ON  EFFERVESCING  POWDERS. 
53 
the  tartaric  acid  loses  nothing,  but  the  bicarbonate  of  soda  Ij 
per  cent. ;  if  the  mixture  is  now  made  and  introduced  into  a  well 
stopped  vial,  it  has  commenced  to  decompose  after  the  lapse  of 
24  hours  and  the  decomposition  progresses  rapidly.  But  if  the 
soda  salt  was  dried  at  167°  F.  (60^  R.)  the  mixture  was  un- 
altered after  having  been  kept  12  days  in  a  closed  vial.  It  is 
the  water  of  combination,  and  not  hygroscopic  water  that  intro- 
duces the  change,  though  damp  favors  it ;  this  water  is  set  free 
at  the  formation  of  tartrate  of  soda,  and  causes  the  moisture  and 
liquefaction ;  it  must  be  allowed  to  evaporate ;  that  takes  place 
easily  from  the  fine  powder  at  the  tension  of  a  low  temperature, 
and  for  this  reason  the  alteration  is  so  little  that  it  is  without 
any  consequence.  Such  a  mixture  which  has  been  in  contact 
with  the  air  for  some  time  and  is  still  unaltered,  commences  to 
change  as  soon  as  it  is  introduced  into  a  stopped  vial.  If  the 
powder  is  directed  to  be  kept  in  a  vial,  it  might  be  more  advi- 
sable not  to  dry  the  ingredients,  but  the  finely  powdered  mix- 
ture. In  no  case,  however,  not  even  with  the  greatest  care  could 
the  powder  be  kept  for  many  years. 
These  remarks  apply  next  to  the  effervescing  powder  of  the 
Prussian  Pharmacopoeia,  with  which  the  experiments  were  made; 
it  is  prepared  of  4  parts  of  bicarbonate  of  soda,  3  parts  of  tar- 
taric acid,  and  7  parts  of  white  sugar.  Immediately  on  throw- 
ing this  powder  into  water,  effervescence  takes  place  violently. 
Other  preparations,  however,  generate  the  carbonic  acid  slowly, 
even  so  slow,  that  the  greater  part  of  the  reaction  takes  place 
in  the  stomach.  By  this  means  quite  a  quantity  of  carbonic 
acid  can  be  introduced  into  the  stomach  at  a  single  dose,  and  is 
there  mostly  generated  by  degrees.  Vogler  gives  the  following 
formula:  Exsiccated  carbonate  of  soda  ^ij,  bicarbonate  of  potassa 
3ij,  sugar  ^ss.  If  three  drachms  of  bicarbonate  of  soda  are 
substituted  in  this  formula  for  the  exsiccated  soda,  a  larger 
amount  of  carbonic  acid  will  be  evolved.  But  as  bitartrate  of 
soda  is  a  heavy  salt  and  only  slightly  soluble  in  cold  water,  the 
idea  suggests  itself  of  looking  for  a  comparatively  more  soluble 
salt,  to  take  the  place  of  the  former  in  such  a  combination. 
Such  a  salt  we  find  in  the  bitartrate  of  soda,  which  is  much 
easier  soluble  in  water  than  cream  of  tartar,  but  does  not  act  so 
violently  on  the  carbonate  as  the  free  acid,  especially  not  if  cold 
