OF ARTS AND SCIENCES. 55 



If in calculating the results of the above bromine determinations 

 we use the atomic weights of Stas, — Br = 79.952, Ag = 107.93, — the 

 per cents found will be in each case only 0.002 higher, which is, of 

 course, an inappreciable difference. Hence, whether we take Stas's or 

 Dumas's values for the atomic weights of bromine and silver, the 

 atomic weight of antimony deduced from the above determinations is 

 exactly 120.00. 



This is certainly a remarkably close confirmation of our previous con- 

 clusion. Indeed the wonderful coincidence between the observed and 

 the theoretical results must be to a certain extent accidental ; for no 

 process of chemical analysis is capable of the accuracy wLich this 

 agreement would imply. Still it should be noticed that the probable 

 errors of the process, so far as they are indicated by the variations 

 from the mean value, are not larger than we might expect would be 

 eliminated by multiplying observations ; and, further, that the mean of 

 the last six determinations which are undoubtedly the most trustworthy, 

 is nearly as close to the theory as the mean of the whole. 



But not only did these experiments on bromide of antimony thus 

 confirm our previous conclusion : they also gave the first definite clew 

 to the explanation of the disagreement with otherwise consistent results 

 which our experiments on chloride of antimony had presented. The 

 one difference between the chloride and the bromide, which appeared to 

 render the last better suited to yield accurate results, was the differ- 

 ence in their hygroscopic qualities. As we have stated, the chloride is 

 one of the most hygroscopic substances known. The bromide is also 

 hygroscopic, but far less so, presenting no unusual difficulties of man- 

 ipulation ; and, since our tests indicated that both substances were 

 otherwise pure, we at once drew the inference that the different results 

 we had obtained with chloride of antimony must depend on the ex- 

 traordinary attraction of this substance for moisture. Before, however, 

 fully following out the clew thus obtained, we made a similar study 

 of the iodide of antimony. 



The iodide of antimony was prepared like the bromide, by shaking 

 up in a glass flask a solution of iodine in bisulphide of carbon with 

 finely pulverized metallic antimony. On filtering and decanting, after 

 the color of the iodine is discharged, a solution having a pale greenish- 

 yellow color is obtained, from which on cooling or on evaporation red 

 crystals of iodide of antimony are deposited. The substance may 

 be purified by recrystallization from the same solvent ; but iodide of 

 antimony is far less soluble in bisulphide of carbon than the chloride or 

 bromide, and cannot therefore be so advantageously treated in this 



