UNGUENTUM HYDRARGYRI NITRATIS. 
61 
ART. VIII. — ON THE PREPARATION OF UNGUENTUM HY- 
DRARGYRI NITRATIS. By Mr. Alsop. 
The remarkable difference in the appearance and quality of 
the Unguentum Hydrargyri Nitratis as usually met with, has 
long engaged my attention, and being a matter of considerable 
practical importance, I am induced to submit a few observa- 
tions to the consideration of the Society. The want of suc- 
cess so frequently experienced, hasbeen rendered the more puz- 
zling by the uniformity of result in the hands of some persons, 
by whom no small degree of mystery has been long affected: 
and while we cannot doubt that the experimenters of the col- 
lege obtained a good article by the formula of the Pharmacopoeia, 
it is a reasonable subject of inquiry, Why so many, although 
professedly using the same formula, are not equally successful? 
and, Why such discrepancy of opinion in this particular 
should be found amongst medical authors? 
The Edinburgh Dispensatory of 1794 gives the following 
formula, viz. — "Quicksilver, loz., nitrous acid, 2 ozs., hog's 
lard, 1 lb. Dissolve the quicksilver in the nitrous acid by 
digestion in a sand heat, and while the solution is very hot, 
mix it with the lard previously melted by itself and just begin- 
ning to grow stiff, stir them briskly together in a marble mor- 
tar, so as to form the whole into an ointment." 
In this process the directions appear to have been framed 
with a view especially to restrain the violent action of the 
nitrate on the fat, and speedily to cool the ointment. 
In the valuable Dispensatory of Dr. A. T. Thompson, 1824, 
after giving the present formula, he recommends the use of 
only one-sixth of lard, by which an excellent ointment appears 
to have been produced; he adds, the observation that " when 
made with a larger proportion of lard, it becomes hard and 
brittle, of a pale, dirty, yellow hue, marbled with green 
blotches." 
On the other hand we find, in the Dispensatory of the 
