HYDRARGYRI UNGUENTUM NITRATIS. 
63 
In the laboratory of John Bell & Co.,* and also in the army- 
laboratory (in both which establishments a most perfect arti- 
cle is produced) I find that but little heat is employed beyond 
what is required to melt the lard, but on the other hand the 
quantities are large, so that a considerable temperature results 
from the decomposition, and the stirring is kept up at inter- 
vals for several hours, by which the evolution of gas is assist- 
ed. I have not as yet minutely examined the gas evolved, or 
the state of the lard and mercury, on which field of labor much 
time might be employed; but I find that the extrication takes 
place at a temperature of about 180°, and that at 212° it is so 
violent that the mixture frequently boils over unless the ves- 
sel is capacious. 
In my first successful experiment with oil of almonds, such 
a temperature was employed, by which the required change 
was effected. If this effervescence is pushed too far, although 
the consistence of the ointment is not injured, the color is de- 
teriorated either immediately, or after a few days, by the par- 
tial reduction of the mercury; the same result is also sure to 
happen if the proportion of acid is not sufficient, and this will 
of course be the case wherever the proportions of the Phar- 
macopoeia are observed, without regard to the specific gra- 
vity of the acid employed. This is the second point on which 
I place peculiar stress. I find the nitric acid supplied to us 
by the most respectable manufacturers ranges usually from 
1.375 to 1.4, equivalent only to from 66 to 73 per cent, of 
standard acid of 1.5, it is therefore necessary to increase the 
quantity in proportion to its deficiency in strength. I ap- 
prehend that this dilution is adopted on account of the sponta- 
neous decomposition of the strong acid, observing at the same 
time that the nitric acid of the Pharmacopoeia is not colorless 
* The following is the formula of J. Bell & Co. 
R Hydrarg. ^viij. 
Acid. Nit. f^xiv. (Sp. g. 1.43.) 
Solve et adde. 
Adipis, lb. iij. 
01. Olivae, lb. ij. 
