44 PEOCEEDINGS OP THE AMERICAN ACADEMY 



4. It must be able to bear a temperature of 300° C. without altera- 

 tion, for in our later determinations the sulphide was heated to this 

 temperature. 



5. It must be soluble in hydrochloric acid ; for allowance was made 

 for the impurity which remained undissolved when the sulphide was 

 decomposed by this reagent. 



Hence, it still appeared, as before, quite impossible that any such 

 impurity could be present ; but, in order to eliminate even more cer- 

 tainly any unforeseen and accidental conditions, we made the following 

 experiments. 



In the first place, we brought together the aqueous solutions of hydro- 

 chloric ^cid, tartaric acid, and sulphide of hydrogen in the same pro- 

 portions, and under the same conditions in which they were used in 

 our antimony determinations ; but, although we made several trials, we 

 obtained in no case the slightest precipitate. 



In the second place, we heated a small amount of the tartaric acid 

 used to 300'^ C, treating it exactly in the same way as the precipitated 

 antimonious sulphide in our analytical processes ; and we found that the 

 small amount of carbonaceous residue obtained was wholly insoluble in 

 hydrochloric acid. 



It would evidently have been more satisfactory to be able to deter- 

 mine the amount of combined sulphur in the gray sulphide, and thus 

 to prove that it exactly supplemented the antimony, as we had endeav- 

 ored to do in the case of the antimonious chloride ; but unfortunately 

 we could devise no method which promised to be satisfactory. We 

 were obliged therefore to rest on the negative evidence, and this seemed 

 to exclude the most obvious explanation of our contradictory results. 

 Of course, we could not reasonably entertain the question that the 

 large excess which the analyses of table pages 40 and 42 presented, 

 when calculated for Sb= 122, was due wholly to an overestimate of 

 the chlorine, because the amount of chlorine was only that which this 

 theory of the composition of SbCl, required ; and, moreover, the con- 

 stancy in the composition of the chloride, after it had been submitted 

 to such various treatment, was surprisingly great, and served to exclude 

 the idea of any error at all comparable with that which the excess in 

 question would imply. We had found apparently that the composi- 

 tion remained sensibly constant, even after the successive distillation of 

 what we had regarded as essentially pure material. We had distilled 

 it in a current of perfectly dry hydrogen, at a temperature below 

 100°, and still obtained in the distillate the same composition as 

 before. We now further made the four additional chlorine deter- 



