60 PROCEEDINGS OF THE AMERICAN ACADEMY 



to produce all the variation from the normal composition which the 

 above results present. A simple calculation will show that an absorp- 

 tion of only j^ ^^ths of one per cent of oxygen, or less than half a milli- 

 gramme by each gramme of iodide of antimony, would reduce the per 

 cent of iodine from the theoretical value, 76.047, to the mean of the 

 above results, 75.832 ; and that a corresponding absorption of three- 

 quarters of a milligramme would reduce the per cent to 75.700, the 

 lowest observed. It is not, therefore, surprising that we could obtain 

 concordant results only with material which had been both purified by 

 crystallization and also recently sublimed. 



Returning now to discuss again the cause of the disagreement of the 

 analyses of antimonious chloride with our otherwise consistent results 

 in regard to the atomic weight of antimony, it was obvious that the 

 strong hygroscopic power of the chloride must lead to a replacement 

 precisely similar to that which is produced in the iodide by direct 

 oxidation ; for, as we have before said, the crystals of antimonious 

 chloride cannot be exposed to the atmosphere for an instant without 

 absorbing a perceptible amount of moisture, and every molecule of 

 water thus absorbed reacts on a molecule of the chloride, thus : — 



SbClg -f H^O = SbOCl + 2 HCl. 



And when the antimonious chloride is boiled, the hydrochloric acid 

 formed is given off, while the oxichloride remains behind, dissolved in 

 the great mass of the liquid. Indeed, it seems impossible, with our 

 ordinary appliances, to pre2:)are or purify antimonious chloride without 

 its becoming contaminated with oxichloride ; and our experiments 

 would indicate that when once it has been formed, as above described, 

 in the mass of the material, it cannot be wholly removed by distillation 

 or crystallization, however often these processes may be repeated. 



Naturally, our attention was very early called to this obvious source 

 of impurity in the antimonious chloride we prepared; and we noticed 

 from the first that, even after the material had been many times dis- 

 tilled, there was always left, on repeating the process, a very small amount 

 of dark-colored residue. We had examined the residue, and found that 

 it was a mixture of chloride and oxichloride of antimony, colored by a 

 trace of carbonaceous material ; and we had made a long series of an- 

 alyses for the purpose of studying the effect produced by the action we 

 have described. The result of these analyses is given in the following 

 table. We started with material already purified by fractional distilla- 

 tion and crystallization, and distilled it ten times in succession ; not, 

 however, carrying the distillation to absolute dryness, but leaving, so 



