478 Mr, Frederick Siemens [May 7, 



combustion are broiiglit into intimate contact with the surfaces to be 

 heated. While combustion is going on in the open space heat is 

 transmitted by radiation only, but after active combustion is com- 

 pleted it is transmitted by contact, and it is in this manner that flame 

 must be applied to boilers, and may be applied equally well to 

 nearly all other heating operations. 



In heating a boiler the intensity of heat produced is not very 

 great, because the relatively cold surfaces abstract heat from the flame 

 very eagerly, thus preventing its temperature from rising above a 

 certain point which is below that of dissociation. But although no 

 dissociation of the products of combustion can take place in boiler 

 firing, the detrimental effect on combustion of the surfaces of the 

 boiler is nevertheless very great, perhaps, indeed, greater than in any 

 other application of firing and heating. The cold surface of the 

 boiler has the power of extinguishing flame altogether, especially if 

 brought into actual contact with it, because, besides the peculiar in- 

 fluence of surfaces on combustion, the cooling in this case is so great that 

 the necessary temperature for combustion cannot be maintained. Thus 

 it seems clear that heating by radiation must be most advantageous for 

 firing boilers, but particular care should be taken that the products of 

 combustion, as distinguished from the flame, are brought as much as 

 possible into contact with their surfaces. Galloway tubes are pre- 

 ferable to bafflers for this purpose, but it will be necessary to be 

 careful that combustion is complete before the products of com- 

 bustion are allowed to come into contact with these tubes or bafflers, 

 as otherwise they would interfere with combustion at that point. 



In the paper I read before the Iron and Steel Institute, to which 

 I have already referred, I described a boiler heated on the radiation 

 principle, fired with the producer gas used in our regenerative gas 

 furnaces, and with that boiler no smoke is produced. I will now 

 describe a boiler worked on the same principle, fired with common 

 coal, by the use of which great saving of fuel is effected, and very 

 little or no smoke is produced. In this boiler one end of the internal 

 flue is lined with brickwork, and contains an ordinary fire-grate, 

 while the longer part is furnished with rings of cast iron or fire-clay, 

 which prevent the flame from striking on the inner boiler surface. 

 The products of combustion, after leaving the inner flue, where 

 the flame has not come into contact with the boiler plates, are con- 

 ducted underneath and at the sides of the boiler, and in these channels 

 they may be directed by means of bafflers against the boiler sides and 

 bottom. If the internal flue of the boiler is so long that the flame 

 ceases before reaching its extremity, bafflers, in the form of cones, may 

 also be placed at its far end for the purpose of ca..sing the products 

 of combustion to strike against its sides. Instead of cones, cross 

 tubes of the Galloway type may be used with advantage, but it is 

 absolutely necessary that active combustion should have ceased before 

 the products of combustion come into contact with cither bafflers or 

 tubes. In a boiler so arranged and constructed that the flame heats 



