234 Mr. J. F. Heyes on the 



experiments on the explosion of carbonous oxide * with 

 oxygen is also probably due to this provisional tetravalency 

 of oxygen. 



Undoubtedly the chief difficulty which is present to the 

 mind in using these links or conceding these valencies, in the 

 case of proposed higher values, is the doubt whether the 

 combination is of the same order or intensity so to speak, and 

 can be strictly called chemical combination in all cases. On 

 this account JProfessor Armstrong | wrote the compounds 



HgCl 3 . 2KC1 and AsF 5 . 2KC1 



tt CI . C1K , „ A F . OIK 



H S01.C1K and FsAs F.ClK- 



But the valency as matter of discussion might perhaps be 

 indicated as 



C1=C1— K 

 Hg< 



X Clr= = Cl— K 



There are many such compounds ; e. g. 

 HgCl 3 . 2NH 4 C1, I11CI3 . 3KC1, A1 2 F 6 . 6NaF, 

 CuCl 2 . 2KC1, TICI3 . 3KC1, Ir 2 01 6 . 6K01, 



FeF 2 .2KF, ?KI 3 .3KI. Ru 2 Cl 6 . GNaCl, 



MgBr 2 . 2KBr. or ? M'"C1 3 . 3MC1. 



These formulae clearly suggest the problem in quanti- 

 valency which lies before us. Certainly such phrases as " re- 

 sidual valency," " surplus affinity," " residual charge on the 

 atoms " are open to the objections which have already been 

 suggested. They may prematurely beg the problems of 

 chemical affinity. Even in the case of PCI 5 there can scarcely 

 be said to be observed a perfect chemical equality of the atoms 

 such as we believe to be in CH 4 . The chlorine is apparently 

 dealt with preferably in two fifths and three fifths in most 

 chemical reactions. Such considerations have long induced 

 Professor Kekule and others to maintain that a phosphorus 

 atom is constantly trivalent. 



For the higher valency under discussion, in the case of 

 oxygen and chlorine, if we are to use other words, it may 

 be found convenient to use a kindred word validity, which 

 has therefore been occasionally used in this paper. We 



H v 



* Water-molecules necessarily present would bo formulated X)==. 



Cf. note on the last page, 

 t B. A. Report, Aberdeen, 1885. 



