EXTRACT ON WARMING BUILDINGS BY HOT WATER. 299 



the rate of cooling will, however, be very different from this ratio; in 

 consequence of the much larger quantity of heat which is contained 

 in the metal itself, than in the steam with which the pipe is filled. 



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

 we take two similar pipes, 4 inches diameter, and i of an inch 

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

 temperature of 212°, the one which is filled with water will contain 

 4 "68 times as much heat as that which is filled with steam ; there- 

 fore if the steam pipe cools down to the temperature of 60° in one 

 hour, the pipe containing 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 of the fluid 

 contained in it. In a stenm 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 the heat from 

 the brick-work around the boiler ; which all tends to increase the 

 effect of the pipes, in consequence of the circulation of the water 

 continuing long after the fire is extinguished ; in fact, as long as 

 ever the water is of a higher temperature than the surrounding air of 

 the room. From these causes, the difference in the rate of cooling 

 of the two kinds of apparatus will be nearly double what is here 

 stated ; so that a building warmed by hot water will maintain its 

 temperature, after the fire is extinguished, about six or eight times as 

 Ions; as it would do if it were heated with steam. 



" This is an important consideration wherever permanence of tem- 

 perature is desirable ; as, for instance, in hothouses, conservatories, 

 and other buildings of a similar description ; and even in the appli- 

 cation of this invention to the warming of dwelling-houses, manu- 

 factories, &c, this property, which water possesses, of retaining its 

 temperature for so long a time, and the very great amount of its 

 specific heat, prevents the necessity for that constant attention to the 

 fire which has always been found so serious an objection to the 

 general use of steam apparatus. 



"The velocity with which a pipe or any other vessel cools when 

 filled with a heated fluid depends principally upon two circum- 

 stances ; the quantity of fluid that it contains relatively to its surface, 

 and the temperature of the air by which it is surrounded ; or, in other 

 words, the excess of temperature of the heated body above that of the 



