1g Dr. Inglis’s Extracts from his Prize Essay on Iodine. 
cipal agent in effecting its decomposition, since in both in- 
stances the temperature was the same, and must have affected 
each alike. As the bichloride of mercury added to a solution 
of the hydriodate of potassa causes the formation of the bin- 
iodide, it might be expected that the protochloride would give 
us the green protiodide, which on trying I found to be the 
case ; when equal parts of calomel and hydriodate of potassa 
are added to each other (the one in solution and the other 
suspended in water) an instant interchange takes place, and 
the green iodide is produced. This took place in all cases, 
whether I used the calomel in excess, or vice versd. But I 
found that on pouring off the supernatant liquid from the 
green iodide, in either of the above instances, and now adding 
the calomel, the precipitation wholly consisted of the beau- 
tiful bright yellow iodide; or, if to a solution of the nitrate 
of mercury in excess, there be added the above-mentioned 
liquid, there is instantly a flocculent precipitation of pure ses- 
quiodide. From these facts I presume that in the process for 
the production of the green iodide there is formed a sesqui- 
chloride of mercury, 7.e. a chloride having one half more 
chlorine in its composition than calomel = (2 Hg +3 Ch, or 
1 Hg + 13Ch), and analogous to the sesquiodide. I men- 
tioned before that the same results always followed whether 
I used the calomel, or the hydriodate of potassa in excess. 
The yellow sesquiodide of mercury may be kept for any 
length of time excluded from the light without changing co- 
lour; but if exposed it soon acquires a dark hue. By heat 
one might suppose it had been converted into the biniodide, 
for it assumes first a red hue, then by continuing the heat it 
fuses and becomes of a deep crimson colour, and _volatilizes 
into crystals of the same tint, but on cooling the original yel- 
low is restored. It is singular enough that exactly an oppo- 
site effect is produced by heat on the biniodide; it is converted 
at 400° Fahrenheit into a deep blood-red-coloured fluid, 
which volatilizing condenses on the sides of the tube into 
yellow acicular crystals, which retain that colour for a consi- 
derable time, unless suddenly cooled or agitated, when the 
characteristic crimson tint of the biniodide again appears. 
The biniodide falls as a rich red powder when solutions of 
the bichloride of mercury and hydriodate of potassa are mixed 
together, and in this form it is generally seen. I, however, 
have procured it in pretty large crystalline cubes by the fol- 
lowing process. I found that it was dissolved in great abund- 
ance by a boiling solution of the hydriodate of zinc. I added 
the powdered biniodide till no more could be taken up, and 
