The great power of a gas-flame does not appear when we try small quantities of it, and allow it to burn quietly, because the air is not intimately brought into contact with it, but acts only on the outside; and the quantity of burning matter in the surface of a small flame is too minute to produce much effect.
But when the flame is produced in large quantity and is freely brought forward into contact and agitated with air, its power to heat bodies is immensely increased. It is therefore peculiarly proper for heating large quantities of matter to a violent degree, especially if the contact of solid fuel with such matter is inconvenient.
As the gas-flame may be made to assume any shape and intensity, and as there is nothing to spill, it may be exhibited under such variety of forms and designs, as cannot fail to give rise to the most tasteful ornamental illumination.
PLATES III. IV. and V. exhibit such designs of different kinds of gas-lamps, chandeliers, lustres, candelabras, &c. as are already in use in this Metropolis.
PLATE III. fig. 1, represents a _Rod Lamp_. The gas passes through the rod _a_, to the Argand burner, which is surrounded by a cylindrical chimney, _c_, swelling out at the lower extremity. The construction of the Argand burner we have mentioned already, _p._ 78.
In all the gas-light burners, constructed on Argand’s plan, care should be taken that the flame be in contact with the air on all sides, and that the current of air be directed towards the upper extremity of the flame. This may be effected by causing a current of air to rise up perpendicular from the bottom of the chimney glass, and to pass out again through the contracted part, or upper extremity of the chimney; but no other current of air should ever be permitted to come near the gas-flame, or enter the glass chimney which covers or defends the light; for if more air be permitted to mix with the flame than is sufficient for the compleat combustion of the coal-gas, it necessarily diminishes the heat, and consequently reduces the quantity of light.
Fig. 2. _A Rod Gas Lamp, with branches._ The gas passes through the hollow rod, _a_, and part of the hollow branch, _b_, to the burner of the lamp. The cylindrical shaped glass, _c_, exhibited in this figure, is not so well adapted for the compleat combustion of coal-gas, as the belly-shaped chimney, _c_, represented in fig. 1, 3, 5, 6, because the ascending current of fresh air is not turned out of its perpendicular course, and thrown immediately in a concentrated state, into the upper part of the flame where the combustion of the gas is less perfect. The exterior current of air which enters at the bottom into the lamp, rises merely with a velocity proportioned to the length of the cylinder, and to the rarefaction of the air in the same, but without being propelled to the apex of the flame, as it should do, and is made to do, in the bellied glass adapted to the lamp, fig. 1.