388 PROCEEDINGS OF THE AMERICAN ACADEMY. 



been proved by long experience to be the most efficient and satisfactory. 

 Commercial, "pure" bromine was partially freed from chlorine by 

 shaking with a fifteen per cent solution of potassic bromide. One fourth 

 of the bromine was then converted to calcic bromide by running it 

 slowly into milk of lime in the presence of a large excess of ammonia. 

 The calcic bromide solution was filtered and concentrated by evapora- 

 tion, and the rest of the bromine was added to it. A little zinc oxide 

 was then added, and after standing over night the bromine was distilled, 

 nearly free from chlorine. Most of the iodine is removed as zinc 

 iodate. After redistilling the bromine, in order to remove any calcium 

 bromide that may have spattered over in the first distillation, it was con- 

 verted into hydrobromic acid by slowly dropping it into a mixture of 

 red phosphorus and hydrobromic acid. The red phosphorus was at first 

 washed free from chlorides. The hydrobromic acid, containing some 

 free bromiue, was distilled. The free bromine liberates any iodine 

 which may have escaped the zinc oxide. The first portion of the distil- 

 late, containing free bromine and iodine, and organic matter, was rejected, 

 and so was the last portion, which may have contained traces of arsenic. 

 The hydrobromic acid was then converted into bromine by distilling over 

 pure manganese dioxide previously treated with sulphuric acid and 

 washed. One half the bromine is obtained by the manganese dioxide 

 alone. As soon as no more bromine comes off, a little redistilled sul- 

 phuric acid is added, and the rest of the bromine was obtained. It was 

 then redistilled several times, rejecting the first and last portions, and 

 finally dried over pure phosphorous pentoxide. 



The silver precipitation also presents no new features, except, perhaps, 

 its somewhat unusual thoroughness. Partially purified silver was dis- 

 solved in nitric acid, diluted, and precipitated with pure hydrochloric 

 acid. After thorough washing the chloride was reduced by invert sugar 

 and sodic hydrate which had been purified by electrolysis. The metallic 

 silver was thoroughly washed, dissolved in nitric acid, and again precipi- 

 tated as chloride and reduced. It was then dried and fused on charcoal ; 

 the lumps of silver were cleaned with sand, dissolved in pure nitric acid, 

 diluted to a volume of two litres, and again precipitated with pure hydro- 

 chloric acid. The resulting chloride was then digested on the steam 

 bath with aqua regia, washed, and once more reduced by invert sugar 

 and sodic hydrate. After drying, it was fused on pure sugar char- 

 coal. The buttons of silver were cleaned with sand, and then puri- 

 fied electrolytically, a small portion being dissolved in nitric acid to 

 serve as the electrolyte, and the rest serving as anode material. The 



