270 ON THE HYDRARGYRO-BINIODIDES OF POTASSIUM, ETC. 
Compounds intermediate in composition may be obtained, 
by allowing the solution of the former to deposite a portion 
of its HgP, by partial cooling, and evaporating nearly to dry- 
ness. These are mixtures in various proportions of HgP+KI, 
and Hgl 2 -f 2KI, which crystallize together being apparently 
isomorphous. My friend Wm, Procter, jr., who has repeated 
and confirmed the results of most of the preceding experi- 
ments,obtained a compound of 2HgI 2 -f3KI, in a yellow crys- 
talline mass. 
The di-hydrargyro-biniodide of potassium, was introduced 
to the notice of the medical profession by Dr. Channing, of 
New York, by a paper published in the Amer. Jour, of Med. 
Sciences, in the year 1834, since which it has been been con- 
siderably used by some physicians in this city, with favorable 
results. It is no doubt a valuable compound where a soluble 
persalt of mercury is required, and may be eligibly substituted 
for the corrosive chloride of mercury, when the administra- 
tion of an iodide is also indicated. 
The ready solubility of the crystals without decomposition 
seems to depend upon their containing a large proportion of 
water of crystallization, and this object is best obtained by 
preparing it in considerable quantity and crystallizing by 
spontaneous evaporation. When wanted in crystals, it may 
be prepared by dissolving 1 equiv. biniodide of mercury, in a 
a strong solution of a little more than 2 equiv. iodide of potas- 
sium, filtering the liquor, and evaporating as above indicated. 
It is usually employed in solution, which may be conve- 
niently made from the proximate elements of the compound. 
Take of Biniodide of Mercury, 
Iodide of potassium, each, 4 grs. 
Water, one fl. oz. 
Dissolve and filter the solution. 
This is about the strength usually employed here. The dose 
is from two to six drops, equivalent to from about the thir- 
teenth to the twelfth of a grain of the double salt. 
A slight excess of the iodide of potassium is here indicated, 
