H. L. Wells — Caesium- and Potassium- Lead Halides. 125 



very soluble and potassium iodide is much more soluble than 

 the bromide and chloride. 



On account of their decomposition by water, no determina- 

 tions of the solubility of the double halides have been made, 

 but it was noticed that the caesium compounds were much, less 

 soluble in the saline solutions than the corresponding potas- 

 sium salts.. This relation corresponds with the observation of 

 Godeffroy,* that while the simple salts increase in solubility 

 from potassium to caesium, the double and complicated salts 

 show a decrease in this direction. 



All the chlorides and bromides described in this article are 

 colorless, or in one case nearly so, except two caesium salts, 

 CsPbCl, and one modification of CsPbBr 3 . The first of these 

 is pale yellow and the other bright orange. These colors are 

 very remarkable since the simple halides from which they are 

 made are all colorless. I have previously observed a similar 

 case, where a colored double halide was formed from two 

 colorless halides, in the compound CsHgBr 3 .f Both double 

 iodides are yellow, the hydrous potassium salt being the paler 

 of the two. 



Analytical Methods. 



Great care was used in selecting homogeneous material for 

 analysis. The crystals were dried as rapidly and thoroughly 

 as possible by pressing them between smooth filter-papers, and 

 where the substance did not lose its luster by the operation, 

 it was then exposed to the air for several hours. 



Water was determined by collecting and weighing it in a 

 calcium-chloride tube, the substance being ignited in a com- 

 bustion-tube, behind a layer of dry sodium carbonate, in a cur- 

 rent of dry air. The water lost over sulphuric acid or at 

 certain temperatures was determined by the usual methods. 



Lead was determined in two ways. With all the caesium 

 salts the substance was dissolved in hot water (an easy opera- 

 tion with all these salts, but impracticable in the case of some 

 of the potassium compounds), and all except a trace of lead 

 was precipitated by ammonium carbonate in presence of am- 

 monium hydroxide. The precipitate of lead carbonate was 

 removed by filtration and the remaining trace of lead was 

 precipitated by passing hydrogen sulphide into the alkaline 

 solution. The lead sulphide was collected and ignited by itself 

 in a porcelain crucible. The amount of this was so small that 

 it was evident that no appreciable error would arise from any 

 lead sulphate that the ignited residue might contain, so that 

 the main precipitate of lead carbonate was ignited in the same 



* Berichte d Chem. Ges., ix, 1365. f This Journal, III, xliv, 221. 



