14 PROCEEDINGS OF THE AMERICAN ACADEMY 



most suitable compound of this element, as yet known, for determin- 

 ing its atomic weight; and the results of fifteen analyses of five dif- 

 ferent preparations of the bromide were published, which gave for 

 the atomic weight in question the mean value 120.00 with an extreme 

 variation between 119.4 and 120.4 for all the fifteen analyses, and be- 

 tween 119.6 and 120.3 for the six determinations in which we placed 

 most confidence. The antimonious bromide used in these determina- 

 tions was purified first by fractional distillation, and secondly by crys- 

 tallization from a solution in suljihide of carbon. In the crystallized 

 product thus obtained, the bromine was determined gravimetrically as 

 bromide of silver in the usual way. Although it seemed at the time 

 that the results were as accordant as the analytical process would 

 yield under the unfavorable conditions, which the presence of a large 

 amount of tartaric acid in the solution of the bromide of antimony 

 necessarily involved ; yet it was obvious that the agreement was far 

 from that which was desirable in the determination of an atomic 

 weight, and our chief confidence in the accuracy of the mean value — 

 independently of its remarkable agreement with previous results — 

 was based on the fact that the known sources of error tended to 

 balance each other. Hence our conclusions were stated with great 

 caution, and the hope was expressed that, after a more thorough inves- 

 tigation of the subject, we might be able " to return to the problem 

 with such definite knowledge of the relations involved as will enable 

 us to obtain at once more sharp and decisive results than are now 

 possible." 



In our previous paper, we described a simple apparatus which we 

 devised for subliming iodide of antimony ; and in a note to the paper 

 we stated that we were a2)j)lyi"g the same process to the preparation 

 of bromide of antimony, and that it promised excellent results. Our 

 expectations in this respect have been fully realized, and the prod- 

 uct leaves nothing to be desired, either as regards the beauty or the 

 constancy of the preparation. The fine acicular crystals are perfectly 

 colorless, and have a most brilliant silky lustre. With ordinary pre- 

 cautions, they can be kept indefinitely without change, and it is easy 

 therefore to determine the weight of the material analyzed to the tenth 

 of a milligramme. 



The material used in the following determinations was first prepared 

 as described in our previous paper. It was then repeatedly distilled 

 from a small glass retort rejecting at each distillation the first and 

 the last portion. Lastly, it was twice sublimed in a slow current of 

 absolutely dry carbonic dioxide. As it was only possible to sublime a 



