IDEAS OF PHYSICAL CHEMISTRY 17 



of bells an equal distance at the same speed; but each bell has 

 its own rates of vibration, its tones and over-tones. You know 

 that in light and heat vibrations, the colors of the spectro- 

 scope are due to the preference which molecules exhibit for 

 certain rates of vibration. . . . 



What now are the forms of energy concerned in causing 

 chemical action? Until recently the chemist has dealt with 

 static chemistry, that is, the science in which the proper- 

 ties of quiescent substances are discussed, rather than with 

 the branch of knowledge which discusses the mechanism of 

 chemical change. Whenever affinity is treated as a specific 

 inherent property of the atoms, we naturally adopt the old- 

 fashioned views first enunciated by Bergmann more than a 

 century ago, that elements unite according to their specific 

 affinity for each other. If two substances are presented to a 

 third which would combine with either of them, it was sup- 

 posed to take up the one for which it had the greater affinity, 

 leaving the other uncombined. This doctrine of elective affini- 

 ties is a comfortable, but unfortunately an incomplete one. 

 It represents only one side of the question. 



If we continue building upon the kinetic theory discussed 

 above, a more complicated process is to be expected. As a 

 matter of fact we find that substances act upon each other 

 not only according to their mutual affinity, but are also 

 influenced by such conditions as their relative quantities in a 

 given space, their temperature, etc. To illustrate the former 

 of these two circumstances, suppose a mixture of equal masses 

 of A and B, which do not act upon each other, to be pre- 

 sented to C, with which both can react, but A more readily 

 than B. A and C will unite, but not to the exclusion of B; 

 there will be a partition of C between A and B, in which 

 A, the more active, gets the greater share of C. When, how- 

 ever, the quantity of B originally present is increased, more of 



