For chemical operations, many forms of lamp are used. The ordinary glass SPIRIT-LAMP, fitted with a ground-glass cap, is quite indispensable for minor experiments. (See engr. 1.)
Stoneware wick-holders are preferable to those of brass, which become greatly heated, and endanger the splitting of the glass. “An effective spirit-lamp may at any time be constructed out of a vial having a glass tube passing through the cork, a cover being formed from a test-tube inverted over the wick, and fitting with moderate tightness on the superior extremity of the cork” (Greville Williams). Alcohol or wood spirit is the fuel used.
The Argand lamp, when intended as a source of heat for chemical purposes, is so modified as to adapt it to burn either oil, spirit of wine, or wood-spirit, and the combustion is greatly aided by the chimney, which in this case is made of copper. (See engr. 2 and 3.) The lamp itself is also made of metal, and furnished with ground caps to the wick-holder and aperture by which the spirit is introduced, in order to prevent loss of spirit by evaporation when the lamp is not in use. When in use this aperture must always be left open, otherwise an accident is sure to happen, as the heat expands the air in the lamp, and the spirit is forcibly expelled.
In those situations in which coal-gas is cheap, it may be used with great economy and advantage as a source of heat in most chemical operations. Retorts, flasks, capsules, and other vessels, can be thus exposed to an easily regulated and constant temperature for many successive hours. Small platinum crucibles may be ignited to redness by placing them over the flame on a little wire triangle. Of the various gas-lamps now used in the laboratory, the first and most simple consists of a common Argand gas-burner fixed on a
heavy and low foot, and connected with a flexible gas-tube of caoutchouc or other material. (See engr. 4.) With this arrangement it is possible to obtain any degree of heat, from that of the smallest blue flame to that which is sufficient to raise a moderately large platinum crucible to dull redness. When gas mixed with a certain proportion of air is burnt, a pale blue flame, free from smoke, and possessing great heating power, is obtained. A lamp for burning the mixture may easily be made by fitting a close cover of fine wire gauze over the top of the chimney of the last-mentioned contrivance. The gas is turned on, and after a few minutes ignited above the wire gauze. (See page 946). The ingenious and useful burners of Bunsen and Griffin are so constructed that gas and air mixed in any proportions, or gas alone, may be burnt at pleasure. Bunsen’s is a most efficient and convenient form of burner. (See illustration on next page.) It consists of a gas jet, surrounded by a metal tube, about 6 to 9 inches high and about 1⁄2 inch in diameter; having at the bottom four large holes. On the admission of air, when the gas is turned on, the air rushes in by these orifices, and mingling with the gas, the mixture ascends to the top of the tube and is there ignited, giving rise to a flame of great heat, but without luminosity, owing to the simultaneous combustion of the carbon and the hydrogen. The burner, however, is so contrived that by shutting off the supply of air entirely, or limiting it, the flame may be made more or less luminous at pleasure. To distribute the flame, a rosette burner is placed on the top of the tube.
An improved variety of this burner has been designed by Bunsen, and is figured below.
Fig. 1.
