^?ptembeM89™'}    British  Pharmaceutical  Conference.  467 
nitrometer  with  the  urea  determination  arrangement  attached .  The  nitrometer 
was  filled  with  water,  and  to  avoid  absorption  of  C02,  a  little  benzene  was  floated 
on  the  surface  in  the  measuring  tube,  the  resulting  presence  of  the  mixed  ben- 
zene and  aqueous  vapor  caused  the  amount  of  gas  evolved  to  exceed  the  theo- 
retical yield  by  about  10  per  cent., so  eventually  mercury  was  employed. 
The  different  samples  were  moistened  with  an  equal  quantity  (2  c.c.)  of 
water.  This  would,  at  same  temperature  and  pressure,  absorb  the  same 
amount  of  gas,  which  would  not  exceed  2  c.c. 
Several  specimens  of  commercial  sodium  bicarbonate  were  first  tried,  and 
were  found  to  give  almost  identical  results,  all  showing  almost  exactly  the 
theoretical  amount  of  C02. 
Then  to  ascertain  whether  the  loss  of  gas  on  granulating  is  due  to  the  heat- 
ing of  the  bicarbonate,  per  se,  the  same  samples  were  exposed  to  a  tempera- 
ture of  ioo°-io5°  C.  for  ten  minutes ;  that  is,  under  the  same  conditions  so  far 
as  heat  is  concerned  as  in  the  process  of  granulation.  The  resulting  loss  in 
weight  amounted  to  about  2  per  cent. ;  this  is  apparently  water,  the  same 
quantity  of  gas  being  evolved. 
The  ingredients  of  the  P.  B.  Sodii  Citro-Tart.  effervescens  were  then  care- 
fully weighed  out  and  well  mixed. 
(1)  Part  of  this  mixture  was  immediately  tested  for  quantity  of  C02. 
(2)  Part  was  dried  below  540  C.  without  granulating  (for  comparison  with 
No.  3),  to  see  how  much  loss  the  necessary  high  temperature  caused,  and 
(3)  The  rest  was  passed  through  the  P.  B.  process,  granulated  and  dried. 
The  two  latter  parts  both  lost  about  10  per  cent,  in  weight  as  the  P.  B.  states, 
but  that  portion  not  heated  much  showed  a  higher  percentage  of  gas  available. 
Citric  acid  loses  nearly  9  per  cent,  of  its  weight  in  water  of  crystallization, 
and  the  amount  present  of  citric  acid  is  only  16  per  cent.  The  other  ingredi- 
ents only  lose  about  2  per  cent,  in  weight  on  treating.  This  loss  is  accounted 
for  by  the  following  : 
Sodium  bicarbonate,  on  combining  with  an  acid,  of  course,  produces  C02  and 
H20,  which  is  lost  on  drying.  This  amounts  to  62  per  cent,  of  the  weight 
taken,  and  as  the  quantity  present  is  about  46  per  cent.,  the  total  possible  loss 
in  this  way  would  be 
46  X  62       0,  , 
- — —  =  28*5  per  cent. 
100 
The  observed  decrease  in  weight  is  about  one-third  of  this,  roughly  indica- 
ting that  about  30  per  cent,  of  sodium  bicarbonate  and  acid  has  combined  dur- 
ing the  process.  To  see  how  far  this  is  actually  the  case,  the  following  figures 
will  show. 
Use  mercury  in  the  nitrometer  ;  if  using  water,  place  a  little  benzine  on  sur- 
face, and  remember  the  results  will  be  10  per  cent,  higher. 
The  Pharmacopoeia  ought,  among  the  characters  and  tests  of  those  prepara- 
tions, to  state  the  least  amount  of  C02  which  each  should  yield  on  the  above 
treatment.  Any  sample  which  does  not  show,  say,  50  per  cent,  of  its  bicar- 
bonate available  for  producing  effervescence,  should  not  find  its  place  in 
modern  pharmacy. 
