w 
34  LIQUOR  FERRI  PERSULPHATIS. 
has  a  slightly  pungent  and  powerfully  astringent  rough  taste,  but 
the  pungency  is  not  of  that  sharp  corrosive  acid  character  that 
belongs  to  the  normal  solution.  Its  specific  gravity  is  1-578  by 
hydrometer.  When  treated  with  concentrated  sulphuric  acid, 
drop  by  drop,  it  is  first  partially  decolorized,  and  then  converted 
into  a  white  moist  solid  like  plaster  paris  in  the  act  of  setting. 
In  composition  this  solution  is  as  follows : 
2Fe2O3  =80x2         =  160=19-185  p.  ct.  )  ,    0„  n  K6Sri_ 
5SO3  =40X5         =200=23-981    «     }  =43-166  per  ct.  2Fe203,5S03 
52-66  HO  =  9x52-66    =474=56-834    "       =56-834       "  Water. 
2Fe2035S03+52-66HO  =834=100  100 
This  is  not  precisely  the  salt  or  solution  of  M.  Monsel,  be- 
cause his  process  does  not  yield  a  salt  of  the  composition  he 
gives  it.    Taking  the  French  Codex  as  authority  for  the  specific 
gravity  equivalent  of  Baume"s  hydrometer  scale,  and  taking 
Ure's  tables  as  given  by  Wood  and  Bache  for  the  strength  of 
acids,  it  was  determined  by  calculation  that  the  process  of 
Monsel  is  deficient  in  sulphuric  acid  by  9-936  per  cent,  to  give 
a  salt  with  the  formula  2Fe2  03  5S03.    Such  a  minus  proportion 
of  S03  in  his  process  tends  strongly  to  the  formation  of  a  por- 
tion of  Fe2  03,  3N05,  and  the  writer  has  found  in  actual  practice 
with  his  formula  that  the  prescribed  quantity  of  nitric  acid, 
though  in  excess  by  calculation,  is  not  sufficient  to  peroxidize 
the  whole  of  the  iron,  unless  the  proportion  of  sulphuric  acid  be 
increased.    This  would  appear  to  indicate  that  in  the  absence 
of  a  definite  proportion  of  S03,  a  portion  of  the  N05  combines 
with  the  excess  of  base,  and  is  not  decomposed  by  the  FeO, 
S03  even  on  boiling.    If  sulphuric  acid  be  dropped  into  such  a 
solution  while  boiling  it  effervesces  and  liberates  nitric  oxide,  as 
nitric  acid  would  under  different  circumstances. 
The  writer  has  used  the  original  process  of  M.  Monsel,  with 
French  weights  and  measures,  and  with  much  care,  but  could 
not  obtain  by  it  a  solution  of  45°  Baume  =  s.  g,  1-454,  but  al- 
ways a  s.  g.  1-52.  This  latter  density  was  also  that  obtained  in 
the  practice  of  the  same  process  by  Prof.  Procter. 
The  writer's  process  above  given  yields  the  compound  2Fe2 
03,  5S03,  but  the  solution  is  a  little  more  dense  than  that  of  M. 
Monsel,  rendered  stronger  in  getting  at  convenient  whole  num- 
bers to  express  the  quantity  and  result.  The  writer  has  used 
this  process  upon  the  various  scales  of  half  ounce,  quarter 
