The figures in the last column refer to the dry acetylene in the gas, no correction having been made for the heat absorbed by the water vapour present. As will appear in Chapter X., the average of actual determinations of the calorific value of ordinary acetylene is 363 large calories or 1440 B.Th.U. per cubic foot. The temperature of ignition of acetylene has been generally stated to be about 480° C. V. Meyer and Münch in 1893 found that a mixture of acetylene and oxygen ignited between 509° and 515° C. Recent (1909) investigations by H. B. Dixon and H. F. Coward show, however, that the ignition temperature in neat oxygen is between 416° and 440° (mean 428° C.) and in air between 406° and 440°, with a mean of 429° C. The corresponding mean temperature of ignition found by the same investigators for other gases are: hydrogen, 585°; carbon monoxide, moist 664°, dry 692°; ethylene, in oxygen 510°, in air 543°; and methane, in oxygen between 550° and 700°, and in air, between 650° and 750° C. Numerous experiments have been performed to determine the temperature of the acetylene flame. According to an exhaustive research by L. Nichols, when the gas burns in air it attains a maximum temperature of 1900° C. ± 20°, which is 120° higher than the temperature he found by a similar method of observation for the coal-gas flame (fish-tail burner). Le Chatelier had previously assigned to the acetylene flame a temperature between 2100° and 2400°, while Lewes had found for the dark zone 459°, for the luminous zone 1410°, and for the tip 1517° C, Féry and Mahler have also made measurements of the temperatures afforded by acetylene and other fuels, some of their results being quoted below. Féry employed his optical method of estimating the temperature, Mahler a process devised by Mallard and Le Chatelier. Mahler's figures all relate to flames supplied with air at a temperature of 0° C. and a constant pressure of 760 mm. Hydrogen . . . . . . . . . . . 1900 1960 Carbon monoxide . . . . . . . . . -- 2100 Methane . . . . . . . . . . . -- _ 1850 Coal-gas (luminous) . . . . . . . . 1712 | " (atmospheric, with deficient supply of air) . 1812 | 1950 " (atmospheric, with full supply of air) . . 1871 _| Water-gas . . . . . . . . . . -- 2000 Oxy-coal-gas blowpipe . . . . . . . 2200 -- Oxy-hydrogen blowpipe . . . . . . . 2420 -- Acetylene . . . . . . . . . . 2548 2350 Alcohol . . . . . . . . . . . 1705 1700 Alcohol (in Denayrouze Bunsen) . . . . . 1862 -- Alcohol and petrol in equal parts . . . . 2053 -- Crude petroleum (American) . . . . . . -- 2000 Petroleum spirit " . . . . . . . -- 1920 Petroleum oil " . . . . . . . -- 1660