On the Atomic Weight of Ghtcinum. 



13 



centigrams of metallic glucinum in bromine vapour. This was purified 

 by sublimation in dry hydrogen, and was finally sublimed into several 

 narrow glass tabes, each of which was sealed up. When a determina- 

 tion was to be made, the two ends of one of these tubes were cut off, 

 and the solid lump of the bromide quickly rammed into a small plati- 

 num tube closed at one end. A cap was fitted on this tube, and it 

 was weighed in the same manner as the chloride. 



The vapour- density was determined like that of the chloride, and 

 the following are the data of the four experiments made : — 



Expt. Substance. Volume of C0 2 . t. d. 



^ 440° [ eva P 0ra * 10n very 



\ slow. 



2 35-9 mgrms. 4'28 c.c. 608 6*487 



3 .... 61-1 „ 7-53 „ 630 6'276 



4 .... 26-0 „ 3-22 „ 606 6*245 



Mean 6"336 



In these experiments there was always a trace of free bromine pro- 

 duced. In experiment 4, where it was largest, the iodine, set free 

 on the addition of potassium iodide, was estimated by centinormal 

 potassium arsenite, of which 0'2 c.c. was required. This corresponds 

 to 0'16 mgrm. bromine, or less than 1 per cent, of the quantity present. 

 The decomposition which had taken place could not, therefore, affect 

 the result to any appreciable extent, and that the substance had com- 

 pletely evaporated was proved by the fact that the small platinum 

 tube weighed the same before and after the experiment within one 

 or two tenths of a milligram. 



The possible densities for glucinum chloride and bromide are — 



For G1"C1 3 276 For G1'"C1 3 4-14, and 



„ Gl"Br 3 .... 5-84 „ Gl'"Br 3 .... 8*76 



The values found were — 



For GlCl a 2-72, and for GlBr 2 6'34. 



It is therefore evident that the molecules of these two sub- 

 stances in the gaseous state are represented by the formulas G1C1 3 

 and GlBr 3 respectively, in which the metal is a dyad, and has the 

 atomic weight 9*1. Thus from Avogadro's law, to which there are no 

 known exceptions, the conclusion is confirmed which was obtained 

 from the specific heat of the element at high temperatures. 



The long disputed question of the atomic weight of glucinum is 

 thus definitely and finally decided in favour of that number which 

 satisfies the requirements of the periodic law, and another element is 

 added to the long list of those whose atomic weights have been cor- 



