I attempted to prepare some mercury (I) iodide earlier on a small scale, by adding mercury metal to a test tube, about 3g or so, added some ACS grade resublimed I2, and after capping the tube with the end of the vial of Hg, heated from below with an ordinary lighter.
First sign of activity was I2 vapor turning the atmosphere inside the test tube violet, then for some reason, it almost exploded, nonviolently, but yellow and red mercury iodides SHOT up over the walls of the tube, nescessitating the scraping off the glass of the HgI, along with excess Hg, and the addition of fresh I2.
The formed iodide wasn't completely free of elemental Hg, even after several additions of I2, so I gave it a water wash and left it in an evapping dish to seperate, I believe I have a mixture of two iodides though, probably mercuric and mercurous, as there are traces of lemon yellow, in there, but the vast majority is a cinnabar-pink color.
How should I get the rest of the I2 to combine, I suppose I could resublime the I2, and use it in the form of a dust, mixed intimately with the mercury remaining, but that, is a royal pain in the rear to do, any better ideas?