OF ARTS AND SCIENCES. 63' 



the small differences of composition which the substitution in question 

 would produce. 



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 discover 

 some method by which the amount of oxichloride of antimony in our 

 preparations might be directly determined. For this purpose, we used 

 first crystallized SbOCl, obtained by the action of alcohol on chloride 

 of antimony in a sealed tube, which we weighed out into a platinum 

 nacelle, and heated to various regulated temperatures, using for this 

 purpose the apparatus already described. It appeared that the decom- 

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

 began between 167° and 175°, but was not completed until between 

 260"^ and 280°. The second stage began at about 320°, but required 

 for its completion a red heat. During both stages, chloride of antimony 

 sublimed ; and there was left in the nacelle at the close of the process 

 beautiful crystals of SbgOg. In another experiment, we used crystal- 

 lized Sb^O^Clg, prepared in the same way as the SbOCl, but with 

 different jDroportions 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 decomposition we have noticed were represented by the 

 following reactions : — 



First stage : 5 SbOCl = Sb.O^Cla + SbClg ; (1) 



Second stage : 3 Sbp^Cl^ = 5 Sb^Og + 2 SbClg ; (2) 



but the relative weights observed in the first two experiments were of 

 no value, because it was evident that a no inconsiderable amount of 

 SbgOg was lost by sublimation. Since, however, the small sublimate 

 of oxide condensed in the glass combustion-tube very much nearer 

 the nacelle than the very much larger sublimate of chloride, we varied 

 the apparatus in our third experiment so far as to place the nacelle 

 in a tube of the shape represented in the accompanying figure. 



This tube was weighed with the nacelle, and 



was so selected that it quite closely fitted f! ^ ^ — -y M 

 the combustion-tube within which it was ' 



placed for heating, as shown in figure by dotted lines. And it is 

 evident that, while with this arrangement the SbClg would be swept 



