OF ARTS AND SCIENCES. 207 



Thirty-seven grams of bromine thus prepared were washed twice 

 with water and distilled four times in two very small flasks with long 

 side tubes, the bulbs being alternately packed in ice and immersed in 

 hot water as they alternately served for condenser and retort. The 

 neck of the one serving as the latter was stopped with a glass rod 

 wrapped in fine asbestos, and this bulb was always cleaned and dried 

 before being in its turn used as condenser. In this way bromine may 

 be indefinitely redistilled with very little escape of vapor and without 

 the least inconvenience. 



The resulting bromine, although free from iodine, of course still con- 

 tained an impurity of chlorine, which it is possible to remove by the 

 solution of the whole mass in concentrated aqueous calcic bromide. 

 The required salt was made by the addition of bromine to a mixture 

 of milk of lime with sulHcient ammonia water to prevent the formation 

 of oxygen salts of calcium. The clear filtrate from this operation 

 was evaporated to dryness, and the slight excess of lime was neutral- 

 ized by means of pure hydrobromic acid. The calcic bromide thus 

 formed was freed from iodine in the manner described in the case 

 of the potassium salt, and a very small amount of the pure product 

 served to dissolve all the bromine previously made. The intensely 

 colored, heavy solution parted with some of its bromine on dilution, 

 and with nearly all the remainder on gentle distillation. 



Bromine thus prepared is absolutely free from chlorine as well as 

 from iodine. After being twice more distilled, it was taken at once 

 for the preparation of the bromide of copper used in the final deter- 

 minations of the atomic weight. The combination of the halogen and 

 the metal took place in a cooled flask containing water, and after its 

 completion the slight excess of bromine — added to insure absence 

 of cuprous bromide — was expelled by gentle evaporation to dryness 

 in a glass dish. The nearly normal cupric bromide was then dissolved 

 in a small amount of water, and the strong solution filtered through 

 asbestos in a perforated crucible. 



All experiments hitherto tried upon the salt had led to the conclu- 

 sion that the solid alone loses bromine in the air, the solution being 

 perfectly stable. If therefore it were possible suddenly to crystallize 

 the salt and immediately to wash and dissolve it, we might hope to 

 obtain a normal solution by a method which would insure perfect pu- 

 rity. This result was at last attained by the concentration of the 

 dissolved cupric bromide, barely acidified with pure hydrobromic 

 acid, to the consistency of syrup, — the containing vessel being left 

 wholly undisturbed in vacuo for thirty-six hours. Upon agitation and 



