BAXTER. — A REVISION OF THE ATOMIC WEIGHT OF BROMINE. 211 



purified either by precipitation as chloride and reduction with invert 

 sugar, or by electrolysis, or by precipitation with ammonium formiate. 

 The metal was then fused before a blowjiipe upon a crucible of the 

 purest lime, and the buttons were thoroughly cleansed with nitric acid. 

 No further purification was considered necessary since the weight of 

 the metal was of no consequence. 



After the silver bromide had been washed by decantation with water, 

 in some cases it was collected in a Gooch crucible in which a disk of 

 filter paper was employed instead of asbestos, and after drying at 100° 

 it was carefully separated fi-om the filter paper. In other cases the 

 precipitate was transferred to a platinum dish, and was drained with 

 a platinum reverse filter ^i with a disk of filter paper. In still others 

 a platinum Gooch crucible with small holes was found to be sufficiently 

 effective as a filtering medium without the use of either asbestos or 

 filter paper. ' 



Before being weighed the silver bromide was fused in a current of 

 air saturated with bromine in a weighed quartz crucible. The air was 

 purified by passing successively over beads moistened with silver 

 nitrate solution, over sodium carbonate, and finally over concentrated 

 sulphuric acid which had been heated to its boiling-point with a small 

 quantity of recrystallized potassium dichromate to eliminate volatile 

 and oxidizable impurities. The air was then passed through dry bro- 

 mine in a small bulb. This apparatus was constructed entirely of glass 

 with ground joints. The tube which conducted the gases into the 

 crucible passed through a Rose crucible cover of glazed porcelain in 

 all experiments except Analyses 28 to 31, in which a quartz cover was 

 employed. The quartz crucibles were always contained in large porce- 

 lain crucibles while being heated. They remained almost absolutely 

 constant in weight during the experiments. The bromine was in each 

 case a portion of the sample from which the silver bromide had been 

 made. 



Next the bromide was heated barely to fusion in a slow current of 

 chlorine, generated by the action of hydrochloric acid upon manganese 

 dioxide, and dried by means of concentrated sulphuric acid. The 

 apparatus for this purpose also was constructed wholly of glass. When 

 the bromine was apparently completely displaced, the silver chloride 

 was heated in the air for a few minutes to expel dissolved chlorine, 

 and then was cooled and weighed. A repetition of the heating in 

 chlorine seldom affected the weight of the salt more than a few hun- 



" Cooke, These Proceedings, 12, 121. 



