OF ARTS AND SCIENCES. 40 



As they at first presented themselves to us, these new results, so far 

 from throwing light on the subject, only rendered the problem the more 

 obscure and baffling. Towards interpreting them however, one point 

 seemed evident ; — that, however little value our own experiments and 

 those of Schneider might have in fixing the atomic weight of antimony, 

 they had at least established, beyond all doubt, the proportion of this 

 element in the gray sulphide weighed in our antimony determinations. 

 For if we assumed, as those experiments indicated, that five-sevenths 

 of the gray sulphide was antimony, then the amounts of antimony 

 and chlorine found in the analysis of antimonious chloride just made 

 almost exactly supplemented each other; while on the other hand, if 

 this material was, as generally believed, pure Sb^Sg, in which Sb : S =:: 

 122 : 32, then our determinations of one or the other of these elements 

 must be greatly erroneous, and the excess obtained far too great to be 

 explained by any known or probable imperfections of our methods. 

 Of course, although the gray sulphide might contain, on the average, 

 five-sevenths of its weight of antimony, it was a possible supposition 

 that it might also occliule a constant amount of some. undiscovered 

 impurity, leaving the proportion of the sulphur to the antimony that 

 which the atomic weights 122 and 32 required ; and, were it not for our 

 previous experience, this would have been the most obvious explana- 

 tion of the discrepancy. Indeed, the new facts led us to re-examine 

 this material, and review our previous conclusions, but with the same 

 result as before. We could discover no impurity except the small 

 amount of carbonaceous material which was so well known and taken 

 into the account, and in our later determination (as is shown by the 

 example on page 69) even this had been reduced to so small an 

 amount as to be wholly insignificant. It is very ditficult in any such 

 case to prove a negative, but in the present instance the following con- 

 siderations appeared conclusive, which on account of their important 

 bearing we in great part recapitulate, although the evidence was again 

 reviewed at this time, 



1. Such an impurity must be comparatively large in quantity, not 

 less than several centigrammes in the amount of the gray sulphide 

 usually weighed. 



2. It must exist to an equal extent in both the native sulphide and 

 the artificial product of our analytical process, for both contain the 

 same percentage of antimony. 



3. It must be derived from antimonious chloride, tartaric acid, hydric 

 sulphide, and water, which were the only reagents used in the process, 

 and from these in the purest condition they could be obtained. 



