360
on, a similar state of affairs would be ultimately reached in the flame of a carbonaceous gas. But since in the latter case the carbon dioxide does not tend to dissociate completely, but only to lose one atom of oxygen, above the limiting temperature for the formation of carbon dioxide, carbon monoxide is still produced, because there is less dissociating force opposed to its formation. Thus at ordinary temperatures the heat of combustion of acetylene is 315.7 calories; but at temperatures where water vapour and carbon dioxide no longer exist, there is lost to that quantity of 315.7 calories the heat of combustion of hydrogen (69.0) and twice that of carbon monoxide (68.2 x 2 = 136.4); so that above those critical temperatures, the heat of combustion of acetylene is only 315.7 - (69.0 + 136.4) = 110.3. [Footnote: When the heat of combustion of acetylene is quoted as 315.7 calories, it is understood that the water formed is condensed into the liquid state. If the water remains gaseous, as it must do in a flame, the heat of formation is reduced by about 10 calories. This does not affect the above calculation, because the heat of combustion of hydrogen when the water remains gaseous is similarly 10 calories less than 69, _i.e._, 59, as mentioned above in the text. Deleting the heat of liquefaction of water, the calculation referred to becomes 305.7 - (59.0 + l36.4) = 110.3 as before.] This value of 110.3 calories is clearly made up of the heat of formation of acetylene itself, and twice the heat of conversion of carbon into carbon monoxide, _i.e._, for diamond carbon, 58.1 + 26.1 x 2 = 110.3; or for amorphous carbon, 52.1 + 29.1 x 2 = 110.3. From the foregoing considerations, it may be inferred that the acetylene-oxygen blowpipe can be regarded as a device for burning gaseous carbon in oxygen; but were it possible to obtain carbon in the state of gas and so to lead it into a blowpipe, the acetylene apparatus should still be more powerful, because in it the temperature would be raised, not only by the heat of formati