168 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Hence the method which answered well in the recent analysis of 

 strontic bromide* was adopted here. The pure recrystallized or 

 sublimed zincic bromide was placed in a platinum boat and kept for 

 some time in an atmosphere of pure dry nitrogen charged with pure 

 hydrobromic acid. It was found that in this way all the water could 

 be expelled from the salt without the introduction of a trace of oxy- 

 bromide ; indeed, zincic bromide which by rapid heating in the air had 

 been partly decomposed could be speedily brought back to its normal 

 condition by fusion in the atmosphere of dry dilute hydric bromide. 

 The presence of the insoluble oxybromide is easily detected by dis- 

 solving the bromide in large amounts of water ; iu every case the 

 bromide used in the analyses below gave an absolutely clear solution. 

 Baric and strontic bromides ignited in the same way give solutions 

 which are absolutely neutral to methyl orange and phenol phthalein ; 

 hence it is most likely than the zincic bromide, which does not admit 

 of similar alkalimetric testing, is also quite normal. For the details 

 the paper upon strontium must be consulted, but a sketch of the appa- 

 ratus will probably suffice. (See preceding page.) In the present 

 case hydrogen could not be added to the nitrogen lor fear of reducing 

 some of the zincic bromide ; but no trouble was experienced from cor- 

 rosion of the boat. When the substance had been kept for some time 

 in a state of tranquil fusion, and had just solidified, the boat was 

 quickly slid into a weighing tube which was in its turn placed in the 

 automatic desiccator tube shown below. After the tube and boat 



had been heated to about 200° for some time in a current of pure dry 

 air, the desiccator tube was raised to a vertical position, the stopper 

 being thus allowed to fall into place. 



After weighing, the pure zinc bromide was dissolved in water and 

 precipitated by means of a slight excess of very carefully weighed pure 

 silver in very dilute solution. The argentic bromide was collected 

 upon a Gooch crucible, the shreds of asbestos carried through (0.05 

 to 0.20 milligram) were collected upon a very small fine filter, and the 

 total weight of the argentic bromide thus obtained gave one ratio upon 

 which to base the atomic weight of zinc. In the third series the filtrate 



* These Proceedings, XXX. 369. 



