642 ANNUAL REPOKT SMITHSONIAN INSTITUTION, 1913. 



high temperatures is possible without the aid of elaborate '' regenera- 

 tive '■ devices; and (4) by reason of the large amount of radiant energy 

 developed, transmission of heat from the seat of combustion to the 

 object to be heated is very rapid. These advantages are so uniquely 

 combined in the new system that the resultant heating-effect is, for 

 many important purposes, not only preeminently economical, but also 

 easy of control. 



II. DIAPHRAGM-HEATING AND ITS APPLICATIONS. 



In this process the homogeneous mixture of gas and air is allowed 

 to flow under slight pressure from a suitable feeding chamber, 

 through a porous diaphragm of refractory material, and to burn 

 without flame at the surface of exit, which is thereby maintained in 

 a state of red-liot incandescence. The diaphragm is composed of 

 granules of fire brick bound together into a coherent block by suita- 

 ble means. Its porosity is graded to suit the particular kind of gas 

 for which it is to be used; but for undiluted coal gas, or coal gas 

 containing only a small proportion of water gas, a diaphragm so 

 porous that the gaseous mixture will readily flow through it at a 

 pressure of one-eighth inch water gauge is employed. It is mounted 

 in a suitable casing ; the space inclosed between the back of the casing 

 and the diaphragm constituting a convenient feeding chamber for 

 the gaseous mixture, which is introduced at the back. Such a mix- 

 ture may be obtained in either of two ways; namely, (1) by means 

 of suitable connections through a Y-piece with separate supplies of 

 low-pressure gas and air (2 or 3 inches water gauge only is sufficient) ; 

 or (2) by means of an injector arrangement connected with a supply 

 of gas at 2 pounds per square inch pressure. In this case the gas 

 draws its own air from the atmosphere in sufficient quantity for com- 

 plete combustion; the proportions of gas and air being easily regu- 

 lated by a simple device. 



To start up a diaphragm, gas is first of all turned on and ignited 

 as it issues at the surface ; air is then added gradually until a fairly 

 aerated mixture is obtained. The flame soon becomes nonluminous 

 and diminishes in size; a moment later, it retreats 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; and, finally, the whole of the 

 surface-layer of granules becomes red hot and an accelerated •' flame- 

 less combustion " comes into play. All signs of flame disappear, and 

 there remains an intensely glowing surface — a veritable wall of fire 

 but without flame — throwing out a radiant heat which can steadily 

 be maintained as long as required. 



The actual combustion in the diaphragm is confined within a very 

 thin layer (one-eighth to one-fourth inch only) immediately below 



