THE  AMERICAN 
JOURNAL  OF  PHARMACY 
DECEMBER,  1902. 
THE  INDICES  OF  REFRACTION  OF  MIXTURES. 
By  James  S.  Stevens. 
Gladstone  and  Dale  have  shown  (see  Preston's  Light)  that  the 
index  of  refraction  varies  with  the  density  in  such  a  manner  that 
a  —  I 
— - —  =  constant,  where  /jl  —  the  index  of  refraction  and  p  the 
density.  This  has  been  applied  to  the  determination  of  the  refrac- 
tive index  of  a  mixture  in  the  following  manner  : 
Let  vv  pl  and  pY  =  the  volume,  density  and  refractive  index  of 
the  first  liquid. 
v2,  (o2  and  p2  =  the  corresponding  terms  for  the  second  liquid. 
Vy  p  and  p.  =  the  corresponding  terms  for  the  mixture. 
and  /j}2  =  the  new  indices  of  the  components  after  the 
mixture  has  taken  place. 
p\   and  p\  =  the  new  densities  of  the  components  after 
the  mixture  has  taken  place. 
Since  mass  equals  volume  times  density,  and  the  mass  of  the 
mixture  equals  the  sum  of  the  masses  of  the  components,  we  have 
P  v  =  pi  Vl  +  P-2  V2- 
Since  volumes  are  inversely  as  densities,  and  since  each  component 
occupies  the  volume  v  in  the  mixture,  we  may  write 
-1  =  lJ  and  _±= 
v      Pi         v  Pi 
(577) 
