OF ARTS AND SCIENCES. 27 



taken. Lastly, from the loss of weight thus observed, the correction 

 to be subtracted from the first weight of the whole precipitate was 

 easily calculated. It is evident that with this apparatus we were 

 enabled to collect and examine the products sublimed during the heat- 

 ing, and form a very accurate estimate of the relative amounts under 

 different conditions ; and it was from the phenomena thus observed 

 that we deduced the inferences which have already been stated. One 

 or two additional remarks, though in part a repetition, are here 

 important. 



1. Although, during the course of the investigation, the experiment 

 was repeated a great number of times, yet in no case, even when the 

 precipitate was dried at 100°, was there the least deposition of water 

 on the walls of the exit tube. Were there as much hygroscopic 

 water present as has been usually supposed, it must have shown itself 

 under these circumstances. Of course, a very minute amount would 

 escape detection, and we sought to obtain more positive evidence, both 

 by means of dried sulphate of copper and also by a chloride of calcium 

 tube ; but the evidence of the first was wholly negative, and from the 

 slight and irregular variations of the last no positive indications could 

 be drawn. In some cases, the weight of the chloride of calcium tube 

 was obviously affected by the vapor of chloride of antimony ; while in 

 other cases, as in the example cited on page 25, the accidental variations 

 in the weight of the tube were greater than the quantity, if any, we 

 sought to estimate. During the charring of the occluded tartaric acid, 

 of course some water must be formed, and the decomposition was made 

 very evident by the familiar empyreumatic odor, which was always 

 plainly perceptible ; but the action was too complex and irregular, and 

 the amount of the products too small, to admit of any trustworthy 

 estimates by the usual methods. 



2. The change of sulphide of antimony from the red to the gray 

 modification is very sudden and striking. The temperature at which 

 it takes place varies between 210° and 220°, depending on conditions 

 which we could not wholly trace. It begins at some one point, and 

 then spreads very rapidly through the mass. During the change, as has 

 been stated, small particles of the material are sometimes projected 

 from the nacelle ; and there is not unfrequently evidence that at some 

 points of the mass the temperature must have risen high enough to 

 volatilize the sulphide of antimony. Frequently also at this time an 

 additional amount of white sublimate was formed, and the peculiar 

 empyreumatic odor again perceived. Under these circumstances, there 

 was always a decided loss of weight. But at other times, especially 



