CHEMICAL PROCESSES IN CELLS. 149 



tricity. All the actual forces have a tendency to be converted into a 

 single actual force, heat; thus, as the motions of bodies decrease through 

 friction and the resistance of the atmosphere, and as the electric current 

 meets with resistance, they are converted into heat. So, also, the form 

 of movement which appears as actual force in the formation of chemical 

 compounds is usually manifested by the development of heat, or occa- 

 sional light ; and the actual forces which disappear in chemical decompo- 

 sition are again usually represented by heat or light. Nearly all bodies 

 are chemical compounds ; that is, their atoms, are bound together by 

 their affinity for their atoms. This also applies to the isolated elements 

 which, in their free state, exist as molecules of like atoms. So long as 

 no external force is brought to bear upon chemical compounds, there is 

 no tendency to decomposition or formation of new compounds. 



Heat is the most ordinary external force which produces chemical 

 change. The stability of chemical compounds may therefore be meas- 

 ured by the amount of heat required to break up the compound. Every 

 compound, even the most stable, may be broken up if the heat is suf- 

 ficient. While C0 2 requires enormous heat to decompose it, the organic 

 compounds of carbon are decomposed at moderate temperature. Conse- 

 quently,^ the latter case the atoms are loosely combined ; that is, in the 

 formation of this combination not all the potential affinity is converted 

 into actual energy, but a considerable degree of potential, with a tendency 

 to form compounds, still remains. When to such compounds heat is 

 applied in a degree equal to the amount of actual energy liberated in the , 

 formation of the compound, the atoms are liberated and again acquire 

 their original potential energy. If a new combination is now formed, 

 the potential is again converted into actual energy, and the latter, in the 

 form of heat, is proportional to the closeness of the new compound. 

 This is the process which is concerned in the burning of every organic 

 compound. Thus, by the artificial application of heat single atoms of the 

 combustible body and of the atmosphere are separated and their combi- 

 nation results in the- liberation of heat, which is itself sufficient to 

 decompose other atomic combinations, and the processes of combustion 

 goes on by itself. The entire amount of heat liberated equals the 

 difference between the amount of heat required to break up the organic 

 compound and the amount liberated in the formation of simpler, closer 

 compounds. If, on the other hand, atoms, if they are separated by 

 considerable force, do not enter into a closer but into a looser compound, 

 more actual energy is lost than is liberated, and a decomposition results 

 in which a certain amount of heat is used up, which in the new combi- 

 nation is present as potential force for future combustions. The amount 

 of potential energy is therefore dependent on the closeness of the chemical 

 combination, and not on the separation of the affinities. As a rule, 



