CALCULATION OF VOLUME OF AIR SUPPLIED. 139 



CALCULATION OF VOLUME OF AIR SUPPLIED. 



The volume of combustion-gases just determined is less 

 than that of the air supplied. Oxygen in forming carbonic 

 acid produces a volume equal to itself; hence there is no 

 change. 



C + O, = CO, 



2 VOls. 2 VOls. 



Oxygen in forming carbonic oxide produces twice the 

 volume. 



C + O = CO 



I VOl. 2 VOlS. 



Hence there is an increase in volume. 



Carbon vapor and hydrogen as free gases or as hydro- 

 carbons increase the volume but slightly. In forming sul- 

 phurous acid with sulphur there is no change of volume. 



S + O, = SO, 



2 VOlS. 2 VOlS. 



Another slight cause of increase is setting free the nitrogen 

 of the coal ; but this is inappreciable. I per cent of nitrogen 

 forms only o. I per cent of the entire volume of gases formed. 



It might be said that, excepting the oxygen changing to 

 water and disappearing by condensation, all the modifications 

 of gaseous volume may be neglected, the increase being more 

 than compensated by the loss due to oxygen. This elimina- 

 tion of oxygen must be allowed for, however. 



A coal containing 4 per cent of hydrogen requires eight 

 times such weight to form water, or 40 grams of hydrogen 

 need 320 grams of oxygen. I litre of oxygen weighs 1.430 

 grams, then 320 grams measure ^j- Q 223.7 litres (7.9 cubic 

 feet). (Or I Ib. of such coal would need 3.6 cubic feet of 

 oxygen.) 



These 223 litres must be added to the volume of the 

 waste gases produced by the coal to obtain the original 



