406 
REMARKS  ON  MONSEl/S  PERSULPHATE  OF  IRON. 
fluid  grammes.  It  would  seem  more  appropriate  to  say,  "  evapo- 
rate until  the  solution  measures  100  fluid  grammes,"  because  on 
trial  the  resulting  solution  measured  130  fluid  grammes,  and  had 
to  be  evaporated  nearly  one  fourth  of  its  bulk  to  get  the  pre- 
scribed measure.  This  discrepancy  between  theory  and  practice, 
has  arisen  from  his  lengthening  the  first  part  of  the  process,  so  that 
more  waste  of  water  occurs  than  is  needful.  It  is  better  that 
the  application  of  heat  should  be  continued  after  the  last  addition 
of  sulphate  of  iron  than  before,  because  owing  to  the  tendency 
of  a  solution  of  sulphate  of  iron  to  dissolve  and  retain  deutoxide 
of  nitrogen,  much  of  this  gas  remains  in  the  solution  giving  it 
a  blackish  brown  color.  The  presence  of  this  gas  is  evidenced 
by  the  escape  of  red  vapors  and  effervescence  when  the  heat  is  as 
great  as  212°  or  more,  without  boiling,  and  its  absence  is  shown 
by  holding  a  piece  of  paper  moistened  with  solution  of  proto- 
sulphate  of  iron  close  to  the  surface  of  the  heated  solution,  which 
should  not  be  colored  if  no  nitrous  acid  is  forming  at  the  surface 
from  the  union  of  deutoxide  of  nitrogen  with  the  oxygen  of  the 
air. 
M.  Monsel  appears  to  lay  much  importance  on  the  fact  that 
the  proportion  of  sulphuric  acid  in  his  salt  is  below  that  neces- 
sary to  make  a  regular  ter-sulphate  of  iron.  The  merit  of  his 
process,  if  its  product  is  really  better  adapted  for  therapeutical 
use  than  the  ordinary  solution  of  persulphate  of  the  Pharmaco- 
poeia directed  in  the  process  for  hydrated  sesquioxide  of  iron, 
rests  in  the  fact  that  by  using  just  the  quantity  of  proto-sulphate 
that  is  necessary  to  decompose  all  the  nitric  acid,  he  insures, 
without  failure,  the  absence  of  that  acid  from  his  solution,  which 
in  fact  may  be  viewed  as  a  mixture  of  the  ter-sulphate  and  bi- 
sulphate  of  sesquioxide  of  iron.  M.  Monsel  is  perhaps  wrong, 
in  attributing  the  formula  2(Fe203)  5(S03)  to  his  salt  which  may 
be  represented  by  the  formula,  Fe203,3S03+Fe20,32S03,  salts 
which  are  known  to  exist. 
As  in  the  next  Pharmacopoeia  there  is  a  strong  probability  that 
a  solution  of  sesquisulphate  of  iron  will  be  made  a  distinct  officinal 
preparation  with  a  view  to  its  use  in  making  hydrated  sesqui- 
oxide of  iron,  Prussian  Blue,  etc.,  it  will  hardly  be  necessary  to 
employ  a  special  formula  for  producing  a  solution  for  haemostatic 
purposes,  because  with  the  requisite  precautions  in  constructing 
