184 
Original Communications. 
Chemical Examination — To a portion of the oxide remain- 
ing after the chalk had been washed away as above, very- 
dilute acetic acid, was added guttatim. Digestion was car- 
ried on in the cold for about two hours, when a solution of 
hydriodate of potassa added to the solution, gave an imme- 
diate precipitate of periodide of mercury, thus indicating 
promptly the presence of a salt of the per oxide of mercury, 
in the solution. 
Another portion of the Hydrargyrum cum Creta, was dif 
fused through water, and acetic acid added, cautiously and 
by single drops, until effervescence ceased. After digestion 
in the cold for one or two hours, solution of hydriodate of 
potassa, gives a red, and pure potassa an orange yellow pre- 
cipitate, conclusive evidence of the existence of per oxide of 
mercury in a preparation which is administered to the most 
delicate stomachs on account of its mildness, and reputed 
character of possessing less irritating properties, than calo- 
mel or any other preparation of mercury ! ! 
A whitish powder, or precipitate, is formed during the di- 
gestion in acetic acid, which becomes yellow when water is 
poured on it. This may be a sub acetate of mercury, as such 
a salt is mentioned by Thompson, to which this property is 
ascribed. 
Every precaution was taken in the above experiments to 
prevent the formation of per oxide during the process, and 
we feel confident that such an effect could not have been pro- 
duced. How the per oxide happened to be present, we can- 
not of course explain; but we think it may have been occa- 
sioned by one or the other of the following causes : — either 
that the oxide when precipitated was heated, to hasten its 
drying, or it was precipitated from some acid, which had a 
disposition to furnish oxygen to the metal, and thus formed a 
combination of a per, and proto salt at the same time. 
Having had occasion subsequently to the above experi- 
ments, to precipitate the oxide from a sulphate of mercury,, 
we observed that the colour of the oxide thrown down by 
potassa, bore a strong resemblance to that of the oxide left 
by the washing, from the Hydrargyrum cum Creta, under ex- 
