314 Mr. J. A. Wanklyn on the Constitution 



proposed to look upon ferric chloride as a compound of the 

 second order of complexity, and showed that on this supposi- 

 tion the atomic weight of iron might be 28 or 56. 



Among other possible views of the constitution of iron-com- 

 pounds (and he extended them to the other metals of the iron- 

 family), Erlenmeyer proposed this : 



Fe iv = 56. 



1 . . Fe CI 4 Hypothetical. 



2 . . Fe 2 CI 4 Ferrous chloride. 



3 . . Fe 2 CI 6 Ferric chloride. 



Of course, on the same principle, chromium-compounds would 

 be represented thus : — 



Gr iv =52'5. 



1 . . €r CI 4 Hypothetical. 



2 . . Gr 2 CI 4 Chromous chloride. 



3 . . Cr 2 CI 6 Chromic chloride. 



In atomicity these metals would be like carbon, compounds 

 2 and 3 being chlorine representatives of the iron and chromium 

 ethylene, Fe 2 H 4 , and ethyl-hydride, Cr 2 H 6 . 



When either these hypothetical chlorides shall have been 

 discovered, or representatives of them shall have been found, 

 this theory will have acquired claims on the attention of chemists. 



There is a chromium representative of the hypothetical chlo- 

 ride. It is chlorochromic acid. 



The analysis and vapour- density of chlorochromic acid agree 

 with the formula Cr O 2 CI 2 . That chlorochromic acid and the 

 proto- and sesqui-chlorides of chromium are of different orders 

 of complexity is proved by the difference in their boiling-points. 

 If anyone maintains the formula of sesquichloride of chromium 

 to be Cr CI 3 , he is at once involved in this absurdity, that there 

 are two chromium-compounds differing only in this, that in the 

 one there is a certain atom of chlorine, and in the other this 

 certain atom of chlorine is replaced by O 2 , but that whilst the 

 former boils at a red heat, the latter (with the oxygen in it) boils 

 a little above the boiling-point, of water. 



It is therefore quite certain that, whilst chlorochromic acid con- 

 tains only Cr in the standard volume, sesquichloride of chromium 

 must contain at least Cr 2 . 



From the close analogy subsisting between sesquichloride of 

 chromium and sesquichloride of iron (the vapour-density of 

 which requires Fe 2 Cl 6 ); it also follows that the molecule of 

 chromic chloride (sesquichloride of chromium) must be Cr 2 CI 6 . 



The relation of chlorochromic acid to chromic chloride having 



