On the Influence of Atomic Weight. 



305 



If sucli a laboratory should be fitted up, it would probably 

 be contemplated that instruction should be given, ultimately 

 at least, as well as research undertaken. But the locale which 

 would be sufficient for research would not necessarily be suit- 

 able for lecturing or other instruction. 



XXXVI. Influence of Atomic Weight. By Thomas Car- 

 nelley, jD.Sc.j Assistant Lecturer on Chemistry in the 

 Owens College*. 



THE object of the present paper is to point out the influ- 

 ence which the atomic weights of the elements have on 

 the chemical, and especially the physical, properties of both 

 elements and compounds. 



As early as 1826, Grmelin (and subsequently Pettinkofer, 

 Dumas, Kremers, Gladstone, Cooke, Low, Odling, Fleay, &c.) 

 directed attention to some curious relations between the atomic 

 weights of certain classes of elements and also between their 

 properties. Many of such relations will at once suggest them- 

 selves. Thus, of the elements CI, Br, and I, bromine stands 

 almost midway between chlorine and iodine, both as regards 

 its atomic weight and its chemical and physical properties. 





Atomic 

 weight. 



Specific 

 gravity of 

 the liquid 

 elements. 



Melting - 

 pointt. 



Boiling- 

 pointt. 



Heat evolved 

 by union with 

 one atom H. 



CI 



I 



Mean of CI and I = 

 Br 



35-5 

 127 

 81-2 

 80 



1-33 at 15° 

 4-00 at 107° 

 2-66 

 2-99 at 15° 



193 

 387 

 292 



248 



240 

 473 

 356 

 331 



23783 



- 3606 



10088 



9322 



Very similar relations exist between Ca, Sr, and Ba, of 

 which Sr holds a position almost intermediate between the 

 other two ; but what has been said with regard to CI, Br, I, 

 will be quite sufficient to illustrate the kind of relations which 

 were pointed out at the time referred to. It was not, how- 

 ever, till within the last fifteen years that these relations were 

 first traced in a systematic manner ; and it is to Newlands, 

 and especially to Mcndeljeff, that we owe a new field of research 

 and a new and powerful method of attacking chemical prob- 

 lems. The importance of the work of Rowlands and Mcndel- 

 jeff cannot be easily overrated. The principle proposed inde- 

 pendently by each of them will serve in the future, and has 

 done to some extent already, to indicate those directions in 



* Communicated by the Author. 



t Reckoned from absolute zero - 273. 



