264 
Dried  Magnesium  Sulphate. 
Am. Jour.  Pbarm. 
.hiue,  1911. 
sulphate  absorbs  moisture  when  exposed  to  the  air  and  thus  tends 
to  revert  toward  the  crystalHne  condition.  As  the  crystalhne  salt 
is  markedly  efflorescent  when  exposed  to  the  air  (even  losing  as 
much  as  7  to  8  per  cent,  of  its  weight)  it  seemed  worth  while  to 
determine  how  far  the  dried  salt  would  absorb  moisture.  Accord- 
ingly a  specimen  which  had  lost  41.2  per  cent,  of  the  original 
weight  during  the  process  of  manufacture,  was  exposed  in  a  hat- 
bottomed  dish  in  a  place  protected  from  dust  and  a  flat-bottomed 
dish  containing  water  placed  beside  it.  The  water  was  replenished 
from  time  to  time  as  it  evaporated  and  the  increase  in  weight  of  the 
exposed  salt  noted.  In  two  months  the  specimen  weighing  5.0027 
gm.  had  gained  1.8 13  gm.  equivalent  to  36.24  per  cent,  of  the 
original  weight. 
The  examination  shows  that  the  dried  magnesium  sulphate  on 
the  American  market  is  far  from  uniform  in  composition.  This 
condition  might  be  explained  from  the  lack  of  authoritative  standards 
for  the  product  in  this  country.  Since  magnesium  sulphate  is 
usually  administered  in  solution  and  since  the  dried  salt  contains 
only  about  50  per  cent,  more  of  real  magnesium  sulphate  (MgS04) 
than  the  official  crystallized  one  it  would  appear  that  the  dried 
salt  is  superfluous.  Probably  for  these  reasons  the  manufacturers 
have  not  considered  the  substance  of  sufficient  importance  to  sub- 
ject its  manufacture  to  proper  laboratory  control. 
Based  upon  the  provisional  academic  standards  as  first  pre- 
pared but  modified  as  found  necessary  by  the  results  of  the  experi- 
mental work,  and  by  the  suggestions  offered  by  those  to  whom  the 
provisional  description  was  submitted  for  criticism,'''  the  following 
standards  for  dried  magnesium  sulphate  are  suggested : 
Dried  Magnesium  Sulphate — Magnesii  Sulphas  Exiccatus. 
Magnesium  Sulphate  dried  at  too°C.  corresponding  to  from  77.5 
to  81.5  per  cent,  absolute  magnesium  sulphate. 
Dried  magnesium  sulphate  may  be  prepared  by  heating  (with 
stirring)  100  parts  of  crystallized  magnesium  sulphate  in  a  tarred 
porcelain  dish  in  a  drying  oven  first  at  a  temperature  of  60°  to  70° 
and  then  at  a  gradually  rising  temperature  until  the  substance  has 
lost  from  37  to  40  per  cent,  of  its  weight. 
*  Our  thanks  are  due  to  those  manufacturers  and  chemists  who  have 
made  suggestions  and  criticisms  in  the  preparation  of  the  provisional 
standards  for  dried  magnesium  sulphate. 
