BENEDICT. — DOUBLE HALOIDS. 219 



An examination of the above two sets of averages establishes beyond 

 a doubt the value of the ignition method of analysis in these com- 

 pounds. With these data the formula nearest approaching their values 

 is SbCl 3 . SbOCl . 2 KC1. 



Calculated * for 

 SbCl 3 , SbOCl, 2 KC1. Found. 



Sb 43.88 43.78 



CI 38.89 38.91 



K 14.31 14.46 



O 2.92 2.96 



100.00 100.11 



It is evident, therefore, that this salt has the formula 



SbCl 3 . SbOCl . 2 KC1. 



SbCl 3 .2KCl [Hexagonal]. 



These crystals are tabular, consisting of a regular hexagonal prism 

 terminated by basal planes. 



With the polarizing microscope it gives a very perfect uniaxial 

 figure of a positive sign. In this figure the yellow ring is the inner- 

 most, therefore p < v. 



It being quite permanent in the air, no difficulty was experienced in 

 making the above examinations. Hot or cold water immediately de- 

 composes it. It is soluble in a solution of tartaric acid, and also 

 readily soluble in dilute hydrochloric acid, from which it can be 

 crystallized. 



The antimony and chlorine were determined by precipitation, and 

 the potassium was weighed as potassic chloride after ignition in a 

 current of dry carbon dioxide gas. In this residue there was not a 

 trace of any insoluble matter (absence of Sb 2 0.,) after ignition. 



Here, all the SbCl 3 was volatilized, giving again the data for the 

 calculation of the percentage composition. 



100.00 99.99 



The loss of 1.51 % in antimony and the gain of 1.49% in potassium 

 were at first difficult to explain, but on taking into consideration the 



* Atomic weights used: — Sb 120; CI 35.456 ; K 39.14; O 16. 



