198 
ON  LIQUOR  MAGNESIiE  CITRATIS. 
Dissolve  240  grains  of  the  acid  in  four  fluidounces  of  the 
water  at  a  heat  below  the  boiling  point,  (about  166°  ;)  saturate 
the  solution  with  the  magnesia  to  be  used,  adding  gradually, 
putting  in  an  excess,  to  insure  saturation.  The  residue,  if 
washed  and  burnt,  will  not  give  off  water  of  combination,  puff 
up  or  char,  showing  it  to  be  free  from  any  organic  salt,  while 
the  opposite  is  frequently  the  case,  if  the  full  equivalent  of 
magnesia  be  added  all  at  once,  or  the  solution  made  at  too  high 
a  temperature. 
We  now  have  a  salt  composed  of  exactly  three  equivalents 
of  base  and  one  of  acid  ;  to  reduce  this  to  an  acid  salt  of  the 
combination  2MgO,  HO,  C12,  H5,  On,  we  add  one-half  an 
equivalent  of  acid,  which,  in  this  case,  is  120  grains,  giving 
three  equivalents  of  base  and  one  and  one-half  of  acid  in  com- 
bination. This  solution,  upon  evaporation  A  the  consistence 
of  a  syrupy  liquid,  retained  its  fluidity  for  several  hours,  after 
which  it  changed  into  a  white,  opaque,  pasty  mass,  readily 
soluble  again  in  hot  water,  which  is  not  the  case  with  the  salt 
containing  three  equivalents  of  magnesia  to  one  of  acid.  This 
would  indicate  that  the  former  salt  would  remain  in  solution 
much  longer  than  the  latter. 
A  precipitate  was  formed  in  a  weak  solution  of  the  perfectly 
neutral  salt  in  less  than  twenty-four  hours  after  cooling. 
To  impregnate  the  solution  with  sufficient  carbonic  acid,  we 
take,  in  addition  to  the  above  quantities,  the  remaining  twenty- 
seven  grains  of  citric  acid,  and  forty  grains  of  bicarbonate  of 
potassa.  We  prefer  this  salt  of  potassa,  from  which  to  obtain 
the  carbonic  acid,  to  the  carbonate  of  magnesia,  on  account  of 
the  large  amount  of  foreign  matter  that  is  almost  always  con- 
tained in  the  latter,  when  prepared  in  large  quantities,  and^ 
being  set  free,  makes  the  solution  more  or  less  cloudy,  accord- 
ing to  the  quality  of  the  carbonate  of  magnesia  used. 
This  solution,  when  finished,  should  contain  of  the  salt, 
2MgO,  HO,  C12,  H5,  On,  about  383  grains,  by  the  following 
equation  :— 201  :  214  :  :  360  :  383/07T.  I  believe  the  Pharma- 
copoeia aims  at  a  solution  to  contain  480  grains  of  the  salt  in 
each  bottle  made  by  the  officinal  formula,  but  experience  has 
shown  the  solution,  as  above  made,  to  be  quite  strong  enough. 
