Mr. M. M. Pattison Muir on Chemical Classification. 259 



the difficulties which have yet to be ovorcomo before this 

 consnmmation is attained, and the dangers into which we run 

 by rashly 2")uyhing to extremes deductions made from an 

 hypothesis which is now but in its infancy. 



29. Part of the general problem presented to the chemist 

 of to-day is to trace the connexion which should exist (if the 

 theory of valency be a true theory) between the properties of 

 chemical compounds and the '' nature " of their constituent 

 atoms. In other words, the chemist is to examine the nature 

 of the elementary atoms ; he is to determine, with the greatest 

 possible care, the physical and chemical constants of these 

 atoms ; he is then to endeavour to arrange them in groups, 

 and he is to trace the influence of the individual atoms in 

 conditioning the properties of their compounds. Turning, 

 then, to the second part of the problem, the chemist is 

 to pursue the inquiries already made into the structure 

 of compounds; he is to endeavour to determine how the 

 atoms are linked together in compounds, and he is to at- 

 tempt to correlate this structure with the general properties 

 of the compounds. He is then to combine both methods, and 

 to ascertain, if possible, in what way the influence of the 

 "nature " of the atoms is itself influenced by the linking of 

 these atoms. He is then to study the transformations of 

 energy which doubtless accompany all changes of structure ; 

 he is to inquire into the nature of chemical energy itself; 

 and, finally, he is to combine the results of all his researches, 

 and, aided by the laws of number and of space, he is to frame 

 a complete system of chemical classification. 



Now it is only within very recent years that that part of 

 the general problem which deals with the connexion between 

 the nature of chemical atoms and the properties of chemical 

 compounds has received any careful investigation. In the 

 remaining paragraphs of this paper I propose to give a brief 

 sketch of what has been done in this direction. 



30. Attempts have from time to time been made, through- 

 out the preceding fifty or sixty years, to trace some connexion 

 between the atomic vreights of groups of elements and the 

 general properties of the elements and their compounds. 



Prout's hypothesis, advanced soon after the enunciation of 

 the atomic theory by Dalton, is well known. The researches 

 of Berzelius, of Marignac, and of Stas, showed that the hypo- 

 thesis of Prout, in its original form at least, was untenable. 

 Gmelin, in the 3rd and subsequent editions of his Handbook, 

 drew attention to regularities in the increase and decrease of 

 the atomic weights of analogous elements. Dumas, Glad- 



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