THE 
AMERICAN  JOURNAL  OF  PHARMACY, 
MAY,  1854. 
REMARKS  ON  THE  PREPARATION  OF  HEAVY  CALCINED 
MAGNESIA. 
By  Thomas  H.  Barr,  of  Terre  Haute,  Indiana. 
(An  Inaugural  Essay  presented  to  the  Philadelphia  College  of  Pharmacy , 
March,  1854.) 
With  a  view  to  discover  if  possible  the  best  practicable  method 
of  preparing  [heavy]  calcined  magnesia,  of  fine  quality  for  use  in 
medicine,  I  have  made  numerous  experiments.  They  are  em- 
bodied in  a  condensed  form  in  the  following  essay. 
In  order  to  make  this  paper  as  complete  as  possible,  I  have  also 
made  quantitative  analyses  of  three  of  the  most  popular  commer- 
cial varieties  of  magnesia  in  use,  and  a  like  analysis  of  one  of  the 
products  prepared  by  myself.  By  a  comparison  of  the  analyses, 
and  the  samples  submitted,  an  estimate  may  be  formed  of  the 
availability  of  the  process. 
The  great  desiderata  to  be  attained  in  magnesia,  according  to 
the  opinion  of  most  pharmaceutists  and  physicians,  are,  purity, 
density,  and  smoothness  or  softness  to  the  touch,  qualities  which 
are  possessed  in  an  eminent  degree,  by  Henry's,  Husband's,  and 
Ellis'  magnesias.  The  processes  by  which  these  are  attained,  have 
long  been  the  subject  of  speculation  among  chemists  and  pharma- 
ceutists, and  partly  led  to  the  examination  of  the  subject  detailed 
in  this  paper.  The  processes  I  have  employed  are  of  four  kinds, 
viz. : 
1st.  The  precipitation  of  sulphate  of  magnesia  by  carbonated 
and  caustic  alkalies. 
2d.  The  decomposition  of  the  chloride  of  magnesium  by  heat. 
3d.  The  precipitation  of  the  chloride  by  carbonated  and  caustic 
alkalies. 
4th.  The  calcination  of  the  regular  mono-carbonate  of  magnesia. 
1st.  (a.)  Boiling  concentrated  solutions  of  sulphate  of  magnesia 
and  carbonate  of  soda,  were  mixed,  and  the  whole  evaporated  al- 
most to  dryness.    More  water  was  then  added3  the  temperature 
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