MI; n.ivK r.rrm:i:i;is"V .\\i MATDI: CPTFIBERTSMN ox THK 



K> as i" irt ri.l "I' ' '' H Br which might have formed since the previous 



experiment. Sim-.- it was neressary for the gas to pass through greased taps more 



.lal.T.it. f.ivr.-niti.Hiis f',,r purification would have l>een useless. The grease used 



s .. illv prep I firoi ; . paraffi md oil. \tter each experiment the 



uir \\liirh entered the refractometer tube was admitted to contact with the 



iiry and alworhed. Any admixture of HBr would have been measurable as 



hydrogen. In the experiments on which we rely to obtain the index the residue was 



negligible. 



/V...-.-I/I//V. In order to reduce the observed refractivity to standard conditions it 

 was necessary to measure the density of vapour employed. For this purpose the 

 bulb containing tin- liquid was connected with a density bulb in parallel with the 

 refractomettT tulx- and a determination of the density of the vapour accompanied 

 each experiment. The atomic weight of bromine was taken as 79'97 (O = 16). 

 Owing to the great al>sorption of the vapour in the green it was necessary to use red 

 light for the determination of the absolute index. With X = 6438 as many as 80 or 

 90 bands could be read, whereas at X 5461 the band system was no longer readable 

 after 25 bands had passed. 



The absolute index was determined from the following five experiments which were 

 well corroborated by several others not quite so trustworthy : 



TABLE II. Refractive Index of gaseous Bromine, X =*6438. 



Owing to the strong absorption of the vapour in the visible region 

 th- dispersion were difficult, and the accuracy attained was much 

 |t -how,, n, the case of chlorine. The following figures show approxi- 

 lu,ds winch were readable at different points of the spectrum :- 

 Number of bands 



readable. 

 . More than 120. 



Ax 10*. 



. 7' J 



,-, 

 RM 



It 



120. 

 115. 



90. 



60. 



A x 10. 

 5600 

 5461 

 5209 

 5085 



Number of bands 



readable. 

 . Less than 30. 

 ,, 25. 

 20. 

 10. 



