302 EXTRACT ON WARMING BUILDINGS BY HOT WATER. 



3 inches diameter will, perhaps, upon the whole, he found the most 

 advantageous ; for they will retain their heat sufficiently long for 

 ordinary purposes, and their temperature can he sooner raised, and 

 to more intensity than larger pipes ; and, on this account, a less 

 number of superficial feet will suffice to warm a given space. 



In adapting the boiler to a hot-water apparatus it is not necessary, 

 as is the case with a steam boiler, to have its capacity exactly pro- 

 portional to that of the total quantity of pipe which is attached to it; 

 on the contrary, it is sometimes desirable even to invert this order, 

 and to attach a boiler of small capacity to pipes of large size. It is 

 not, however, meant, in recommending a boiler of small capacity, to 

 propose also that it should be of small superficies ; for it is indispen- 

 sable that it should present a large surface to the fire, because, in 

 every case, the larger the surface on which the fire acts, the greater 

 will be the economy in fuel, and, therefore, the greater will be the 

 effect of the apparatus. 



"The sketches of the boilers, figs. 16 to 26, are several different 

 forms which present various extents of surface in proportion to their 

 capacity. 



" All except the first two, however, have '^but a small capacity, 

 relatively to their superficies, compared with boilers which are used 

 for ster.m. There is no advantage whatever gained by using a boiler 

 which contains a large quantity of water ; for, as the lower pipe 

 brings in a fresh supply of water as rapidly as the top pipe carries 

 the hot water off, the boiler is always kept absolutely full. The only 

 plausible reason which can be assigned for using a boiler of large 

 capacity is, that as the apparatus then contains more water, it will 

 retain its heat a proportionably longer time. This, though true in 

 fact, is not a sufficient reason for using such boilers ; for the same 

 end can be accomplished, either by using larger pipes, or by having a 

 tank connected with the apparatus which can be so contrived, by 

 being enclosed in brick or wood, or some other non-conductor, as to 

 give off very little of its heat by radiation, and yet to be a reservoir of 

 heat for the pipes after the fire has been extinguished. If this tank 

 communicates with the rest of the apparatus by a stop-cock, the pipes 

 can be made to produce their maximum effect in a much shorter time 

 than if this additional quantity of water had been contained in the 

 boiler, and a more economical and efficient apparatus will be ob- 



