1G2 



S. HADA: HOW MERCUROUS AND 



each other ; one, first in interest and importance, is that all mercurous 

 salts dissociate, in the strict sense of this term, into mercury and 

 mercuric salts, in presence of water ; and, reciprocally, that all 

 mercuric salts combine with mercury, in presence of water, to form 

 mercurous salts, when these have any existence. Although not 

 generally known, and without having led to the full recognition of 

 that proposition, many observations have already been made by 

 chemists and pharmacologists working upon the salts of mer- 

 cury, which lend every support to it. Reference to these obser- 

 vations will be made where they become applicable ; here, it is only 

 necessary to state that Rose held so strongly that mercurous salts in 

 solution readily decompose into mercuric salts and mercury, as to deny 

 existence to any precipitated basic mercurous salts, treating the basic 

 part of the precipitates as a mixture of mercuric basic salt and mercury, 

 the other part being sparingly soluble normal mercurous salt. His 

 right view of the case was thus based on a wrong apprehension of 

 some of the facts. It seems proper for me to mention that only after 

 I had discovered for myself the facts described in this paper was I able 

 to make anything of the confused records of them to be found in 

 chemical literature. 



In accordance with the laws of dissociation, decomposition of 

 mercurous salts into mercury and mercuric salts increases with rise of 

 temperature and only progresses freely so long as the mercury set free 

 is continuously removed from the field ; and, conversely, combina- 

 tion of mercuric salts with mercury only becomes complete in presence 

 of excess of the metal and at lower temperatures, unless the mercurous 

 salt produced is insoluble and thus goes out of the field, as in the 

 case of the chloride. Combination with mercury does not occur 

 at all when the mercurous salt is incapable of existing, as is the 

 case with the cyanide, with the sulphide, with double sulphites, thio- 



