314 



Dr. T. Carnolley on the 



This eighth group, as previously remarked, is a very peculiar 

 group. The elements belonging to it resemble one another in 

 many respects ; thus : — (1) they are all of a grey colour and 

 are difficult of fusion ; (2) they possess in a high degree the 

 power of condensing and giving passage to gases, as in the 

 case of Pd, Pt, Fe, &c; (3) their highest oxides are bases or 

 acids of little energy, and are easily reducible to lower oxides, 

 which are far more basic ; (4) their salts form stable com- 

 pounds with ammonia &c. 



Atom Analogues. — From what has been said above, it will 

 be seen that the position of an element R in the system of 

 elements is determined by the series and group to which the 

 element R belongs, and therefore by the elements X and Y 

 standing on either side of it in the same series, and also by the 

 elements R' and R x/ standing above and below it in the same 

 subgroup — thus, 



Group. 



W 



Series : — X 



R 



IV 



and this in such a way that the properties of R are the mean 

 of those of X, Y, R', and K". The elements X, Y, K', K" 

 are termed by Mendeljeff the atom analogues of the element R. 



Group VI. 



S 



Series 5: — As 



Se 



Br 



Te 



Here As, Br, S, and Te are the atom analogues of Se, the 

 atomic weight of which is equal to the mean of those of the 



other four elements ; thus j =79. So much, 



then, for the influence of the atomic weights of the elements 

 on their chemical properties. We shall now endeavour to 

 point out this influence on the physical properties ; and for the 

 sake of illustration we will take the melting-points, as they are 

 capable of being represented numerically. In the following 

 Table the elements are arranged exactly as in Mendeljeff's 

 original Table (vide supra), the only difference being that the 

 atomic weights are replaced, where possible, by the corre- 

 sponding melting-points. 



