338 



Mr. W. J. Sell and Prof. W. J. Lewis. [Feb. 14, 



expel excess, the iodine then precipitated [by AgNO 3 , and 

 whole pretty strongly acidified with HNO 3 , gave O36523 gram 

 Agl. 



3. 0'6262 gram salt, treated exactly as in 2, gave 0*84773 gram 

 Agl. 



The Periodide (Black Long Needles). 



1. 0-2655 gram leaves on ignition 0'01305 gram O 2 3 . 



2. O3818 gram, dissolved in sulphurous acid, excess of latter ex- 



pelled by heat, silver nitrate added, and whole acidified with 

 nitric acid, gave 0'5191 gram Agl. 



3. 0'1748 gram, treated exactly as in 2, gave 0'23665 gram Agl. 



Periodide of Chromium Urea (Crystallised from Alcohol). 

 The periodide is crystallised for the most part in simple hexagonal 

 prisms terminated by the base. The crystals formed on another 

 occasion had the same habit with the edges of the base terminated by 

 narrow planes p and TT. The system is rhombohedral, and one small 

 crystal was observed with several well-developed planes on it. 

 This crystal consists of the forms o(lll), r(100), z(122), ^(722), 

 T(544), &(2ll), a(10l). Badly developed planes were also observed 

 on a few other crystals. They are (8ll), (922), and #(52l). The 

 following table gives the observed angles, as also the angles calculated 

 from the element D = 33 38'. 



