214  PROCESS  FOR  DENSE  AND  SOFT  MAGNESIA. 
ON  A  PROCESS  FOR  MAKING  DENSE  AND  SOFT  MAGNESIA. 
By  Thomas  Weaver. 
A  read}'  process  for  the  manufacture  of  a  magnesia  of  this 
description  has  long  been  a  desideratum,  and  the  subject  of  fre- 
quent experiments,  as  it  can  now  be  obtained  only  in  bottles  at 
a  price  inconveniently  high  to  a  large  class  of  purchasers.  The 
researches  of  Mr.  Thomas  H.  Barr,  published  in  this  Journal, 
vol.  xxvi.  page  193,  are  among  the  most  useful  pertaining  to  the 
study  of  this  subject,  although  the  products  obtained  by  him, 
both  by  the  precipitation  of  the  carbonate  from  hot  concentrated 
solutions  of  the  carbonate  of  soda,  and  sulphate  of  magnesia  and 
subsequent  calcination,  and  that  by  the  decomposition  of  the 
chloride  at  a  high  heat,  were  pronounced  rather  inferior  in  soft- 
ness, though  exceeding  in  specific  gravity,  and  absolute  amount 
of  magnesia,  the  specimens  of  Henry's,  Husband's,  and  Ellis'  ex- 
amined. Having  been  much  interested  in  the  experiments  of 
Mr.  Barr,  I  have  frequently  recurred  to  the  subject,  and  reason- 
ing from  the  known  fact,  that  the  density  of  the  carbonate,  bears 
a  close  relation  to  the  temperature  at  which  it  is  formed,  have 
arrived  at  the  following  process  for  the  precipitation  of  a  car- 
bonate, which  by  calcination  at  a  proper  temperature  yields 
magnesia  in  a  remarkably  soft  and  elegant  condition.  And  in 
offering  this  simple  formula  to  pharmaceutists,  it  is  with  a  hope 
that  it  may  induce  those  having  a  demand  for  a  fine  quality  of 
magnesia,  to  prepare  it  for  themselves,  and  to  attempt  further 
improvements  in  its  preparation,  as  it  will  be  seen  to  possess 
the  merit  of  cheapness,  and  may  be  accomplished  without  the 
use  of  costly  apparatus. 
Take  of  Sulphate  of  magnesia,       .        .       siv.  3ij. 
Bi-carbonate  of  soda,        .       .  ^iij. 
Nitric  acid, 
Carbonate  of  soda, 
Water,  of  each  a  sufficient  quantity. 
Dissolve  the  sulphate  of  magnesia  in  six  ounces  of  water,  add 
a  fewT  drops  of  nitric  acid,  and  boil  for  fifteen  or  twenty  minutes; 
then  add  sufficient  carbonate  of  soda,  dissolved  in  a  little  water  to 
produce  a  slight  precipitate,  and  continue  boiling  for  some  time, 
filter,  and  set  aside  to  cool.  Triturate  the  bi-carbonate  of  soda 
with  about  eight  ounces  of  cold  water,  and  add  it  to  the  cold  solu- 
