their several processes; not to say that they are wholly dependent upon this science for the artificial production of their most valuable mordants, and for some of their most beautiful and brilliant colours.* The art of BLEACHING, which is so intimately connected with calico-printing, has also received such improvement from the science of chemistry, that no man is now capable of conducting it to the best advantage, without a knowledge of the principles on which the present practice is established. The manufactures of EARTHEN-WARE and PORCELAIN, which were so much improved and extended by the ingenious and industrious Wedgwood, and which are become by his means a source of national wealth, and give employment to * An instance or two will render this evident. Formerly a calico-printer required many weeks to produce a printed cotton with some colours, such as an olive ground and yellow figures; a scarlet pattern on a black ground; or a brown ground with orange figures-but, by means of chemical preparations, the whole of this work may now be done in a few days; patterns, more delicate than ever, may be produced; and all with a degree of certainty of which former manufacturers had no idea; the system being now entirely altered. According to the former practice, the mordant was first applied to those parts of the cloth that were intended to be olive, brown, or black; it was then necessary for the piece to remain some time before it could be dyed, and afterwards to be exposed in a bleaching-ground a sufficient time to clear those places from the colouring matter of the dye which had not been acted upon by the mordant: a different mordant was then applied by the pencil; and it was necessary to pass the whole piece through the dyeing-copper a second time, in order to give the desired colour to those particular parts and finish the pattern. Now, all these effects are produced by dyeing the cloth a self colour in the first instance, and afterwards merely printing the pattern with a chemical preparation, which discharges a part of the original dye and leaves a new colour in its stead. Thus a brown may be changed in an instant to an orange; a dark olive to a yellow; or a black to a bright scarlet. In consequence of similar improvements, rich chintz patterns, which formerly required two years or more to be completed, are now commonly finished in a few weeks. thousands of the community, are dependent upon chemistry for the successful management of all their branches, from the mixture of the materials which form the body of the ware, to the production of those brilliant colours which give a value to the manufactures by their permanency and beauty. Mr. Wedgwood was so sensible of the importance of chemistry to these arts, that he not only applied to the study of the science himself, but, upon the death of the celebrated Dr. Lewis (author of the Commercium Philosophico-Technicum,) actually engaged his assistant a Mr. Chisolme, to experimentalize with him, and to devote his whole attention to the improvement of the manufacture by the application of his chemical knowledge, of which perhaps few men in the kingdom at that time had a larger share. A faint idea of the advantages which he derived from these sources may be conceived from the following circumstance :-Dr. Bancroft, in his "Philosophy of Permanent Colours," when treating on iron, says, "I remember having been told by Mr. Wedgwood, that nearly all the fine diversified colours applied to his pottery were produced only by the oxides of this single metal." This one fact is sufficient to show with what assiduous application he must have studied chemical science, and how insufficient every attempt to bring his manufacture to the perfection which it has now attained, would have been, without this attention. The sister art, that of making GLASS, is also entirely chemical, consisting in the fusion of siliceous earth with alkali and the oxides of lead. In this trade, as well as in many others, the chemical manufacturer, and the man of enlightened experience, will have many advantages. He will not only know how to analyse his alkalies and to ascertain their exact value before he purchases, but will be enabled on chemical principles to ascertain the exact quantity necessary for any fixed portion of silex, which to those who are ignorant of our science must always be a matter of uncertainty, and must repeatedly subject them to losses and disappointment. The TANNING OF HIDES is a process which was formerly earried on by persons who merely followed a routine of operations, to which they had been accustomed, without knowing the real cause of any of the changes produced. It has now, however, been well ascertained, that the whole art consists in impregnating the animal matter with that peculiar principle taken from the vegetable kingdom called tan, (or tannin,) the effect of which may be explained entirely on chemical principles. It is also now known that many substances, besides oak bark, contain tan; and to chemistry we are indebted for the means of discovering with accuracy the quantity of tan which the several astringent vegetables contain. Besides, this principle having been formed artificially by a modern chemist, it is not improbable that, whenever these manufactures pay a proper attention to the science we recommend, they may be able to direct us how to prepare for them, in our laboratories, the article in question, so as entirely to supersede the use of oak bark. This would be an event of great national importance, as the demand at present is so great, that it is not only imported from the continent, but trees, it is well known, have been actually cut down on purpose for the bark. Should the chemical tanner not be fortunate enough to make a discovery of the kind just mentioned, he will at least be able to analyse the substances now in use, and to appreciate their relative value; a matter of no small moment to a man who operates upon a large scale. Chemistry will enable him also to combine the tanning principle with the skins, so as to form leather the most impervious to moisture; and to give the hides the greatest increase of weight in the least possible time: -and these are the main secrets on which the profit of the trade chiefly depends. The manufacturers of MOROCCO LEATHER, an article entirely new in the productions of this country, have the utmost reason to regret the want of chemical knowledge. Till within these few years, the consumers of morocco depended entirely on a foreign supply, many fruitless attempts having been made to prepare the article in this country. Later trials, with various chemical mordants, have, however, so far succeeded, that several manufactories have been established in the metropolis, where the most beautiful moroccos are now prepared at prices which have superseded the necessity of all foreign importation. Notwithstanding this, some colours are still produced by these manufacturers in a tedious and expensive way :-a series of well-conducted and appropriate chemical experiments would no doubt direct them to prepare the same colours, with greater certainty, and by a more economical process. The manufacture of SOAP, an art of considerable importance, and which materially aids the revenue of the country, has in general been conducted, like many of the foregoing, without any regard to system: and yet, perhaps, there is no manufacture which can be benefited in such various ways by chemistry as this. To those who are designed for this trade I have no hesitation in recommending the study of the science as a matter of the first importance. Many thousands per annum, now lost to the community, would be saved, if the trade were in general carried on upon scientific principles. Make a soap-boiler a good chemist, and you teach him how to analyse barilla, kelp, potass, &c. so as to ascertain the proportion of alkali in each,— the only sure guide to purchasing with advantage and profit, which with the common manufacturer is mere chance. When these articles are at an exorbitant price, he will have recourse to various residuums, which he will decompose by chemical means, and make use of as substitutes. He will learn, in choosing his tallows, how to avoid those which contain a large portion of sebacic acid, which require much more barilla than good tallow, and yet produce less soap. He will know how to oxidize the common oils and oil dregs, so as to give them consistence, and render them good substitutes for tallow,-and how to apportion his lime so as to make his alkali perfectly caustic, without using an unnecessary quantity of that article. He will be aware of the advantage to be derived from oxidizing the soap while boiling. A knowledge of chemical affinities will teach him how, at a cheap rate, to make as good and as firm soap with potass, as with the mineral alkali; and how to take up the heterogeneous salts, so as to give the alkali full opportunity of forming a chemical combination with the oils, tallows, &c. And lastly, he will know how to make use of the waste lyes so as to decompose the salts which they contain, and convert them to good and serviceable alkali fit for future operations. Manufacturers of soap, in general, avail themselves of none of these advantages. The manufacture of CANDLES, which is often connected with the foregoing, though it is of comparatively small importance, may yet derive advantages from chemistry, which would repay the study. Foreign tallows, which frequently contain a large portion of acid, rendering them inferior to the English, may be purified at the most insignificant ex |