134 H. L. Wells — Ccesium- and Potassium-Lead Halides. 



The salt is usually permanent in the air, but in dry weather 

 the crystals gradually become opaque, and over sulphuric acid 

 about two thirds of the water is rapidly given off. 



KPbJBr v — This salt crystallizes in square plates, sometimes 

 3 or 4 mm in diameter. It can be readily distinguished from 

 the other double bromides, not only by its form, but from the 

 fact that it quickly assumes a pale green color when exposed 

 to daylight. On long exposure, or in direct sunlight, this 

 color changes to a pale dirty-brown. I have observed that 

 lead bromide itself becomes nearly black on long exposure to 

 daylight. This fact does not appear to be generally known. 



The samples analyzed were made under the following con- 

 ditions : 



Volume 

 KBr. PbBr 2 . Volume. for lgKBr. 



A 400 g 130 1050 cc 2f 



B .... 400 150 1250 3| 



C 200 75 1000 5 



The results of the analyses are as follows : 



Calculated 

 A. B. C. for KPb 9 Br 6 . 



Potassium 4-75 4'75 4-71 4-58 



Lead 49-22 4941 48-48 48-53 



Bromine....- 47-03 46'98 46-89 46-89 



101-00 100-84 100-08 lOO'OO 



KPbI % . 2P^O. — It has already been mentioned that this is the 

 only double iodide that either Rem sen and Herty or I have 

 been able to make. It forms slender, pale yellow needles, and 

 is produced under a great variety of conditions. Two samples 

 were analyzed. A was made with about 450 g KI, 75 g PbI 2 , and 

 600 co volume. For B about 40(J g KI, 45 g PbI 2 and 280 cc volume 

 were used. 



A. 



Potassium 6-03 



Lead 30 73 



Iodine 57'57 



Water 5-26 





Calculated 



B. 



KPbI 3 . 2H 2 0. 



6-07 



5-90 



30-13 



31-21 



56-99 



57-46 



6 04 



5-43 



99-59 99-23 lOO'OO 



The salt is apparently stable in the air, but it loses water in 

 the desiccator. 



Sheffield Scientific School. 

 New Haven, Conn.. October, 1892. 



