CONTRIBUTIONS FROM THE CHEMICAL LABORATORY OF 

 HARVARD COLLEGE. 



THE SIGNIFICANCE OF CHANGING ATOMIC VOLUME. 



IL — THE PROBABLE SOURCE OF THE HEAT OF CHEMICAL 

 COMBINATION, AND A NEW ATOMIC HYPOTHESIS. 



By Theodore William Richards. 



Presented January 9, 1901. Received January 14, 1901. 



I. Presentation of the Facts. 



In a paper first presented to the American Academy of Arts and 

 Sciences in May, 1900, then revised and printed in the Proceedings a 

 year later,* certain interesting facts concerning the significance of chang- 

 ing atomic volume were pointed out and emphasized. It was shown 

 that the contractions and expansions occurring in liquids and solids during 

 chemical reaction are related to the affinities concerned, as nearly as we 

 can estimate those affinities. A greater affinity seems to produce a 

 greater contraction, if the compressibilities concerned are equal. It 

 seemed possible that this idea might have very fundamental and far 

 reaching applications as to matters of fact, and might lead moreover to a 

 somewhat new conception of the atomic hypothesis. 



Many such applications have already been tested with plausible results. 

 The complete detailing of the ramifications of this idea would need the 

 compass of a book ; in the present paper the attempt will be made 

 merely to sketch the relations of a single side of the question. 



In the paper already referred to the suggestion was made that the 

 heat of chemical reaction might be traceable to the work done by chemi- 

 cal affinity in compressing the substances concerned. The discussion 

 below will show the close relationship which exists between these facts. 



The most serious diflaculty in the way of determining the relationship 

 is the extreme scarcity of data concerning compressibility. Obviously 



* These Proceedings, 37, 1 (June, 1901). 



