HOT WATER. 



327 



bj the chimney — the whole being taken up by the sur- 

 rounding water. The economy, therefore, of fuel in 

 such an apparatus is very great. It is evident that 

 excess of draught must be carefully guarded against, 

 so much only being allowed as will consume the fuel 

 steadily, which is easily learned by experience. The 

 necessity, also, of keeping the aperture in front close, 

 so that air enters the furnace only through the ash-pit, 

 is hence evident. The water (as may be observed in 

 Fig. 31) is in close and immediate contact with the 

 red-hot fuel on all sides, no black smoking coals inter- 

 vening, as in most kinds of boilers ; hence the great 

 power in proportion to size." 



The economy of fuel in these boilers is not their 

 principal advantage ; but their great recommendation is 

 a long-continued and steady heat. When properly 

 managed, they may be depended on for preserving the 



Fiff. 32. 



liciit for from fifteen to twenty hours. They have been 

 successfully applied to all descriptions of hot-houses, 



