OP ARTS AND SCIENCES. 17 



results were somewhat higher than his is perfectly evident. When- 

 ever sulphide of antimony is precipitated under the conditions we have 

 described, it always carries down with it, not only a small amount of 

 tartaric acid, but also a very appreciable quantity of oxichloride of 

 antimony, SbOCl, which, like the impurity first named, cannot be re- 

 moved by washing the precipitate. The molecular weight of SbOCl 

 (171.5) differs but slightly from the equivalent weight of Sb^Sg (168), 

 so that, were the precipitate dried at 100'*, a small admixture of this 

 compound would not sensibly atfect the total weight. But, as soon as 

 the temperature reaches 170'', this oxichloride begins to be decomposed, 

 SbClg volatilizes, and the more stable oxichloride Sb^O^Cl^ is formed. 

 At a low red heat, this last compound is also in its turn decomposed, 

 still more SbClg escapes in vapor, and the final residue is antimonious 

 oxide in a crystalline condition. These changes may be represented 

 thus : — 



1st. 5 SbOCl = SbAClg -f SbCIg. 

 2d. 3 Sb,05Cl2 = o Sb203 + 2 SbClg. 



At least, these are the reactions when SbOCl is heated by itself in 

 an atmosphere of CO2, as we shall show further on in this paper. In the 

 presence of a large mass of Sb2S.,, containing also a trace of organic 

 matter, these effects are undoubtedly somewhat modified and have not 

 been exactly traced. But whenever a precipitate of SbgSg formed as we 

 have described is heated much above 150°, it yields a white sublimate ; 

 and this sublimate, which we have repeatedly tested, consists chiefly of 

 antimony. At times it was pure chloride of antimony which crystal- 

 lized on the walls of the glass tube used in the experiment ; but, 

 when very small in amount, the sublimate was an amorphous white 

 powder, which appeared like oxichloride of antimony, and which 

 may have been formed by the action of a minute quantity of 

 chloride of antimony on the products of the decomposition of the 

 equally small amount of tartaric acid also occluded by the precipitate. 

 It has long been known that precipitated sulphide of antimony dried at 

 100° loses weight when heated to a higher temperature, and it has 

 generally been assumed that this loss was due to hygroscopic water. 

 But red sulphide of antimony, when precipitated as we have described, 

 is not in the least hygroscopic and can be dried perfectly at 100". At 

 least, we have never been able to obtain evidence that, after being 

 thoroughly dried at this temperature, it ever contains water as such ; 

 and we are confident that the loss of weight is due solely to the causes 



VOL. XIII. (n. s. v.) 2 



