170 HEATING BY HOT WATER, HOT AIR, AND STEAM. 



much larger quantity of heat contained in the metal, than in the 

 steam with which the pipe is filled. 



The specific heat of cast iron being nearly the same as water, 

 the water being 1000 and the iron 1100, if we take two similar 

 pipes, four inches in diameter and one fourth of an inch thick, 

 the one filled with water and the other with steam, each at the 

 temperature of 212, the one which is filled with water contains 

 4-68 times as much heat as the one which is filled with steam. 

 Therefore, if the pipe with the steam cools down to the temper- 

 ature of 60 in one hour, the one filled with water would require 

 four hours and a half, under the same circumstances, before it 

 reached the like temperature. 



But this is merely reckoning the effect of the pipe and the 

 fluid contained in it. In a steam apparatus, this is all that is 

 effective in giving out heat ; but in a hot-water apparatus there 

 is likewise the heat from the water contained in the boiler, and 

 even of the brick-work around the boiler, all which tends to 

 increase the heat of the pipes, long after the fire is extinguished. 

 In the one, the heat will continue to circulate through the pipes 

 as long as any heat remains about the fire-place, because the 

 circulation will continue in the pipes until the whole apparatus 

 is cooled down. But, in the case of steam pipes, as soon as the 

 water in the boiler falls below the boiling point, (212,) circula- 

 tion ceases, and the pipes then begin to cool, the remaining heat 

 in the boiler and furnace goes for nought. 



From these causes the difference in permanency of hot water 

 and steam will be clearly apparent, and the fact of a house 

 heated with hot water keeping up its temperature at least six 

 times as long as one heated with steam, will be fully understood 

 by those interested in the matter. These considerations are of 

 the utmost importance to those erecting horticultural build- 

 ings, or, indeed, any other kind of buildings requiring artificial 

 heat. This admirable property, which water possesses, of re- 

 taining its heat, of carrying it to any distance, and, without 

 difficulty, giving it out gradually, or retaining it for many hours, 

 renders it of vast importance to gardeners, and prevents the 

 necessity of that constant attention to the fire, which forms so 

 serious an objection in all other methods of heating. 



