H. L. Wells — Rubidium-Lead Halides. 35 



The amount of water in the salt seems somewhat uncertain, 

 but, since there was no evidence of loss of water by efflores- 

 cence and since the salt was simply air-dried without being 

 pulverized, the above formula is preferred to Rb 2 PbCl 4 .H 3 

 which requires 2*99 per cent of water. The water was deter- 

 mined by heating to about 200° ; at 100° the salt lost only 

 about oue quarter of its water in twelve hours. 



1 : 2 Rubidium-Lead Chloride, RbRb 2 Cl b : — This compound 

 forms small, prismatic crystals which are usually grouped side 

 by side in nearly parallel position. It is produced from solu- 

 tions which are more dilute than those from which the pre- 

 ceding salt is prepared, and it is formed under rather wide 

 limits of conditions. Two separate crops gave the following 

 analyses : 



Calculated for 

 Found. RbPb 2 Cl 5 



Rubidium 13-09 12*68 12*63 



Lead 60-57 61*05 61-15 



Chlorine.-.- 26-19 26*29 26*22 



99*85 100-02 100-00 



2:1 Rubidium-Lead Bromide, 2 Rb.Pb Br 4 . H^O /—This 

 salt resembles the corresponding chloride, both in its formation 

 and appearance. Two crops gave the following analyses : 



Calculated for 

 Found. 2Rb 2 PbBr 4 .H 2 



Rubidium 23-17 22*73 24*19 



Lead... 30*29 30*81 29*29 



Chlorine 45'04 45*26 



Water . 1*55 1*51 1*27 



100*09 100*00 



1 : 2 Rubidium- Lead Bromide, RbPb^Br 5 : — This forms 

 square plates. It is readily prepared since it is formed under 

 considerable variations of conditions. 



Rubidium . 



Found. 

 9*81 



Calculated for 

 RbPb 2 Br 5 

 9*50 



Lead 



Bromine 



45*74 



44*62 



46*03 

 44*47 



100-17 100-00 



1:1 Rubidium- Lead Iodide, RbPbI r 2JI^O : — This is the 

 only double iodide that could be produced under widely vary- 

 ing conditions. It forms very slender, hair-like prisms of a 



