266 ON THE HYDRARGYRO-BINIODIDES OF POTASSIUM, ETC. 
On cooling, the solution deposites one-third of the biniodide 
of mercury in crystals, and a salt remains in the liquor which 
may be obtained in crystals by evaporation. 
These crystals, in the case of biniodide of mercury and 
iodide of potassium, resemble crystallized sulphur, and con- 
sist of 
1 atom iodide of potassium, 
2 " biniodide of mercury, 
6 " water. 
They are decomposed by water, one-half of the biniodide 
precipitating, and the salt which remains consists of 
1 atom iodide of potassium, 
1 " biniodide of mercury. 
The substance of the above is taken from an abstract of 
Boullay's paper, published under the authority of PAcad. des 
Sciences, in the Journal de Pharmacie, tome 13me, p. 435. 
As the results of some experiments I have made on these 
double iodides lead to somewhat different conclusions, I will 
present them in detail, premising that M. Boullay's chief ob- 
ject in his paper was to illustrate the theory of electro-chemi- 
cal combination, by an examination of the double iodides ge- 
nerally, and that his attention does not appear to have been 
particularly directed to those of biniodide of mercury and 
iodide of potassium. 
1st. To a saturated solution of KI, as much Hgl 2 was added 
as it would dissolve at a boiling temperature, by which a so- 
lution was obtained containing 
165 parts KI, 
385 " Hgl*, 
which is a little more than three atoms Hgl 2 , to four atoms 
KI. From this solution, on cooling, Hgl 2 is rapidly deposited, 
but if it be boiled nearly to dryness, a yellowish crystalline 
mass results, containing all the Hgl 2 . 
Thinking a larger portion of Hgl 2 might be taken up if it 
