432 Wells and Campbell — Double Chlorides, Bromides 



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



(NHJ.ZnCl, (NH 4 ) 2 ZnCl 4 NH 4 ZnCI 3 . 2HO 



(NH 4 ) 2 ZnCl 4 .H 2 KZnI 3 



Na,ZnCl 4 . 3H 2 NaZnl, . HH 2 



K 2 ZnCl 4 NaZnF, 



(NH 4 ) 2 ZnBr 4 KZnF 3 



(NH 4 ) 2 ZnI 4 NH 4 MgCl s .6H 2 



Na„ZnI 4 . 3H 2 NaMjrCI, . H 2 



K 2 ZnI 4 KM^-C1 3 .6H 2 



K,ZnF 4 RbMgCI,.6H,0 



(N H 4 ) 2 ZnF 4 . 2H a NH 4 MgBr 3 . 6H 2 

 KMgBr, . 6H 2 

 NH 4 McrI 3 .6H 2 

 KMgi;.6H 3 

 NaMgF 3 



There is but a single 3 : 1 salt, corresponding to our new 

 caesium compounds of that type. This was described by 

 Marignac. A few 1 : 1 zinc salts have been described, hence it 

 is remarkable that caesium zinc salts of this type could not be 

 obtained in a pure condition, for previous experience in this 

 laboratory has shown that caesium usually forms less soluble 

 and more stable double halides than the other alkali-metals. 

 All the previously described magnesium salts belong to the 

 1 :1 type* to which our caesium salts belong, and like the latter 

 nearly all have six molecules of water. 



The caesium-magnesium bromide is formed under narrower 

 limits of conditions than the chloride, while no iodide could 

 be prepared, for caesium iodide crystallized unchanged from 

 syrupy solutions of magnesium iodide; This behavior was 

 quite unexpected in view of the fact that the ammonium and 

 potassium double iodides are known, and we have here another 

 instance where caesium, in spite of its usual tendency to form 

 double salts, is inferior in this respect to other alkali-metals. 

 The idea suggests itself that great differences between the 

 atomic weights of the alkali-metal and the less positive metal 

 are unfavorable for the formation of double salts, but more 

 facts will be necessary in order to establish such a rule. 



The caesium-magnesium salts show an increase in ease of 

 formation from the iodide to the chloride. Such a gradation, 

 both in variety of salts and ease of preparation, is evident in 

 a number of series of double halides which have been studied 

 in this laboratory, and the well known tendency of fluorides 

 to form double salts indicates that the gradation probably ex- 

 tends to these compounds. 



*Lerch has shown (J. Pr. Ch., IT, xxviii, 338) that the salts 2KBr.MgBr a . 

 6H 2 and 2NH 4 Br . MgBr 2 . 6H 2 of Lowig do not exist. 



