84 



Professor Alex. B. W. Kennedy 



[April 21, 



Fig. 1. 



R ADIATI ON 



minutes further in special illustration of my subject. Fig. 1 shows 

 fairly accurately how far we have got in working at the efficiency of 

 this kind of transformation. We start with a given amount of 

 potential energy, know T n within very narrow limits, represented for us 

 by a pound of coal with a sufficient weight of circumambient atmo- 

 sphere. Let us represent this known amount of energy, as in the 



figure, by 100 per cent. What 

 becomes of all this if the coal be 

 burnt in the furnace, say, of an 

 ordinary boiler, and if we endeavour 

 to utilise this combustion energy in 

 the conversion of water into steam ? 

 On the left hand of my diagram you 

 may see what often enough happens 

 in every-day careless working ; on 

 the right hand you may see what 

 happens in thoroughly good work- 

 ing with real care, but without any 

 special apparatus. You will see 

 that the amount of heat taken up 

 by the steam varies from 50 to 80 

 per cent, of the whole heat ; that a 

 small amount, from 5 per cent, down 

 to nothing, is lost in imperfect com- 

 bustion, that is, in the formation of 

 carbonic oxide ; that a very much 

 larger amount goes up the chimney, 

 having been expended in heating 

 the waste gases ; and that finally 

 another large amount is purely 

 wasted, being lost in radiation 

 and otherwise. Now I ask you to 

 notice particularly two things, first, 

 looking at the right hand of the 

 diagram, how much there is still 

 possible. The efficiency of the pro- 

 cess is about 80 per cent. The 

 remaining 20 per cent, is all that 

 can be saved. Of this some portion 

 must go in heating the chimney 

 gases. It is the price paid for the 

 draught of the chimney. We must also lose something by radiation ; 

 that is inevitable. We cannot look, therefore, to any very astound- 

 ing increase of economy in boiler work over the best that has been 

 clone. Secondly, I ask you to notice what an enormous amount is 



* The blocks illustrating this abstract have been kindly lent by the Editor of 

 the Electrician. 



40- 



30- 



20 



10- 



STEAM 



