Proceedings of the Polytechnic Association. 741 



Mr. Charles E. Emery in a few remarks stated that lie did not 

 think that mere openings provided in subterranean ways would prove 

 sufficient to properly ventilate the same, but that special arrangements 

 would be required to efteet this purpose. 



The object is to determine, approximately, the quantity of heated 

 gases that must be removed from a railway tunnel to keep the air 

 pure. As a starting point, we may suppose that a heavy train is 

 dra^vn past a given point every five minutes by a locomotive of 400 

 horse-power. Taking the time when tlie train is being brought to 

 rest and the stoppages into consideration, we may safely assume that 

 the power required would average 300 horse-power acting continu- 

 ously. Three hundred horse-power passing every five minutes is 

 equivalent to sixty horse-power passing every minute. Supposing 

 that coke is burned and the steam exhausted into condensing-tanks, 

 we may assume, as a maximum, that it would require seven pounds 

 of fuel per horse-power per hour, equal to seven-sixtieths of a pound 

 per horse-power per minute, or seven pounds for the sixty horse- 

 power passing every minute. Each pound of coke would require 

 theoretically about twelve cubic feet of air, and practically at least 

 twenty feet. Considering the greater density of the resulting 

 carbonic acid gas, the bulk of the escaping gases would not be 

 increased by heat to twenty-five cubic feet per pound of coke. As 

 seven pounds are burned per minute, 175 cubic feet of heated gases 

 would issue from the smoke pipe during that time at a temperature 

 of at least 500 degrees. If the gases mixed with four times their 

 volume of air in the tunnel, at say seventy degrees, we should be 

 obliged, in order to secure ventilation, to withdraw 700 cubic feet of 

 heated air and gases, at a temperature of 156 degrees, every minute. 

 At an average speed of eleven miles j)er hour the heated air would 

 be distributed over 1,000 feet in the length of the tunnel. "Were 

 ventilators placed about one-twentieth of a mile apart, each one 

 should deliver nearly 200 cubic feet of air per minute. Such a 

 quantity of air cannot be displaced by simply putting openings 

 through the surface at intervals, but it may be by constructing two 

 sets of openings, those for cold air at tlie street level, and high 

 chimneys, built in the adjoining buildings, to carry ofi" the heated air. 



It is more than probable that* the figures given are too small, by 

 half, to meet the requirements of a tunnel in this city. The object 

 of tlie calculation is to show that the subject of ventilation in an 

 underground way is not to be trifled witli ; that it cannot be accom- 



