578  Refraction  of  Mixtures. 
Now,  by  Gladstone's  law, 
^  —  I  _  ji\  —  I  ■     ft\  —  I 
'Am.  Jour.  Pharm. 
.  December.  1902. 
and 
Pi 
fh  —  1 
Pi 
—  i 
Since  /jl —  I  represents  the  excess  of  refraction  due  to  the  pres- 
ence of  molecules 
&•  —  i)  =  {fi\  —  i)  +  i). 
Substituting  in  this  equation  the  values  given  in  those  above,  we 
have 
V  V 
If,  now,  we  know  the  relative  volumes  of  each  component  in  the 
mixture,  and  the  original  refractive  indices  of  the  components,  we 
may  find  that  of  the  mixture. 
The  object  of  the  following  experiments  was  to  test  this  law  for 
mixtures  of  various  oils  with  alcohol.  The  work  was  carefully  per- 
formed by  Miss  Marie  C.  Rice,  a  student  at  the  University.  Unless 
otherwise  specified,  vx  —  v2  or  the  volumes  of  the  components  were 
taken  equal. 
table. 
Liquid, 
Alcohol  
Oil  of  cloves  
Mixture  
Spearmint  
Mixture  
Tansy   
Mixture  
Lavender  .  .  ...  .  .  .  .  ..  .  .  . 
Mixture  
Mixture  1:5  
Oil  of  cloves  and  alcohol  1:4.  .  . 
Refraction 
Index. 
1 '3615 
1-5302 
*  "4475 
1:4853 
1-4269 
1-5016 
1*4295 
1  "4533 
1-4120 
i'3789 
1  "3973 
By  Formula. 
1-4464 
i'4233 
I"43I5 
1  "4073 
1*3779 
1-3926 
