564 
Sulphurous  Acid  in  Lime  Juice. 
{ 
Am.  Jour.  Pharm. 
December,  1909. 
sodium  sulphite)  was  then  added  to  the  juice  in  the  proportion  of 
1  part  in  100,000.  This  quantity  of  S02  stained  the  lead  paper 
brown. 
The  above  test  will  detect  less  than  1  part  of  S02  in  100,000, 
but  the  latter  figure  may  be  taken  as  the  practical  limit. 
QUANTITATIVE  METHOD  FOR  THE  DETERMINATION  OF  S02  IN 
Distil  100  c.c.  of  juice  in  a  current  of  C02  after  the  addition  of 
about  5  c.c.  of  20  per  cent,  solution  of  glacial  phosphoric  acid 
until  75  c.c.  have  passed  over.  The  distillate  is  received  in  a 
Fresenius  absorption  flask  containing  25  c.c.  of  a  1  per  cent,  solu- 
tion of  sodium  bicarbonate.  The  flask  is  attached  to  the  condenser 
by  means  of  a  perforated  rubber  stopper.  The  outlet  of  the  flask 
is  connected  with  a  U-tube  containing  10  c.c.  of  the  bicarbonate 
solution. 
When  the  distillation  is  finished,  the  liquid  in  the  flask  and  U- 
tube  is  transferred  to  a  separator  and  shaken  out  twice  with  chloro- 
form, using  10  c.c.  each  time.  After  the  chloroform  has  been 
separated,  25  c.c.  of  n/10  iodine  solution  is  added  and  the  excess 
of  iodine  titrated  with  n/10  thiosulphate.  Each  c.c.  n/10  iodine  is 
equal  to  0.0032  Gm.  S02. 
The  distillate  is  shaken  with  chloroform  to  remove  the  traces  of 
essential  oil,  which  would  otherwise  combine  with  the  iodine  as 
previously  stated. 
The  above  method  gives  fairly  good  results  as  will  be  seen  from 
the  following  figures : 
If  more  than  0.05  per  cent.  S02  is  present,  50  c.c.  or  less  of  the 
sample  should  be  used. 
LIME  JUICE. 
100  c.c.  Lime  Juice  Taken. 
S02  present 
S02  found.  . 
No.  1 
0.036  Gm. 
0.034  Gm. 
No.  2 
0.036  Gm. 
0.032  Gm. 
Analytical  Department. 
Parke,  Davis  &  Company. 
