Candles are made from spermaceti, the process being very similar to that employed in making them of tallow; they are also made of various mixtures of tallow, spermaceti, and wax; certain proportions of which constitute the article termed composition candles. The meritorious investigations of M. Chevreul, concerning the true nature of fatty substances, which were published a few years ago in the Annates de Chimie, appear to have opened a wide and diversified field for the operations of the manufacturer and the experimentalist. By dissolving fat in a large quantity of alcohol, and observing the manner in which its different portions were acted upon by this substance, and again separated from it, M. Chevreul found that fat is composed of an oily substance, which remains fluid at the ordinary temperature of the atmosphere, and of another fatty substance which is much less fusible. Hence it follows that fat is not to be regarded as a simple principle, but as a combination of the above two principles, which may be separated without alteration.

To the former of these substances, which melts at 450° Fahr., and has very much the appearance and properties of vegetable oil, M. Chevreul gave the name of elain, and to the latter, which melts at 100°, he gave the name of stearin; this is separated from the former by crystallization in the form of small silky needles, while the elain is obtained by evaporating the spirit. M. Bracconet subsequently employed a simpler process to obtain the elain and stearin; he squeezed the tallow between folds of porous paper, which absorbed the elain, leaving the stearin between; the paper being afterwards soaked in water, yielded up its oily impregnation. The principle of M. Brac-conet's process is now extensively applied by manufacturers, who employ powerful presses to squeeze the fluid oil from the tallow In the year 1825, M. Gay Lussac, the celebrated French chemist, also took out a patent for this country for the employment of the stearin (termed likewise margaric acid from its chemical properties) in the manufacture of candles; the patent likewise extending to a new mechanical construction of candles. Of the several processes that may be employed for obtaining the margaric acid for this purpose, two are particularly descriptive in the specification, namely, saponification and distillation.

The first is to be effected by incorporating any of the alkalies with the fat, as is done in the making of soap, and then decomposing the soapy fluid by an acid that has the greatest affinity to the peculiar alkali employed. It is recommended that the decomposition be effected in a large quantity of water, heated by steam, which should be kept well stirred. Being afterwards allowed to rest, the products will float on the surface in a condensed and solid form. If the tallow or fat, thus purified from the matters soluble in water, should still contain any of the salts employed in the previous process, it is to be washed by additions of fresh quantities of warm water, until they are perfectly discharged. This being done, and the mass of fat having become solid by cooling, it is to be subjected to the action of a powerful press, similar to those used for expressing oil from seeds, when the fluid oleic acid (or elain) will run off, leaving the mar garic acid in the press, from which product the candles are to be made. The distilling process is conducted by exposing the fat, in an ordinary still, to the heat of a furnace.

Steam is also to be introduced into the still to facilitate the operation, and to carry over those products which are soluble in it, through the worm or condenser, into a receiver. Care must be taken in regulating the heat of the furnace, to prevent discolouring the materials in the still The fat thus prepared is to be purified by washing, and then subjected to pressure as in the previously described process. For the more perfect purification of the fat, both the foregoing operations of saponification and distillation may be combined, and the residue after subjected to pressure. The margaric acid may also be bleached by exposure to the air and sun the same as in the bleaching of wax; the oleic acid, or fluid oil, may also be whitened by similar means, and be applied generally to the same purposes as the vegetable oils. The form of M. Gay Lussac's candles is that of hollow cylinders, through which a stream of air passes to the wick (on the principle of the argand burner in lamps) for the purpose of producing a perfect and vivid combustion of the tallow.

He directs that the wick be formed of cotton yarn twisted rather more closely than usual; this yarn is to be wound spirally round a metallic rod or thick wire, in the same manner as wire is sometimes coiled round the large strings of musical instruments. These rods, covered as described, are to be inserted into the moulds used for making candles; and when the candles have been cast, and the tallow become hard, the wires are to be withdrawn, leaving the wicks behind in the candles with a perforation, or air passage, equal to the size of the rods, throughout their whole length. We have thought it proper to introduce this account of M. Gay Lussac's specification of his patent, because it affords clear and judicious instructions in conducting similar operations. The pro-cesses possess scarcely any originality in the mode of procedure; and as regards the invention of the candle itself, the French chemist is just twenty years behind two of our own countrymen, namely, Messrs. Desormeaux and Hutchings, who took out a patent for the identical contrivance in the year 1805. It is perhaps worthy of notice here, that this invention affords a very remarkable proof that many individuals may, without communication or knowledge of each others' ideas, invent precisely the same thing.

The writer of this article, about ten years ago, spontaneously thought of the same contrivance, and made a candle of the kind, which is represented in the annexed cut. The dotted lines at a mark out the central aperture for the air; and the wick, which is bedded in the middle of the thickness of the hollow cylinder of tallow, is a common argand wick. This candle, although not fabricated in a workmanlike manner, gave good indications of success under proper management. Upon mentioning the project to some friends, we learned to our surprise that several other persons had entertained the same propositions, each person imagining himself to be the sole inventor. In like manner we were informed by the before-mentioned gentleman, Mr. Desormeaux, that he had patented the invention at the time 6tated; that a large manufactory was commenced for the purpose of making the article, with every probability of success; and that the reason why the manufacture of them was not carried forward, had no reference to the practicability of the scheme. Seeing that the subject has been taken up by scientific as well as practical men, we are confirmed in our opinion that important results may yet flow from prosecuting the plan, if undertaken by some intelligent person.