CALORIC, HEAT, FIRE. 19 



oxygen of the atmosphere becoming decomposed, and 

 evolving or setting it at liberty. It may be observed, 

 that oxygen owes its gaseous state to the caloric which 

 it contains, and in the process of combustion the oxygen 

 combines with the base of the body consumed and forms 

 an oxide, while the caloric escapes. The strongest heat 

 produced by combustion is that by means of the com- 

 bination of the oxygen and hydrogen gases,* a small 

 stream of which ignited, and made to fall on watch- 

 spring or even platina wire, will make it to melt like 

 wax. 



Percussion and friction are well-known mechanical 

 means of producing caloric. A blacksmith will, by ham- 

 mering a piece of iron, very soon make it sufficiently hot 

 to light a match. The heat produced is attributed to 

 the compression of the particles of the body forcing out 

 a portion of its latent caloric. In strong percussions 

 the first blow produces the greatest degree of heat, which 

 gradually decreases until it is exhausted; it will not 

 again produce heat until it has been exposed to the fire, 

 or has had some means of imbibing free caloric ; when 

 this is effected, the caloric will continue in a latent state 

 until it is again acted upon. In the collision of the flint 

 and steel, so much caloric is disengaged that the metallic 

 particles struck off are actually melted ; this is evident 

 from the pear-like form that such particles assume. 

 Friction is considered a continued series of percussions, 

 and the heat sometimes arising therefrom is very great. 

 Forests have been known to be fired by the friction of 

 the branches of the trees ; and coaches have been burnt 

 by the friction of the wheels. Most savage nations pro- 

 duce fire by the friction of two pieces of wood. Count 

 Romford, by boring cannon under water, so heated 

 it by the friction that he made it boil, and actually boiled 

 in it a piece of beef. 



Caloric is also sometimes produced by chemical mixture, 

 although not always ; for in some instances chemical 

 mixture produces cold. It may, however, be taken as a 

 general rule, that when substances become more con- 



* S"e article Gaseous Bodies. 



