504 
PHARMACEUTICAL MEETING, 
Mercuric Iodide, Hgl 2 .28’6 
Mercurous Iodide, Hg I.58 - 4 
Metallic Mercury, Hg.13 0 
1000 
It thus became evident that the green product was far from what it should 
be, according to the formula given by the Pharmacopoeia. 
I then prepared some of the iodide, continuing the trituration until the green 
colour had passed to the dingy yellow, which, according to the London Phar¬ 
macopoeia is characteristic of the product. A portion of this compound was 
then analysed, and the following results obtained:— 
Mercuric Iodide.5 0 
Mercurous Iodide.92-8 
Metallic Mercury.2-2 
100-0 
On comparing these numbers with those preceding it will be seen that by 
continuing the trituration the red iodide had to a great extent disappeared, and 
so had the free mercury. No doubt these two substances had entered into com¬ 
bination and formed a further portion of the mercurous iodide. The results 
so far, then, seem to admit of an easy explanation. By the constant trituration 
the last portions of the metallic mercury reach a state of extremely fine division. 
In this state the metal possesses somewhat of a blue colour (well known to us 
in blue pill, etc.), which, mixed with the yellow of the mercurous iodide already 
formed, would produce a green. According to this view, therefore, the green 
of the iodide is due to a mechanical mixture of mercurous iodide and mercury. 
It equally follows from this that the true colour of pure mercurous iodide must 
be yellow. This explanation derives additional support from the fact that the 
green powder cannot be obtained and kept of any uniform tint. As first got it 
is a decided grass-green, but even while it is drying, however carefully the light 
be excluded, the colour changes, approaching more and more to yellow. At the 
same time that this change goes on the proportion of mercuric iodide diminishes, 
and consequently the proportion of metallic mercury must diminish also, thereby 
lessening the green and augmenting the yellow colour. 
In Gmelin’s 1 Handbook ’ three iodides of mercury are described ; namely, 
the mercurous iodide, the mercuroso-mercuric iodide, and the mercuric iodide. 
The first, as I have already mentioned, is stated to be green, dark green, or 
yellowish-green; the second yellow, and the third red. Three processes are 
given for the production of mercurous iodide. The first is by direct combi¬ 
nation of mercury and iodine. It is the method of the Pharmacopoeia which I 
have examined with the results stated. The second is to decompose calomel 
with iodide of potassium. In the third process mercurous acetate is substituted 
for calomel. The second of these methods is stated to yield “ pure green ” mer¬ 
curous iodide. As I had entirely failed to obtain such a body by direct com¬ 
bination, I made several careful experiments with this process of double decom¬ 
position. 235 - 5 grs.* of calomel were triturated with 166 grs.* of iodide of 
potassium previously dissolved in a little water. The mixture was allowed to 
remain for twenty-four hours and then filtered, the precipitate washed and dried. 
The product was of a fine dark green colour, and entirely different to any 
iodide I had previously obtained. Upon testing it, however, I found it to con¬ 
tain a large quantity of undecomposed calomel. Its weight was also much less 
than theory would indicate. By analysis the following numbers were obtained :— 
* Equivalent quantities. 
