12 



Prof. T. S. Hnmpidge. 



apparatus was gently heated, and" dry carbonic acid passed through it 

 by a glass tube going to the bottom of the platinum vessel, until the 

 issuing gas was completely absorbed by caustic potash.* The glass 

 tube was then gradually withdrawn, and the temperature raised. As 

 soon as the temperature had become constant, which was easily seen 

 by the mercury remaining stationary in both tubes and the resistance 

 of the pyrometer being constant, the cork at the top of the vessel was 

 removed for an instant, the small platinum tube with the substance 

 dropped in, and the cork immediately replaced. The equilibrium 

 was thus hardly disturbed, and a few minutes afterwards the substance 

 was allowed to fall into the heated vessel. 



In the two following determinations (the only ones which were 

 made) evaporation commenced at once, and was complete in about 

 twenty seconds. The following are the data of these two experi- 

 ments : — 



Exp. Substance. Displaced C0 2 . t. d. 



1 26-4mgrms. 7'47 c.c. " 635° 2*733 



2 28-0 „ 7-98 785 2714 



Mean 2724 



After each experiment the platinum vessel was washed out with a 

 mixture of potassium iodide and starch, but no trace of free chlorine 

 was found. The small platinum tube was then washed with water, 

 dried, and weighed ; this gave the weight of the substance used. 



The vapour- density of glucinum bromide was next determined in 

 the same apparatus. This substance can be obtained like the chloride, 

 by heating the metal in dry hydrobromic acid, but, owing to the diffi- 

 culty of obtaining a regular stream of the dry gas, it is best prepared 

 by burning the metal in gaseous bromine. Combination between the 

 two elements takes place at a low red heat, with brilliant incan- 

 descence. The crude bromide is afterwards purified by resubliming it 

 in a current of hydrogen or carbonic acid. Like the chloride, it can 

 be sublimed unchanged in carbonic acid. Grlucinum bromide sublimes 

 at a lower temperature than the chloride, and, unlike the latter com- 

 pound, vaporises before it melts. It begins to volatilise at about 450°. 

 When carefully sublimed at a low temperature, it forms beautiful 

 snow-white silky needles, and does not attack glass if air and moisture 

 are perfectly absent. If heated in the presence of air, free bromine is 

 at once produced. 



A quantity of the crude substance was prepared by heating a few 



* There was always a minute bubble of air left unabsorbed by the potash, even 

 when the gas was passed throiigh the apparatus for 20 hoxirs. It was probably 

 due to diffusion through the caoutchouc connexions, and did not appear to in- 

 fluence the results. 



