THE POSSIBLE SIGNIFICANCE OF CHANGING 

 ATOMIC VOLUME. 



By Theodore William Richards. 



Presented May 8, 1901. Received April 16, 1901. 



Compressibility is a universal property of matter. It is so essential 

 an attribute of the experimental universe that it is ascribed even to the 

 imponderable and imaginary ether as well as to " material." The three 

 states of matter are compressible in very varying degrees, dilute gases 

 being compressible to a great extent, highly compressed gases and liquids 

 to a far less extent, and solids to an extent usually even less than liquids. 

 The first case has been studied in great detail, the last two scarcely at all. 



Compressibility is simply an evidence of work done upon a system by 

 a given pressure. It' the application of considerable pressure in a system 

 causes only a slight change of volume, it is evident that there must be 

 other powerful influences at work. Clearly a clue as to the variation in 

 these influences can be found in the quantitative study of the phenomena. 



In all reversible cases which may be studied directly, an increase in 

 pressure is accompanied by an increase of resistance to pressure and a 

 diminution of volume. This depends upon the fundamental idea of 

 equilibrium, and is a special case of the general principle sometimes 

 named after Le Chatelier. Working backwards from this idea, one may 

 infer with regard to any given substance at a given temperature, that it 

 is under the influence of great pressure if its volume-change is unusually 

 small under addition of a given pressure. 



There are two conceivable causes of great compression in a substance. 

 The pressure may be applied from the outside, or it may be due to the 

 mutual internal attraction or affinity of the smallest particles of the 

 substance for one another. That is, the substance may be compressed 

 either by an outside pressure, or by the intensity of its own cohesion. 

 The first may be typified by highly compressed gases, the second by 

 liquids, whose small compressibility may be taken as evidence of great 

 compression. 



