LIQUOR  FERRI  PERSULPHATIS. 
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Liquor  Ferri  PersulpTiatis. 
Monsel's  Solution. 
Take  of  Sulphate  of  Iron,       one  hundred  parts, 
Sulphuric  acid,  nine  parts, 
Nitric  acid,  twelve  parts, 
Distilled  water,  a  sufficient  quantity. 
Into  a  tared  basin,  of  the  capacity  of  three  hundred  parts, 
weigh  in  succession,  thirty  parts  of  distilled  water  and  the  acids, 
place  the  basin  over  a  lamp,  and  add  the  sulphate  of  iron.  Heat 
the  mixture  to  brisk  ebullition,  with  constant  stirring,  and  finally 
add  distilled  water  until  the  solution  weighs  one  hundred  and 
fifty  parts. 
If  the  crystallized  sulphate  be  clean  and  dry,  and  the  acids 
be  of  officinal  strength,  the  quantities  given  are  so  nearly  exact 
that  the  process  is  easy  and  the  result  accurate.  If  the  materials 
be  not  officinal,  it  should  not  be  undertaken  without  close  cal- 
culation of  their  strength. 
The  addition  of  the  acids  to  the  water  in  the  capsule  produces 
sufficient  heat  to  start  the  reaction,  and  the  flame  of  a  good 
lamp,  gas  burner,  or  furnace  then  keeps  up  and  increases  the 
heat  as  the  nitric  acid  is  decomposed,  so  that  nothing  is  lost  by 
violence  of  reaction  from  too  much  heat  at  first,  whilst  the 
heating  progresses  as  the  nitric  acid  diminishes,  so  that  no 
troublesome  frothing  is  encountered,  and  by  the  time  all  the 
crystals  are  dissolved  the  liquid  will  be  well  heated,  and  the 
nitric  acid  and  protoxide  of  iron  will  have  finished  their  reaction. 
The  slow  solution  of  the  large  crystals  also  economizes  nitric 
acid  by  controlling  the  violence  of  the  reaction,  while  the  heat 
is  still  great  enough  to  perfect  the  reaction  as  it  progresses. 
The  subsequent  boiling  is  intended  to  drive  off  oxides  of  nitrogen, 
and  to  effect  this  within  practically  useful  limits  it  need  not  be 
long  continued.  The  whole  process  should  be  conducted  under 
a  hood  to  avoid  the  nitrous  vapors.  The  solution  should  be 
allowed  to  cool  before  its  final  adjustment,  otherwise  the  evapor- 
ation that  takes  place  whilst  cooling  would  reduce  the  weight 
materially. 
The  resulting  solution  is  a  syrupy  liquid  of  a  deep,  rich  ruby 
or  brownish  ruby  color,  very  different  from  the  dull  reddish 
brown  of  the  normal  solution  of  tersulphate.    It  is  odorless,  but 
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