482 Wells, Wheeler and Penfield — Rubidium and 



a = 83° 20'. If taken in the ordinary monqclinie position with 

 e as the prism 11< ► and a? as the orthodome 101, tlie axial ratio 

 from the above measurements becomes d\h;c= -8319 : 1 : •4511 

 /3 = 83° 20'. 



Method of Analysis. 



The methods used for the analyses of the potassium and 

 rubidium trihalides were exactly the same as those mentioned 

 in the article on caesium trihalides. 



The crystals were prepared, for analysis by pressing between 

 papers and at the same time crushing them somewhat. In 

 some cases, where the bodies were very easily decomposed, 

 this was done in cold weather out of doors, but even with this 

 precaution it was not possible to dry them very thoroughly or 

 to avoid a considerable amount of decomposition. 



This body can be prepared by dissolving 55 g. of rubidium 

 iodide in enough water to make a solution of 50 c.c, adding 

 60 g. of iodine, warming until solution takes place and cooling 

 to ordinary temperature. A mass of large crystals in parallel 

 position, forming steps, is usually formed. 



Calculated 

 Analysis gave for Rbl . I 2 . 



Rubidium. 18-32 18-32 18-33 



Iodine 81-07 81-67 



A specific gravity determination, made in the mother-liquor 

 at 22° gave the number 4*03. This cannot be considered very 

 exact on account of the difficulty of obtaining the mother-liquor 

 in such a condition that it neither dissolves nor deposits the 

 substance. A sample of mother-liquor, of specific gravity 2 -19, 

 was found to contain 1-61 g. of Rbl . I„ in 1 c.c. The com- 

 pound therefore dissolves in about one third its weight of 

 water at 22°. It is interesting to notice here that under nearly 

 the same conditions, the corresponding caesium compound, 

 Csl . I 2 , requires more than one hundred parts of water to dis- 

 solve it. It is expected that this great difference in solubility 

 will form the basis of a useful method for separating the two 

 metals. 



RbBr.Brl. 



This compound can be readily made by dissolving, with the 

 aid of heat, 30 g. of iodine and 20 g. of bromine in a saturated 

 aqueous solution of 40 g. of rubidium bromide and cooling. 

 The facility with which this body crystallizes is remarkable. 

 The large crystals have a color and luster much like the 

 mineral pyrargyrite, "ruby-silver." 



