4>86 P, C. Ray — Mer citrous Nitrite and itsJDerivatives. [No. 4, 



On Mercurous Iodide — A neio Method of its Preparation. 



The yellow residue in the flask (see previous paper) consisting pre- 

 sumably of a mixture of mercurous iodide and the unacted-upon 

 mercurous nitrite was well powdered and introduced into a combustion 

 tube, plugged with asbestos and heated in a tube-heater (Rohren- 

 Oefen.). The powder occupied nearly one-third the length of the tube. 

 When the temperature rose to about 135°0, nitrous fumes began to be 

 disengaged, and an oily liquid collected at the mouth of the tube. This 

 liquid is nitro-ethane, a portion of which obstinately remains ab- 

 sorbed in the hard mass of the mixture referred to above. 



On heating more than two hours from 155° to 163 d , for the most 

 part stationary at the latter temperature, a thin deposit of lustrous 

 lemon-yellow scales was obtained. The yield however was very poor. 

 Next day the heat was raised to 192°, and the temperature maintained 

 nearly constant for three hours : a sublimate of a compact mass of 

 yellow and orange-yellow crystals was the result. 



In another experiment the sublimation was carried on between 

 190°-210°C. stationary for the most part at 210°, in this case orange- 

 yellow crystals were obtained. In several experiments, however, 

 conducted within the above range of temperatures, the sublimate 

 which was deposited nearest the source of heat was of a dark brown 

 tint ; next to it was a deposit of orange-yellow and yellow tablets 

 respectively ; and, last of all, near the mouth of the tube was a ring 

 of scarlet crystals of mercuric iodide. Sometimes it so happened that 

 by far the larger proportion of the sublimate was of scarlet mer- 

 curic iodide ; but whether this was due to the decomposition or 

 dissociation of mercurous iodide formed at first (Hg 2 I 2 = HgI 2 + Hg) 

 or not is not clear. More than a dozen experiments were carried on, 

 and the experiences accruing therefrom are recorded above. 



General properties : — In Yvon's* experiment in which Mercurous 

 Iodide was prepared by the direct union of the elements, only the 

 yellow and orange-yellow crystals are described. According to this 

 chemist sublimation begins at 190° C. My own experience confirms his 

 in the main, though I have noticed that a small quantity of mercurous 

 iodide almost always sublimes between 163° and 170° C. 



The dark brown variety when powdered and kept in contact with 

 dilute nitric acid turns dirty yellow, and the orange-yellow under 

 similar conditions orange-red, without undergoing change in the com- 

 position ; but boiled for some time with the dilute acid, both these 

 varieties are gradually transformed into mercuric iodide, and from the 



* Compt. Rend. 76, p. 1607. 



