262 
Dried  Magnesium  Sulphate. 
Am.  Jour.  Pbarni. 
Jnne,  1911. 
sulphate  (MgSO^)  yet  the  purity  rubric  demanded  by  this  same 
authority  is  only  70  per  cent,  of  anhydrous  substance.  The  salt 
is  also  official  in  the  Swiss  Pharmacopoeia,  the  method  of  prepara- 
tion being  similar  to  that  prescribed  in  the  German  Pharmacopoeia 
except  that  the  crystallized  salt  is  allowed  to  effloresce  in  the  air 
before  heating. 
Dried  magnesium  sulphate  was  prepared  by  several  methods. 
The  first  was  by  the  method  prescribed  in  the  German  Pharma- 
copoeia. This  consists  in  drying  the  crystallized  salt  on  the  water 
bath  with  stirring  until  the  substance  has  lost  from  35  to  37  per 
cent,  of  the  original  weight.  Owing  to  the  time  required  it  was 
found  impracticable  to  dry  the  crystallized  salt  on  the  water  bath 
until  the  specified  loss  had  cccurred.  A  specimen  of  50  gm.  of 
the  commercial  salt  was  dried  in  this  manner  during  several  work- 
ing days  and  the  loss  amounted  to  but  33.7  per  cent,  instead  of  a 
minimum  of  35.0  per  cent.  A  duplicate  lost  33.8  per  cent,  in  45 
hours  drying.  Magnesium  sulphate  was  determined  in  this  speci- 
men and  75.2  per  cent,  of  the  anhydrous  salt  found.  When  dried 
at  100°  in  the  air  oven  for  4  hours  a  loss  of  3.4  per  cent,  was 
noted  in  the  same  specimen. 
Dried  magnesium  sulphate  was  also  prepared  by  heating  100  gm. 
of  crystalHzed  magnesium  sulphate  in  an  air  oven,  first  at  a  tem- 
perature of  60-70°  and  then  at  a  gradually  rising  temperature 
until  the  specimen  practically  ceased  to  lose  weight.  A  loss  of 
41.2  per  cent,  w^as  noted.  Several  days'  heating  at  a  temperature 
of  100°  with  occasional  maxima  of  110°  failed  to  secure  a  loss  of 
43  per  cent,  as  required  by  the  former  Austrian  Pharmacopoeia 
(corresponding  to  the  formula  MgS04.H20).  This  specimen  con- 
tained 84.7  per  cent,  anhydrous  magnesium  sulphate. 
The  most  satisfactory  method  of  preparation  was  found  to  be  to 
dry  the  crystallized  salt  at  a  temperature  of  60-70°  with  stirring 
and  finally  at  100°  until  a  loss  of  37  to  40  per  cent,  had  been 
obtained.  A  specimen  so  prepared  which  had  been  dried  until  39.9 
per  cent,  of  the  original  weight  had  been  lost  contained  81.9  per  cent, 
of  anhydrous  magnesium  sulphate. 
Three  specimens  of  dried  magnesium  sulphate  bearing  the 
labels  of  as  many  makers  were  purchased  on  the  open  market  and 
examined  with  reference  to  their  content  of  anhydrous  magnesium 
sulphate  and  to  their  loss  when  dried  at  100°.  Apparently  as  a 
protection  against  moisture  all  of  the  specimens  purchased  had 
