This section is from the book "The New Cookery", by Lenna Frances Cooper. Also available from Amazon: The New Cookery.
The gas flame consists of three distinct portions. The inner portion which is almost invisible consists of the un-burned gas which comes in a constant stream, due to the pressure of the gas system. Surrounding this inner portion is a luminous section which consists of carbon particles heated to the point of luminosity by the ignited hydrogen. The outer portion of the flame forms an almost invisible sheath consisting of the burned particles of carbon and the hydrogen. The inner or dark portion gives absolutely no heat. The luminous portion supplies some heat, but the greater amount of heat is supplied by the outer, the almost invisible section. When more gas is supplied than can be oxidized, the carbon particles of the gas are only partially oxidized, and hence produce a yellow flame rather than a blue one. This is due to too great a pressure or an insufficient amount of air which is necessary for the combustion. The gas flame must have oxygen as well as any other flame. This is admitted through a small opening called the mixer, which is placed a short distance from the flame. Indeed, if a sufficient amount of oxygen is admitted through the mixer, it is possible to oxidize all of the carbon particles so that the luminous portion is omitted entirely. This then produces the blue flame, so much desired for heating purposes.
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