34 H L. Wells — Rubidium-Lead Halides. 



double halides was arrived at by Wells and Wheeler* from ex- 

 periments with caesium chloride and lead bromide. Hertyf 

 has more recently arrived at the same conclusion from his 

 investigation of the mixed double bromide and iodide of potas- 

 sium and lead. It is not safe to conclude, however, because 

 definite mixed double halides do not occur in some cases, that 

 they are never formed. It is certain that there is a tendency 

 toward the formation of such definite compounds in many cases. 

 For example, it is to be noticed that in the above analysis of 

 NH 4 Cl.PbI 2 .2H 2 there is only a slight variation from the 

 composition required by the formula, while, from a solution of 

 the same ingredients, another type of salt was deposited which 

 was almost free from iodine. The compound Cs 2 HgCl 2 I 2 4 

 described by one of us, is evidently a definite mixed double 

 halide which is not intermediate in its properties between the 

 corresponding chloride and iodide, and which has a constant 

 composition. A number of other caesium-mercuric halides 

 were described, which approached a constant composition when 

 made under varying conditions. 



Sheffield Scientific School, March, 1893. 



Art. IY. — On the Rubidium-Lead Halides, and a Summary 

 of the Double Halides of Lead • by H. L. Wells. 



The cassium-lead and potassium-lead halides have already 

 been studied in this laboratory, and an account of the ammo- 

 nium compounds is given in the preceding article. It has 

 therefore seemed desirable to make an investigation of the 

 rubidium salts in order to make the work more complete. 



2 : 1 Rubidium-Lead Chloride, ttRb^PbCl^H^O : — This was 

 formed by dissolving lead chloride in a solution of rubidium 

 chloride which was so concentrated as to be almost saturated 

 when cold. It forms colorless, transparent, slender, flat prisms 

 which retain their luster on exposure to the air. Two sepa- 

 rate crops were analyzed. 



Calculated for 

 Found. 2Rb 2 PbCl 4 .H 2 



Rubidium 29*63 29*35 32*39 



Lead 41*41 41*75 39*20 



Chlorine 26*'73 26*84 26*90 



Water 2*29 2*01 1*51 



100*06 100*45 100*00 



*This Journal, lxv, 129. f Am. Chem. Jour., xv, 81. 



X This Journal, xliv, 232. 



