( 
* 
i6o Mr. Chenevix's Observations and Experiments 
sensible portion of water of crystallization. The same may be 
said of corrosive sublimate. 
It now remains to speak of the real hyperoxygenized muriate 
of mercury. I passed a current of oxygenized muriatic acid 
gas through some water, in which there was red oxide of mer- 
cury.* After a short time, the oxide became of a very dark 
brown colour; and a solution appeared to have taken place. The 
current was continued for some time; and, when I thought 
that a sufficient quantity of the oxide had been dissolved, I 
stopped the operation. The liquor was evaporated to dryness ; 
and the salt was thus obtained. There evidently was in the 
mass a great proportion of corrosive sublimate, as might be 
expected, from what I had observed to take place in the forma- 
tion of the other salts of this acid; but, by carefully separating 
process, there is disengagement of nitrous gas, together with oxidizement and solution 
of some of the mercury. When he boils the acid upon the remaining mercury, there 
is no further disengagement of gas ; yet more mercury is dissolved. The nitrate of 
mercury, therefore, rather contains an oxide less oxidized after ebullition than before 
it. The true difference is in the subnitrate of mercury, precipitated, as I before said, by 
the water in which the muriate of soda was dissolved. And the orange coloured powder, 
which remains after an attempt to sublime Scheele s calomel, is to be attributed to , 
the same cause. To prepare calomel in the humid way, uniform as to itself, and in all 
respects similar to that prepared In the dry way, it is necessary, either to use the nitric 
solution before it has boiled, or to pour some muriatic acid into the solution of muriate 
of soda, previously to mixing it with the boiled solution of nitrate of mercury. In the 
•first case, no precaution is necessary; and, in the latter, the oxide of mercury, which 
the nitrate of mercury has, by boiling, taken up m excess, finds an acid which is ready 
to saturate it. All the mercurial oxide being thus converted into calomel, none of that 
subnitrate of mercury can be present. 
The objections made by a medical gentleman against Scheele’s calomel, when this 
Paper was read before the Royal Society, led me to reconsider the subject, and to 
■undertake the investigation detailed in this note. 
,# I used either of the red oxides of mercury, indiscriminately. 
