380 PROCEEDINGS OF THE AMERICAN ACADEMY. 



The presence of an unreduced bromide was first detected by Mr. Baxter 

 in the course of his work on cobaltous bromide, and some interesting 

 details involved in its discovery will be recorded in the paper upon that 

 subject. The amount present varied with the temperature used in the 

 sublimation, but was otiierwise surprisingly constant. The concurrent 

 sublimation of the two salts is undoubtedly similar to the distillation of 

 organic substances with steam, sodic bromide possessing a small constant 

 vapor-tension at the constant temperature of about 900° used in the 

 sublimations. 



After the completion of a series of reductions of nickelous bromide 

 containing this impurity of sodic bromide, a final attempt was made to 

 obtain the salt of nickel in a state of absolute purity. We expected 

 that platinum would be attacked by the mixture of bromine vapor, hydro- 

 bromic acid, and nickelous bromide, which exists in the red-hot tube 

 during the sublimation of the salt, but platinum is the last resort in cases 

 of this kind. In order to sacrifice as little of the precious metal as pos- 

 sible in our desperate experiment a large porcelain tube was lined with 

 platiimm foil,* and inside of this was placed a platinum boat containing 

 the metal to be converted into bromide. In each of two separate speci- 

 mens of nickelous bromide made in this apparatus merely a trace of 

 sodium was found, but unfortunately enough platinum was present to 

 render the results valueless. They are not included in the tables below. 

 Only a small strip of the foil was injured, the very hot parts and the cool 

 parts being alike untouched. After these exj)«riraents we abandoned 

 the attempt to prepare absolutely pure nickelous bromide, and returned 

 to the use of the porcelain tube for the sublimations ; for sodium 

 is an impurity much more easily weighed than platinum, under the 

 circumstances. The only method of obviating the difliculty would have 

 been to use a tube of nickel for the sublimation ; but the obtaining and 

 moulding of a large amount of the metal in a perfectly pure state prom- 

 ised to be so troublesome that we have not yet attempted this improve- 

 ment. 



The arrangement for supplying and purifying the large volumes of 

 hydrogen needed in this research was gradually evolved from the simple 

 form used in the first experiments to an elaborate piece of apparatus 

 which will be described in detail in the paper upon cobalt. 



The preparation of bromine and of the other materials has been de- 



* This idea was suggested by Professor H. B. Hill. Compare also Penfield, 

 Zeitschr. Anorg. Chera., VII. 22. 



