10 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



In these figures one may find traces of many properties associated 

 with firmness of structure or intensity of self-affinity. For example, 

 the order of sequence of the energy-quotients agrees essentially with 

 that of tenacity and of hardness. There is some relationship also to 

 boiling points and melting-points, although here there are more ex- 

 ceptions. " Chemical affinity " is so much affected by electrical relations 

 and by atomic volume that one would expect to find regularity only on 

 comparing similar elements. Such comparison (zinc with cadmium, or 

 carbon with silicon) seems to show that the energy-quotient tends to 

 increase with diminishing atomic weight. 



Having thus plausible inference, from independent sources, as to the 

 relative values of the compressing agencies existing in metals at the 

 ordinary temperature, it is worth while to study the correction which 

 must be applied to the volume-change exhibited in chemical combina- 

 tion with another element. In zinc the self-affinity is so great (boiling 

 point = 1200° A), and the metal is hence already so compressed, that 

 a given further pressure causes less change in its volume than it would 

 cause in the case of mercury. That is, the mercury contracts more 

 than zinc when it is oxidized. Hence the difference between the 

 volume of the oxide and the volume of the metal gives too low a 

 value for the volume of the combined oxygen in the case of mercury. 



