A REVISION OF THE ATOMIC WEIGHT OF BROMINE. 55 



Sample I was first completely dissolved in calcic bromide which had been 

 made from about one-third of the original material by means of lime and am- 

 monia, and was then distilled from the solution. The product was covered 

 with several times its volume of water, and was converted into hydrobromic 

 acid by means of pure hydrogen sulphide which had been generated from fer- 

 rous sulphide with dilute sulphuric acid, and which had been thoroughly washed 

 with water. After filtration from the precipitated sulphur and bromide of sul- 

 phur, the acid was boiled for some time, with occasional addition of small quan- 

 tities of recrystallized potassium permanganate to eliminate the iodine. Finally 

 the residual hydrobromic acid was heated with an equivalent amount of re- 

 crystallized permanganate, and the bromine was condensed in a flask cooled 

 with ice. 



Sample II was first converted into hydrobromic acid by means of red phospho- 

 rus and water, and the hydrobromic acid was then distilled, after having been 

 boiled with an excess of bromine. An equivalent amount of permanganate was 

 added, and the bromine liberated was separated from the solution by distilla- 

 tion. About one-fourth of the product was next transformed into calcic bro- 

 mide by means of ammonia and lime which was free from chloride, and the re- 

 maining three-fourths of the bromide were dissolved in the calcic bromide and 

 distilled. Still a third distillation from a bromide was carried out by reducing 

 the product of the second distillation with hydrogen sulphide and subsequently 

 oxidizing the hydrobromic acid with the purest recrystallized potassium per- 

 manganate, after boiling the acid with several small portions of permanganate 

 to eliminate last traces of iodine. 



Sample III was obtained by preparing calcic bromide from a portion of 

 Sample II and distilling the remainder of Sample II from solution in this 

 bromide. 



In the case of Sample IV the processes of reduction to hydrobromic 

 acid with hydrogen sulphide and oxidation of the hydrobromic acid with pure 

 permanganate were four times repeated. After each reduction the hydro- 

 bromic acid was boiled with free bromine to remove iodine. 



Sample V was three times reduced with hydrogen sulphide and oxidized with 

 permanganate. One-fourth the product was converted into calcic bromide and 

 the remainder was dissolved in this calcic bromide and distilled. 



Thus Sample I was twice distilled from a bromide; Sample II was treated 

 three times in the same way; and Samples III, IV, and V four times. 



Shortly before use each sample was distilled and converted into ammonium 

 bromide by slow addition to an excess of redistilled ammonium hydroxide. 

 The solution was then boiled to expel the excess of ammonia. 



SILVER. 



Several different samples of silver were employed, many of which have 

 already been used in atomic weight researches in this laboratory, and have 



