UNGUENTUM HYDRARGYRI NITRATIS. 
65 
In one experiment with a less proportion of acid, and in 
which the heat had been carried too far, so as to produce a 
greenish color, the proper yellow was restored on adding a 
few drops more of the acid, by which the nature of the 
change appears to be indicated. 
From these experiments and observations, it is evident that 
it is not indispensable to operate on large quantities in order 
to obtain a good article; and that a long continued stirring is 
not required: a careful regulation of the temperature, with at- 
tention to the strength of the acid employed, are the points 
of chief importance. We are also confirmed in the belief that 
the proportions ordered by the college, are fully adequate to 
the purpose, if acid of standard strength be employed, or an 
equivalent quantity if of inferior density. 
Before concluding these remarks, I will quote the directions 
of Dr. Duncan, before alluded to, which have but recently at- 
tracted my observation, seeming, as they do, to embody the 
principles which I have recognized. " Dissolve the mercury 
in the acid, and pour the solution, while still hot, into the 
lard, melted in the oil, and also still hot, and mix in a vessel 
capable of containing five times the quantity, as a violent ef- 
fervescence takes place. If it should not froth up, the action 
must be assisted by heat." This process, we are informed, 
is originally that of Mr. Duncan, of Edinburgh, and yields 
the most perfect citrine ointment, preserving a fine golden 
color, and the requisite softness. 
Lond. Pharm. Trans. Sept. 1, 1841. 
vol. viii. — NO I. 
9 
