AjanJuOa%ryr.906rm'}      Inorganic  Chemistry  of  the  U.S. P.  23 
but  is  3  per  cent,  stronger  in  the  1 890  U.S.P.  than  in  the  present. 
The  ferric  chloride  in  the  present  Pharmacopoeia  is  obtained  by 
evaporation  of  the  liquor.  The  volumetric  assay  is  the  same  as 
before  except  that  instead  of  weighing  for  analysis  0-56  gramme  of 
the  salt  1  gramme  is  taken,  dissolved  in  100  c.c.  of  water  and  55.5 
c.c.  of  this  solution  taken  for  analysis. 
No  method  for  the  preparation  of  any  of  the  scale  salts  is  given. 
Ferri  et  ammonii  sulphas  has  the  formula  FeNH4(S04)2  -f  I2H20. 
Ferrum  Reductum. — A  new  assay  method  for  this  substance  has 
been  introduced.  In  the  method  of  the  old  pharmacopoeias  mercuric 
chloride  was  digested  with  a  weighed  quantity  of  the  reduced  iron. 
This  converted  the  iron  into  ferrous  chloride,  and  was  then  titrated 
with  decinormal  potassium  permanganate  V.  S.  to  permanent  red 
color.  To  confirm  the  assay  it  was  recommended  to  decolorize  the 
solution  with  a  few  drops  of  alcohol,  then  to  add  1  gramme  of 
potassium  iodide  and  digest  for  half  an  hour,  cool  and  titrate  with 
decinormal  sodium  thiosulphate  in  presence  of  starch  as  an  indicator. 
This  method  gave  very  satisfactory  results,  but  the  new  official 
method  which  was  devised  by  E.  Schmidt  (Proc.  Soc.  German  Natu- 
ralists and  Physicians,  September,  1897)  and  which  is  official  in 
the  new  German  Pharmacopoeia,  is  considered  the  most  reliable  and 
up-to-date. 
7he  New  Assay  Method  is  as  follows  :  A  definite  weight  of  pure 
iodine,  say  2-6  grammes  is  introduced  into  a  flask  with  6  c.c.  of 
water,  2  grammes  of  potassium  iodide,  and  0  55 5  gramme  of  reduced 
iron ;  the  flask  is  securely  stoppered  and  set  aside  for  one  hour. 
Then  water  is  added  to  make  100  c.c.  Of  this  solution  25  c.c.  is 
taken  and  titrated  with  tenth-normal  sodium  thiosulphate  V.  S.  until 
a  brown  color  is  discharged,  and  the  calculation  made. 
The  iodine  reacts  with  the  pure  iron,  forming  ferrous  iodide  as  per 
equation  Fe  +  2I  =  Fel2,  but  does  not  react  with  the  iron  oxide 
present.  The  uncombined  iodine  is  then  found  by  titration  with 
the  thiosulphate  V.  S.  and  from  this  it  is  easy  to  calculate  the 
quantity  of  iodine  which  combined  with  the  iron  present  (251  8 
grammes  of  iodine  represent  55-5  grammes  of  iron). 
Reduced  iron  should  contain  not  less  than  90  per  cent,  of  pure 
metallic  iron.  Directions  for  detecting  limit  of  sulphide  and  for 
arsenic  are  given  ;  the  modified  Gutzeit's  test  for  the  latter  being 
employed. 
