H. L. Wells — Double /Salts of Zead Tetrachloride. 185 



hours was collected upon a Goocli filter. The rubidium in 

 this precipitate was determined and found to amount to *0318 g . 

 One cubic centimeter of the solution dissolved, therefore, *003 s 

 of the lead salt, equivalent to "00086 s of rubidium. The ex- 

 periment was made at about 20°. 



Caesium- Plumbic Chloride, Cs^PbCl^: — This salt is very 

 readily prepared by passing chlorine into solutions containing 

 lead chloride and a large excess of caesium chloride. When 

 hydrochloric acid is present, the excess of csesium chloride is 

 unnecessary, but in that case the precipitate is very finely 

 divided. The precipitate begins to form in solutions that are 

 nearly at a boiling temperature. A crop obtained without the 

 use of hydrochloric acid was analyzed. It was washed with 

 hydrochloric acid containing chlorine and air-dried. 



Calculated for 

 Found. Cs 2 PbCl 6 . 



Caesium 38*51 38*78 



Lead _ 30*05 30*17 



Chlorine... 30*99 3105 



99*55 100*00 



Loss on heating 10*96 CL 10*35 



~ 2 



The salt usually has a lemon-yellow color, but, when very strong 

 hydrochloric acid is Used and a large excess of lead chloride is 

 present the precipitate has a dark brown color. Such a crop 

 gave the following analysis : 



Calculated for 

 Found. Cs 2 PbCl 6 . 



Caesium _.. 38*19 38*78 



Lead 2964 30*17 



Chlorine 31*35 31*05 



9918 100*00 



Loss on heating 11*09 Cl 2 10*35 



This is evidently the same compound as the lemon-yellow salt. 

 The cause of the brown color is not known. The presence of 

 lead dioxide in it does not seem probable on account of the 

 strong acid that was used, and, moreover, experiment showed 

 that this oxide was instantly dissolved 

 by the mother-liquor. It was suspected 

 that this was a dimorphous form of the 

 compound, but Mr. Louis Y. Pirsson, who 

 has kindly made a microscopic examina- 

 tion of both products, has found that 

 both are isometric and octahedral in 

 habit. He noticed that while the yel- 

 low salt forms perfect octahedrons, the 

 brown compound occurs in octahedral 



