ON  LIQUOR  MAGNESI2E  CITRATIS. 
197 
making  this  preparation,  while  others  use  the  calcined,  some- 
times freshly-burned,  but,  in  a  majority  of  cases,  after  it  has 
been  standing  more  or  less  time,  absorbing  moisture  and  car- 
bonic  acid  from  the  atmosphere,  others  using  the  freshly-pre- 
cipitated carbonate  in  the  form  of  a  magma,  and  some  employ 
carbonic  acid  apparatus  in  the  process.  I  might  mention  many 
methods  of  preparing  it,  all  of  which  only  tend  to  confuse 
matters,  and  make  the  solution  of  various  and  unknown 
strengths.  For  instance,  a  solution  is  made  by  a  certain  for- 
mula, using  magnesia  from  a  newly-opened  can  ;  the  combina- 
tion takes  place  without  effervescence  or  other  signs  of  com- 
bination than  a  rise  in  temperature.  Two  months  later,  the 
solution  is  made  by  the  same  formula,  the  magnesia  in  the 
meantime  having  been  exposed  more  or  less  to  the  action  of 
the  surrounding  Atmosphere ;  the  result  is  a  rapid  evolution 
of  gas,  showing  that  the  magnesia  has  absorbed  moisture 
and  carbonic  acid.  It  is  obvious  that  the  second  solution  is 
weaker  than  the  first,  containing  relatively  less  magnesia  and 
more  citric  acid,  so  that  a  salt  is  obtained  of  unknown  compo. 
sition.  A  knowledge  of  these  facts  has  led  me  to  a  further  in- 
vestigation of  the  subject. 
Four  hundred  and  fifty  grains  of  citric  acid  require  for 
saturation  134/^/V  grains  of  magnesia,  (201  :  60  :  :  450  : 
134:jQ6j,)  or  about  fourteen  grains  more  than  the  designated 
amount  in  the  officinal  formula,  so  that  the  salt  formed  in  that 
solution  contains  nearly  three  equivalents  of  base.  This,  we 
know,  does  not  furnish  a  permanent  solution ;  hence,  we  look 
for  a  salt  of  different  composition,  with  which  to  make  a  per- 
manent solution.  Prof.  Maisch  suggests  an  acid  salt,  the  one 
containing  two  equivalents  of  magnesia.  .  This  could  be  very 
easily  obtained,  if  we  knew  the  composition  of  the  magnesia 
used ;  but,  as  this  cannot  be  done  without  a  special  examina- 
tion, we  take  the  following  method  of  obtaining  this  two-thirds 
salt  in  solution.    For  one  bottle, 
Take  of  Citric  acid,  387  grains. 
Magnesia  or  carbonate,  q.  s. 
Water,  q.  s. 
Bicarbonate  of  potassa.  40  grs. 
Syr.  of  citric  acid,        f|  jss. 
