10 PROCEEDINGS OF THE AMERICAN ACADEMY 



excess of the normal proportion. These crystals were made by fusing 

 the native mineral with an excess of metallic antimony, and pouring 

 out the still melted mass from the crucible, after a portion had crystal- 

 lized. But although the crystals were extremely brilliant, and had at 

 least this outward characteristic of a definite compound, yet, when 

 dissolved in hydrochloric acid out of contact with the air,* the excess 

 of metal was left undissolved in the condition of a fine powder. 



For the reasons we have stated, we liave always had great confidence 

 in the results of Schneider, while on the other hand we have felt that 

 both in the case of the oxide of antimony weighed by Dexter, and the 

 chloride of antimony used by Dumas, we could not from the nature of 

 the case have any satisfactory evidence that the material analyzed had 

 the exact atomic composition assigned to it. The antimonic oxide is 

 a perfectly amorphous and inert powder, in regard to which we have 

 neither the evidence of physical properties nor of chemical reactions 

 on the point in question. Moreover, our knowledge of the circumstances 

 under which it is formed would lead us to suspect an admixture of a 

 lower oxide in the product, which would be protected from oxiilation 

 (during the ignition) by the surrounding mass, and protected to the 

 same degree under the same conditions. Again, in SbO^ the weight 

 of tlie oxygen is only about one-fourth of that of the antimony, so 

 that a very small variation in the weight found would make, in the 

 result, all tlie difference which is in ipiestiou. In chloride of antimony, 

 on the other hand, the amount of chlorine is nearly equal to that of the 

 antimony ; and for this reason, as well as because chlorine can be so 

 accurately determined, this substance would seem at first sight to be 

 the best adapted of all others for determining the atomic weight of 

 antimony. Our experience, however, has not confirmed this first im- 

 pression ; for although we have found no difficulty whatever in obtain- 

 ing the matei'ial beautifully crystallized and free from such impurities 

 as we should ordinarily look for, yet it is so wonderfully hygroscopic 

 and liable to alteration that we have not as yet succeeded in preparing 

 it for analysis under such conditions that we could feel assured that 

 it was wiiolly free from moisture or the resulting oxichloride of anti- 

 mony ; and although with sufficient labor and ingenuity the difficulties 

 in the way could undoubtedly be overcome, yet a substance which 

 must be guarded with such precautions is not the best adapted for 

 determininn; an atomic weiirht. AVhen, therefore, we had devised the 



* Antimony is wholly insoluble in hydrochloric acid out of contact willi 

 the air. 



