210 CHEMICAL DISCOVERY AND INVENTION 



a moment later it retreats on to the surface of the diaphragm, 

 which at once assumes a bluish appearance. Finally, all signs 

 of flame disappear and there remains an intensely glowing 

 surface. The temperature thus attained is high enough even to 



melt platinum. Consequently in 

 applying the principle to the con- 

 struction of a furnace for fusion or 

 other purposes in which a high 

 temperature is required the choice 

 of the contact material is neces- 

 sarily rather limited. Practically 

 all solids except calcined magnesia 

 and carborundum are excluded. 



In raising steam three forms of 

 apparatus may be adopted. In the 

 case of a multitubular boiler in 

 which the heating tubes pass through 

 the body of the boiler containing 

 the water, the tubes are packed 

 with the refractory contact material 

 in a granular state. The com- 

 bustible mixture of air and gas 

 passes through these tubes, and the 

 control of the heat communicated 

 to the boiler and the amount of steam raised, is effected either 

 by adjustment of the amount of gas admitted or by working the 

 tubes in groups, so that any number can be brought into action 

 as required. 



The diagrammatic section of an experimental boiler on this 

 construction with ten tubes is shown in the figure. The tubes 

 are 3 feet long and 3 inches in diameter, fixed in a cylindrical 

 steel shell capable of withstanding a pressure of over 200 Ibs. 

 per square inch. Three only of the tubes are shown here. The 

 gaseous mixture was forced through the tubes from a special 

 feeding chamber attached to the front plate of the boiler ; the 

 products of combustion after leaving the boiler passed through 

 a small heater containing nine tubes by which the water before 

 entering the boiler could be warmed. The feed water on entering 

 was at the temperature 5*5 C., or nearly 42 F., on passing to 

 the boiler the temperature was 58 C., or about 136 F. The 

 successful results obtained with this apparatus led to the erection 



FIG 56. 



SECTION OF DIAPHRAGM FOB, 

 SURFACE COMBUSTION (BONE). 



