LECTURE xv.] HISTORY OF CHEMISTRY. 331 



particular. 190 He arrives at the conclusion that the atomic 

 refraction of multivalent elements is variable, and that that of 

 carbon, for instance, is distinctly greater when double or triple 

 carbon linkings (or unsaturated carbon valencies, as he calls 

 them) occur in the compound. He determines the amount of 

 the increase for one ethylene linking and for one acetylene 

 linking, and then again calculates the molecular refractions ; 

 and in this way he frequently arrives at numbers which coin- 

 cide with the observed values. Later investigations of Nasini 

 and Bernheimer 191 and of Kanonnikoff 192 have only partially 

 confirmed the conclusions of Briihl ; but the latter still hopes 

 to be able to get rid of the exceptions. 193 J. Thomsen has 

 shown, however, that many of the values found by Brtihl can 

 also be calculated without the assumption of double or triple 

 carbon linking. 194 These investigations attain a special im- 

 portance from the fact that, according to the conclusions of 

 Exner, 195 the molecular refractions furnish, at the same time, 

 the " true molecular volumes." 



I cannot here enter more particularly into a discussion of 

 other investigations which are designed to show, in a similar 

 manner, a connection between physical and chemical pro- 

 perties ; and I shall content myself by drawing attention to 

 individual ones. Thus there are the investigations which 

 demonstrate a relation between the lowering of the freezing 

 points of solutions and the molecular weights of the substances 

 in solution (Coppet 1% and Raoult 197 ), and which are connected 

 with similar earlier experiments; 198 the research of G. Wiede- 

 mann on molecular magnetism ; 199 and the investigations on 

 the transpiration of gases by Graham, 200 by O. E. Meyer, 201 



190 Annalen. 200, 139 ; 203, I, 255, 363 ; 211, 121, 371. m Beiblatter 

 zu Wiedem. Ann. 7, 528 ; Accad. del Lincei [3] 18, 19, etc. 



192 Berichte. 14, 1697 ; 16, 3047 ; J. pr. Chem. [2] 31, 321 ; 32, 497. 



193 Annalen. 235, I. 194 Berichte. 19, 2837. 195 Monatshefte. 6, 249. 

 196 Ann. Chim. [4] 23, 366 ; 25, 502 ; 26, 98. 197 Comptes Rendus. 

 94, 1517 ; 95, 187, 1030; Ann. Chim. [5] 28, 133 ; [6] 2, 99, 115 ; 4, 401; 

 8, 289, 317. 198 Blagden, Phil. Trans. 1788, 277 ; Riidorff, Pogg. Ann. 

 114, 63 ; 116, 55 ; 145, 599. 199 Pogg. Ann. 126, i ; 135, 177. ' m Phil. 

 Trans. 1846, 573 ; 1849, 349- 201 Pogg. Ann. 125, 586 ; 127, 253, 353. 



