196 THE POPULAR SCIENCE MONTHLY. 



One pound of coal is capable, if all the heat of combustion is util- 

 ized, of raising the temperature of a room, twenty feet square and 

 twelve feet high, to ten degrees above the temperature of the outer 

 air. If the room were not ventilated at all, and the walls were com- 

 posed of non-conducting materials, the consumption of fuel to maintain 

 this temperature would be very small, but, in proportion as the air 

 of the room was renewed, so would the consumption of fuel necessary 

 to maintain that temperature increase. If the volume of air contained 

 in the room were changed every hour, one pound of coal additional 

 would be required per hour to heat the inflowing air, so that, to main- 

 tain the temperature at ten degrees above that of the outer air during 

 twelve hours, would require twelve pounds of coal. 



The principle of the ordinary open fireplace is that the coal shall 

 be placed in a grate, by which air is admitted from the bottom and 

 sides to aid in the combustion of coal ; and an ordinary fireplace, for 

 a room of twenty feet square and twelve feet high, will contain from 

 about fifteen to twenty pounds at a time, and, if the fire be kept up 

 for twelve hours, probably the consumption will be about one hundred 

 pounds, or the consumption may be assumed at about eight pounds 

 of coal an hour. 



One pound of coal may be assumed to require, for its perfect com- 

 bustion, 150 cubic feet of atmospheric air; 8 lbs. would require 1,200 

 cubic feet ; but, at a very low computation of the velocity of the gases 

 in an ordinary chimney-flue, the air which would pass up the chimney 

 at a rate of from 4 to 6 feet per second, or from 14,000 to 20,000 cubic 

 feet per hour, with the chimneys in ordinary use, and I have often 

 found a velocity of from 10 to 12 feet per second giving an outflow of 

 ah* of from 35,000 to 40,000 cubic feet per hour this air comes into 

 the room cold, and when it is beginning to be warmed it is drawn 

 away up the chimney, and its place filled by fresh cold air. A room 

 20 feet square and 12 feet high contains 4,800 cubic feet of space. In 

 such a room, with a good fire, the air would be removed four or five 

 times an hour with a moderate draught in the chimney, and six or 

 eight times with a blazing fire ; the air so removed would be replaced 

 by cold air. The atmosphere of the room is thus being cooled down 

 rapidly by the continued influx of cold air to supply the place of the 

 warmer air drawn up the chimney. The very means adopted to heat 

 the room produces draughts, because the stronger the direct radiation, 

 or rather the brighter the flame in open fireplaces, the stronger must 

 be the draught of the fire and the abstraction of heat. The only way 

 to prevent draughts is to adopt means for providing fresh warmed air 

 to supply the place of that removed. 



The most natural way of providing warmed air is to utilize the ex- 

 cess of heat which passes up the chimney, beyond what is required for 

 creating an adequate draught, and to use this heat to warm fresh air ; 

 and the warmed air should be admitted into the room in such places 



