X 1 INTRODUCTION. 



As the amount of heat produced is proportional to the kinetic energy, which is 

 transformed through the concussion, we must find an adequate measure for both 

 forces. 



Heat-Unit. As a standard of measure of heat, we have the " heat-unit " or 

 calorie. The "heat-unit " or calorie is the amonnt of energy required to raise the 

 temperature of 1 gramme of water 1 centigrade. The "heat-unit " corresponds to 

 425*5 gramme-metres, i.e., the same energy required to heat 1 gramme of water 

 1 C. would raise a weight of 425*5 grammes to the height of 1 metre; or, a weight 

 of 425*5 grammes, if allowed to fall from the height of 1 metre, would by its concus- 

 sion produce as much heat as would raise the temperature of 1 gramme of water 1 C. 

 The " mechanical equivalent " of the heat-unit is, therefore, 425*5 gramme-metres. 



It is evident that from the collision of moving masses an immeasurable amount of heat can 

 be produced. Let us apply what has already been said to the earth. Suppose the earth to be 

 disturbed in its orbit, and suppose further that, owing to the attraction of the sun, it were to 

 impinge on the latter (whereby, according to J. R. Mayer, its final velocity would be 85 

 geographical miles per second), the amount of heat produced by the collision would be equal to 

 that produced by the combustion of a mass of pure charcoal more than 5000 times as heavy 

 (Julius Robert Mayer, Hclmholtz). 



Thus, the heat of the sun itself can be produced by the collision of masses of cold matter. 

 If the cold matter of the universe were thrown into space, and there left to the attraction of its 

 particles, the collision of these particles would ultimately produce the light of the stars. At 

 the present time, numerous cosmic bodies collide in space, while innumerable small meteors 

 (94,000 to 188,000 billions of kilos, per minute) fall into the sun. The force of gravity is 

 perhaps, in fact, the only source of all heat {J. R. Mayer, Tyudall). 



We have a homely example of the transformation of kinetic energy into heat in the fact that 

 a blacksmith may make a piece of iron red-hot by hammering it. Of the conversion of heat 

 into kinetic energy we have an example in the hot watery vapour (steam) of the steam-engine 

 raising the piston. An example of the conversion of potential energy into heat occurs in a 

 metallic spring, when it uncoils and is so placed as to rub against a rough surface, producing 

 heat by friction. 



4. Chemical Affinity : Relation to heat. Whilst gravity acts upon the particles 

 of matter without reference to the composition of the body, there is another atomic 

 force which acts between atoms of a chemically different nature ; this is chemical 

 affinity. This is the force in virtue of which the atoms of chemically different 

 bodies unite to form a chemical compound. The force itself varies greatly between 

 the atoms of different chemical bodies; thus we speak of strong chemical affinities 

 and weak affinities. Just as we were able to estimate the potential energy of a 

 body in motion from the amount of heat which was produced when it collided with 

 an unyielding body, so we can measure the amount of heat which is formed when 

 the atoms of chemically different bodies unite to form a chemical compound. As 

 a rule, heat is formed when separate chemically-different atoms form a compound 

 body. When, in virtue of chemical affinity, the atoms of 1 kilo, of hydrogen and 

 8 kilos, of oxygen unite to form the chemical compound water, an amount of heat is 

 thereby evolved which is equal to that produced by a weight of 47,000 kilos, falling 

 and colliding with the earth from a height of 1000 feet above the surface of the 

 earth. If 1 gramme of H be burned along with the requisite amount of O to form 

 water, it yields 34,460 heat-units or calories : and 1 gramme carbon burned to car- 

 bonic acid (carbon dioxide) yields 8080 heat-units. Wherever, in chemical processes, 

 strong chemical affinities are satisfied, heat is set free, i.e., chemical affinity is 



