REFRACTION AM' l>lsri;i;sl<>N OF Till. 1 1 A LOGENS, HALOGEN ACIDS, ETC. 9 



Beyond 5461 the number of Iwinds read was not sufficient to ensure trustworthy 

 values. 



The following table gives the experimental values in column 2 : 



TABLE III. Dispersion of gaseous Bromine. 



The experimental numbers fall approximately on a smooth curve which is given by 



D 4'2838 x 10* 7 



(M-!) 



(t/,,76) 3919'2 xlO* 7 - 3 ' 



The figures calculated from this equation are given in column 3. 



Relation of Dispersion to Absorption. As in the case of chlorine a test was made 

 for a rapid change of refractivity affecting a narrow section of the spectrum, but none 

 was detected. 



In this case also the change of refractivity is small compared with the increase of 

 the absorption as we pass from the red to the green. 



IODINE. 



Previous Measurements. The only determination of the refractive index of iodine 

 on record is that of HURION,* who gives M = 1 '00205 for the red and 1 '00192 for the 

 violet. He employed a prism and heated the iodine to 700 C. 



It was hoped that with a refractometer a higher degree of accuracy could be 

 obtained, but the results of experiment were disappointing. The absorption band 

 which has its maximum at X 5000 extends so far into the red that, with the 

 faint light available in a Jamin apparatus, the band system was very soon 

 obliterated. 



In the red (X = 6438) as many as 21 bands could be observed with difficulty, but 



VOL. ccxm. A. 



* 'Journal de Physique,' I., VII., p. 181. 

 C 



