THE QUANTITY OF RESIDUAL VALENCE POSSESSED 

 BY VARIOUS MOLECULES 



BY A. P. MATHEWS 



All, or nearly all molecules .possess some power of com- 

 bining with molecules of the same or different kinds. This 

 combining power is called the residual valence, or affinity, 

 of the molecule. Thus ammonia, NH 3 , will unite with water 

 or acids, a molecule of hemoglobin with oxygen, glucose and 

 probably all salts with water when they dissolve in it, and 

 other examples of this power of molecular union might be 

 given. 



The importance of residual valence to the molecule is 

 generally recognized. It is probable that, with the possible 

 exception of ionic reactions, these molecular unions precede, 

 and are a necessary condition for, most chemical interactions 

 between molecules; for molecules do not seem to affect each 

 other by simple contact, but only when they are united into 

 a new molecule by chemical bonds. It would seem that it is 

 only when they are thus united that the atoms of two mole- 

 cules are able to interchange and undergo those rearrange- 

 ments resulting in the birth of new molecular species. 



The importance of residual valence makes it desirable to 

 know how much of it is possessed by each species of molecule. 

 Since it is possible that this amount may not always be the 

 same even for the same species of molecule, a method must 

 be used in determining the average amount which will examine 

 the molecular system without disturbing it. For example 

 not all the molecules of carbon dioxide may be in a condition 

 to unite with water at the same instant. Many facts indicate 

 that of all the molecules of oxygen in the air only a few, at any 

 instant of time, are in a condition to unite with oxidizable 

 substances. The number possessing residual valence is small. 

 This changing molecular condition seems analogous to, and 

 is very possibly essentially identical with, the varying condi- 

 tion of atoms of radium which only occasionally become 



