644 ANNUAL REPOET SMITHSONIAN INSTITUTION, 191a. 



means of attaining radiant heat can hardly fail to find new indus- 

 trial uses. The evaporation and concentration of liquids by means 

 of radiant energy emitted from a diaphragm fixed in a horizontal 

 plane above the surface of the liquid is readily carried out. 



For example, the evaporation of a solution of sodium silicate 

 (water-glass) is an operation which could not be satisfactorily per- 

 formed by the ordinary means of heating the vessel by flame from 

 below\ By the new method, however, only the topmost layers of the 

 liquid are heated ; the radiant energj- of the diaphragm is instantly 

 transmitted to the surface of the liquid, where it is absorbed and 

 utilized for the evaporation. The sodium silicate separates out as a 

 skin on the surface of the liquid, it is then dried by the radiant heat, 

 and at intervals the crust of dry sodium silicate may be skimmed off. 

 In this wa,y, we are not only able to evaporate the solution with a 

 great economy of heat, but we are also able to complete the evapora- 

 tion of highly concentrated solution much more easily than by means 

 of heat" applied from below. 



III. INCANDESCENT SURFACE COMBUSTION IIS A BED OF REFRAC- 

 TORY GRANULAR MATERIAL. 



This process is applicable to all lands of gaseous or vaporized 

 fuels, and to a great variety of both small and large scale industrial 

 heating purposes. It consists essentially in injecting through a suit- 

 able orifice, at a speed greater than the velocity of back firing, an 

 explosive mixture of gas (or vapor) and air, in their combining pro- 

 portions, into a bed of incandescent granular refractory material, 

 which is disposed around or in proximity to the body to be heated. 



Figure 1 shows the process as applied to the crucible furnace. The 

 crucible is surrounded by a bed of highly refractory granular ma- 

 terial. The mixture of gas and air is injected at a high velocity 

 through a narrow orifice in the base of the furnace, and as it im- 

 pinges upon the incandescent bed, combustion is instantaneously com- 

 pleted without flame. 



The seat of this flameless combustion is in the lowest part of the 

 bed; and the burnt gases, rising through the upper layers, rapidly 

 impart their heat to the bed, maintaining in it a high degree of in- 

 candescence. Figure 2 shows a similar arrangement for the heating 

 of a muffle furnace, an arrangement which needs no further expla- 

 nation. 



It is obvious that this process is adaptable to many other furnace 

 operations, as, for example, the heating of retorts, annealing fur- 

 naces, and the like. It is not essential that the bed of refractor}^ ma- 

 terial shall be disposed around the vessel or chamber to be heated ; it 

 may be equally well packed into tubes, or the liJke, traversing the sub- 

 btance to be heated. This latter modification is important in relation 



