OF ARTS AND SCIENCES. 



85 



only just above, the boiling point of mercury ; and, before the observa- 

 tion can be taken, it will be necessary to adapt some form of air 

 thermometer to the necessary conditions. 



Orthorhombic Antimonious Iodide. 



We first met with this new substance while examining with a micro- 

 scope the product obtained by subliming hexagonal iodide of antimony, 

 in the apparatus represented in the accompanying figure, which we 

 described in our previous paper (page 57) ; and we at once recognized, 



both by its color and its form, tlie isouieric modification of which we 

 were in search. It appeared in small greenish yellow sprays, sparingly 

 distributed among the red plates of the hexagonal iodide. Its color was 

 precisely that of the solution of the iodide in carbonic disulphide ; and, 

 as shown in Plate II., the serrated edges of the crystalline sprigs pre- 

 sented very much the appearance of a picket fence, repeating at each 

 point the characteristic angle of 60°. 



It soon appeared that the yellow iodide was always formed when 

 iodide of antimony was sublimed at a low temperature, and that this 

 was the one condition necessary. Iodide of antimony begins to volatil- 

 ize far below its melting point, even at 100'^ C. ; and, if it is sublimed 

 between two watch-glasses at a temperature not exceeding 114'^, the 

 yellow modification is the sole product. It condenses them in beautiful 

 feather-like sprays, on which, however, no definite form can be distin- 

 guished. The process, also, is exceedingly slow, and tlie product very 

 small. A much larger yield is obtained when the iodide is sublimed at a 

 temperature just above its melting point, in a current of inert gas suffi- 

 ciently strong to sweep the vapor at once into a cool condenser, — con- 

 ditions, which are perfectly realized in the apparatus we have described. 



