RICHARDS. — SOURCE OF CHEMICAL HEAT. 411 



in. Summary. 



The contents of the paper may be divided into two parts : In the first 

 part is set forth an approximate generahzation which rests upon facts 

 alone. This part of the paper can be overthrown only by the proof that 

 the facts upon which it rests are erroneous. In the second part of the 

 paper a plausible hypothetical interpretation of the facts is given. This 

 part of the paper stands ready to share the fate of all hypotheses, — 

 namely, to retire into oblivion if it is not capable of aiding the discovery 

 of truth. 



In brief, the chief points touched upon may be summed up as follows : — 



I. (rt) It has been shown that the contraction exhibited during 

 chemical combination is in many cases approximately proportional to the 

 heat evolved. 



(b) Upon correcting the results for known differences of compressibility, 

 the approximation becomes closer. 



(c) An approximate calculation of the work which would probably be 

 involved by the compression of a gram-atom each of sodium and chlorine 

 into the space occupied by a gram-molecule of salt showed this work to 

 be of the same order of maijnitude as the actual heat of formation. 



(d) From these facts and calculations the inference is drawn that the 

 heat of chemical reaction is chiefly due to the energy required for the 

 compression which takes place in the reaction. 



(e) Possible corrections are pointed out. 



(f) An explanation is given upon the same basis of the mechanism of 

 the heat of adsorption, adhesion, and change of allotropic form. 



II. (a) While the evidence is not exact, it affords a strong presump- 

 tion in favor of the hypothesis of compressible atoms. The possibly far- 

 reaching effect of this simple and plausible hypothesis upon chemical 

 theory is pointed out. 



(b) There is given a list of the especially prominent aspects of the 

 question which will form the subjects of immediate experimental and 

 theoretical study in this Laboratory. 



Cambridge, Mass., U. S. A. 



