ON HYDRARGYRI IODIDUM V1RIDE, B. P. 
503 
copoeia. This is expressly implied by the “ Synonym IIydrargyri Iodidum 
Land.” given in the description of the preparation in the last edition of the 
British Pharmacopoeia. In both works the chemical compound mercurous 
iodide is obviously meant and the British Pharmacopoeia defines this by giving 
the formulae “ Ilg 2 I or Hgl.” But the London Pharmacopoeia, in describing 
this compound, states, that “ when freshly prepared it is dingy yellow while 
the British Pharmacopoeia names it “ Green Iodide,” and describes it as “ a dull 
green powder.” This discrepancy occurring in the description of a definite 
chemical body is a little remarkable, and requires some explanation. The pro- 
cesses and the proportions of ingredients given in the two Pharmacopoeias are 
almost identical; yet according to one authority we obtain a yellow, and 
according to the other a green product. 
I have frequently made the iodide of mercury according to the London Phar¬ 
macopoeia, and have always found that it possessed a dull yellow colour, cer¬ 
tainly with a shade of green upon it, but nevertheless the yellow vastly prepon¬ 
derating. Yet chemical authorities generally indicate that mercurous iodide is 
a green substance. In Gmelin’s ‘ Chemistry ’ mercurous iodide is variously de¬ 
scribed as “ a green,” “ a dark green,” and u a yellowish-green but no men¬ 
tion is made of its being yellow. The British Pharmacopoeias of 1864 and 1867 
are therefore in accord with the leading chemical manual. 
Being desirous of understanding this matter more perfectly, I made a few 
experiments to elucidate the point. Upon repeating the process as given in the 
British Pharmacopoeia I found that the first effect of triturating the mercury 
and iodine with the spirit was to obtain a red colour; due, no doubt, firstly to 
the solution of the iodine, and secondly to the formation of the red iodide of 
mercury ; but after continuing the trituration for some time the mass became 
a decided dark green. This then was the point at which I was to transfer the 
product to filtering-paper and dry it by exposure in a dark room. But instead 
of doing this I continued the trituration until the mass was dry. As the rub¬ 
bing proceeded I found the green colour rapidly disappeared, the powder became 
more and more yellow, and the ultimate result was a yellow substance with a 
dingy greenish tint upon it. The question that arose, therefore, was to ascer¬ 
tain the composition of the product at the two periods ; namely, at the period 
in which it was decidedly green, and at the subsequent period when it became 
permanently yellow. To solve this point 200 grains of mercury and 127 grains 
of iodine were triturated with a little spirit until the dark green colour was 
obtained. A portion of this iodide was then taken for immediate analysis, and 
the remainder put in a dark place to dry. The analysis was effected as fol¬ 
lows :— 
A known quantity of the iodide was washed with boiling absolute alcohol, 
the washings evaporated to dryness, and the residue weighed ; it consisted of 
red or mercuric iodide. The insoluble portion was dried and divided into two 
parts ; one was dissolved in hydrochloric acid and chlorate of potash, the solu¬ 
tion evaporated to near dryuess, diluted, precipitated with stannous chloride, 
and the precipitated metallic mercury collected and weighed; the other half of 
the powder was digested with finely granulated zinc and diluted acetic acid, 
whereby an amalgam of zinc was formed, the iodine passing into solution as 
hydriodic acid. After some time the liquid was poured off, nitrate of silver 
added to it, and the precipitated iodide of silver collected and weighed. Other 
methods of analysis were also employed, but the above were found sufficiently 
satisfactory. As some objection might be taken to the use of boiling alcohol, 
the red iodide was also estimated by washing with ether. 
The result of the analysis of the green powder was as follows, the moisture 
being excluded :— 
