252 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Accordingly, to every apparent gram of ferrous bromide a vacuum cor- 

 rection of 0.000118 gram was added. The vacuum correction of silver 

 bromide was assumed to be +0.000046, and that of silver to be 

 —0.000031, The atomic weights used in the calculations are : Oxygen, 

 16.000; Bromine, 79.955; and Silver, 107.93. 



The weights, which were of brass, platinum plated, were carefully 

 standardized to hundredths of a milligram. 



Both ferric and chromic salts show a tendency to be occluded by pre- 

 cipitates, and it was feared that difficulty might arise from this source. 

 The close agreement of the results obtained by weighing the silver 

 bromide with those calculated from the weight of the silver shows that 

 no error of the sort actually existed. The ratios of silver to silver 

 bromide in the two analyses in which both substances were determined 

 are 57.444 and 57.442. 



One point remains to be considered, — the presence of alkaline bromides 

 in the salt. All bromides made by sublimation in porcelain tubes have 

 been shown to contain sodium bromide in appreciable quantities. An 

 attempt was made to determine the amount of this impurity by reducing 

 the ferrous bromide in hydrogen and subsequently leaching out the 

 soluble salts remaining. This method was used in the cases of cobalt 

 and nickel, and afforded at the same time a means of determining the 

 per cent of metal in the salt. Unfortunately the method was not prac- 

 ticable in this case, for although ferrous bromide is slowly reduced in 



