28 PROCEEDINGS OF THE AMERICAN ACADEMY 



when the precipitate contained no oxichloride of antimony and h;id 

 been heated for several hours to a temperature near the point of con- 

 version, the change was attended with no loss of weight which was 

 appreciable, as, for example, in the experiments cited on page 2r>, and 

 in the determination numbered 13 below. After conversion, as we 

 found in several experiments, the gray sulphide may be heated to 

 2o0<' or even 300° without further loss. 



The change of condition just described is not attended, however, with 

 any very marked amount of condensation. We made the following 

 determinations of the specific gravity of the sulphide of antimony in 

 the two conditions. The specimens were weighed in alcohol of known 

 density, and the specific gravity referred to water by calculation. An 

 air pump was used to remove any entangled air. 



Red Sulphide of Antimony dried at 180°. 



1. Specific Gravity determined at 26°. 7 =z 4.226. 



2. „ „ „ „ 23°. = 4.223. 



Gray Sulphide of Antimony* converted at 210°. 



1. Specific Gravity determined at 28'' = 4.288. 



2. . 27'^ — 4 -^HO 



The published determinations of the specific gravity of the native 

 antimony glance give values varying between 4,52 and 4.75 ; and 

 Heinrich Rose gives f for the specific gravity of the artificial product 

 made by melting together tlie constituents the value 4.614, and for the 

 same, after pulverizing, 4.641. He also gives for the precipitated 

 sulphide the value 4.421. It is evident, therefore, that the value varies, 

 but in the above determinations the comparison of the two modifica- 

 tions were made under as nearly as possible identical conditions. Pos- 

 sibly, the decomposition of the occluded tartaric acid, producing a more 

 or less spongy condition in the mass, may be the cause of the observed 

 differences. 



In the later determinations, when for the reasons we have stated 

 the occlusion of tartaric acid was large, the gray sulphide, after having 

 been weighed, was always dissolved in hydrochloric acid, and the car- 

 bonaceous residue estimated. The solution, having been mixed with 



* Same as obtained in determination of table, pages 36-7, No. 8. 

 t Poggendorff, Anniilen, Ixxxix. 122. 



