32 



HOT WATER APPARATUS. 



adoption, for the same effect can be accomplished hy using larger sized 

 pipes, or by having a reservoir at one end of the apparatus so contrived, 

 by being enclosed in brick v\-ork or other non-conducting materials, as 

 vdll prevent such reserv oir from giving off much of its heat by radiation, 

 and the heat so retained in such reservoir will give out its heat to the 

 pipes as the heat entering them from the boiler decreases. Or if the 

 communication between such a reservoir and the pipes be cut off by a 

 stop cock, the maximum temperature can be attained in the pipes in a 

 much shorter period than if the whole volume of water had been con- 

 tained in the boiler. 



The advantages of small boilers, such as Nos. 4, 5, 6, and 7, and also 

 of the annexed fig., providing that an extreme be not fallen into, is, that 



boilers containing a small quantity of water become sooner heated, 

 require less consumption of fuel, and the rapidity of the circidation is 

 more rapid from them than in others. 



There is," says Mr. Hood, 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 kept always absolutely full." 



The capacity of the boiler and its operations depends a great deal on 

 the extent of its sm-face exposed to the action of the fii'e, and this surface 

 should in all cases be proportioned to the quantity of pipe intended to be 

 heated by it. To ascertain this, the following simple data has been laid 

 down by Mr. Hood, reckoning the smface which a steam boiler exposes 

 to the fire, at fom' square feet for each cubic foot of water evaporated per 

 horn', and calculating the latent heat of steam at one thousand degrees, 

 we shall find that the same extent of boiler surface which wo tdd evaporate 



