THE  AMERICAN 
JOURNAL  OF  PHARMACY 
AUGUST,  igoi.  W?, 

ROTATION  OF  THE  PLANE  OF  POLARIZATION  BY 
MIXTURES. 
By  W.  Porter  Bkck,  Tutor  in  Physics. 
The  University  of  Maine. 
The  experiments  described  in  this  paper  were  suggested  by  Prof. 
James  S.  Stevens,  and  carried  on  by  the  writer  during  the  past 
year.  They  had  for  their  general  object  an  investigation  of  the 
rotation  of  the  plane  of  polarization  by  mixtures,  as  compared  with 
that  produced  by  the  separate  ingredients.  A  Laurent  polaris- 
trobometer  was  used,  the  special  feature  of  which  is  a  semi-circular 
plate  of  quartz  which  serves  to  retard  half  of  the  rays,  so  that 
under  certain  well-understood  conditions  there  is  an  equal  illumina- 
tion of  the  field.  The  source  of  light  used  was  a  sodium  flame 
produced  by  saturating  the  wick  of  a  large  alcohol  lamp  with  com- 
mon salt. 
Assuming  the  truth  of  the  law  connecting  the  degree  of  rotation 
with  the  tube  length,  the  first  part  of  the  experiment  consisted  in 
determining  whether  the  apparatus  available  was  sufficiently  accu- 
rate for  the  proposed  investigation.  A  triangular  trough  with  one 
angle  very  small  was  made  water-tight  and  covered  on  two  sides 
with  strips  of  paper  perforated  at  equal  distances.  It  was  proposed 
by  sighting  through  opposite  apertures  to  measure  the  rotation 
due  to  a  sugar  solution,  whose  thickness  increased  as  one  passed 
from  the  apex  to  the  base  of  the  triangle.  It  was  found,  however, 
that  the  refractive  effect  of  the  glass  sides,  which  could  not,  of 
course,  he  placed  parallel  to  each  other,  prevented  the  field  from 
being  observed. 
(367) 
