18 Wells and Foote — Double Fluorides of 



Art. IY. — On the Double Fluorides of Caesium and Zir- 

 conium j by H. L. Wells and H. W. Foote. 



In connection with his comprehensive work on zirconoflu- 

 orides, Marignac* has investigated the double fluorides of 

 zirconium with ammonium, sodium and potassium, and since 

 the corresponding caesium salts have never been investigated, 

 we have undertaken a study of them. 



The following table gives Marignac's ammonium and potas- 

 sium salts, together with those which we have prepared with 

 caesium : 



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



3NH 4 F.ZrF 4 2NH 4 F . ZrF 4 ._ 



3KF.ZrF 4 2KF . ZrF 4 KF . ZrF 4 . H o 



2CsF.ZrF 4 0sF.ZrF 4 .H;O 2CsF.3ZrF 4 . 2H 2 



The analogy between two types of caesium and potassium 

 salts is complete, while one type varies in each series. ~No 

 evidence has been found that caesium, in this case, forms a 

 greater variety of compounds than potassium. 



The symmetrical arrangement of the vacancies in the table, 

 where no salts have been discovered, indicates that alkaline 

 fluorides of lower molecular weight combine with a relatively 

 smaller number of molecules of zirconium fluoride, while those 

 of higher molecular weight combine with a greater number of 

 such molecules. 



The 2 : 1 type is the only one occurring in all three series. 

 This is the common and usually the only type of double halo- 

 gen salts formed by tetravalent elements, hence its occurrence 

 in all cases was to be expected. The single sodium salt 

 described by Marignac, 5NaF . 2ZrF 4 , does not correspond to 

 any of the compounds in the above table, but it is to be noticed 

 that the composition corresponding to this formula varies but 

 little from that required for 2NaF . ZrF 4 . Although Marignac's 

 work on this salt was, as usual, very thorough and careful, it 

 seems possible that his products may have been the 2 : 1 salt 

 containing a small amount of some impurity, possibly a 3 : 1 

 compound. 



Marignac described the salts Mn 2 ZrF 8 . 6H 2 0, Cd 2 ZrF 8 . 6H 2 0, 

 Zn a ZrF 8 . 12H 2 and Cu 2 ZrF 8 . 12H 2 0, all of which correspond 

 to a 4 : 1 type which has not been obtained with the alkali- 

 metals. This type and those given in the preceding table 

 make five varieties of zirconofluorides, one of which has been 

 discovered in the present investigation. 



* Ann. Chim.Phys., Ill, lx, 257. 



