250 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



washed red phosphorus and water, and the resulting hydrobromic acid, 

 which contained a considerable excess of bromine, was freed from iodine 

 by distilling off this bromine. After several distillations the hydrobromic 

 acid was converted into bromine by treatment with recrystallized 

 potassium permanganate. The resulting bromine was thus distilled a 

 second time from a solution of a bromide of much greater purity than in 

 the first case. Analysis of this bromine was carried out by precipitating 

 a known weight of silver with a slight excess of ammouic bromide made 

 from this bromine. 



This value is almost identical with the average of Stas's experiments, 

 57.4445, and shows conclusively that both bromine and silver were pure. 



Method op Analysis. 



The method of analysis was as follows. The salt was dissolved in 

 water which had been slightly acidified with sulphuric acid to prevent 

 the formation of insoluble basic ferric salt, and the trace of insoluble 

 residue was collected upon a small filter paper and determined as previ- 

 ously described. The solution of ferrous bromide, which had been 

 diluted to a volume of at least four hundred cubic centimeters by the 

 wash waters, was then oxidized by adding slowly, through a funnel tube 

 with a fine tip which dipped below the surface of the solution, slightly 

 less than the calculated amount of a solution of potassic dichromate. 

 This solution contained one and one-half grams of potassic dichromate 

 in a liter of solution, together with a slight excess of the quantity of 

 sulphuric acid necessary to complete the reaction. The dichromate had 

 been recrystallized from the purest water, and the sulphuric acid had 

 been redistilled, so that no halogens could have been contained in the 

 oxidizing solution. In Analyses 1 and 2 an excess of the calculated 



