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



pipette made only a small drop of the saturated solution, and 

 held 0*00031 gr. of iodine. This was determined by filling 

 and emptying the pipette ten times, and determining the 

 iodine volumetrically, with sodium thiosulphite. 



The graduated tube was divided into 20 parts, and the 

 amounts of iodine that could be present with amounts of CS 2 

 varying from 1 to 10 divisions, without showing the iodine- 

 gas spectrum, were determired. With the tube half-full of 

 CS 2 , it was possible to add iodine until the tube was quite 

 opaque ; consequently densities greater than *5 that of liquid 

 CS 2 could not be investigated. 



The values found directly are not in shape for discussion, 

 since as we increase the density of the vapour we also 

 increase its amount ; in other words, we are working with 

 varying amounts of solvent as well as varying densties. 



To reduce these varying amounts of solvent to unity is 

 very simple, and the results are given in the following table. 

 For the various densities 8 are given the amounts of iodine % 

 which can be mixed with 1 gram of the CS 2 vapour without 

 the lines appearing in the spectrum • or, in other words, the 

 amounts of iodine which 1 gram of CS 2 will dissolve at 

 different densities. 



If the tube contain m grams CS 2 with m ! grams of iodine, 

 and if v be the volume of the tube in c.cm., then 





8 



m 



X = 



mf 



m * 





1 Gram CS 2 . 





S(H 2 0=1) 



•05 







x> 



iodine in grs. 

 •00300 



•10 









•00325 



•15 









•00350 



•20 









•00375 



•25 









•00440 



•30 









•00514 



•35 









•00600 



•40 









•00686 



•45 









•00741 



•50 









•00851 



The values plotted on co-ordinate paper (Hg t 4), the 8 

 values as abscissae, the x as ordinates, show that the solvent 

 power increases rapidly with the density. Any point on the 

 .plane to the left of the curve represents a mixture which 

 shows the iodine lines in the spectrum, any point to the right 

 a mixture in which they are invisible. If the tube holds a 



