562  Sulphurous  Acid  in  Lime  Juice.  { 
Am.  Jour.  Pharm 
December,  1909. 
n/10  iodine  may  be  employed,  diluted  with  water  to  give  the  desired 
volume.  The  method  and  apparatus  may  be  simplified  without 
material  loss  in  accuracy  by  omitting  the  current  of  C02,  adding  10 
c.c.  of  phosphoric  acid  instead  of  5  c.c.,  and  dropping  into  the  dis- 
tilling flask  a  piece  of  sodium  bicarbonate,  weighing  not  more  than 
one  gramme,  immediately  before  attaching  to  the  condenser.  The 
carbon  dioxide  liberated  is  not  sufficient  to  expel  the  air  entirely 
from  the  apparatus,  but  will  prevent  oxidation  to  a  large  extent. 
The  U-tube  trap  may  also  be  omitted  if  the  end  of  the  condenser 
tube  is  made  to  extend  below  the  surface  of  the  iodine  solution,  and 
the  distillation  conducted  with  a  steady  flame.  When  the  distilla- 
tion is  finished,  wash  the  contents  of  the  U-tube  into  the  flask,  and 
determine  the  excess  of  iodine  with  standard  thiosulphate  solution. 
One  c.c.  n/10  iodine  is  equivalent  to  0.0032  Gm.  S02." 
In  the  qualitative  test  using  25  c.c.  of  filtered  lime  juice,  the  lead 
paper  was  stained  a  dark  brown.  A  blank  test  proved  the  absence 
of  sulphur  in  the  reagents. 
In  the  quantitative  test  two  determinations  on  different  samples 
gave  the  following  results : 
Amount  of  lime  juice  taken         C.c.  n/io  iodine  consumed      Equivalent  to  grammes  SO2 
No.  i,  100  c.c.  6.7  c.c.  0.0214  Gm. 
No.  2,  100  c.c.  7.1  c.c.  0.0227  Gm. 
These  results,  both  qualitative  and  quantitative,  would  seem  to 
indicate  the  presence  of  S02 ;  but  the  samples  in  question  were 
guaranteed  free  from  S02,  and  a  more  detailed  examination  proved 
that  the  official  quantitative  method  is  misleading  in  the  case  of  lime 
juice. 
A  number  of  limes  were  obtained  and  the  juice  expressed  by 
means  of  an  ordinary  lemon  press.  After  filtering  the  juice,  the 
official  qualitative  method  was  applied  with  the  result  that  the  lead 
paper  was  stained  a  dark  brown  about  equal  in  tint  to  that  obtained 
from  the  juice  in  question.  Whether  the  sulphur  in  lime  juice  is 
present  as  a  sulphide  or  easily  reducible  organic  compound  has 
not  been  determined.  The  point  is  that  a  very  marked  tint  is  pro- 
duced on  the  lead  paper  when  lime  juice  is  tested  by  the  official 
process. 
In  this  connection  it  may  be  of  interest  to  note  that  lemon  juice 
also  acts  in  a  similar  though  not  so  pronounced  a  manner. 
On  applying  the  quantitative  method  to  the  freshly  expressed 
