15 & Mr. Chenevix's Observations and Experiments 
These proportions are different from those given by Lemery, 
Geoffroy, Bergman, &c. But, without calling in question the 
accuracy and skill of these chemists, it is fair to assert, that 
the pure materials used by modern chemists, are more likely to 
lead to sure results, than the impure reagents of the ancients. 
In these salts we find another instance, that, in proportion as 
metallic oxides contain a greater quantity of oxygen, they require 
a greater quantity of acid to enter into combination with them. 
The method I have followed, to ascertain the proportions just 
stated, may appear, at first view, not to be the shortest that I 
might have adopted. But I have tried others, and have found 
none so accurate. It is impossible, synthetically, to convert a 
given quantity of mercury into calomel, in such a manner as to 
be certain that none of it is in a different state from that re- 
quired. And, if we would attack calomel analytically, the action 
of the alkalis, without which we cannot proceed, is such as to 
alter the nature of the oxides. I have also made many com- 
parative experiments, by dissolving calomel in nitro-muriatic 
acid, (which converted it into corrosive sublimate,) and then 
precipitating by ammonia ; but I have not found these trials so 
successful as those I have described. The nature of the preci- 
pitate from corrosive sublimate by ammonia, certainly differs, ac- 
cording to the excess of acid that may be present ; and mercury 
seems to have the power of existing in many degrees of combi- 
nation with oxygen. The only precaution absolutely necessary, 
in this mode of operating, is, that while the mercurial salt is in 
an open vessel, it should not be exposed to a degree of heat 
capable of volatilizing any part of it. 
The quantity of mercury ordered in the London Pharma- 
copoeia, to convert corrosive sublimate into calomel, is g pounds 
