TRANSACTIONS 



OF THE 



Notta g>rottatt itiHtttnte of ^mnn 



SESSION OF 1924-1925 

 (Vol. XVI, Part 3) 



The Action of Aqueous Ammonia on Mercurous Chloride. — 

 By Harold S. King, Assistant Professor of Chemistry, 

 Dalhousie University, Halifax, Nova Scotia. 

 (Read 8 December, 1924) 



Mercurous chloride is turned grayish black by the action 

 of aqueous ammonia. This is the standard method used in 

 the qualitative analysis of mercury in the mercurous state. 

 Though the test is extremely easy to carry out in the labora- 

 tory, theoretically it presents many intricate and scientifically 

 interesting problems. 



Before we can assign an equation to the reaction, we must 

 consider the empirical formula for mercurous chloride. The 

 structural formula is necessary for a more thorough considera- 

 tion of the mechanism of the reaction. 



It has long been known that mercurous chloride contains 

 one atom of chlorine for each atom of mercury. The molec- 

 ular weight of the compound, however, is a point of dispute. 

 Many chemists support the view that the molecule is HgCl, 

 analogous to cuprous chloride; while others consider that 

 there are substantial data in favor of the formula HgjCU. 



Since mercurous- chloride passes into the vapor phase be- 

 low 400°C., it is natural to suppose that vapor density deter- 

 minations would give a definite answer to support one view or 

 the other'. At 518" the vapor density is 235.5 (0. = 32). 

 This seems to'indicate that the formula HgCl is correct. But 

 it has been suggested that, if the dimolecular form were to dis- 

 sociate in the gaseous state into metallic mercury and mercuric 

 chloride, HgjCU = Hg-|-HgCli, then the vapor density of the 



