Proceedings of the Polytechnic Association. 887 



tlie g-rate to the fii-e. Tlie experiment, in every instance, resulted in 

 l^utting out tlie fire, and, of course, the thing was condemned, 



Mr. J. K. Fisher said it was not possible to burn smoke after it 

 was made ; the carbonic acid acts like a damper and puts the fire out. 

 A system of fuel-saving, in which the returning of the smoke, or 

 part of it, to the furnace, M'as tried some years ago on a boat on the 

 Hudson river. Mr. Stetson, who was employed to examine it, stated 

 to the Polytechnic Association that the boat saved fuel and lost more 

 money than any other boat. The return of all the smoke must 

 necessarily prevent fresh air from entering the furnace, and the fire 

 must go out ; and a return of part of it must hinder combustion ; 

 and it is considered by experimenters in this matter, particularly by 

 C. Wye Williams, that smoke once made cannot be burned. Sir 

 Goldsworthy Gurney tried many ways to burn it, and succeeded 

 only by first absorbing the carbonic acid from it by passing it 

 through sand mixed \vith quicklime, a process impracticable for 

 steam purposes. If, in some cases, it has appeared that smoke has 

 been burned, it probably was because there was little or no carbonic 

 acid, and much carbonic oxj'd and hydrogen in it, as in the gases in 

 Siemans' furnace ; but to Ijurn sucli matter is not to burn common 

 smoke ; it is in fact a deception which may mislead the inventor 

 more than it can mislead ordinary practitioners. In reference to 

 what has just been said, that in common practice double the quan- 

 tity of air theoretically required is drawn through the grate, he 

 would refer to the analysis of gases from the smoke boxes of locomo- 

 tives b_y Ebelman and Sauvage. In passenger locomotives that 

 worked with fires twelve inches deep, there was twelve per cent of 

 air and no carbonic oxyd mixed with the normal products of com- 

 bustion ; and in freight engines that worked with fires eighteen 

 inclies deep, there was little air and so much carbonic oxyd as to 

 indicate a loss of seventeen per cent of the fuel. These analj'ses 

 indicate that with a forced draft, and the fires not too deep, a most 

 perfect combustion, without much excess of air, may be attained bj 

 a skillful fireman ; and any contrivance to burn smoke can have 

 little use but to prevent waste by unskillful firemen or by ill-con- 

 structed apparatus. It is very seldom now that blue flame is seen 

 coming from the smoke pipes of our steamboats, as tliey now use 

 very thin fires, which does not make so much carbonic oxyd as a 

 thick fire. 



Prof. J. A. Whitney described a furnace lately invented, in which. 



