1889.J On Salts of a Base containing Chromium and Urea. 337 



The Periodide. 



When a warm solution of iodine in potassium iodide is added to 

 a warm and moderately concentrated solution of the normal iodide, a 

 considerable crop of crystals separates out on cooling in transparent 

 brown-red micaceous scales. If, however, the solutions are heated to 

 near the boiling point before mixing, or are more dilute, especially if 

 the quantity of iodine added is small, the crystals deposited are in the 

 form of long opaque black needles, having a well-marked green 

 reflection, which is, to a certain extent, lost on drying. Not unfre- 

 quently, however, both forms are deposited from the same solution. 

 The apparent dissimilarity of form and general appearance led to the 

 analysis of the two modifications being conducted separately. The 

 numbers obtained, however, are identical, and lead to the formula 

 (CON 2 H 4 ) 12 Cr 2 I 6 6I 2 , being assigned to this remarkable substance. 

 The difference in appearance of the two forms is possibly due to 

 certain of the faces in one being differently developed to those in the 

 other. Both yield apparently identical crystals when deposited by 

 spontaneous evaporation from alcoholic solutions, or from the nearly 

 boiling solution in aqueous potassium iodide. 



The substance dissolves freely in alcohol, very sparingly in benzene, 

 and is scarcely affected by chloroform, only just sufficient being dis- 

 solved to communicate a violet colour. 



The Periodide (Red-brown Transparent Six-sided Plates'). 



1. 0-1849 gram salt leaves on ignition 0' 00895 gram O 2 3 . 



2. 0-2703 gram salt, dissolved in dilute sulphurous acid, warmed to 



