A%Jp0r1iir,'i887arm' }  The  Polariseope  as  a  Revealer  of  Adulterations.  163 
different  limits,  this  difference  in  the  polarizing  angle  will  determine 
an  adulteration.  And  where  dextrogyre  oils  are  adulterated  with  Isevo- 
gyre  oils,  a  most  valuable  test  is  obtained  in  quantitative  analysis,  as 
well  as  qualitative,  its  delicacy  being  proportioned  to  the  variations 
between  the  two  oils  and  the  narrow  limitations  which  each  has  by 
itself  when  pure.  For  instance,  if  it  is  found  that  a  certain  essential 
oil  always  polarizes  between  — 50°  and  — 60°  to  the  left,  and  another  oil 
always  between  +50°  and  +60°  to  the  right,  it  follows  that  there  is  a 
difference  between  these  two  oils  of  100  to  120  degrees  ;  so  that  if 
mixed  in  equal  proportions,  the  angle  of  polarization  would  be  near 
zero,  on  the  scale. 
Now,  as  to  the  test  in  question,  five  samples  of  pure  Wayne  county 
peppermint  oil  were  examined,  which  polarized  as  follows  :  — 55°, 
46°,—  46°,—  52°,—  52°, averaging—  50.2°.  Five  samples  of  nat- 
ural oilof  camphor  were  also  examined,  theaverageof  polarization  being 
+65°,  making  the  average  difference  between  the  camphor  and  pep- 
permint oils  1 15.2  degrees.  Five  samples  of  the  adulterated  oil  were  now 
examined,  which  were  found  to  average  — 9°,  being  deficient  from  the 
average  of  Wayne  county  oil  40.8  degrees.  This  deficiency  as  com- 
pared to  the  difference  between  the  Wayne  county  peppermint  oil  and 
the  oil  of  camphor,  showed  an  adulteration  of  115.2:41.2  or  35.8 
per  cent. 
For  the  purpose  of  analyzing  the  adulterated  oils  further,  I  sub- 
mitted them  to  fractional  distillation  in  ten  fractions,  which  exhibited 
great  differences  in  polarization,  seven  of  these  fractions  polarizing  to 
the  right,  which  would  indicate  more  than  50  per  cent,  adulteration. 
The  fact  of  a  polarizing  test  showing  such  a  great  amount  of  adulte  r- 
ation may  be  due  to  oil  of  camphor  having  been  exclusively  used 
which  polarizes  as  nearly  to  zero  as  possible. 
The  tests  of  the  adulterated  oils,  when  divided  into  ten  fractions, 
as  to  specific  gravity,  polarization  and  boiling  points  are  as  fol- 
lows, the  oil  being  distilled  in  a  glass  retort  with  as  gentle  a  heat  as 
possible,  over  a  wire  cloth  without  die  addition  of  water : 
No.  of  Polarization.  Sp.  Gr.  Boiling  Point. 
Fraction.  At  15.5°C.  Centigrade. 
1  +30  (to  right)  .9115  182° 
2  +29       "  .9145  185 
3  +28       "  .9205  188 
4  +21      "  .9265  192 
5  +17       "  .9315  197 
