284 P. T. Walden — Double Chlorides and Bromides, etc 



pound Rb,FeCl 6 described by Godeffroy* could not be made 

 although a hydrous salt of the same type was prepared with 

 caesium. A most careful series of experiments using large 

 quantities of the constituent chlorides, was made in the 

 attempt to prepare the rubidium salt just mentioned. It is 

 not believed to be possible that Godeffroy obtained this com- 

 pound and his error was probably due to his neglecting the 

 water of crystallization in the salt Rb 2 FeCl 5 H a O. There is 

 not a great difference between the theoretical composition 

 required by a 3 : 1 anhydrous compound and the 2 : 1 salt with 

 one molecule of water, especially as far as the chlorine and 

 iron are concerned. This can be seen from the following com- 

 parison. . 



Calculated for Calculated for 



Rb 3 FeCl 6 . Rb 2 FeCl 5 HoO. 



Rubidium 48-83 4044 



Iron. 10-65 13-29 



Chlorine 40-52 42-01 



Water 4-26 



100-00 lOO'OO 



Since the hydrous 2 : 1 salt is easily prepared, ic therefore 

 seems certain that this must have been the single salt described 

 by Godeffroy. 



The following is a list of the salts obtained. 



3 : 1 Type. 2 : 1 Type. 1 : 1 Type. 



Cs a FeCI,.H Cs„FeCl 5 .H o CsFeCl 4 .£H D 



. <XFeBr 5 . H 2 CsFeBr 4 



Rb 2 FeCl 5 . II 2 



Rb„FeBr. . H 2 



K 2 FeC] 6 .H 2 0f 



(NH 4 ) 2 FeCl 5 .H 2 0t 



NH FeBr . 2H „0 



It will be noticed that the type 2 : 1 is the most frequently 

 recurring, being found in every case except with potassium 

 and ammonium bromides. The salts of this type, as might be 

 expected, are also the most stable and easily made, especially 

 with caesium chloride where it is formed through a very wide 

 range of conditions leaving only a narrow margin for the other 

 two members of the series. It is remarkable in view of these 

 facts that this type should not have been obtained with 

 ammonium bromide while the 1 : 1 type, which is compara- 

 tively unstable in other cases, is made without difficulty. 



* Arch. Pharm. [3], ix, 343. 



t These two salts have been previously described by Pritzsche, J. pr. Chem., 

 xviii, 483. 



