506 
PHARMACEUTICAL MEETING. 
Lastly, it results that the London Pharmacopoeia gives the most accurate 
description of this compound, although the British Pharmacopoeias are best in 
accord with chemical manuals. 
• Dr. Redwood said they must all feel greatly indebted to Mr. Wood for the 
pains he had taken in investigating this subject, upon which he had certainly 
thrown a great deal of light. There was, however, one part of the subject which 
he (Dr. Redwood) could have wished that he had explained a little more than 
he had done, and that was the part referred to in nearly the last sentence of his 
remarks, in which he stated that the so-called green iodide of mercury, of the 
Pharmacopoeia, which was more strictly yellow than green, might be obtained in 
a stable condition. Now, to his mind, that was really the most important feature 
of the whole question. He had always been of opinion that this iodide of mer¬ 
cury would have been much better out of the Pharmacopoeia than in it, and mainly 
because he had always looked upon it as a most uncertain aud unstable com¬ 
pound, and on that account very unsatisfactory. He had found, however, that 
there were certain medical men who attached importance to its use in medicine, 
and who had contended for its retention in the Pharmacopoeia, and hence, no 
doubt, it had been retained in it. But every one who had had any experience with 
reference to this iodide, prepared in the manner indicated in the Pharmacopoeia, 
and this, it still appeared, was the best method of preparing it, must be aware 
that the preparation so produced was subject to constant change, and especially 
when exposed to the light. Now, what he should be really glad to know was, 
what evidence had Mr. Wood that the preparation, when obtained in a definite 
condition, was stable, and could be retained in that state. He had prepared this 
iodide of mercury, or had had it prepared under his inspection hundreds of times ; 
and he could quite agree with what Mr. Wood had stated, that in preparing it 
by the method indicated, by trituration, if they continued the trituration until 
it became dry in the mortar, the product would be of a dingy greenish-yellow. 
It might be called a greenish-yellow or yellowish-green compound. If the pro¬ 
duct so obtained were submitted to sublimation, it became, on first subliming it, 
and while it was still warm, of a bright red colour, which, after a little time, 
passed as it cooled to a brighter yellow than that which existed before it was 
submitted to sublimation. Chemical authorities had all agreed in representing 
that yellow compound as an iodide standing higher than the so-called green 
iodide. There were thus three distinct compounds described,—the green, the 
yellow, and the red. He (Dr. R.) had never taken the pains to investigate, 
analytically, so carefully as Mr. Wood had done, the true composition of the 
compound in the various states in which it had been obtained. He had himself, 
as the authors of the Pharmacopoeia who had introduced it into that work ap¬ 
peared to have done, rather followed the authority of such works as Gfrnelin’s 
‘ Chemistry,’ where the results of many investigators w r ere given, than worked 
out the subject for himself as Mr. Wood had done. He looked upon the result 
of Mr. Wood’s investigation, so far as it went, as very satisfactory ; but, as he 
had said before, it would be more satisfactory to his mind if Mr. Wood would 
show upon what grounds he stated that this iodide of mercury, when obtained 
in the condition of mercurous iodide, that is the lowest iodide, was a stable com¬ 
pound, and could be kept and used in that state without undergoing subsequent 
change. 
Dr. Attfield wished to make a few remarks in the same direction as those 
made by Dr. Redwood, namely, as to the stability of mercurous iodide. He be¬ 
lieved that the author of the process, referred to by Mr. Wood,—that of mixing 
calomel with iodide of potassium,—proved that mercurous iodide, even when 
pure, was not stable; that, even when not exposed to light, it decomposed. 
