302  Magma  Magnesia.  {Am'jiiyri9i3arm' 
MAGMA  MAGNESLE.1 
By  George  M.  Beringer. 
The  National  Formulary  directs  that  Magnesia  Magma,  com- 
monly called  Milk  of  Magnesia,  be  made  by  pouring  a  filtered 
solution  of  8 1  Gm.  of  Sodium  Hydroxide  in  4000  cc.  of  Water 
into  a  filtered  solution  of  250  Gm.  of  Magnesium  Sulphate  in  4000 
cc.  of  Water.  The  precipitate  is  washed  by  decantation,  then 
drained  and  mixed  with  sufficient  water  to  make  the  product 
measure  1000  cc. 
This  looks  like  an  exceedingly  simple  formula  that  should 
yield  a  satisfactory  preparation.  However,  in  my  experience,  it 
has  not  proven  so,  and  several  modifications  are  necessary  and 
are  included  in  the  improved  formula  now  presented. 
The  author  of  the  N.  F.  formula  aimed  to  obtain  a  very  fine 
precipitate  by  using  very  dilute  solutions  and  precipitating  at  room 
temperature.  He  succeeded  in  doing  this,  but  the  precipitate  is 
so  light  and  commonly  so  bulky  that  it  is  with  difficulty  that  it  can 
be  reduced  to  a  volume  of  1000  cc.  and  remain  sufficiently  fluid  to 
pour.    The  resulting  magma  usually  resembles  thick  starch  paste. 
An  examination  of  the  wash  water  shows  that  the  Magnesium  is 
not  all  precipitated.  This  is  readily  understood  when  the  formula 
is  critically  examined.  The  quantity  of  Sodium  Hydroxide  directed, 
81  Gm.,  is  shown  by  calculation  to  be  the  theoretical  amount  of 
pure  anhydrous  Sodium  Hydroxide  that  would  be  required  to 
react  with  250  Gm.  of  Magnesium  Sulphate,  U.  S.  P.,  but  as 
Sodium  Hydroxide,  U.  S.  P.  contains  about  90  per  cent,  pure 
NaHO,  it  is  self-evident  that  the  formula  directs  an  insufficient 
amount. 
The  chemist  has  been  taught  the  difficulty  of  completely  pre- 
cipitating Magnesium  Hydroxide  in  the  presence  of  alkaline 
chlorides  or  sulphates  and  that  an  excess  of  the  solution  of  potassa 
or  solution  of  soda  is  necessary  and  that  "  the  separation  of  this 
precipitate  is  greatly  promoted  by  boiling  the  mixture."  The 
present  N.  F.  formula  has  insufficient  alkali  instead  of  an  excess, 
1  Read  at  the  annual  meeting  of  the  New  Jersey  Pharmaceutical  Associa- 
tion, June  11,  1913. 
