252 PROCEEDINGS OF THE AMERICAN ACADEMY 



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." Unfortunately this investigation has been delayed by 

 causes beyond our control. 



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 aftplying the same process to the preparation 

 of the 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 kejJt indefinitely without change, and it is easy 

 therefore to determine the weight of the material analyzed to the 

 tenth of a milligramme. 



We have carefully studied the causes of error involved in the 

 analytical process of determining bromine in an aqueous solution of 

 bromide of antimony aud tartaric acid by the usual gravimetric 

 method. These causes we propose to discuss in a future more 

 extended paper. In this preliminary notice, we have only space to 

 state that we have satisfied ourselves that the small differences be- 

 tween the results previously obtained arose wholly from the analytical 

 process, and not from any want of constancy in the material analyzed ; 

 and further that these sources of error are to a very great extent un- 

 der control. Moreover, we have found that the volumetric determina- 

 tion of bromine by silver was not materially affected, if at all, by 

 the same causes. We have thus been led to devise a mode of testing 

 the atomic weight of antimony, which, while it has all the advantages 

 of the gravimetric method previously employed, is free from its 

 sources of error. 



If the atomic weight of antimony were 122.00, it would require 

 1.7900 grammes of pure silver to precipitate the bromine from a solu- 

 tion of 2.0000 grammes of antimony bromide, while if the atomic 

 weight of antimony were 120.00 it would require 1.8000 grammes of 

 silver. Now it is easy to estimate volumetrically jfo of this differ- 

 ence with great certainty. We therefore prepared with great care 



