206 PROCEEDINGS OF THE AMERICAN ACADEMY. 



which had been generated from ferrous sulphide with dihite sulphuric 

 acid, and which had been thoroughly washed with water. After filtra- 

 tion from the precipitated sulphur and bromide of sulphur, the acid was 

 boiled for some time, with occasional addition of small quantities of 

 recrystallized potassium permanganate to eliminate the iodine. Finally 

 the residual hydrobromic acid was heated with an equivalent amount 

 of recrystallized permanganate, and the bromine was condensed in a 

 flask cooled with ice. 



Sample II was first converted into hydrobromic acid by means of 

 red phosphorus 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 distillation. About one fourth of the 

 product was next transformed into calcic bromide by means of am- 

 monia and lime which was free from chloride, and the remaining three 

 fourths of the bromine were dissolved in the calcic bromide and dis- 

 tilled. 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 re- 

 crystallized potassium permanganate, 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 reduc- 

 tion the hydrobromic acid was boiled with free bromine to remove 

 iodine. 



Sample V was three times reduced with hydrogen sulphide and oxi- 

 dized 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 am- 

 monium hydroxide. The solution was then boiled to expel the excess 

 of ammonia. 



H'dirr. — Several different samples of silver were employed, many 

 of which have already been used in atomic weight researches in this 



