regarded as Compounds of the First Order. 453 



is i, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, aud 18, bat some 

 of these are ill-defined. 



Another example of the co-ordination number twelve is 



seen in the alloy -~->[Na*Zn 13 ]E •>. The frequency of this 



number is interesting, because eight is the highest co- 

 ordination number found in complex compounds, e. g. 

 (Ba8NH 3 )01 2 , according to Werner [Neuere Anschauungen 

 auf dem Gebiete der anorganischen Ckemie, 3rd ed. p. 52). 

 Quite recently however, Hiittig (Zeitsch. fur anorganische 

 und allgemeine CJiem. cxiv. p. 161 (1920)) has prepared a 

 compound FeCl 3 12NH s or (Fel2NH 3 )01 3 



These views may be extended to alloys in which the co- 

 ordination number as expressed by the usual formula does 

 not admit of symmetrical distribution in space. For just as 

 in the series (Co6NH 8 )Cl 3 , (Oo5NH 3 Cl)C] 2 , (Co4NH 3 Cl 2 )Cl, 

 etc., the chlorine atoms complete the octahedron when the 

 ammonia molecules are insufficient, so in the alloy NaCd 5 , 

 the octahedron may be completed by the electron of the 



r E i 



sodium atom, as seen in the formula [_Na*-Od 5 J • Similarly 

 the compounds FeZn 7 and NiZn 7 may be written 



LFg a 'Zd 7 JE 7 and [_Ni*ZnJ E 



one of the valency electrons from the iron and nickel atoms 

 respectively completing a cube with the seven zinc atoms 

 around the kernel. 



The structure of the alloys mentioned above has hitherto 

 been the despair of all valency theories, and the fact that 

 they fall so readily into the scheme of chemical combination 

 is strong evidence of the correctness of the point of 'view 

 developed in this paper. 



Further support for the above theory of amalgams, etc., 

 is provided by the following considerations regarding 

 ammonium amalgam. 



Cobaltic chloride CoCl 3 is incapable of existence, the at- 

 tractive force of the cobalt (secondary negative affinity) being- 

 sufficient to extract an electron from one of the chloride ions 

 with the production of cobaltous chloride and chlorine. If, 

 however, the secondary negative affinity of the cobalt is 

 partially saturated by the free secondary positive affinity of 



the nitrogen atoms in six molecules of ammonia <■ NH 3 -<---, 



the electron can no longer be extracted from the chlorine 

 atom and hexammine cobaltic chloride (Co6NH 3 )Cl3 is a 

 stable substance. Now, in ammonium 



(-■•■ >H A 2 E,N A E 4 HV --■)<— E- >, 



