The Economic Production of Artificial Heat. 401 



Tlie chief heat-giving constituent of coal is its carbon, which, 

 in the bituminous kinds, varies from sixty-five to ninety-five 

 per cent. One pound of good coal will raise about sixty pounds 

 of water from the freezing to the boiling point ; but small coal 

 of the same kind will raise only about forty-five pounds through 

 the same number of degrees. Watt was able, on an average, 

 to evaporate seven and a-half pounds of water with one pound 

 of coal ; and with ordinary boilers, there has not been much 

 change in this respect since his time. A cylindrical boiler will 

 evaporate only seven pounds; but a " Cornish" boiler, ten and 

 a- quarter pounds ; and a locomotive boiler, with one pound of 

 coke, from eight to nine and a-ha]f pounds. If the full effect 

 of one pound of coal were obtained, it should evaporate about 

 sixteen pounds ; but a large portion of the heat usually passes 

 off into the chimney. 



Charcoal. — As might be expected, equal weights of dry 

 charcoal afford equal amounts of heat, at whatever temperature 

 it is burned, provided it is changed into carbonic acid by union 

 with a sufficient amount of oxygen. One pound of wood char- 

 coal will raise about seventy pounds of water from zero to the 

 boiling-point : and a cubic foot of charcoal from soft wood weighs 

 about eight and a-half pounds, but from hard wood about twelve 

 and a-half. One pound of peat charcoal w T ill raise upwards of 

 sixty pounds of water from zero to the boiling-point. 



Coke. — This substance is of very different qualities, accord- 

 ing to the coal from which it is made, and the mode of its 

 manufacture ; oven coke is far the best, gas coke being mere cin- 

 der. The density of coke, its most important quality, depends 

 on the quantity manufactured at once— since, the greater this 

 is, the greater the pressure, and therefore the greater the com- 

 pactness of the result ; on the temperature at which it is manu- 

 factured — since if this is high enough, the bicarburetted hy- 

 drogen evolved will deposit half its carbon on the coke; and on 

 the time during which it is kept in the oven — since continued 

 heat causes it to contract. One pound of good coke will raise 

 sixty-five pounds of water from zero to the boiling-point, while 

 one pound of the coal from which it is made will raise only 

 sixty pounds through the same number of degrees. 



Heat. Production of heat from fuel. — Open fire-places, or ■ 

 stoves, are most usually employed for the purpose of heating 

 apartments ; the former are more agreeable, the latter more 

 economical. When an open fire-place is properly constructed, 

 the effect obtainable from it is sufficient, under ordinary circum- 

 stances : but, in cold regions, such as a large portion of North 

 America, it would be very ineffective for heating or culinary 

 processes ; and hence the almost exclusive use of stoves through 

 so great an extent of the New World. They are generally 



