604  Commercial  Sodium  Bicarbonate.  {^^'bIII'-^^ 
no  color.  This  precipitate  was  found  to  be  due  to  the  presence  of 
ammonia  in  these  two  samples.  With  a  saturated  aqueous  solution  of 
magnesium  sulphate  no  precipitate  was  formed  with  any  of  the  sam- 
ples, indicating  less  than  the  limit  of  carbonate  for  the  commercial 
variety. 
The  volumetric  methods  for  the  estimation  of  total  bicarbonate 
were  next  experimented  with.  For  the  pure  sodium  bicarbonate  the 
Pharmacopoeia  directs  that  4*2  gms.  of  the  salt  should  require  not  less 
than  49*5  cc.  of  the  vol.  sol.  of  oxalic  acid  for  neutralization,  corres- 
ponding to  at  least  99  per  cent,  of  NaHCOg.  For  the  commercial 
variety,  4*2  gms.  of  the  salt  should  require  not  less  than  47 '5  cc.  of 
the  vol.  sol.  of  oxalic  acid  for  neutralization,  correspouding  to  at 
least  95  per  cent,  of  iS^aHCOg.  It  must  be  stated  here,  that  this 
method  of  estimating  the  salt  will  not  give  correct  results  when  it 
contains  normal  carbonate,  for  in  that  case  the  percentage  of  XaHCOj 
will  be  indicated  too  high  and  in  some  cases  be  above  100,  according 
to  the  amount  of  Na2C03  present.  As  will  be  seen  by  the  following 
results,  the  volumetric  method  as  directed  in  the  Pharmacopoeia  for 
the  estimation  of  total  acid  carbonate  is  incorrect  and  cannot  be  used 
to  obtain  accurate  results.  In  executing  this  estimation  an  excess  of 
noted  volume  of  standard  oxalic  acid  solution  was  first  added.  The 
CO2  was  expelled  by  boiling  and  then  triturated  by  standard  soda  solu- 
tion. The  percentages  given  below  are  the  equivalents  of  NaHCOg, 
according  to  the  above  method,  but  go  to  show  the  inaccuracy  of 
same. 
No.  (1),  100-17  per  cent.  ;  (2),  99-73  per  cent.;  (3),  99-53  per 
cent.;  (4),  100-73  per  cent.  ;  (5),  101-19  per  cent.  ;  (6),  99-94  per 
cent.  ;  (7),  99-63  per  cent.  ;  (8),  100-20  per  cent.  :  (9),  99-71 
per  cent.  ;  (10),  102-38  per  cent.  ;  (11),  100-83  per  cent.  ;  (12), 
99-72  per  cent.  ;  (13),  99-66  per  cent.  ;  (14),  101-03  per  cent.  : 
(15),  102-37  per  cent.;  (16),  103-48  per  cent. 
After  completing  these  preliminary  tests  and  estimations  it  was 
thought  advisable  to  make  complete  quantitative  analyses  of  all  the 
samples.  On  referring  to  numerous  authorities  for  a  method  of 
estimating  the  normal  carbonate  in  the  bicarbonate,  none  could  be 
found.  The  following  method,  however,  was  devisefl  and  used  to 
estimate  the  moisture  and  the  normal  carbonate  present.  In  a  com- 
bustion tube  connected  with  absorbing  apparatus  for  HgO  and  COg,  a 
weighed  quantity  of  the  salt  was  heated  for  about  half  hour.  Sodium 
