298 EXTRACT ON WARMING BUILDINGS BY HOT WATER. 



manence of temperature of the two methods, we shall find a very re- 

 markable difference in favour of pipes heated with hot water. 



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

 the weight of water at 21 2°, is about as 1 to 1694 ; so that a pipe 

 which 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 be withdrawn from the steam pipes, the, temperature will soon fall 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 

 he,at ; and this heat, in passing from the latent to the sensible state, 

 will again raise the temperature of the pipes. But as soon as they 

 are a second time cooled down below 212°, a further portion of steam 

 will condense, and a further quantity of latent beat will pass into the 

 stale of heat of temperature;* and so on until the whole quantity of 

 latent beat has been abstracted, and the whole of the steam con- 

 densed ; in which state it will possess just as much heating power as 

 a similar bulk of water at the like temperature; that is, the same as 

 a quantity of water occupying t -gVt P art the space which the steam 

 originally did. 



" The specific heat of uncondensed steam compared with water is, 

 for equal weights, as "8470 to 1 ; but the latent heatf of steam being 

 estimated at 1000°, we shall find the relative heat obtainable from 

 equal weights of condensed steam and of water, reducing both from 

 the temperature of 212° to G0°, to be as 7 425 to 1 ; but for equal 

 bulks it will be as I to 228; that is, bulk for hulk, water will give 

 ovit 228 times as much heat as steam, on reducing both from the 

 temperature of 212° to 60°. A given bulk of steam will therefore 

 lose as much of its heat in one minute as the same bulk of water will 

 lose in three hours and three quarters. 



"When the water and the steam are both contained in iron pipes 



* The heat of temperature is that which is appreciable by the 

 thermometer; and the term is used in contradistinction to latent 

 heat, which is not capable of being measured in a direct manner by 

 any instrument whatever. 



-j- The results of different experiments on the subject of the latent 

 heat of steam, although somewhat various, are yet sufficiently near 

 for all practical purposes. Watts's experiments give 900° to 950°; 

 Lavoisier and Laplace, 1000°; Mr. Southern, 945°; Dr. Ure, 967° 

 to 1000° ; and Count Rumford, 1000°. 



