BAXTER. — REVISION OF THE ATOMIC WEIGHT OP IRON. 253 



moist hydrogen, it is a very difficult matter to avoid considerable sublima- 

 tion of the salt during the process, and complete reduction could be 

 obtained only at a temperature at which all the sodic bromide sublimes 

 out of the boat. Recourse was taken to the method of precipitating the 

 iron from a solution of the salt with ammonia, and determining the 

 sodium in the filtrate. The solution of sodium and ammonium bromides 

 was evaporated to dryness, and after the ammonium salts had been 

 volatilized by gentle ignition, the residue was taken up with water and 

 again evaporated with a slight excess of sulphuric acid. Finally the 

 residue was ignited in a stream of ammonia. These operations were 

 carried out entirely in platinum vessels, and the water used was con- 

 densed in a block tin condenser and collected in platinum. The residues 

 obtained in this way gave no test for any metal except sodium when 

 examined spectroscopically. 



Although the porcelain tubes were exactly similar to those used in the 

 sublimation of cobalt, nickel, and uranium bromides, the amount of 

 the alkaline impurity is slightly larger than that found in those cases. 

 Presumably this difference is due to the unglazed porcelain boats, which 

 it was hoped would be more resistant to the action of hydrobromic acid 

 gas, but which were attacked very badly during the sublimation. The 

 attacking of the boat may have been due to tlie fact that the ferrous 

 bromide fused in the boat while the other bromides did not fuse to a 

 noticeable extent. 



Since in the cases of cobalt and nickel, where the question of impurity 

 introduced from the porcelain tubes was sifted to the bottom, sodium was 

 the only metal found, it is reasonable to conclude that here also sodium 

 was the only impurity. Sodium bromide contains a higher percentage 

 of bromine than ferrous bromide, hence the weights of silver and silver 

 bromide determined by analysis of the sublimed salt are slightly too 



