ORIGIN OF ELEMENTARY SUBSTANCES. 129 



IV. 



. O , 12 = C =12 



1 X 27 . o = Al = 27 



2X27— 12= — = 42 



3 X 27 —12 = — =69 



4 X 27 —12 = — = 96 



5 X 27 — 12 = Yt =123 



6 X 27 — 12 = lu =150 



7 X 27 —12 = E =177 



8 X 27 — 12 = Tl =204 



9 X 27 —12 = Th =231 



It will be observed that there are three elements missing 

 in this group, the atomic weights of which can be pre- 

 dicted in like manner with those of the missing elements 

 in the preceding groups. The Table also affords the means 

 of correcting and determining the atomicities of elements 

 of the series which, from their rarity, have not been 

 sufficiently investigated. It will be further observed that, 

 besides the similar numerical relations of the members of 

 this group with those shown in Tables II., III., the atomic 

 weights are all multiples of 3, and are classified accordingly 

 as forms of H^n. 



The spectral reactions of this series of elements are 

 remarkable from the oxides of carbon and of erbium giving 

 a spectrum of lines at low temperatures, and by the sim- 

 plicity of the spectral lines of indium and thallium in the 

 more refrangible parts of the spectrum. The atomic 

 weights of C, Al, Tl, and Th, are identical with those 

 generally received, and afford presumptive evidence that 

 the atomic weights of the intermediate members are equally 

 correct. It will, however, be observed that the atomic 

 weights of yttrium and indium are douljlc the accepted 

 numbers (Yt = 6i7, In=:75-6); but in regard to the latter 

 element, it has not yet been definitely agreed which 

 multiple of 37*6, the original determination, shall be the 

 classical one, as the atomicity has been fixed by different 

 chemists at 75-6, 113, and 150, the number assigned to 



SER. III. VOL. X. K 



