CHAP. II.] 



THE ART OF WARMING. 



353 



water compresses when its temperature rises, so as to avoid the 

 effects of the expansion of the liquid and of the steam which is 

 formed, the pressure of which latter may reach a considerable number 

 of atmospheres. 



The method of heating by hot water at high pressure is subject to 

 serious drawbacks. It may cause a fire by setting light to the wood 



FIG. 243. Perkins's high pressure system of heating by hot water. 



adjoining the pipes. If the steam escape through any joints or 

 cracks it might occasion explosions or dangerous scalds. 



A third method, namely, that of heating by the circulation of 

 steam, is based upon the great quantity of latent heat given out by 

 steam in condensing. It requires pipes of but small dimensions ; 

 but its many drawbacks, the variations of temperature arising from 

 any neglect in attending to the fire, the condensations, blows, fractures 



A A 



