50 
Polarimeter  and  its  Use. 
km.  Jour  Pharir- 
Jan.,  1880. 
in  construction  and  working  has  been  sought  for  its  special  requirements.^  There 
is,  however,  good  reason  to  believe  that  of  the  other  spheres  of  usefulness  as  yet 
unknown  (in  addition  to  those  which  are  known)  some  are  closely  allied,  whilst 
•others  belong  to  the  domain  of  pharmacy.  By  its  means  (as  already  stated)  the 
purity  of  the  alkaloids  can  be  readily  determined  j  castor  oil,  croton  oil,  and  doubt- 
less some  others  of  this  class  possess  their  specific  rotatory  powers,  whilst  the 
majority  of  essential  oils  do  so  in  a  high  degree,  Landolt,  who  has  worked  largely 
with  bodies  of  a  definite  and  constant  chemical  constitution,  does  not  appear  to 
have  as  much  faith  in  its  application  to  essential  oils  on  account  of  some  amount  of 
variation  dependent  on  soil,  climate,  etc  ,  and  in  his  recently  published  memoir  he 
devotes  but  little  space  and  consideration  to  them. 
Oil  of  turpentine  and  other  volatile  oils  were,  however,  amongst  the  first  liquids 
examined  in  this  way,  and  connected  with  which  an  interesting  incident  occurred, 
Biot,  in  announcing  his  discovery  in  18 18,  called  special  attention  to  the  fact  that 
whilst  in  quartz  or  rock  crystal  there  existed  two  opposite  directions  of  rotation,  in 
oil  of  turpentine  the  rotation  was  in  one  direction  only,  viz.,  from  the  right  to  the 
left  of  the  observer,  and  this  was  the  same  in  direction,  although  slightly  different  in 
degree  for  all  samples  examined.  This  statement  remained  unchallenged  until  1843, 
when  Dr  Leeson  read  a  paper  before  the  Chemical  Society  of  London,  entitled 
Observations  on  the  Circular  Polarization  of  Light  by  transmission  through 
Fluids."  In  this  paper  he  stated  that  every  sample  of  oil  of  turpentine  which  had 
been  examined  possessed  a  right  handed  rotation  coinciding  in  direction  with  that 
produced  by  essence  of  lemon.  These  conclusions  were  so  thoroughly  opposed  to 
those  of  Biot,  that  Dr.  Pereira  undertook  to  further  investigate  the  subject,  and  by 
procuring  reliable  samples  of  French  oil  of  turpentine  from  M.  Guibourt,  of  Paris, 
he  was  enabled  to  demonstrate  the  fact  that  both  observers  were  correct  j  that  the 
French  oil  rotated  to  the  left,  the  English  or  American  to  the  right,  and  that  a  mix- 
ture of  the  two  in  proper  proportions  possessed  no  rotatory  power  whatever  ("Pharm. 
Jour,,"  [i],  vol.  v.,  p.  67), 
My  first  experience  in  the  use  of  the  polarimeter  was  in  a  direction  not  altogether 
pharmaceutical,  but  one  which  nevertheless  merits  attention  from  pharmacists,  viz., 
in  the  examination  of  urine;  it  is  a  legitimate  branch  of  our  calling  and  one  which 
medical  men  are  usually  willing  to  delegate  to  us;  it  possesses  considerable  interest 
and  the  remuneration  is  not  influenced  by  unfair  competition  on  the  part  of  unedu- 
cated outside  traders.  It  was  diabetic  urine  containing  in  round  numbers  only  2 
grains  sugar  per  ounce  ;  subsequently  other  experiments  were  made  with  samples 
containing  larger  quantities,  but  my  experience  led  me  to  the  conclusion  that  this 
method  of  determination  is  more  troublesome  and  not  more  accurate  than  the  cop- 
per test  of  Fehling  or  the  recent  one  of  Pavy,  although  its  use  has  been  recom- 
mended by  Mehu  and  others.  Passing  on  to  essential  oils,  the  work  became 
i  iteresting,  although  occasionally  disappointing  ;  for  example,  essential  oil  of  bitter 
almonds  distilled  in  this  country,  that  from  abroad  which  is  often  obtained  from  a 
1  Those  who  are  interested  in  the  various  kinds  of  sugar  will  do  well  to  peruse  an  excellent  paper  by 
Dr.  O.  Hesse,  "The  Behavior  of  Solutions  of  some  Substances  to  Polarized  Light,"  ("  Pharm.  Jour.,"  3d 
series,  vol.  vii,  pp  i8i,  410  and  473.) 
