272 ON THE HYDRARGYRO-BINIODIDES OF POTASSIUM, ETC. 
hoi, it is also decomposed, HgP is dissolved, and may be ob- 
tained by evaporating the alcohol, and Hgl remains. 
On referring to Boullay's paper on the double iodides, be- 
fore mentioned I find that observations nearly similar have 
induced him to consider it a compound of the biniodide and 
iodide of mercury, and this appears its more probable compo- 
sition, as it is scarcely to be supposed that the action of such 
feeble re-agents, would occasion its conversion into the binio- 
dide and protiodide, if these did not previously exist in it. If 
this be the case it is a compound of 1 atom of biniodide and 1 
atom of protiodide of mercury, united by the feeble affinity 
which would a priori be supposed to exist between sub- 
stances approaching each other so nearly on the electro-che- 
mical scale, and its formula is HgP -f- Hgl. 
*/l compound of biniodide of mercury and ammonia. — On 
adding ammonia in excess to a solution of the di-hydrargyro 
biniodide of potassium, I noticed a white precipitate to form. 
When the solution was concentrated the precipitate was dense, 
consisting of minute white acicular crystals; when a diluted 
solution was employed, no precipitate at first ensued, but 
upon standing, long snowy needles crystallized from it. 
These crystals were decomposed on drying, ammonia being 
evolved and biniodide of mercury remaining, which still re- 
tained the shape of the crystals, but had lost their consist- 
ence, falling to powder on the slightest friction. A similar 
change was rapidly produced by washing them with water, 
the white compound being first converted to an orange color, 
and, by further washing, to the brillant scarlet red of the bin- 
iodide of mercury. 
The same compound is formed by digesting biniodide of 
mercury, with the aid of heat, in a large excess of strong aqua 
ammonia, or ammoniated alcohol, by which the biniodide is 
dissolved ; upon cooling the liquor, the white double salt crys- 
tallizes from it. 
The evanescent nature of this compound rendered it diffi- 
cult to analyze, as it was found impossible to dry it without 
decomposition, even at a low temperature, under an air-pump. 
