H. L. Wells — Ccesium- and Potassium-Lead Ilalides. 123 



Lowig, as already mentioned, has described the compound 

 K,PbBr 4 . 1 have been unable to find his original article, but 

 from the fact that I have not obtained an anhydrous form of 

 this compound, I believe that he overlooked the water of 

 crystallization or dehydrated the salt before analyzing it. 



A bromide, K 2 Pb 3 Br 8 is mentioned by Berthelot.* He does 

 not give any analysis or description of it, and I am convinced 

 from my own experiments that he obtained a mixture of 

 KJPbBr 3 '. iH 2 and KPb 9 Br e . 



Stroheckerf states that he produced three different chlorides 

 of potassium and lead by mixing potassium chloride and lead 

 nitrate solutions. It is remarkable, considering the abundance 

 and cheapness of the materials and the ease with which large 

 quantities of the double salts can be made, that he did not 

 obtain them in sufficient quantities for exact analyses. Since 

 I have succeeded in making only two double chlorides, I be- 

 lieve that one of Strohecker's salts, which he describes as 

 feathery, was simply lead chloride. 



The results of previous investigators may be summed up 

 by saying that it is probable that no potassium lead halicles 

 have been correctly described, if water of crystallization is 

 taken into consideration, except two of Remsen and Herty's 

 salts, KPbBr, . H 2 and KPM, . 2H 2 0. 



Method of Preparation. 



Both the csesium and potassium salts have been investigated, 

 in every case, by making hot, aqueous solutions of the com- 

 ponent halides and cooling to crystallization. Some previous 

 investigators had used solutions of lead nitrate and an alka- 

 line halide for the purpose, but their example has not been 

 followed, because it was not believed that the presence of an 

 alkaline nitrate would in any way facilitate the operation, and 

 it was feared that it might incur contamination in some cases. 

 The conditions were gradually varied from a point where the 

 alkaline halide crystallized out, to a point where the lead 

 halide was deposited uncombined, and the experiments were 

 so carefully carried out and so frequently repeated that it 

 seems scarcely possible that any double salt was overlooked. 



The salts have been made on a rather large scale. In the 

 case of the CEesium compounds, the rarity of the material made 

 it necessary to perform the separate experiments with only 

 about 50 or 75 grams of a caesium halide, but in making the 

 potassium salts 400 or 500 grams of a potassium halide were 

 frequently used. 



* Ann. Ohim. Phys.. V. xxix, 289, 1883. 

 % Jahresbencht, 1869, 282. 



