193 M. Stas on the Determination of Atomic Weights. 



and freed from sulphuric acid by a dilute solution of chloride of 

 barium. The decanted liquid was heated to boiling, and chlo- 

 ride of barium added so long as the precipitate formed was re-dis- 

 solved. The solution was poured into porcelain dishes, and by 

 rapid cooling the bromate of potassium deposited in as fine 

 powder as possible ; for only by this means could all admixed 

 chloride of potassium be washed away. From the filtrate more 

 barium-salt is obtained by a repetition of the same treatment. 

 It is purified by threefold recrystallization, and by heating partly 

 changed into bromide of barium. The subsequent separation of 

 bromine is effected as above. Pure bromine boils at 63° under 

 a pressure of 759'7 millims. When solid, it looks like iodine, 

 with more of a steel-grey colour, however. A dilute aqueous so- 

 lution is intense and of a pure yellow. The bromide of potas- 

 sium prepared from this bromine was identical with that pre- 

 pared from bromate of potassium or barium. The weighing of 

 the bromine was effected in a closed glass tube provided with 

 capillary tubulures. One end of this tube dipped in a flask 

 filled with standard solution of sulphurous acid; in the bottom 

 of this flask an S-tube was fused. The flask was also connected 

 with a potash -apparatus, also containing sulphurous acid. The 

 S-tube is closed by a caoutchouc stopper, and the flask cooled 

 to 0°. Before one end of the bromine-tube is broken off, the 

 bromine itself is made to freeze. The bromine is now gradually 

 allowed to enter the sulphurous acid, which is always kept cool, 

 and the bromine is finally heated. On cooling, sulphurous acid 

 ascends into the bromine-tube. The other point of the latter is 

 then broken off, all parts of the apparatus washed out, and the 

 whole liquid poured into the solution of sulphate of silver which 

 in the mean time has been prepared. If bromine and silver are 

 taken in the ratios of the atomic weights 80 and 108, there is 

 only a very slight excess of silver. The bromide of silver pre- 

 cipitated in the absence of Ag Br is pale yellow, but becomes 

 dark yellow on being heated, or by treatment with bromide of 

 potassium. If white and dark yellow bromide of silver be treated 

 with zinc and sulphuric acid, in the first case a blackish grey and 

 sometimespurple,butinthe latter a pure white silver is precipitated. 

 The results of all the experiments were as follows : — 



100 parts of silver yield 174*083 parts Ag Br* 



Pour experiments. Com-1 n „ A noo . -„ , 



plete synthesis. j> 17*088 parts AgBrf 



Marignac found (1843) 174-077 parts AgBr 



Prom the ratio of the atoO lry . ~„„ . A ^ 

 mic weights we have J^-077 parts AgBr 



* One experiment, in which only Ag and Ag Br were weighed, 

 t Prom the ratio of the Ag and Br weighed. 



