44 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 



65 



possible beyond a certain number (cf. the instability of C1 2 7 and 

 Mn 2 7 ) . This would account for the steady progress from trivalence 

 to divalence that has just been noted. Subjoined is a list of the 

 valences of the transition metals in their chlorides : 



The numbers in heavy type represent the chlorides that are stablest 

 to oxidation or reduction (as far as the relations could be ascer- 

 tained), and the decrease in effective valence from left to right is 

 brought out clearly. The values in parentheses do not of neces- 

 sity belong to this scheme, but can be due to the other phase of the 

 atom's structure : however, the tendencies of the two phases may 

 coincide, as in the case of Zn, Cd, and Hg. (Monovalent Hg, in the 



