If the gas is made to issue by a circular rim of about twelve inches diameter; it forms a sort of an Argand lamp on a great scale, and it is manifest that a circumference of three feet of flame will heat the air very rapidly, and with such uniformity that we need no longer be exposed to the partial heating occasioned by the strong draft of a large fire. A lamp of this description in the centre of a large room, with a very small fire to secure a gradual renewal of the air would enable us to enjoy the most healthful and agreeable temperature. From trials made on this subject, I am enabled to state, that three Argand’s lamps, consuming five cubic feet of gas per hour, are sufficient to keep a room 10 feet square at a temperature of 55° Fahr. when the air without doors has a temperature of freezing.[25] [25] Mr. DALTON’s method of ascertaining the comparative quantity or effects of heat evolved during the combustion of different inflammable gases, and other substances capable of burning with flame, as stated in his System of Chemistry, vol. I. p. 76, deserves to be recommended to those who are more immediately interested in this subject. The process, which is simple, easy, and accurate, is as follows: Take a bladder of any size, (let us suppose for the sake of illustration, the bladder to hold or to be equal in capacity to 30,000 grains of water,) and having furnished it with a stop-cock and a small jet pipe, fill it with the combustible gas the heating power of which is to be tried. Take also a tinned iron vessel with a concave bottom of the same capacity, pour into it as much water as will make the vessel and water together equal to the above stated bulk of water in the bladder, viz. 30,000 grains. This being done, set fire to the gas at the orifice of the pipe, and bring the point of the flame under the bottom of the tinned vessel, and suffer it to burn there, by squeezing the bladder till the whole of the gas is consumed. The increase of temperature of the water in the tinned vessel being carefully noticed before and after the experiment, gives very accurately the heating power of the given bulk of the inflammable gas. It was thus proved that-- Olefiant gas raises an equal volume of water 14° Carburetted hidrogen, or coal gas 10 Carbonic oxid 4 Hidrogen 5 Spermaceti oil 10 grains burnt in a lamp raised 30,000 grains of water 5 Tallow 5 Wax 5,75 Oil of turpentine 3 Spirit of wine 2