212 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



In thermochemical reasoning particularly, accurate data possess a 

 significance wholly denied to cruder results. The relations between 

 the heat of formation of organic substances, if determined accurately 

 enough, may be hoped to throw light on organic structure and the 

 nature of valence. Approximate values are of no use at all for such 

 a purpose. Enough has been done already to suggest relations of a 

 highly interesting sort between heats of combustion, heats of evapo- 

 ration, compressibility, and many other properties; and to add sup- 

 port to the theory of compressible atoms. 1 Moreover, taken in con- 

 nection with more precise knowledge of the free energy of chemical 

 changes, the new results will permit the evaluation of bound energy, 

 and give results which may decide whether or not bound energy is 

 really a simple function of change of heat capacity, as has been more 

 than once intimated. 2 There is time now only to suggest possibilities, 

 each of which would take hours to elucidate. 



How can we collate all the varying properties so as to show their 

 many-sided relationships ? How can we piece together the scattered 

 evidence so as to synthesize an adequate conception of the ultimate 

 nature of tilings ? These questions may never be adequately 

 answered, but science must ceaselessly endeavor to solve the problem 

 which they present. 



A first step is clearly to find the way in which each property varies 

 hi relation to every other. With this in mind, let us appeal to the 

 irregular system of the periodic classification, which formed the sub- 

 ject of the Faraday lecture by MendeleefT 22 years ago. Tins mys- 

 terious index of uncharted tendencies must hide within itself guiding 

 ideas capable of pointing us onward. 



Clearly each property must receive, not merely qualitative, but 

 strictly quantitative treatment. With this hi mind, let us compare 

 our various facts by plotting atomic weight in one direction, and all 

 the other properties in another. Then by noting the parallelism or 

 antiparallelism of the wavy lines many relationships may be traced. 

 The device is not new. Carnelley compared Lothar Meyer's atomic 

 volume curve with that of melting points, and other similar data 

 have been plotted ; but the method has not been used to its full 

 extent. 



Let us then turn to the diagram (fig. 3) in which the variations in 

 a number of properties are plotted with relation to the atomic 

 weights. Prominent among the lines is the atomic-volume curve just 

 mentioned. Below it is plotted the almost parallel line depicting the 



1 Richards, Proceedings American Academy, 1908, vol. 39, p. 5S1; also Zeitsch. physikal. Chem., 1904, vol. 

 49, p. 15. 



2 Helmholtz, Lewis, van't Hoff, Nernst, and Haber, as well as the author and many others, have con- 

 tributed to this discussion. An interesting resume^ with references to many of the original papers, will 

 be found in Haber's Thermodynamics of Technical Gas Reactions (translated by Lamb), London and 

 New York, 1908. 



