VI 11 PREFACE. 



believe there have been used only three terms which need 

 explanation even to the tyro. The latent caloric of steam, or 

 the caloric of elasticity, is that which is required to change 

 water from a fluid to an elastic gaseous state, without in- 

 creasing its temperature, and the latent caloric of water or 

 the caloric of fluidity, is that which is absorbed by ice when 

 it changes to water, without increasing its temperature. 

 The learner may understand the nature of this latent caloric 

 in the following manner. 



Suppose a tin vessel containing a pound of snow at the 

 temperature of zero, Fahr. with a thermometer in it, and 

 the whole placed over some regular source of heat, so as to 

 cause the thermometer to rise one degree every second ; at 

 the end of 32 seconds the thermometer will be at 32. Sup- 

 pose now the caloric to continue to enter the vessel with the 

 same rapidity, the thermometer will remain stationary at 

 32 for 140 seconds, and at the end of this time the snow 

 will all be melted. The caloric which went into the snow 

 to melt it, is called 140 of caloric of fluidity. 



As soon as the snow is all melted, the thermometer will 

 begin to rise again, and continue to rise one degree every 

 second for 180 seconds, provided the barometer stands at 

 30 inches, and the caloric flows in with the same velocity, 

 it will then be at the temperature of 212 ; at which point 

 it will stand for 1030 seconds, and during all this time the 

 water will constantly be changing to steam or vapor, and at 

 the end of 1030 seconds it will all be "evaporated. The 

 caloric which entered the water during this change, is called 

 the caloric of elasticity. 



The specific caloric of a body is its capacity of being 

 heated, as compared to that of water. For example ; if the 

 same quantity of caloric which heats a pound of water one 

 degree will heat a pound of air 4, the specific caloric of air 

 is called 0.25. 



