MERCURIC SALTS CHANGE INTO EACH OTHER. ^3 



Mercury oxalates. 



Work upon the oxalates was unnecessary. It is known that 

 mercurous oxalate heated to 100° changes partly into mercury and 

 mercuric oxalate under the influence of its water of crystallisation. 



The decomposition of mercurous carbonate is so intimately 

 connected with that of the oxide, that it will be noticed in that 

 connection. 



Mercury chlorides. 



Conversion of mercuric to mercurous chloride. — A cold solution of mer- 

 curic chloride, violently shaken in a bottle with large excess of mercury, 

 quickly becomes deprived of all dissolved salt, in consequence of the 

 conversion of the mercuric to mercurous chloride. Filtered thoroughly 

 bright, the water gives only a faint browning with hydrogen sulphide. 

 Such a simple way of removing mercuric chloride from solution may 

 possibly find practical applications. The conversion, however, cannot 

 be completed in the presence of much alkali chloride. 



(Literature and criticism). — Gay-Lussac was aware that finely divid- 

 ed mercury acts freely upon a solution of mercuric chloride. It is also 

 well known that when mercuric chloride and mercury are rubbed 

 together with a little water or alcohol, as a first step in preparing 

 calomel, much mercurous chloride is produced before heating. Yet in 

 any edition of Gmelin's Handbuch, or in any other treatise, so far as I 

 know, we find only that mercury and mercuric chloride form mer- 

 curous chloride when heated together ; while among the wet ways of 

 forming it, the direct union of mercury and mercuric chloride is not 

 specifically given. Union in this way is not, indeed, well adapted to 

 the preparation of mercurous chloride, but, as a mode of its formation, 



