H. L. Wells — Ccesium- Mercuric Halides. 225 



Cs z IIgCl h is made by dissolving a comparatively small quan- 

 tity of mercuric chloride in a nearly saturated caesium chloride 

 solution. It is deposited on cooling, but the best crystals are 

 obtained by spontaneous evaporation. If too much of the 

 mercuric compound is added or if too much water is present, 

 other double salts or mixed products will be obtained. On the 

 other hand, if too little mercuric chloride is present, caesium 

 chloride crystallizes out. The limits of the conditions under 

 which it is formed are narrow, but by repeated trials, with 

 slight variations suggested by previous results, a pure product 

 is readily obtained. It forms slender, radiating prisms which 

 are easily distinguished from the compounds with which it is 

 liable to be mixed. 



The following analysis was made of a sample which was 

 rapidly dried on paper, but not air-dried. The small amount 

 of water found was probably simply moisture. It was deter- 

 mined by direct weighing in a calcium-chloride tube. 



Calculated for 

 Found. Cs 3 HgCl 5 . 



Caesium... 51-15 51-38 



Mercury 24-84 25*76 



Chlorine,.. 21-79 22-86 



Water 1'69 0-00 



99-47 100-00 



Os^HgCl A is produced, by cooling a hot solution, when a 

 little more mercuric chloride or water is used than in the case 

 of the last salt. The conditions for its formation are narrow. 

 It forms large but usually very thin plates which are readily 

 distinguished from the other double-chlorides. A sample was 

 dried on paper for analysis. 



Calculated for 

 Found. Cs 2 HgCl 4 . 



Caesium 44-06 43-75 



Mercury 32*90 



Chlorine 22*87 23-35 



Water... 0-52 0-00 



100-00 



GsHgCls is dimorphous, forming, according to circumstan- 

 ces, cubic or orthorhombic crystals. The cubic form is pro- 

 duced, under widely varying conditions by cooling dilute 

 aqueous solutions, when caesium chloride is considerably in 

 excess. The orthorhombic form is deposited when caesium 

 chloride is not in great excess and by one or more recrystal- 



Am. Jour. Sci. — Third Series, Vol. XLIV, No. 261. — September, 1892. 

 15 



