PHOSPHORUS, SULPHUR, AND SELENIUM. 



39 



supposed to be the most probable. If the theory of compressible atoms is 

 used as a guide, it is reasonable to suppose that when a substance is sub- 

 jected to but slight internal pressure from its cohesion, an outside press- 

 ure would produce a greater change of volume than the same outside 

 pressure would produce upon a similar substance, already much com- 

 pressed. Such is the case with sulphur and selenium. This is merely 

 carrying the arguments drawn from the fact concerning phosphorus and 

 the inferences concerning carbon to the comparison of two similar 

 elements, instead of simply to the comparison of the different states of the 

 same element. 



These results will be considered in relation to one another and also in 

 relation to the compressibilities of the other elements in another paper of 

 this series,* as well as in a future paper in which their relations to the the- 

 ory of compressible atoms will be more clearly set forth. The present 

 investigation aims only to present the facts in order that they may go on 

 record at once. 



It remains only to state the results in terms of the three pressure stand- 

 ards commonly accepted. 



Average compressibilities of C, Si, P, S, and Se, between 

 100 and 500 atmospheres. 



In conclusion, it is a pleasure to express our thanks for the generous 

 support of the Carnegie Institution of Washington. 



*See p. 65 of this publication. 



