124: H. L. Wells — Ocesium- and Potassium-Lead Halides. 



Solutions which were neutral or slightly acid were generally 

 used. The effect of the presence of a large amount of free 

 acid, hydrochloric, hydrobromic or hydroiodic, as the case re- 

 quired, was also carefully studied, but these had no apparent 

 effect upon the results. 



Very large crops of the potassium salts were sometimes 

 formed, so that the homogeneity of the mass was doubtful. 

 In such cases the greater part of the crop was removed and 

 satisfactory crystals were obtained by dissolving the remainder 

 in the mother-liquor by the aid of heat and cooling. 



The caesium material used was wholly from the pollucite of 

 Hebron, Maine.* The salts were carefully purified for this 

 investigation. Godeffroy's methodf was found to be very 

 satisfactory for the purpose of separating caesium from the 

 sodium and potassium which accompany it in the mineral. 



Kahlbaum's potassium chloride, bromide and iodide were 

 usually used for making the potassium salts, but for a few 

 experiments the ordinary medicinal potassium bromide was 

 substituted. Since some of the analyses of the double bro- 

 mides show an excess over 100 per cent, it is suspected that 

 the salts contained a little chlorine. Calculation shows that 

 one per cent of chlorine replacing bromine would cause an 

 excess of - 71 per cent if the chlorine was weighed as silver 

 chloride and calculated as bromine. 



The lead halides which were used were prepared by our- 

 selves from reliable materials. 



General Properties. 

 * 



The lead double halides are all decomposed by water, and 

 the presence of a large excess of the alkaline halide is neces- 

 sary for the formation of all the compounds to be described 

 except CsPb a Cl 6 and CsPb 2 Br 6 , which are almost stable with 

 water. The concentration of the alkaline halide solution 

 evidently determines, in the cases of the chlorides and 

 bromides, the type of salt produced. Since the simple 

 caesium halides are much more soluble than those of potas- 

 sium, it is possible to use them in much more concen- 

 trated solutions, and the salts Cs 4 PbCl 6 and Cs 4 PbBr 6 are 

 readily obtained. In the case of potassium bromide the solu- 

 tion becomes saturated with the simple salt by concentration 

 just beyond the point where K 2 PbBr 4 . H„0 is obtained, and 

 with potassium chloride, which is less soluble than the bromide, 

 the limit is reached at the compound 3KPbCl 3 . H 2 0. The 

 apparent existence of only a single double iodide, both with 

 caesium and potassium, is remarkable since caesium iodide is 



*This Journal, III, xli, 213. + Berichte d. Chem. Ges., vii, 375. 



