Mr. M. M. Pattison Muir on Chemical Classification. 195 



sions regarding the comparative avidity of different acids for 

 the same base* ; and when these studies shall have been ex- 

 tended and generalized, we shall most probably be able to 

 connect together chemical action and chemical composition. 

 Questions concerning composition which appear almost inca- 

 pable of solution by the ordinary method of reactions are even 

 now beginning to be solved by the thermochemical method f. 



But I cannot pursue this part of the subject further. I 

 would only allude to the results obtained by Tyndall J as estab- 

 lishing a connexion between absorptive power of gases for heat 

 and chemical composition; to the experiments of IludorfF§, 

 as pointing to a distinct connexion between lowering of tem- 

 perature during solution of salts in water and the molecular 

 weights of these salts ; and to Guthrie's researches on '^ Salt 

 Solutions and Attached Water " || . The experiments of Gamgee 

 upon the poisonous activity of ortho-, meta-, and pyrophos- 

 phoric acids, communicated to the Glasgow Meeting of the 

 British Association, point to a connexion between chemical 

 structure and physiological action. 



22. The results of those experiments which have already 

 been made upon the physical properties of groups of com- 

 pounds justify us in concluding that there is a close connexion 

 between these properties and the chemical composition of the 

 compounds. To render this connexion more definite, to ex- 

 hibit it as a quantitative connexion, will be one of the future 

 triumphs of chemical science. 



Assuming a certain valency for a given number of elements, 

 we are able to deduce a number of possible formulae for the com- 

 pounds produced by the union of these elements. Many of these 

 possible compounds have the same empirical formula. By actual 

 examination we find that many compounds really exist each 

 having that empirical formula which has been theoretically de- 

 duced ; but we are able, from a study of the physical properties 

 of these compounds, to say that they are really distinct bodies ; 

 we are able further to trace somewhat regular gradations of ]:)hy- 

 sical properties among them ; it may be that we are able to pre- 

 pare the complete series of isomeric compounds as laid down by 

 theory, and to arrange them in a connected group, or groups, 

 the members of which exhibit definite relations of physical 



* See article " Chemistry," by Armstrong, JEncyclojJ. Brit. 9tli edit. 

 p. 489 &c. 



t For an example of the application of this method see the article re- 

 ferred to (pp. 497, 498), where the composition of periodic acid is dis- 

 cussed. 



X Contributions to Molecular Physics, pp. 69-144. 



§ Poc>g. Ann. vol. cxiv. p. 62 ; vol. cxvi. p. 55. 



II Phil. Mag. [V.J vol.i. pp. 354, 446; vol. ii. p. 213. 



2 



