140 



ON THE SETTING OF STEAM BOTLERS. 



By this second combination tlie volume of the gas is 

 doubled and a large amount of heat is lost in the work of 

 expansion, the heat falls from 14,500 units for the first lb. 

 of carbon to the amount due to the imperfect combustion of 

 2 lbs. carbon, viz. 4,400 x 2 = 8,800, showing a loss of 5,700 

 units of sensible heat, besides the loss of 14,500 which 

 ought to have been obtained from the complete combustion 

 of the second pound of carbon. Should the furnace be ill 

 supplied with air and the process stop here, this is the 

 enormous waste constantly going on, to say nothing of the 

 loss due to the escape of a large quantity of unconsumed 

 carbon in the form of smoke. 



If, however, air is plentiful, oven should this second 

 combination take place, the continuation of the process will 

 be this. 



The 4§- lbs. of carbonic oxide, containing 2 lbs. of carbon, 

 will combine with 2«- lbs. oxygen and form TJf lbs. carbonic 

 acid, giving the additional heat duo to the combustion of 

 4:5 lbs. of carbonic oxide ; that is to say — 



4 ;^ CO + 2 ;^ = 7 .', CO2 = 20,200 



to which, if wo add the lioat produced by the imperfect 



combustion of 2 lbs. carbon, viz. 8,800, we obtain that due 



to the complete combustion of 2 lbs. carbon, or 



14,5fX)x 2 = 29,000. 



These facts show the imi)ortaiico of getting a sufficient 

 supply of air into the furnace, seeing that by enabling each 

 pound of coal to combine with its proper 0(iuivalont of 

 oxygen, more than throe times the quantity of heat is gener- 

 ated than when the supply is limited ; and of course the 

 evaporation is correspondingly rapid. But it must be borne 

 in mind that the supply of air may be overdone. Air is not 

 composed of oxygen only ; but three-fourths of it by weight 

 is nitrogen, an incombustible gas that passes unchanged as 



