1914] on Surface Combustion 47 



and the diaphragm constitatmg a convenient feeding-chamber for 

 the gaseous mixture. Such a mixture may be obtained in either of 

 two ways, namely (1) by means of suitable connections through a 

 Y-piece \Yith separate supplies of low pressure gas and air (2 or :-> 

 inches W.G. is sufficient), or (2) by means of an " injector" arrange- 

 ment connected with a supply of gas at a pressure of 1 to 2 lb. per 

 sq. inch ; the gas in this case draws in its own air from the atmo- 

 sphere in sufficient quantity for complete combustion, the proportions 

 of gas and air being easily regulated by a simple device. 



We will now start up a diaphragm. Gas is first of all turned on 

 and ignited as it issues at the surface ; air is then gradually added 

 until a fully aerated mixture is obtained. The flame soon becomes 

 non-luminous, and diminishes in size ; a moment later, it retreats on 

 to the surface of the diaphragm, which at once assumes a bluish 

 appearance ; soon, however, the granules at the surface attain an 

 incipient red heat, producing a curious mottled effect ; finally, the 

 whole of the surface layer of granules becomes red-bot, and an accele- 

 rated " surface combustion " comes into play. All signs of flame 

 disappear, and there remains an intensely glowing surface throwing 

 out a genial radiant heat which can be steadily maintained for as long 

 as required. 



Whilst the diaphragm is in operation before you, I may point out 

 some of the more striking features of the phenomenon which it 

 presents. Firstly, the actual combustion is confined within a very thin 

 layer — \ to \ inch only — immediately below the surface, and no heat 

 is developed in any other part of the apparatus. Kindly observe 

 that whilst the front of the diaphragm is intensely hot, the back of 

 the apparatus is so cold that I can lay my hand on it. Secondly, 

 the combustion of the gas, although confined within such narrow 

 limits, is perfect, for when once the relative proportions of gas and 

 air have been properly adjusted, no trace of unburnt gas "escapes 

 from the surface. Thirdly, the temperature at the surface of the 

 diaphragm can be instantly varied at will by merely altering the rate 

 of feeding of the gaseous mixture ; there is practically no lag in the 

 temperature response, a circumstance of great importance in opera- 

 tions where a fine regulation of heat is required. Fourthly, a plane 

 diaphragm such as this may be used in any position, i.e. at any 

 desired angle between the horizontal and vertical planes. Fifthly, 

 the diaphragm method is amenable to a variety of coml^ustible gases 

 — coal or coke oven gas (either undiluted or admixed with water 

 gas), natural gas, petrol-air gas, carburreted water gas are all well 

 suited in cases where unimpeded radiation is required. Finally, the 

 mcandescence in no way depends upon the external atmosphere. 

 When once the diaphragm has become incandescent, and the propor- 

 tions of air and gas supplied in the mixing chamber at the back have 

 been properly adjusted, the surface will maintain its incandescence 

 unimi3aired, even in an atmosphere of carbon dioxide. 



