568 
Laboratory  Notes. 
\m.  Jour.  Pharm. 
Dec.,  1878. 
ate  of  magnesium  itself.  But  in  the  use  of  this  article  as  a  material 
for  certain  preparations,  even  traces  of  some  of  the  foreign  substances 
named  would  become  "  pharmaceutical  impurities."  Essential  waters 
made  with  carbonate  of  magnesium,  containing  sulphates  and  soluble 
carbonates,  become  contaminated  with  these  salts,  and  the  alkalinity, 
due  to  the  presence  of  sodium  carbonate,  may  prove  a  very  serious 
incompatibility  with  salts  of  the  potent  alkaloids  which  are  often  put 
up  in  these  solutions. 
To  furnish  some  evidence  as  to  the  purity  of  the  carbonate  of  mag- 
nesium in  use,  its  examination  was  assigned  to  Mr.  R.  H.  Wallace. 
The  following  are  his  results  : 
Carbonate  of  Magnesium.  No.  1.  No.  2.  No.  3. 
Magnesium,  as  oxide,  .        .    40*31  per  cent.    38  56  per  cent.    42*12  per  cent. 
C02,  of  carbonate,  .        .        33*25  32-18  34'°5 
Water  of"  hydration,  .        .    22*67  22.30  2158 
Calcium,  as  oxide,  .        .          161  2*15  1*25 
Sodium,  as  oxide,      .  .        ....  2  50  .  .  . 
Iron,  as  ferric  oxide,  .       .          0*21  0*34  traces 
Sulphates,          ....   traces  traces  .  .  . 
Chlorides,      .        .  .       .         ...  traces  .  .  . 
Silica,       .       .       .  .        ....  traces  traces 
Total,  ...        98*05  98*03  99*00 
No.  I  was  of  Pattinson's  manufacture,  No.  2  of  Jenning's,  No. 
3  from  Germany.  The  carbonate  of  magnesia,  as  manufactured  under 
different  conditions,  varies  very  considerably  in  the  degree  in  which  it 
is  a  basic  carbonate.  Deducting  the  carbonic  anhydride  of  the  calcium 
and  sodium  carbonates,  we  have,  for  No.  I,  94^98  per  cent,  of  mag- 
sium  carbonate  ;  for  No.  2,  89*58  per  cent.  ;  and  for  No.  3,  96*77 
per  cent. 
Two  samples  of  calcined  magnesia  were  examined,  with  the  follow- 
ing results  : 
Calcined  Magnesia.  No.  i.  No.  2. 
Magnesium,  as  oxide,        .....  89*67  per  cent.    96*21  per  cent. 
Water  of  hydration,       .....  5*85  ... 
Calcium,  as  oxide,       ......  1*89  1*19 
Sodium,  as  oxide,    .        .        .        .               .  1*23  *8o 
Iron,  as  ferric  oxide,    ......  '27  '12 
Silica,  .........  trace  trace 
Chloride  and  carbonate,       .        .      •  .       .       .  trace  .  .  . 
Total,     .  98*91  98*32 
No.  i  was  "  Husband's  Calcined/'  and  No.  2  was  u  Powers  & 
Weightman's  Heavy  Calcined." 
University  of  Michigan^  } 
School  of  Pharmacy,  Nov.  5,  1878.  j 
