Pentahalides, with their Crystallography. 45 



closely with, the melting and whitening points of RbCl . C1L 

 so that it is evident that there is a loss of two atoms of chlo- 

 rine before much further decomposition takes place. In view 

 of this fact it is remarkable that, when samples of JRbCl . C1 3 I 

 and RbCl . C1I were exposed to the air side by side for three 

 months, the compound containing the greater amount of 

 chlorine was almost completely decomposed while the other 

 remained nearly unchanged. It is therefore probable that 

 RbCl . C1 3 I decomposes at ordinary temperatures by losing C] 3 I 

 as a whole, while by heating another decomposition takes 

 place. 



KCl . CI J. 



This compound, first described by Filhol, has been prepared 

 for the sake of studying its crystalline form. It is easily 

 made by the method which has be.en given for the correspond- 

 ing rubidium compound. The crystals obtained by cooling are 

 in the form of very slender needles, but by evaporating the 

 mother-liquor from these at ordinary temperature thicker 

 prisms suitable for measurement can be obtained. 



Calculated 

 Analysis gave for KCl . C1 3 I. 



Potassium 11-98 12-66 



Chlorine 45-31 -46-10 



Iodine 42*50 4i'23 



Na CI . CI J. 2H 2 0. 



To prepare this substance, sodium chloride and iodine in the 

 calculated proportions are mixed with insufficient water to dis- 

 solve the sodium chloride even on heating, chlorine is added 

 to saturation at a gentle heat and the liquid is filtered while 

 still warm. The solution on cooling to a low winter tempera- 

 ture gives a crop of slender needles, but better crystals are 

 obtained by evaporation in a desiccator. Some of the latter, 

 quickly dried on paper, gave the following results on analysis : 



Calculated 

 Found. for NaCl . C1 3 T . 2H 2 0. 



Sodium. 7-17 7'01 



Chlorine.. . 42-92 43-29 



Iodine 38-23 38-71 



Water 12-84* 10-97 



The water was determined by direct weighing in a calcium 

 -chloride tube, the halogens being retained by an ignited mix- 

 ture of lead oxide and lead chromate. 



* Determined in a separate sample. 



