We shall now proceed to notice one or two lamps adapted to the burning of concrete oils and solid unctuous substances, as fat, tallow, butter of cacao. For the purpose of illumination these substances are on a par with oil, affording an equally brilliant light and at a much less cost; but in order to burn them in a lamp it is requisite previously to render them fluid, and to maintain them in that state so long as the lamp is in use. Various arrangements are employed for this purpose, but the principle is the same in all ; viz. to convey a portion of the heat arising from the flame of the lamp to the combustible matter, by means of some good conductor, as an iron or copper tube or wire inserted in the combustible mass, and coming in contact or nearly so with the flame. A very simple lamp of this description is exhibited in the annexed cut ; a is the fat rendered fluid, lying in the body of the lamp ; (the cover of the lamp being removed to show the interior ;) c is a small tube to convey air into the middle of the flame (to perfect the combustion, on the principle of the Argand burner); this tube opens at the lower end into the large tube b, as shown by dots ; a small perforation is also made at d, to allow the air to flow freely into the tube c, when the lamp is fixed in the socket of a candlestick. On each side of the air tube a short piece of copper pipe is fixed by hard solder, for holding the cotton wicks ; these tubes (which ought to be longer) get intensely hot, and, by the conducting power of the metal, the heat is trans mitted to the fat, which, melting in consequence, flows up the wick like fine oil, but infinitely preferable, on account of its diffusing no unpleasant smell during the combustion.
The Hon. E. Cochrane obtained a patent for a lamp, named by him the " Patent Dissolvent Lamp," which, like the one ,just described, is calculated to burn tallow and concrete oils. These lamps, which have been very extensively manufactured in a variety of elegant forms by Mr. Jose, of Regent-street, afford an extremely brilliant light at a very small cost. The engraving and descrip tion in the following page will explain the principle of these lamps. a a are two solid bent metal rods that conduct the heat received from the flame of the lamp to the tallow contained in the reservoir b ; the ends of these conductors are there fore made to descend to the bottom of the reservoir ; c c are two apertures (with covers that screw on) made in the supply pipe, for the purpose of pouring in a small quantity of melted tallow upon lighting the lamp, after which the heat from the combustion being con ducted into the reservoir, the supply of fluid tallow is uniformly kept up until it is all consumed.
We extract from a printed circular of the manufacturer the following observations on the advantages at tending the use of these lamps :— " To those acquainted with the superior combustible properties of tallow and cocoa-nut oil, it is un necessary to say more than that these lamps effectually melt and burn both, and that the price of the latter, at the manufactory, is 2s. 6d.
per gallon ; but to others, to whom their good qualities are less known, it is necessary to state, that from the comparatively small portion of oxygen necessary to complete their combustion, the total absence of smoke and smell is insured, and the brilliancy of the flame is such as no lamp ever before produced, and nothing but the best gas-light can equal. To families who kill their own meat, innkeepers, proprietors of cook-shops, &c. &c. a two-fold ad vantage will be found in the use of these lamps, as it is not merely tallow that they bum, but grease of every description, such as dripping, pot skimmings, &c. &c., a pound of which, value about 3d., will continue to burn for full twelve hours in a common-sized dis solvent Argand burner, to yield light equal to eight candles, being no more than a farthing an hour." The following ingenious plan for a lamp to burn under water appeared in the Register of Arts, in connexion with a diving apparatus, for examining the breaches in the Thames Tunnel, and might very often be of service in the diving bell, when the water, as is frequently the case, is so disturbed that sufficient light is not refracted through it at great depths to permit accurate examination. A spherical or cylindrical vessel is to be provided, similar to the vessels containing the portable gas for burning; into this a few atmospheres of pure oxygen are to be condensed by a syringe, through a valve at the bottom : a short jet tube is then to be screwed into the top of the vessel. A lantern, with a strong and powerful reflector, must be attached to the upper part of the vessel containing the condensed oxygen, permitting the jet tube to enter the lantern. The top of the lantern must be provided with a screw eap; a piece of wax candle may be advantageously employed for the light. It is needless to say that the apparatus mast be air and water tight. Immediately before use, pour into the lamp a solution of caustic alkali,potash or soda, and screw on the cap; then turn the cock gently to admit a sufficient quantity of oxygen through the jet tube, to support the combustion of the candle. The products of the combustion will be carbonic acid and water; the former will be absorbed by the alkaline solution as it is formed, and the latter will be condensed by the sides of the lantern ; the oxygen admitted will unite with the nitrogen of the air of the lantern (which is not consumed), and will form a supply of ordinary atmospheric air.
The annexed figure represents a lamp as constructed by the inventor, which, upon trial, was found to answer very well.