I 



HEAT. 45 



changed to a liquid, or a liquid to a gas ; here a much great- 

 er amount of heat or repulsive force is required, on account 

 of the cohesion of the particles to be separated. In order to 

 separate the particles of the solid, precisely as much force 

 must be parted with by the warmer liquid body as keeps an 

 equal quantity of it in its liquid state ; it is, indeed, only with 

 a more striking line of demarcation, the case of the hot and 

 cold bladder a part of the repellent power of the hot parti- 

 cles is transferred to the cold particles, and separates them in 

 their turn, but the antagonist force of cohesion or aggregation 

 necessary to be overcome, being in this case much stronger, 

 requires and exhausts an exactly proportionate amount of 

 repellent force mechanically to overcome it ; hence the differ- 

 ent effect on a body such as the common thermometer, the 

 expanding liquid of which does not undergo a similar change 

 of state. Thus, in the example above given, of the mixture 

 of cold with hot water, the hot and cold water and the 

 mercury of the thermometer being all in a liquid state before, 

 and remaining so after contact, the resulting temperature is 

 an exact mean ; the hot water contracts to a certain extent, 

 the cold water expands to the same extent, and the ther- 

 mometer either sinks or rises the same number of degrees, 

 accordingly as it had been previously immersed in the cold 

 or in the hot solution, its mercury gaining or losing an equiva- 

 lent of repellent force. In the second instance, viz. the mix- 

 ture of ice with hot water, the substance we use as an indi- 

 cator, i. e. mercury, does not undergo the same physical 

 change as those whose relations of volume we are examining. 

 The force viewing heat simply as mechanical force which 

 is employed in loosening or tearing asunder the particles of 

 the solid ice, is abstracted from the liquid water, and from 

 the liquid mercury of the thermometer, and in proportion as 

 this fotce meets with a greater resistance in separating 

 the particles of a solid than of a liquid, so the bodies 

 which yield the force suffer proportionately a greater con- 

 traction. 



