26 PEOCEEDINGS OF THE AMERICAN ACADEMY 



varying from 100° to 130° C. in different cases ; and, with time enough, 

 the lower temperature seemed to be equally effective. Thus in one 

 case we have the following weights recorded : — 



Weight of SbgSg dried in a steam-chest . . . 2.1700 grammes. 



„ same after 30 minutes at 150° . . 2.1685 „ 



„ „ „ additional . 2.1685 „ 



„ „ conversion at 210^ . . 2.1677 „ 



By drying, as is well known, the precipitate shrinks to a very small 

 volume. A small portion was then taken and dissolved in hydro- 

 chloric acid, in order that we might be sure no free sulphur was 

 present; but so effectual were the precautions against oxidation we 

 have described, that after our process was perfected we obtained in no 

 case the least trace of residue. The larger part of the dried precipitate 

 was next transferred to a platinum nacelle ; and, the weight of this 

 portion having been exactly determined, the nacelle was introduced 

 into a glass tube about three-fourths of an inch in diameter. The por- 

 tion of the tube holding the nacelle was heated by au air bath, through 

 which the tube passed and was tightly held. This air bath was made 

 of sheet iron. It had a double bottom, and a tubulature on one side 

 for a thermometer. The cover consisted of a thin sheet of mica, 

 through which the nacelle could be seen within the tube, and every 

 change accurately observed. The bath was heated by a common gas 

 burner, and the temperature regulated by regulating the flow and 

 pressure of the gas. During the heating, a slow current of hydrogen 

 was passed through the tube. This gas, made from oil of vitriol, zinc, 

 and water, in a large germinator, was first purified by passing through 

 solutions of caustic potash and nitrate of silver, and afterwards dried 

 by sulphuric acid and chloride of calcium. The gas entered and 

 passed out through tightly fitting corks, and the glass exit tube was 

 made small in order that the least condensation of moisture on its walls 

 might be the more apparent.* In this simple apparatus, the dried pre- 

 cipitate was maintained at a temperature between 180" and 200'', until 

 the weight was constant. The nacelle was then again returned to the 

 tube and heated to 210°, or until the conversion of the red sulphide of 

 antimony into the gray modification took jjlace, and the weight again 



* The apparatus is the same as that subsequently used for the sublimation 

 of bromide and iodide of antimony, and figured on page 57, with this excep- 

 tion, that the large adapter whicli there servps as a receiver is replaced by a 

 small glass tube, as described above. 



