THE MECHANICS OF VENTILATION. 469 



The specific gravity of sixteen candle power gas is approximately 0.450, 



common air at a temperature of 60° being unity, A pound of air at 60° 



contains exactly 13.09 cubic feet; consequently, a pound of coal gas of a 



specific gravity 0.450 and at the same temperature contains : 



13.09 



=29.09 cubic feet. 



0.450 



A cubic foot ot such gas therefore weighs 



1.00000 



=0.0343 pounds. 



29.09 



Taking the percentage of the constituents of coal gas as given above, we 



have the following for the weight in pounds of each in a cubic foot of gas : 



Hydrogen, ., 0.01501 



Marsh Gas, 0.01388 



Carbonic Oxide, 0,00203 



Olefiant Gas, .0.00225 



Nitrogen, 0.00036 



Oxygen, ...,.0.00016 



Carbonic Acid, 0.00025 



Aqueous Yapor, , ...0.00034 



0.03428 

 Multiplying each of these weights by the caloric modulus for the correspond- 

 ing element and we have the number of heat-units evolved in the combustion 

 of that element, and the sum of these units will be the theoretical heat ob- 

 tained by the combustion of a cubic foot of gas. The calculation referred to 

 the Fahrenheit scale will stand as follows : 



Hydrogen, .34462x0.01501x1.8 = 931.09 



Marsh Gas, 13063x0.01388x1.8 = 326.36 



Carbonic Oxide, 3403x0.00203x1.8= 12.42 



Olefiant Gas, 11657 x 0.00225 x 1.8 = 48.00 



1317.87 

 heat units. 

 The remaining constituents are non-combustible. 



The caloric moduli for the different gases as here used were obtained by 

 combustion in an atmosphere of pure oxygen, while combustion in practice 

 will, of course, take place in common air. Comparing this calculated amount 

 of heat with the observed amount, obtained by caloriraetrical tests of illu- 

 minating gas of the candle power and specific gravity above given, shows 

 that a reduction of the calculated heat of forty per cent, is necessary to make 

 calculation agree with experiment. This reduction is undoubtedly owing 

 largely to imperfect combustion, in addition to difference of condition. 

 Making such reduction we have 1317.85 x 0.6 = 790.7 = aj)proximate num- 

 ber of heat-units from the combustion of one cubic foot of sixteen candle 

 power illuminating gas. 



