470 Dr. T. Carnelley on the 



because the atomic weight of F is less than that of CI ; but 

 in other respects the spectrum is very different from those of 

 CI, Br, and I. These facts, it appears to me, agree perfectly 

 well with MendeljefFs theory of odd and even members of a 

 group (vide supra) ; for CI, Br, and I are odd members, 

 whilst F is an even member of the halogen group of elements. 



Sulplmr Group (S, Se, Te). Ditte (Compt. Rend, lxxiii. 

 p. 622) has also examined the spectra of this group by pass- 

 ing the induction-spark through the vapours of their chlorides 

 and eliminating the lines due to CI; and he found : — (1) That 

 the spectrum of S extends between the divisions 22 and 120 

 on the micrometer. It shows two maxima, one being a double 

 line in the yellow, and the other in the commencement of the 

 blue- (2) The spectrum of Se begins at 19 and ends at 125, 

 and also shows two maxima, the first between the yellow and 

 green, and the second in the blue. (3) The spectrum of Te 

 begins at 18 and ends at 146, and also shows two maxima, 

 one in the indigo and the other in the violet. 



The spectra of this group thus increase in range, especially 

 towards the ultra-violet end, as we pass from S to Te, i. e. 

 with the atomic weight. Each of the spectra likewise shows 

 two maxima, one being superior to the other ; and as we pass 

 from S to Te, the two maxima move towards the violet 

 end. 



Phosphorus Group (P, As, Sb, Br). — Ditte (Compt. Rmd. 

 lxxiii. p. 738) has likewise found : — (1) That the spectra of 

 the chlorides of the elements belonging to the phosphorus 

 group expand more and more, especially towards the violet 

 end, as the atomic weight of the positive element increases, or 

 in proportion as the properties of the element approach to 

 those of the metals. (2) The spectra of the chlorides of this 

 group all have three maxima of luminous intensity, due to very 

 brilliant lines separated by comparatively dark intervals. 

 These three maxima move towards the violet end as the atomic 

 weight of the positive element increases. 



Carbon and Silicon Group (C, Si, Ti, Zr only were examined) . 

 — The spectra of this group have been investigated by Troost 

 and Hautefeuille {Compt. Rend, lxxiii. p. 620) bypassing the 

 induction-spark through atmospheres of the chlorides and eli- 

 minating the lines due to CI. They found : — (1) That as we 

 pass from C to Si, and thence to Ti and Zr, i. e. as the atomic 

 weight increases, the rays become more and more refrangible. 

 (2) The spectra of each element has three maxima, caused by- 

 groups of luminous bands. (3) As the atomic weight of the 

 element increases, these three maxima advance more and more 

 towards the violet. Lead also, though not examined by Troost 



