OP ARTS AND SCIENCES. 17 



made by tlie distillation of a mixture of potassic permanganate with 

 a dilute solution of an excess of potassic bromide and pure sulj^huric 

 acid. Before being converted into hydrobromic acid the bromine 

 was redistilled after solution in potassic bromide and agitation with 

 zincic oxide.* The bromine was in the first place poured into pure 

 baric hydroxide, and, after the separation of the greater part of the 

 baric bromate, was converted into hydrobromic acid by pure sul- 

 phuric acid. The baric hydroxide is easily freed from the usual 

 trace of chlorine by five recrystallizations from hot water; in this 

 case the substance was crystallized nine times. The sulphuric 

 acid had been redistilled three times, the first and last portions 

 being rejected. 



The dilute hydrobromic acid, containing a small amount of free 

 bromine set free by the remaining baric bromate, was distilled. 

 The colored first portion of the distillate was thrown away, and a 

 portion of the second fraction was analyzed to prove its purity. 

 1.82471 grammes (in vacuum) of silver,! dissolved with all pos- 

 sible care in the purest nitric acid, yielded 3.17641 grammes (in 

 vacuum) of argentic bromide upon precipitation with a slight ex. 

 cess of the acid. Hence the percentage of silver in the precipitate 

 must have been 57.446, a result which is essentially identical with 

 Stas's result 57.445. 



In this hydrobromic acid a portion of the pure baric carbonate 

 was dissolved, and the solution was evaporated with a slight excess 

 of baric carbonate to the point of crystallization. The crystals were 

 dried over the water bath and ignited at a dull red heat over a Ber- 

 zelius lamp for half an hour. The filtered solution was allowed to 

 stand until neutral to phenol phthalein, showing that all the small 

 amount of baric hydroxide formed upon heating had been eliminated, 

 and after filtration was evaporated. As before, the mother liquor 

 was rejected; the crystals were washed twice with pure redistilled 

 alcohol and dried in the air. These crystals formed the first 

 preparation, designated I. a, and served for the two preliminary 

 analyses. 



The second preparation of baric bromide was made from a similar 

 specimen of baric carbonate by its solution in hydrobromic acid, 

 prepared essentially in the manner described in the work upon the 

 atomic weight of copper, t To test the purity of this acid 1.60376 



* Stas, Mem. Acad. Belg., N. S., XLIIL, Part II , p. 38. 

 t See page 22 of this paper. J These Proceedings, XXV. 197 



VOL. xxviii. (n. s. .\x ) 2 



