The Argand burner with double chimney, shown in Fig. 7, is also an economical one for a small consumption of gas. The air admitted to both the inside and the outside is raised to a high temperature by passing along the spirals of a second and transparent chimney, C¹, which surrounds the cylindrical glass, C. The gas itself is heated by passing through this hot chamber before reaching the outlet orifices; so that the mixture of air and gas takes place under the most favorable conditions for their perfect combustion.

The burner is an ordinary Argand, which may terminate below in a small chamber for the gas and air to mingle. But this is not necessary; and the usual arrangement for mixing the air and gas may be adopted. The outer air enters at the top of the central chimney, C and passes into the annular space between the two glasses; then descends by the two spiral passages, which surround the cylindrical glass and terminate in a portion hermetically sealed by a brass plate attached to the supply-pipe. All the parts of the burner are thus surrounded by a highly-heated atmosphere, especially at the bottom of the double chimney; and it will be readily understood that, if the branches which lead the gas to the burner are constructed of a highly conductive metal, the gas will become heated in its turn by passing through passages raised to a high temperature.

The elements are therefore dissociated or separated before their final combination; thereby raising the calorific and luminous effect to the highest possible degree. Such a burner can, of course, be made as small as may be required; thus lending itself admirably to the subdivision of illumination. The only precaution required is to properly proportion the sectional area of the hot-air passages to the radiant surface of the flame, so that the heat does not become too intense at the lower portion of the burner.

Fig. 8 shows a double flame burner on the principle of Mr. Heron's, but with admission of hot air into the angle formed by the flames. As exemplified by Mr. Heron, if two equal batswing burners separately give a certain amount of light, on the two flames being brought into contact, so as to form a single flame, the luminosity is considerably increased, owing to the condensation of heat which results from their meeting. The two incandescent sheets are, as it were, forced into one another, so as to be combined.

FIG. 8.

The high-power burners of Douglass, Coze, Mallet, and others were designed on this principle; but its application to uninclosed burners was not very satisfactory, because the great cooling down of the inner surface of the flames by the strong draught of cold air impaired their illuminating power. To counteract this difficulty, M. Somzee adopts a heating burner, A, which he places between the two batswing burners, B, so that the products of combustion rise in the angle made by the two lighting flames, as shown; thus greatly increasing their luminosity while maintaining a low consumption of gas.

M. Somzee also raises the illuminating power of an ordinary flat-flame burner by causing an obscure effluvium to traverse the dark portion of the flame. The effect of this is to increase the activity of decomposition in this portion, so that the particles of carbon are the more readily set free, and remain longer in suspension in the luminous zone. The obscure effluvium may be determined between two points by the electric current, or be caused by the heating of an imperfect conductor by the current; or, again, it may result from a metal conductor heated by the reactions produced in the middle of the flame, by separating the cone of matter in ignition. The effect may be compared with that obtained by the concentration of two sheets of flame; but in this case the sheets are formed by the constituent parts of one and the same flame, whence results a more complete utilization of the elements composing it. This system is, in fact, a simplification of the arrangement adopted in the double-flame burner seen in Fig. 8.

Fig. 9 shows a reflecting and regenerative burner with double glass. The crown, made of metal polished on both sides, has a circular groove, G, for receiving the end of the central chimney, C, and presenting an annular aperture by which the products of combustion enter. The second glass, C¹, is fastened to the collar of the burner carrier, and does not come into contact with the metal crown; so as to allow the air to enter from outside for supplying the burner. The gas enters by the pipe, T, provided with a cock. This pipe is continued to the top of the apparatus, and there spreads out into the form of a dome; thus dividing into two compartments the trunconic chamber, S¹ S², whence the hot gas returns to the body of the burner, B.

FIG 9.

On the burner being lighted from below, the products of combustion rise in the inner chimney, and enter the heater, which they traverse through its entire extent, while impinging against the outside of the gas reservoir, to which they give up a large portion of their heat. They then pass by the passage, D, into the atmosphere or into a chimney. The air necessary for combustion enters at the top of the outer globe, and becomes highly heated in its passage through the space comprised between the two glasses of the burner. In this way it reaches the burner, and forms an intimate mixture with the small jets of gas which compose the flame. The gas, on leaving the supply-pipe, T, fills one of the compartments, S¹ S², of the heater, and then returns by the second compartment, and again descends by the casing of the supply-pipe, having its temperature still further raised by contact with the internal radiation of the flame.

Under these conditions, all the parts of the burner are supplied by heated air, and the combustion becomes very active; thus increasing the intensity of the flame, and consequently that of the light afforded, while at the same time effecting a saving of 50 per cent. of gas. This burner may be made of any size, and for consumptions not exceeding that of an ordinary Argand. In fact, the gas is consumed at a low pressure, escaping with no greater force than that due to the heat of the products of combustion. It is sufficiently expanded on coming into contact with the current of hot air, the activity of which is regulated by the height of the apparatus, that is to say, by that of its two chimneys. The mixture is made in such proportion as to obtain from the gas and air as great a degree of luminosity as possible. The high temperature of the gas, and the independent means of heating the air and gas, constitute the essential principles of this burner. - Journal of Gas Lighting.