MATTER, LIVING FORCE AND HEAT. 1 5 



what we have already stated, you will perceive that in order to 

 remove the particles violently attracting one another 

 asunder, the expenditure of a certain amount of living force 

 or heat will be required. Hence it is that heat is always 

 absorbed when the state of a body is changed from solid to 

 liquid, or from liquid to gas. Take, for example, a block of 

 ice cooled down to zero ; apply heat to it, and it will 

 gradually arrive at 32°, which is the number conventionally 

 employed to represent the temperature at which ice begins 

 to melt. If, when the ice has arrived at this temperature, 

 you continue to apply heat to it, it will become melted ; 

 but its temperature will not increase beyond 32 until the 

 whole has been converted into water. The explanation of 

 these facts is clear on our hypothesis. Until the ice has 

 arrived at the temperature of 3 2° the application of heat 

 increases the velocity of rotation of its constituent particles ; 

 but the instant it arrives at that point, the velocity produces 

 such an increase of the centrifugal force of the particles 

 that they are compelled to separate from each other. It is 

 in effecting this separation of particles strongly attracting 

 one another that the heat applied is then spent ; not in 

 increasing the velocity of the particles. As soon, however, 

 as the separation has been effected, and the fluid water 

 produced, a further application of heat will cause a further in- 

 crease of the velocity of the particles, constituting an increase 

 of temperature, on which the thermometer will immediately 

 rise above 32 . When the water has been raised to the 

 temperature of 212 , or the boiling-point, a similiar pheno- 

 menon will be repeated ; for it will be found impossible to 

 increase the temperature beyond that point, because the 

 heat then applied is employed in separating the particles of 

 water so as to form steam, and not in increasing their 



