122 H. L. Wells — Ccesium- and Potassium-Lead Halides. 



and Herty nor I have been able to prepare them. Although 

 these iodides and Boullay's salt, K 4 PbT g , belong to types which 

 certainly exist, I am inclined to believe, with Remsen and 

 Herty, that the products which gave these formulae were 

 mixtures of KPbI 3 .2II 2 and KI. The absence of more 

 than one iodide in the caesium series strengthens this view. 



Remsen and Herty obtained the salt KPbI 3 2H 2 under 

 wide variations of conditions and I have confirmed their 

 results. This salt was first obtained by Boullay* and analyzed 

 by him, after drying over lime, in an anhydrous condition. 

 Berthelotf has described a compound, K 4 Pb 3 I 18 . 6H 2 0, which 

 differs but slightly in required composition from the above 

 salt, and his description of it agrees with that compound. 

 There is no doubt, therefore, that he really obtained the com- 

 pound KPbI 3 . 2H 2 () and that his analyzed products were 

 slightly contaminated with potassium iodide. Berthelot at- 

 tributes K 4 Pb 3 T 10 to Boullay. The latter chemist, however, 

 derived the correct formula, equivalent to KPbl,, from his 

 analysis, but since this did not agree closely with theory, 

 Gmelin^: derived the above-mentioned formula from it, and 

 this has been frequently copied in more recent chemical litera- 

 ture. 



Schreinemakers,§ in connection with an investigation on the 

 equilibrium of the double salt of iodide of lead and potassium 

 in aqueous solution, has assumed that Ditte's formula was cor- 

 rect as far as the composition of the anhydrous compound was 

 concerned. By making a number of water determinations, 

 without determining lead, potassium or iodine, he arrived at 

 the formula K 2 PbI 4 . 2fH 2 0. It is absolutely certain, from 

 his description of the salt and his method of preparing it, that 

 he had the compound KPI>I 3 . 2H 2 ; moreover, his water 

 determinations. 5*52, 5 72, 5'89, 5 93 and 5'16 per cent, agree 

 satisfactorily with the calculated amount, 5*9<>, for this salt. 



Remsen and Herty made only a single chloride, and likewise 

 only one bromide. The other chloride, and the two bromides 

 belonging to other types crystallize beautifully and are as 

 easily made as the salts which they prepared, and it is a strange 

 coincidence that the latter happened to correspond in type to 

 the iodide which they had obtained. I have confirmed the 

 composition of their bromide, KPbBr 3 . H 2 0. but their chlo- 

 ride, to which they gave the formula KPbCl 3 is evidently 

 identical with the compound which I have found to be un- 

 doubtedly hydrous, 3KJPI.C1,. H a O. 



* Ann. Chim. Phys., II. xxxiv, 336, 1827. 

 f Ann. (him. Phys., V, xxix. 289. 1883. 

 \ ' Handbook." English ed.. 1850, v, 161. 

 §Zeitschr. Physikal. Ohem., ix, 57, 1892. 



