BENEDICT. — DOUBLE HALOIDS. 215 



The method next attempted was that described by Professor J. 

 Lawrence Smith,* for the determination of alkalies in silicates. This 

 consists essentially in rendering the antimony insoluble by fusion with 

 pure calcic carbonate. Then in precipitating the dissolved calcic chlo- 

 ride by pure ammonia carbonate and igniting the evaporated filtrate 

 till all ammonium salts are volatilized. This gave very close results. 

 But later a method was employed which gave at once the total amount 

 of potassic chloride as it existed in the salt. This consisted in igniting 

 the weighed salt in a porcelain boat in a current of dry carbon dioxide 

 till all the volatile matter (SbCl 3 ) was given off. The ignited mass 

 was weighed and then dissolved in water, any insoluble portiou being 

 filtered and weighed. The difference in the two weights gives the 

 amount of soluble matter which is potassic chloride. 



Oxygen was estimated directly by weighing the insoluble portion of 

 the residue from the ignition described under the head of potassium 

 determination. This residue is Sb 2 3 . In Professor Cooke's paper 

 previously referred to,f there is a description of the decomposition of 

 SbOCl to Sb 2 3 . 



"Meanwhile we instituted a series of experiments with a view of 

 studying the decomposition which the oxichloride of antimony under- 

 goes under the action of heat, in the hope that we might thus dis- 

 cover some method by which the amount of oxichloride of antimony 

 in our preparations might be directly determined. ... It appeared 

 that the decomposition took place in two stages. The first stage of 

 the decomposition began between 167° and 175°, but was not com- 

 pleted until between 260° and 280°. 



" The second stage began about 320°, but requires for its completion 

 a red heat. During both stages the chloride of antimony sublimed, and 

 there were left in the nacelle at the close of the process beautiful crys- 

 tals of Sb 2 3 . In another experiment we used crystallized Sb 4 5 Cl 2 

 prepared in the same way as the SbOCl, but with different proportions 

 of alcohol and chloride of antimony. In this case the decomposition 

 did not begin until 320°, but in other respects both the process and the 

 products were as in the first experiment. It was quite evident that 

 the chemical changes which took place in the two stages of decompo- 

 sition we have noticed were represented by the following reactions : 



First stage, 5 SbOCl = Sb 4 5 Cl 2 + SbCl 8 ; (1) 



Second stage, 3 Sb 4 5 Cl 2 = 5 Sb 2 3 + 2SbCl 3 ; (2) 



* Am. Journal of Science, Second Series, XV. 234, and XVI. 53. 

 t These Proceedings, XIII. 63, 64. 



