Am.  Jour.  Pharm. 
December,  1911. 
I       Assay  of  Citral  in  Lemon  Oil.  559 
depending  on  the  use  of  hydroxylamine  hydrochloride,  and  Romeo  * 
outlined  a  titration  method  which  was  published  by  the  Messina 
Chamber  of  Commerce  and  successfully  followed  in  the  analysis  of 
a  number  of  pure  oils. 
In  1909  Hiltner^  published  the  description  of  a  colorimetric 
method  which  together  with  that  of  Chace  ^  has  been  outlined  by 
Leach  in  his  Food  Inspection  and  Analysis. 
The  Pharmacopoeial  assay  of  oil  of  lemon  is  without  doubt 
known  to  all  pharmacists,  chemists  and  analysts.  In  our  hands, 
with  careful  manipulation  and  some  degree  of  patience,  it  has 
given  fair  but  not  satisfactory  results.  We  have  found  the  end 
point  very  uncertain  and  we  have  always  felt  that  the  assay  was 
extremely  tedious,  demanding  much  of  the  analyst's  time  and  atten- 
tion and  frequently  causing  trouble  and  annoyance. 
One  of  the  chief  sources  of  trouble  is  the  sodium  sulphite  used 
in  the  analysis.  During  the  course  of  some  routine  work  we  were 
much  surprised  to  obtain  results  which  could  not  be  accounted  for 
until  we  examined  the  reagent  in  question.  Two  analyses  of  the 
salt  showed  that  it  contained  about  4  per  cent,  of  sodium  sulphite, 
instead  of  being  chemically  pure  as  the  label  stated.  The  rest  had, 
with  amazing  rapidity,  been  oxidized  to  the  sulphate.  We  studied 
this  matter  a  little  more  closely  and  found  that  another  sample  of 
sulphite,  containing  water  of  crystallization,  which  had  been  assayed 
in  June,  and  found  to  comply  with  the  U  S.  P.  requirements,  con- 
tained approximately  76  per  cent,  of  Na2S037H20  in  September. 
Elvove  in  a  previous  number  of  this  journal  ^  has  recorded  a  thor- 
ough investigation  of  this  subject.  Our  on^y  comment  is  that  all 
sulphite  should  be  roughly  assayed  by  the  U.  S.  P.  method  just 
before  using  and  that  an  amount  of  salt  should  be  taken,  which 
contains  the  equivalent  of  10  grams  of  anhydrous  sodium  sulphite 
or  20  gms.  of  sodium  sulphite  containing  7  molecules  of  water  of 
crystallization  for  each  100  cubic  centimetres  of  water  used  in  mak- 
ing up  the  solution.  , 
Another  debatable  point  involves  the  amount  of  rosolic  acid 
T.  S.  which  is  to  be  used  in  the  assay.  Our  own  experience  has 
shown  that  the  indicator  should  be  added  at  intervals  during  the 
*  Chem.  Druggist,  74,  81. 
^J.  Ind.  and  Eng.  Chem.,  i,  798. 
•This  Journal,  82,  211. 
