66 PROCEEDINGS OP THE AMERICAN ACADEMY 



way, nor can the small amount of carbonaceous impurity which the 

 crystals acquire from the solvent be so easily removed. Moreover, 

 iodide of antimony cannot be so readily distilled as the chloride or 

 bromide, on account of its high boiling point, which is above that of 

 metallic mercury. But another property of iodide of antimony which, 

 so far as we know, has not hitherto been noticed, interferes still 

 more seriously with these methods of purifying this substance. In 

 all its conditions, it undergoes a more or less rapid oxidation in 

 contact with atmospheric air, forming oxi-iodide of antimony (SbOI) 

 and free iodine. When iodide of antimony is rapidly boiled in a small 

 flask, so that the body and most of the neck are kept full of vapor at 

 the boiling-point, the action at the surface of contact of the vapor 

 and the air is very striking ; iodine is set free in vapor, with its 

 familiar violet color, while the oxi-iodide is precipitated in clouds, 

 forming a most beautiful phenomenon. So also when the greenish- 

 yellow solution (above described) of the iodide in bisulphide of carbon 

 is exposed to the air and light, it rapidly becomes colored red from the 

 liberation of iodine, and at the same time turbid from the deposition 

 of the insoluble oxi-iodide. Even the crystals of iodide of antimony, 

 when kept in the light, slowly become opaque from the formation of 

 the same oxi-iodide ; while the odor and staining of the stopper of the 

 bottle furnish abundant proof of the liberation of iodine. The study 

 of these phenomena was most interesting, and the results obtained will 

 be described in another pa,per. It is sufficient for the present to say 

 that they pointed out to us a great source of impurity in iodide of 

 antimony, and fully explained the want of accordance in our analyses 

 of the crystals of this substance as first prepared. It was evident that 

 we could only hope to purify the material by distilling or subliming it 

 in an atmosphere of inert gas ; and we devised the apparatus represented 

 in the accompanying figure for this purpose, which we have since 

 found very generally useful for all sublimations where the temj)erature 

 required does not exceed that which can be measured with a mercury 

 thermometer. The apparatus has been already referred to (page 26), 

 and requires no further description. It was a simple modification of the 

 apparatus used before for drying at a regulated temperature the precipi- 

 tates of sulphide of antimony, which, as we have stated, was so arranged 

 that the character of any sublimates which might be given off could be 

 observed. We used the same glass tube passing through the sheet-iron 

 air-bath, with its transparent mica cover, only we added a common glass 

 adapter, selected so that its mouth just fitted over the open end of the 

 tube. A platinum nacelle containing iodide of antimony, which had 



