64 
HYDRARGYRI UNGUENTUM NITRATIS. 
acid, but a pale nitrous, which latter acid is supplied in 
commerce of a much greater density, and approaching 1.5. 
At first sight I was struck by the large proportion of acid 
in the formula of Dr, Duncan, viz, three times the quantit}^ of 
the mercury, and in that of the army laboratory which is as 
follows, — mercury, 1.1b. 51 ozs., nitric acid 3.1b. 9 ozs., lard 
8.1b. 4 ozs., olive oil, 5 pints, wine measure, but on reducing 
the proportions to accord with the relative strength of the 
acid, as regards that of the army laborator}', I find no mate- 
rial variation from the Pharmacopoeia order. 
The difficulty in the preparation of a good article, from the 
reasons stated, is less obvious to those who prepare it in large 
quantities, and much stress has been laid on the long conti- 
nued stirring. In order to meet the case more fully, I have 
made my experiments on very small quantities, and will now 
detail one of the series. 
The acid employed was colorless, and of sp. gr. 1.41 con- 
taining by Dr. Ure's tables about 73 per cent, of acid of 1.5, 
and estimating the fluid drachm at 57 grains,* we have the 
following construction of the formula, 11 x57x1.5=940 
weightof 11 fluid drachms of standard acid,940x VV"" 8 = 160 
grains of acid of 1.41 to a drachm of mercury. 
One drachm of mercury was accordingly dissolved without 
additional heat, in 160 grains of acid as above ; the solution 
was then added to 6 drachms of lard and 4 fluid drachms of 
olive oil (the proportions of the college) previously melted 
together in a water bath, and heated to about 190°; a brisk ef- 
fervescence took place; it was kept in the water bath about 
fifteen minutes, when it assumed the proper color, and 
slightly boiled over; it was then taken out, and the stirring 
continued for about ten minutes, and then left until the next 
morning, when it was slightly stirred. A specimen of this I 
have the pleasure to submit to the Society; it has been made 
about three weeks. 
* Fifty-seven grains is the weight of a fluid drachm, old measure, but 
in the imperial scale it is reduced, I find, to 54.7. 
