BENEDICT. — DOUBLE SALTS OF ANTIMONY. 11 



The following salts have been prepared and analyzed, and the 

 formula) deduced for them are : — 



The materials used in the preparation of these salts were obtained 

 as follows. The antimonious chloride and calcic chloride were the 

 '* chemically pure " products of the market. The antimonious bromide 

 was made by the direct union of finely powdered metallic antimony 

 and bromine in carbon bisulphide, after the manner described by Pro- 

 fessor Cooke.* The calcic bromide and magnesic bromide were made 

 by the action of pure hydrobromic acid upon pure calcic carbonate and 

 magnesic carbonate respectively. 



No difficulty was experienced in obtaining the three salts just named 

 by mixing their components in approximately molecular proportions, 

 adding just enough free acid to effect the complete solution of the 

 antimony salt and evaporating the mixture in a crystallizing dish in 

 a vacuum over sulphuric acid. Fortunately there was a room in the 

 laboratory in which the temperature could be regulated quite easily so 

 as to keep it at about 0° Cent, and not let it fall low enough to solidify 

 the mixtures, thus offering the most favorable conditions to crystalli- 

 zation. The large isolated crystals were removed in the cold room, 

 crushed in a mortar, hastily rubbed between filter papers and placed 

 in glass-stoppered weighing bottles. Of necessity this operation re- 

 quired considerable dexterity to prevent any change in weight, but 

 experience has shown that the whole operation can be performed in 

 45 to 50 seconds, with no appreciable change in the composition of 

 the salt. 



With but one exception the analysis of thesre salts presented no 

 great difficulty. 



Antimony was determined in the usual manner, by weighing as 

 antimonious sulphide. All the precautions of this determination, as 

 advi.sed by Professor Cooke in his fundamental work on the atomic 

 weight of antimouy,t were closely observed. 



Bromine and chlorine were determined as their respective silvei 

 salts. The presence of tartaric acid necessary for the solution of the 

 antimony salt interferes to some extent in this determination by pre- 



* These Proceedings, XIII. 52. 

 t Ibid., XIII. 1-114. 



