118 ACTION OF AQUEOUS AMMONIA ON 



electrons in compounds. Kinetic vibration also tends to break 

 down the molecule. But heat alone is not sufficient; at least 

 a trace of water must be present to catalyze the dissociation. 

 The action of water is possibly that of making the unshared 

 electron pair in the additional octet about one of the mercury 

 atoms more mobile so that it can migrate to the other mercury 

 with the formation of the metal. 



This type of structure may be applied to other mercurous 

 compounds than the halides. Mercurous nitrate is Hg3(N03)j 

 .2HjO, which might be represented as mercuro diaquo mercuric 

 nitrate or [Hg = Hg(H20)2] (N03)2. According to this structure, 

 the nitrate ions are not held in the complex, but are free to ionize 

 in solution. The great solubility of mercurous nitrate in con- 

 trast to the insolubility of the halides is thus accounted for. 



From the isotopic point of view mercurous chloride is very 

 complex. F. W. Aston* has shown that mercury is a mixture 

 of isotopes. By the mass spectrograph method, he obtained a 

 band from mass number 197 to 200 probably including isotopes 

 for each unit within this range, in addition to lines at mass 

 numbers 202 and 204. That is, mercury may consist of a mix- 

 ture of six isotopes of mass numbers 197,198, 199, 200, 202 and 

 204. He also found chlorine to be a mixture of two isotopes with 

 mass numbers 35 and 37. If the structure of mercurous chloride 

 is Hg = HgCl2, then 108 isotopic isomers are possible. 



We are now in a position to consider the reaction between 

 mercurous chloride and aqueous ammonia. This is best ex- 

 pressed by the equation 



Hg.Cl,-h2NH, = Hg-fHgNH,Cl + NH,Cl. 



The formation of metallic mercury as one of the products of the 

 reaction has not been universally accepted. R. J. Kane' 

 believed that HgjNHjCl was formed instead of mercury and 

 infusible white precipitate. This view has persisted in many 

 text books to the present day. Therefore the most important 

 question to settle concerning the reaction is whether or not 

 metallic mercury is formed. C. Barfoed'" exposed the dry 



