THE PREPARATION OF MATERIALS. 



brownish in color, but this caused no inconvenience in the present case, 

 as the bromine was to be subsequently distilled. In order to liberate the 

 halogen, the bromide was treated in strong solution with less than the 

 calculated quantity of bromate and an excess of pure sulphuric acid. The 

 acid was added drop by drop to the mixed solution of salts in an apparatus 

 made entirely of Jena glass, which was kept surrounded by ice-water. 

 The bromine which volatilized on account of the heat of the reaction was 

 caught in a condenser under water; to this was added the remaining 

 bromine, which had been separated from the supernatant solution by 

 means of a separating funnel. 



The bromine thus obtained was twice distilled by steam heat into water 

 in a Jena glass condenser, packed in ice. It was kept in a well-seasoned 

 bottle with double ground-glass stoppers. 



The product was certainly free from non-volatile materials, and could 

 have contained only iodine and perhaps a trace of sulphuric acid as 

 impurity. It will be seen that these were eliminated in the subsequent 

 work. This was the only sample of bromine prepared ; it was used in all 

 the preparations of bromide, as the quantitative results indicated that 

 it was very pure. 



POTASSIC BROMIDE. 



The problem of obtaining potassic bromide from the oxalate and bro- 

 mine had been carefully considered before these substances had been 

 prepared. Only two methods recommended themselves for the present 

 purpose, although the bromide can be obtained from these two materials 

 by a variety of reactions, which would ordinarily be acceptable. Here, 

 however, simplicity, completeness, and theoretical correctness must all be 

 fulfilled ; that the methods adopted really possessed these advantages in 

 their favor must be admitted after careful perusal of the following descrip- 

 tion of the details. 



In some preliminary experiments it was shown that by adding an excess 

 of bromine to the oxalate and evaporating off the excess, a very pure 

 bromide quite free from oxalate is obtained. Accordingly, a quantity of 

 the first sample of five times crystallized potassic oxalate was treated with 

 an excess of bromine, the bromine being added in small quantities from a 

 dropping-funnel. The solution was held in a quartz dish, which was 

 carefully hooded to prevent entrance of dust. When the action had 

 ceased, the solution was heated on a steam-bath until any traces of iodine 

 and all excess of bromine had been expelled. The solution was found 

 to be entirely free from oxalic acid upon testing with calcic nitrate in a 

 solution faintly acid with nitric acid. Although it was wholly colorless 

 while in the quartz dish, after being concentrated in platinum it developed 

 a very faint yellow tinge. Upon recrystallizing three times this color was 



