RICHARDS AND BAXTER. — ATOMIC WEIGHT OF COBALT. 117 



in a state of great purity, and this metal therefoi-e joins the ranks of those 

 elements whose atomic weights may be determined by reference to silver 

 through the most satisfactory of all processes of precipitation. 



The Preparation and Properties op Cobaltous Bromide. 



All the cobaltous bromide used in this research was prepared by 

 passing bromine vapor over hot spongy cobalt. The sublimation of the 

 salt is much less troublesome than that of the corresponding salt of 

 nickel. The bright green anhydrous crystals of cobaltous bromide are 

 very much less easily decomposed than the brown nickel compound by 

 water or oxygen at a high temperature, in spite of the fact that cobaltous 



O 



.^^ 



E 



^^sa 



Fig. 1. Section op Apparatus for Sublimation. 



A = glass tube for admitting bromine vapor. O = outer porcelain tube. I = inner 

 porcelain tube. T = gla.ss outlet tube. F = perforated Fletclier furnace. 

 R = boat containing cobalt. S = Sublimed bromide. 



bromide is very much the more hygroscopic and soluble in water when 

 cold. In no case was a trace of an oxide of cobalt found amons: the 

 crystals of bromide used for the analyses. 



The first experiments were carried on in a hard glass tube heated by 

 a "combustion" furnace, but as the high heat necessary to volatilize 

 cobalt bromide played sad havoc with the glass, porcelain tubes, heated 

 by means of a perforated Fletcher furnace,* were substituted. The 

 arrangement was similar to that used in the research upon nickel. Into 

 one end of a large porcelain tube (of which the internal diameter was 28 

 millimeters) was ground a glass connector fused to the apparatus for 

 supplying a mixture of bromine vapor, h\ drobromic acid, and nitrogen ; 

 while inside of the other end was " telescoped " a closely fitting smaller 

 porcelain tube designed to serve as the receiver of the sublimed material. 



* These Proceedings, XXXII. 63. 



