182 II. L. Wells — Double Salts of Lead Tetrachloride. 



oxides of chlorine formed when chlorine is passed into the solu- 

 tion. 



Nikolukine has succeeded in isolating double salts of lead 

 tetrachloride with ammonium aud potassium chlorides. He 

 showed that these compounds contain lead and extra chlorine 

 in the proportion required for PbCl 4 , but there is no evidence 

 in the abstracts of his article* that he determined the composi- 

 tion of the double salts. His original article in Russian is not 

 accessible to me. Nikolukine prepared the compounds by dis- 

 solving lead dioxide in concentrated hydrochloric acid in sealed 

 tubes, and adding the alkaline chlorides to the solutions thus 

 produced. He describes the double salts as having a lemon- 

 yellow color, and states that they are pretty stable, the ammo- 

 nium chloride compound being decomposed at 120°. 



The present investigation has been undertaken with the view 

 of determining the composition of the salts which Nikolukine 

 discovered, and especially in order to investigate the corre- 

 sponding rubidium and caesium compounds, which, from anal- 

 ogy, were expected to be more insoluble and stable than the 

 potassium salt. As a result, it has been found possible to pre- 

 pare the whole series in a state of purity, and the expectations 

 in regard to the easy preparation of the rubidium and caesium 

 salts have been fully realized. The following salts are to be 

 described : 



(NH 4 ) 2 PbCl 6 

 K,PbCl 6 

 Rb 3 PbCI fi 

 Cs 2 PbCl 6 



These salts are all yellow, and they all crystallize in the 

 isometric system with an octahedral habit. 



These salts show a new relation between lead and other 

 metals of Mendeleefl's group IV, with which this type is very 

 common, especially among the double fluorides. It is to be 

 noticed also that this type is almost invariable among the 

 double salts which tetrahalides form, for platinum, iridium, 

 osmium and palladium give analogous, isomorphous com- 

 pounds, while, as has been recently shown by Dr. H. L. 

 Wheeler of this laboratory, tellurium gives an extensive series 

 of octahedral salts of this type. The octahedral form of the 

 anhydrous salts of this type is very characteristic, and it seems 

 to be universal, except among the fluorides. 



All of the lead salts to be described are decomposed by water 

 with the formation of lead peroxide. Chlorine is usually set 

 free at the same time. It may be assumed that two successive 

 reactions take place, which may be represented by the follow- 

 ing equations : 



*Berichte, xviii, 370, 1885; Jour. Chem. Soc, 1, 123. 



