716 TRANSACTTOyS OF THE AMERICAN INSTITUTE. 



length, to sustain perfect combustion more than five to six feet 

 from the end of the tube. Tlie most exhaustive experiments have 

 demonstrated that but about five feet of the tubes in ordinary 

 boilers are of any value in making steam. 



In the safety boiler, the spaces for admixture of the air and 

 gases of the fuel and for coirbustion, are ample, extending the 

 whole length and width of the boiler, between the rows of tubes. 

 This peculiarity of construction in this boiler makes it — we think 

 it will be acknowledged on examination — the most economical in 

 fuel of any steam generator produced. The tubular boiler, not- 

 withstanding its imperfect combustion, is, owing to its large pro- 

 portion of tube surface, the most economical form; but the safety 

 boiler is composed entirely of tube surface, and it is all efiective, 

 on account of perfect combustion. We have thrown out the thick 

 uhell which is the uneconomical portion of the tubular boiler. 



There are certain conditions necessary to obtain the best economy 

 in any boiler, viz: proper combustion of the fuel, and a proper 

 umount of heating surface in contact with the water to absorb the 

 heat evolved by the combustion of the fuel. In order to obtain 

 I'.omplete combustion, it is necessary to have a sufficient amount of 

 liir mixed with the gases of the fuel to support such combustion; 

 and sufficient combustion room above the fuel to permit the thorough 

 admixture of the air and gases. The want of properly arranged 

 and sufficient combustion room is the cause of great waste of fuel, 

 as the gases in such cases pass off without being burned. It is also 

 necessary that a proper amount of grate surface should be given, 

 to correspond with the heating surface of any boiler. The required 

 proportion between grate surface and heating surface, and combus- 

 tion room varies under different conditions, according to the amount 

 of draft, the kind of fuel used, &c. 



Now, a great point in favor of the economy of the Ifeafety boiler 

 is its adaptability to any and all conditions of use. While other 

 boilers are confined to the proportions, in these respects, upon which 

 they were originally constructed, the safety boiler can be erected 

 to conform to any required conditions. The amount of heating 

 surface, grate surface, combustion room, etc., can be proportioned 

 and arranged in any manner required to suit the conditions under 

 which it is to be used, or can be changed after erection with little 

 ti'ouble. The thinness of the metal of the tubes is also in favor of 

 economy. All the heating surface is one-eighth of an inch iu 

 thickness. 



