HEATIA'G BY HOT WATER, HOT AIR, AJS'D STEAM. 169 



« 



heating is nullified, namely, the diffusion of heat at a low tem- 

 perature. A given length of steain pipe, however, will afford 

 more heat than one heated by hot water, by the aggregate cal- 

 culation of its specific heat. But, if we consider the relative 

 permanency of temperature, we shall find a very remarkable dif- 

 ference in favor of pipes heated by hot water ; and the calculations 

 here given are fully confirmed by experience and observation. 



The weight of steam, at the temperature of 212°, compared 

 with the weight of water at 212°, is about as 1 to 1694, so that 

 a tube that is filled with water at 212° contains 1694 times as 

 much matter as one of equal size filled with steam. If the 

 source of heat be withdrawn from the steam pipes, the temper- 

 ature will soon fall below 212°, and the steam immediately 

 in contact with the pipes will condense ; but, in condensing, 

 the steam parts with its latent heat^ and this heat, in passing 

 from the latent to the sensible state, will again raise the tem- 

 perature of the pipes ; but, by the withdrawal of the heat from 

 the boiler, the action of the cold air on the pipes quickly con- 

 denses the whole of the steam contained in them, which, when 

 condensed, possesses just as much heating power as the same 

 bulk of water at a similar temperature. This water now occu- 

 pies only y^V^- part of the space which the steam originally did 

 in the pipes. 



The specific heat of uncondensed steam, compared with water, 

 is, for equal weights, as -8470 to 1 ; but the latent heat of 

 steam being estimated at 1000 degrees, we shall find the relative 

 heat obtainable from equal weights of condensed steam and of 

 water, reducing both from the temperature of 212° to 60°, to be 

 as 7-425 to 1 ; but for equal bulks it would be as 1 to 228 ; that 

 is, bulk for bulk, water will give out 228 times as nmch heat as 

 steam, reducing both to the temperature of 60°. A given bulk 

 of steam, therefore, will lose as much of its heat in one minute, 

 as the same bulk of water will lose in three hours and three 

 quarters. 



It must be considered, however, that when the water and 

 steam are both circulated in iron pipes, the rate of cooling will 

 be somewhat different from this ratio, in consequence of the 



