Dr. Inglis’s Extracts from his Prize Essay on Iodine. 19 
then placed this saturated solution under the exhausted re- 
ceiver of an air-pump; in a short time the biniodide began to 
be deposited, and svon they increased and assumed the form 
of large regular cubes. The hydriodate of zinc that remained 
was capable of dissolving a fresh quantity of biniodide, or of 
redissolving that which was crystallized from it: the crystals 
contain no zinc; they are acted on by chemical agents and 
by heat just in the same manner as the precipitated biniodide, 
and are quite distinct from the hydrargo-biniodide of zinc to 
be mentioned hereafter. ‘The biniodide of mercury is sufh- 
ciently soluble in an excess of the hydriodate of potassa, from 
which there results on slow evaporation a yellow salt, which 
I discovered many months ago, and called it the double hy- 
driodate of the biniodide of mercury and potash, because 
I found that whenever it was brought in contact with water, 
instant decomposition took place, the water from its strong 
affinity for hydriodic acid removed it, and the red biniodide 
was precipitated. Bonsdorff, however, calls this compound the 
hydrargo-biniodide of potassium. * * * 
On mixing bichloride of mercury in powder to a saturated 
solution of hydriodate of potassa, and agitating together, the 
whole becomes nearly asolid red mass, and much heat is at 
the same time generated. * * * This red iodide is formed by 
many other processes, as when a solution of bicyanuret of 
mercury is added to an alcoholic solution of iodine, in which 
case it instantly precipitates. 
When the yellow sesquiodide is kept for some time under 
water, and exposed to light, very good small cubic crystals of 
the red iodide are found covering the surface; but the method 
I described above is the best one for obtaining it in its cry- 
stalline form. 
I have reason to think that there is another iodide of mer- 
cury, of a blue colour; it is formed by freely exposing in an 
open vessel the red iodide with an excess of metallic mercury. 
In the course of three or four weeks the surface assumes a 
decidedly blue tint. I have not as yet further examined this 
compound. * i = ii * * 
On examining the crystal of the iodide of lead with the aid of 
the microscope, it is found to be a flat six-sided cry- 
stal [prism?]. This, next to the tetrahedron, appears, 
from what I have observed to be the most common 
form of crystallization. * * *. I found that when, in- 
stead of using just a neutralizing sufficiency of hydriodate of 
potassa and acetate of lead, the hydriodate was added in excess, 
there was thrown down a white soft powder and not the yellow 
iodide. And by ammonia the yellow iodide is converted into 
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