106 
Original Communications. 
large, bright spot of reduced mercury, which formed the 
usual amalgam. 
B. Another drop of the solution on glass, over a spirit 
lamp, was evaporated, and the heat being increased, an 
orange red residuum was left — red oxide of mercury. 
C. To a few drops of the solution, a solution of hydriodate 
of potassa was added, on a piece of glass ; a greenish yellow 
and brilliant red precipitate, partially blended, were formed — 
the iodide and per-iodide of mercury. 
This series gave convincing proof of the presence of mer- 
cury, but the question was still, whether calomel or corro- 
sive sublimate? The following experiment satisfactorily 
solved that, and the character of the powder was fully esta- 
blished. 
4th. The remaining portion of the suspected powder was 
placed near the lower end of an open tube, and the heat of a 
spirit lamp applied. Almost the whole substance was sub- 
limed, and condensed on the upper surface of the tube, in a 
beautiful pearly white powder. As in the first experiment, a 
small carbonaceous residuum remained. 
A Liquid potassa added to this, gave a black precipitate — 
black oxide of mercury. 
B. Lime water placed upon it, also gave a brownish black 
precipitate — black oxide of mercury. 
The difference in the shades of the black oxide of mercury 
precipitated from calomel by these respective reagents, is 
familiar to all chemists and pharmaceutists, and no shadow 
of doubt was left that the powder left with us for examina- 
tion was calomel, — proto-chloride of mercury. 
We have been thus minute in the detail of our experiments, 
from having frequently felt the want of minuteness in the 
descriptions of and directions for analysis, given in the text 
books. Our experiments were all accomplished by the aid 
of a small tube, spirit lamp, three or four watch glasses, and 
the back of a gold watch and penknife. In no case was more 
than two drops of the solution employed, and for each series 
of the experiments not more of the powder, in bulk, than one- 
third of a grain of calomel was at our disposal. What a 
