HEATING BY FLUES. 



145 



In estimating the relative merits of the 

 different modes of heating, we should also 

 consider that the difference in the quality 

 of fuel is very variable; and even in that 

 most common of all combustible material, 

 coal, we find a great difference in its heat- 

 ing powers, arising from its differences 

 of chemical composition. Experiments 

 have been made by Watt, Rumford, 

 Black, and many others, as to the amount 

 of heat procurable from Newcastle coal 

 of a fair average quality. According to 

 Watt, 1 lb. of coal will boil 45 lb. of 

 water taken at 55° of temperature. Black's 

 computation is, that the same weight of 

 coal will boil 48 lb. of water taken at 

 a mean temperature ; while Rumford 

 makes it capable only of heating 36t 2 <j lb. 

 to the same degree, the temperature of 

 water being 32°. If we take the medium, 

 therefore, of these experiments, the result 

 will be, that 1 lb. of coal will boil 39 lb. 

 of water taken at a temperature of 32°. 

 From these data we can readily deter- 

 mine the quantity of coal necessary to 

 heat any given length of pipe of hot 

 water; for as 100 feet in length of a 

 4-inch pipe contains 544 lb. of water, 

 13.9 lb. of coal will be required to raise 

 the temperature of this quantity of water 

 180° — that is, from 32°, or freezing point, 

 to 212°, the boiling point. And, again, 

 if the water loses 1° per minute, the 

 above quantity of coal will supply 100 

 feet of pipe during three hours, provided 

 the temperature remains constant in the 

 atmosphere to be heated. 



§ 2. — HEATING BY FLUES. 



Having in a preceding section remarked 

 on flues generally, we shall now proceed to 

 consider them individually. 



The Chinese, from the earliest ages, 

 used flues in the walls of their houses, as 

 well as under the pavement of the floors of 

 their rooms : the latter of these they call 

 the ti-kang, and the former the tong-Jcang, 

 the heated air and smoke of which ascend 

 into the spaces of a hollow wall, — a mode of 

 wall-building long known in the Celestial 

 Empire. The large orangery built by 

 Sir William Chambers, and still existing 

 in the Royal Gardens at Kew, was heated 

 by the latter means. 



Earthenware or can flues. — It has been 



VOL. I. 



already observed that these are of various 

 kinds, the most primitive being tubes 

 Fig. 139. of brick 



earth, ta- 

 pering at 

 one end, 



so as to join more readily with each 

 other, vide fig. 139 ; they are usually 

 about 2 feet in length, and 10 inches in 

 diameter. 



Fire-clay flues, with spigot -and -faucet 

 joints — fig. 140. These 



Fig. 140. 



Fig. 141. 



are a great im- 

 provement 

 on the last, 

 as they are 

 stronger, less 

 liable to warp 

 in burning, 

 and have a much neater appearance. They 

 can also be jointed so as to prevent the 

 escape of gaseous matter. They have been 

 successfully used as an economical substi- 

 tute for cast-iron pipes for circulating hot 



water. They 

 can be mould- 

 ed with elbow 

 turns, as in fig. 

 141 ; and are 

 set on earthen- 

 ware chairs, fig. 142, to clear them of the 

 ground, and to keep them 

 steady. In heating by hot 

 water, the pipes are sup- 

 ported by similar chairs hol- 

 lowed out both above and 

 below. 



The modifications of fire-clay flues are 

 the square, fig. 143, egg-shaped, fig. 144, 



Fig. 143. 



Fig. 145. 



and round-topped, fig. 145— very excel- 

 lent improvements, both in strength and 



T 



