18 
ON  TINCTTJRA  FEERI  CHLORIDI. 
meet  the  test  of  ignition,  by  which  98  grs.  of  pure  hydrated 
sesquioxide  of  iron  should  lose  18  grs.  ;  and  provided  it  con- 
tained protocarbonate  of  iron,  the  loss  would  be  so  much  the 
greater,  as  every  58  grs.  of  this  latter  substance  would  deter- 
mine a  loss  of  18  grs.  additional. 
Perhaps  it  would  be  well,  in  order  to  a  better  understanding 
of  the  whole  subject,  to  look  at  the  officinal  formula  of  our  Phar- 
macopoeia, and  by  means  of  the  necessary  tables  calculate  the 
relative  quantities  of  acid  and  iron  in  the  solution. 
The  formula  is  as  follows  : 
Take  of  Subcarb.  Iron,  half  a  pound. 
Muriatic  Acid,  (sp.  gr.  1-16)  one  pint. 
"With  directions  to  digest  with  heat  until  dissolved. 
Now  a  pint  of  water  weighs  7291  grs. ;  a  pint  of  acid  will  there- 
fore weigh  (7291  xl«16)  8457  grs.  According  to  Ure's  tables, 
muriatic  acid,  sp.  gr.,  1-16,  contains  31-3  per  ct.  of  chlorine. 
The  pint  will  consequently  contain  (8457  X  31-3)  2647  grs.  of 
chlorine. 
Sesquichloride  of  iron,  Fe2Cl3  has  for  its  composition  56  grs. 
of  iron  to  106-26  grs.  chlorine,  and  by  proportion  the  2647  grs. 
chlorine  require  1398  grs.  iron  to  combine  with  it. 
Again,  although  there  appears  to  be  an  uncertainty  as  to  the 
precise  composition  of  subcarb.  of  iron,  it  is  generally  regarded 
as  a  hydrated  sesquioxide  of  iron,  Fe203-|-2HO,  containing  a 
small  but  variable  amount  of  carb.  of  protoxide.  The  equivalent 
for  the  hydrated  oxide  is  98,  or  when  calcined  80.  The  equiv- 
alent of  iron  in  these  two  forms  would  be  the  same,  or  56.  If 
the  preparation  of  iron  is  the  hydrated,  by  means  of  this  pro- 
portion, as  56  iron  :  98  hyd.  sesquiox.  :  :  1398  iron,  we  obtain 
2446  grs.  of  hyd.  sesquiox.  iron  as  requisite  to  saturate  1  pint  of 
muriatic  acid. 
If  the  iron  were  anhydrous,  the  relative  amount  required 
would  be  g  as  much,  or  1997  grs.  In  either  case  the  quan- 
tity is  considerably  less  than  that  given  in  the  formula,  namely 
2880  grs.  Another  remark  should  be  made,  as  still  further  in- 
creasing the  disparity  between  the  calculated  and  given  propor- 
tions, and  that  is  the  considerable  escape  and  loss  of  muriatic 
vapors,  during  the  oft  prolonged  heating  and  digestion. 
This  gas  is  given  off  freely,  even  at  moderate  temperatures, 
