ON  FERRI  SUBCARBONAS. 
19T 
These  were  all  treated  with  muriatic  acid,  45  grs.  of  each 
with  132  grs.  of  acid,  and  gently  heated.  The  subcarbonate 
dried  at  80°  F.  dissolved  with  much  effervescence,  and  was  per- 
fectly soluble,  producing  a  clear  solution,  without  a  particle  of 
cloudiness.  No  difference  of  solubility  or  color  was  observed 
between  the  two  specimens  dried  under  different  circumstances 
of  exposure,  at  80°  F. 
The  specimen  dried  at  180°  to  190°  F.  was  as  imperfectly 
soluble  in  acid,  as  those  dried  by  sand  bath  heat  in  the  other 
instances. 
While  experimenting  with  these  different  modes  of  preparation, 
there  seemed  to  be  a  loss  of  weight  when  a  high  heat  was  used 
in  the  drying.  To  determine  more  accurately  this  loss,  45  grs.  of 
the  precipitated  (moist)  protocarbonate  of  iron  last  described, 
was  dried  at  the  temperature  of  80°  F.,  and  the  same  quantity 
of  the  moist  precipitate  dried  at  a  sand  bath  heat  of  180°  to 
190°  F.  When  thoroughly  dried,  the  portion  subjected  to  the 
gentle  heat  weighed  15  grs.  and  the  other  only  10-5  grs. 
This  difference  of  4-5  grs.  may  be  attributed  to  loss  of  water 
of  hydration  and  carbonic  acid,  which,  when  present  in  the  salt, 
dried  at  a  gentle  heat,  has  a  tendency  to  promote  its  ready  solu- 
bility in  muriatic  acid. 
From  these  various  modes  of  preparing  and  drying  subcar- 
bonate of  iron, — it  would  seem  that  dilute  solutions  mixed  hot, 
and  the  resulting  precipitates  dried  at  a  temperature  not  exceed- 
ing 80°  F.,  make  a  salt  freely  soluble  in  muriatic  acid.  A  heat 
higher  than  this,  in  every  case  rendered  the  subcarbonate  less 
soluble. 
From  the  appearance  of  the  precipitated  carbonate  of  iron 
generally  found  in  commerce,  it  is  not  unlikely  that  a  large  pro- 
portion of  it  is  made  without  regard  to  the  officinal  directions, 
and  probably  dried  at  high  temperatures.  Sometimes,  no  doubt, 
the  soluble  salt  of  iron  used  contains  impurities,  which  remain 
in  the  preparation.  With  reference  to  the  preparation  of  Tinc- 
tura  Tferri  Chloridi  from  precipitated  carbonate  of  iron,  there 
seems  to  be  no  difficulty  if  the  officinal  directions  are  observed, 
both  in  the  preparation  of  the  subcarbonate  and  the  tincture. 
A  gentle  heat  is  described  in  our  Pharmacopoeia  as  between 
90°  and  100Q  F.,  and  this  is  the  temperature  indicated  for  the 
drying  of  the  precipitated  carbonate  of  iron. 
