428 Mr. R. W. Wood on the Absorption Spectrum of 



the tube, and bisulphide of carbon added up to the 11th mark. 

 The absorption spectrum showed no trace of the lines. Half of 

 the contents was then removed, and the amount of bromine in 

 this determined. On sealing and reheating the tube the 

 lines were distinctly visible, as was to be expected, and CS 2 

 was added little by little until the lines just disappeared. 

 Half of this new quantity was then removed, and the same 

 process repeated. In this way data were obtained from 

 which the following table has been made. The curve is 

 shown in fig. 5. 



1 Gram CS 2 . 



0=1). 



X, bromine in grs. 



X (Bromine). 

 X (Iodine). 



05 



•0182 



6-1 



10 



•0200 



6-1 



15 



•0241 



6-9 



20 



•0263 



7-0 



25 



•0299 



6-8 



30 



•0350 



6-8 



35 



•0415 



6-9 



40 



•0499 



7-3 



45 



•0623 



8*4 



50 



•0802 



9-4 



In the third column of the table is given the ratio of the 

 X values for bromine and iodine for the corresponding 8 

 values. A given amount of CS 2 vapour at any density from 

 •05 to '40 will dissolve from 6 to 7 times as much bromine 

 as iodine. Liquid bromine and CS 2 appear to be miscible in 

 all proportions. 



These investigations show that to a certain amount of CS 3 

 vapour a certain definite amount of iodine vapour (depending 

 on the density of the OS 2 ) can be added without causing the 

 lines characterizing the spectrum of iodine vapour to appear. 

 If more iodine vapour be added, the lines are at once seen. 

 The conclusion that one naturally draws is that the iodine 

 molecules bind themselves in some way to the CS 2 molecules, 

 and are incapable of exercising the selective absorption 

 peculiar to the molecules of pure iodine gas. On this 

 supposition, we may look on the curves in figs. 4 and 5 as 

 solubility curves, and may consider, in a certain mixture of 

 CS 2 and iodine or bromine vapour, the halogen as existing in 

 two states, one part dissolved in the CS 2 vapour, and the 

 other free. 



Hannay and Hogarth have shown (Proc. Roy. Soc. xxx. 

 pp. 178 & 484, 1880) that non-volatile solids in solution are 



