ON HYDRARGYRI IODIDUM VIRIDE, B. P. 
507 
Now, if this were so, he thought they would be in a position to recommend 
therapeutists not to use this mercurous iodide. They had heard a great deal 
lately about the desire on the part of a number of influential gentlemen to re¬ 
view their present system of therapeutics; and a society had been formed with 
that object, and one of the first requirements they had put fortli was that they 
must have pure drugs to experiment with. In most instances the chemist and 
druggist must take a lower position than the medical practitioner ; but when it 
came to a question of purity of drugs, then he thought the former was entitled 
to take the higher ground ; in this instance, telling therapeutists that they must 
not use the green iodide of mercury, for they could never depend on any two 
samples being alike. 
Mr. Wood said he certainly used the word ‘ permanent,’ but he used it in a 
very relative sense. He did not intend to imply that the mercurous iodide was 
a body by any means as stable as the red iodide, for instance, or the other com¬ 
pounds of mercury of a very definite character. But he meant that at any rate it 
was more stable in its appearance than the green iodide ; for, as he had already 
stated, if they made the green iodide strictly according to the instructions given, 
it was impossible to keep that for many hours without its becoming lighter and 
lighter in colour, losing more and more of its green and assuming more and more 
of a yellow colour. It ultimately attained to a maximum of yellow, and there it 
stayed so long as it was mercurous iodide. As to the decomposition which that 
underwent afterwards, that was a further question. But as far as his experience 
went, while it was almost impossible to make the green iodide of mercury by 
strictly following the instructions of the British Pharmacopoeia, in such a manner 
as to keep its colour for several days or even for a day, it would be quite possi¬ 
ble to make yellow iodide according to the instructions of the London Pharma¬ 
copoeia, to keep its colour, not only for days, but for weeks, and, under suitable 
circumstances, it would maintain its yellow colour even for months. He had a 
bottle at the present time which must certainly have been made for two months. 
The contents of that bottle had as decided a colour, a dirty yellow, as at the be¬ 
ginning ; no change of colour whatever could be distinguished. Being desirous 
of ascertaining what kind of substance was sent out by other makers, he obtained 
some, but found it to be quite as yellow as that which he made himself. The 
bottle which he got quite two months ago was identical in its appearance with 
what it was when it first came to him. Whether it had undergone much change 
in composition, he was not prepared to state, because he had not examined these 
compounds after they had been kept for any length of time. It was quite con¬ 
ceivable they might undergo decomposition, and yet that that decomposition 
should not materially affect the colour. That might be so or it might not; but, 
speaking generally, he could confirm what Dr. Redwood and Dr. Attfield had. 
stated, that this body, relatively to other chemical compounds and murcuric 
iodide, was an uncertain body. If it were exposed to the light for an hour, it 
would become quite dark upon the surface, and, if kept, it must be kept in the 
dark. He wished to state that he had solely examined the yellow iodide of mercury 
which was produced by trituration. The ultimate result of trituration was of a 
dirty yellow colour ; and that he believed to be a pure mercurous iodide. It 
was that which he had analysed, and which he had found to contain mercury 
and iodine in the preparation of mercurous iodide. That, when sublimed, 
yielded a sublimate which, after cooling, was of a brilliant yellow ; but whether 
that sublimate was of the same composition as the powder which was submitted 
to sublimation he was not at all sure. The similarity of colour would not be a 
proof that it was identical in composition. He thought it would generally be 
observed that when the yellow powder was sublimed, there were amongst the 
crystals some globules of metallic mercury; and it might be, therefore, that by 
the action of heat, it was resolved into mercury, and that three-fourths iodide, 
which was the composition assigned to it by chemical authorities. 
