Mr. R. Hunt 071 Triiiodtde of Mercuri/. 27 



I have no doubt that the incipient separation of the laminss 

 would have terminated in confirmed cataract had it not been 

 observed in time, and its progress arrested by the means al- 

 ready mentioned. Since that time the eye, though exposed 

 to the hardest work, has preserved its strength, and is now as 

 serviceable as it had ever been. 



*'If the cataract had made greater progress, and resisted 

 the simple treatment which was employed, I should not have 

 hesitated to puncture the cornea, in the expectation of chan- 

 ging the condition of the aqueous humour by its evacuation, or 

 even of injecting distilled water or an albuminous solution 

 into the aqueous cavity." 



VI. On Tritiodide of Mercury. By Mr. Robert Hunt*. 



¥ AM not aware that any one has observed more than two 

 combinations of iodine and mercury, the yellow iodide 

 and the scarlet biniodide; therefore a short account of a 

 third may not be uninteresting. 



If with a saturated solution of the iodide of potassium we 

 unite as much iodine as it will dissolve, and then add a sufficient 

 quantity of the bichloride of mercury to separate the iodine 

 of the salt, instead of the scarlet biniode, a purple-brown 

 powder will be precipitated, which will be found to be one 

 proportional of mercury combined with three proportionals 

 of iodine, or 



Iodine 72-11 . ,^^ 



Mercury.. ^^.^ | m 100 parts. 



Three equivalents of iodine being 126x3 = 378 



One equivalent of mercury 202 



580 is its 



equivalent number. 



The tritiodide of mercury is soon resolved by exposure to 

 the air into the biniodide, as it is also by alcohol, which se- 

 parates one proportional of iodine. Heat likewise drives off 

 a portion of the iodine, and the binary compound results. 

 But if it is exposed in a strong glass tube filled with carbonic 

 acid or the vapour of aether, and hermetically sealed, to the 

 heat of a spirit flame, it sublimes in deep amber- colon red aci- 

 cular crystals, which are tolerably permanent in the air. 



It is soluble in hot chloride of sodium, from which on cool- 

 ing black fibrous crystals form, which I suspect to be a 

 compound of chloriodic acid and soda ; but I have not yet 

 had an opportunity of properly examining this compound. 



* Communicated by the Author. 

 E2 



