Logarithms of relative thicknesses in m.m. of Nj 1000 solutions 
compounds obtained from pyridine and collidine. 437 
Oscillation frequencies 
I. Full curve : Collidine 
Dotted curve : 9-Chlorocollidine 
Dot and dash curve : Collidine hydrochloride 
II. 7-Chlorolutidine 
29 
2 
