Am.  Jour.  Pharm. 
July,  1917. 
Magma  Magnesia. 
307 
the  formulas  advanced  have  been  only  partly  satisfactory.  Let  us 
just  briefly  review  some  of  the  shortcomings  of  the  most  important 
formulas. 
We  all  know,  for  instance,  that  the  N.  F.  Ill  formula  was  un- 
satisfactory in  that  it  took  actually  months  for  the  magma  to  settle 
down  to  the  required  volume.  Of  course,  in  order  to  avoid  that 
inconvenience,  directions  were  given  to  transfer  the  magma  to  a 
muslin  strainer  and  allow  to  drain.  That,  however,  is  not  a  very 
satisfactory  way  of  doing,  because  of  the  messiness  attending  the 
process.  Furthermore,  by  bringing  the  magma  down  to  the  required 
volume  in  order  to  have  a  preparation  in  accordance  with  the  N.  F. 
Ill  requirements,  one  incurred  the  still  greater  embarrassment  of 
having  a  product  that  was  not  pourable.  To  correct  this  short- 
coming, various  modifications  of  the  formula  were  suggested,  such 
as  boiling  the  magma,  reducing  the  amount  of  water,  etc.  As  all 
these  changes,  however,  proved  more  or  less  unsuccessful,  the  con- 
clusion was  drawn  that  it  was  practically  impossible  to  prepare  a 
satisfactory  magma  by  the  interaction  between  magnesium  sulphate 
and  sodium  hydroxide.  Some  other  chemical,  it  was  thought,  was 
necessary  to  react  with  sodium  hydroxide  in  order  to  obtain  a  satis- 
factory preparation.  Hence,  in  the  present  U.  S.  P.  formula  the 
magnesium  sulphate  is  replaced  by  magnesium  carbonate ;  a  change 
which  is  unfortunate.  In  the  first  place,  magnesium  carbonate  is 
at -all  times  more  expensive  than  magnesium  sulphate.  Secondly, 
the  sodium  carbonate  resulting  from  the  interaction  between  mag- 
nesium carbonate  and  sodium  hydroxide  is  necessarily  consider- 
able, and  for  that  reason  the  preparation  requires  a  great  deal  of 
washing  in  order  to  free  it  from  the  nauseating  alkaline  taste  which 
sodium  carbonate,  as  long  as  the  merest  trace  is  present,  lends  to  it. 
Lastly,  magnesium  carbonate,  being  insoluble  in  water,  cannot  pos- 
sibly be  freed  from  those  accidental  mechanical  impurities  which 
are  present  in  all  chemicals  in  varying  amounts.  Therefore,  this 
feature  of  insolubility  is  a  matter  of  no  small  consideration,  for  if 
we  wish  to  have  a  first-class  preparation,  it  must,  above  all  things, 
be  free  from  an  admixture  of  mechanical  impurities. 
In  recent  years  still  another  method  has  been  advanced,  which, 
if  it  only  yielded  a  more  satisfactory  product,  would  indeed,  to  the 
busy  pharmacist,  be  a  very  welcome  method.  The  chemical,  mar- 
keted for  the  express  purpose  of  preparing  magma  magnesia  by  this 
method,  is  said  to  be  a  hydrated  magnesium  oxide  which,  in  order 
