412 
Ferric  Chlorides. 
f  Am.  Jour.  Pharm. 
1     August,  1884. 
These  classes  are  in  the  one  case  oxygen  substitutions  of  the  normal 
salts,  and  in  the  other  case  hydroxy  1  substitutions.  In  connection 
with  certain  non-volatile  polybasic  carbon  acids  the  stability  of  the 
two  kinds  is  equally  good.  But  in  the  case  of  various  mono-basic  vol- 
atile acids,  mineral  or  carbon,  the  oxygen  substitutions  are  remarkably 
unstable,  particularly  in  very  concentrated  or  extremely  dilute  solu- 
tions. On  the  other  hand,  the  hydroxyl  salts  are  much  more  perma- 
nent, but  in  strong  solutions  are  liable  to  change  into  the  other  class 
from  the  chemical  separation  of  water. 
Normal  ferric  hydrate  or  ferric  hydroxide  may  be  viewed  as  a  com- 
plete hydroxyl  substitution  of  a  normal  ferric  salt.  This  compound, 
even  in  the  humid  state,  soon  loses  half  of  its  water,  and  is  thus 
changed  to  an  oxy-hydrate  or  hydro-oxide.  On  drying,  the  loss  of 
water  amounts  to  two-thirds  of  the  whole,  and  the  body  is  reduced 
to  the  form  FeO(OH).  The  normal  ferric  hydrate  dissolves  with 
tolerable  readiness  in  most  acids,  yielding  soluble  ferric  salts.  As  the 
separation  of  water  proceeds  the  insolubility  augments,  and  hence  the 
dried  hydrate  unites  with  a  very  limited  number  of  acids.  Owing 
to  the  comparative  slowness  with  which  the  ferric  hydrate  obtained  by 
precipitation  with  ammonia  dissolves  in  acids,  it  seems  likely  to  be 
even  then  a  partial  anhydrate. 
In  the  " Pharmacist"  for  December,  1873,  the  writer  called  atten- 
tion to  the  fact  that  a  ferric  hydrocarbonate,  Fe2C03(OH)4,  is  obtained 
by  pouring  solution  of  ferric  sulphate  into  excess  of  disodic  carbonate. 
It  was  found  that  this  compound,  aside  from  various  other  advan- 
tages, dissolves  much  more  rapidly  and  copiously  in  acids  than  the 
customary  hydrate.  More  recently  the  writer  ascertained  that  sodium 
bicarbonate  is  superior  in  a  variety  of  aspects,  and  also  relatively 
cheaper.  Theoretically,  100  parts  of  solution  of  ferric  sulphate 
require  36*22  parts  of  the  sodium  salt  for  precipitation,  but  in  prac- 
tice it  is  advisable  to  employ  about  42  parts  of  it. 
The  so-called  dialyzed  iron  was  once  wrongly  supposed  to  be  a  col- 
loidal form  of  ferric  oxide  or  hydrate.  It  is  now  known  to  be  a  ferric 
hydrochloride,  possessing  a  low  equivalence  of  chlorine.  It  is  ordi- 
narily prepared  by  macerating  for  a  considerable  time  a  large  excess  of 
ferric  hydrate  in  weak  chlorhydric  acid.  In  "  New  Remedies "  for 
January,  1881,  the  writer  recommended  the  use  of  ferric  hydrocar- 
bonate for  this  purpose,  owing  to  its  greater  purity  and  speed  of  solu- 
tion. The  formula  which  was  then  submitted  for  making  a  solution 
of  triferric  hydrochloride,  Fe3Cl(OH)s,  yielded  a  very  concentrated 
