Inorganic  Chemistry  of  the  U.S. P.  557 
were  weighed  off  for  analysis.  It  is  not  an  easy  matter  to  do  this, 
because  when  exposed  to  air  the  potassa  rapidly  absorbs  both  car- 
bon dioxide  and  water  in  sufficient  quantity  to  materially  increase 
its  weight,  even  whilst  the  weighing  is  being  done.  The  new 
process  directs  that  about  1  gramme  be  introduced  into  a  stoppered 
weighing  bottle  and  its  weight  accurately  ascertained.  Another 
improvement  is  the  use  of  methyl  orange  instead  of  phenolphthalein 
as  indicator. 
Soda  is  now  Sodii  Hydroxidum. — It  should  be  90  per  cent.  pure. 
It  is  intensely  alkaline  and  imparts  an  intense  yellow  color  to  the 
flame.  It  is  tested  for  organic  and  insoluble  matters,  potassium, 
carbonate,  silicate  and  heavy  metals.  It  is  assayed  volumetrically 
in  the  same  manner  as  potassium  hydroxide.  No  method  for  its 
preparation  is  given.  It  enters  into  liquor  sodii  hydroxidum. 
Much  that  was  said  of  potassium  hydroxide  is  also  true  of  sodium 
hydroxide.  In  the  old  Pharmacopoeia  the  heavy  metals  are  detected 
by  the  sulphide  test,  whilst  in  the  new  by  the  time-limit  test. 
The  old  also  gives  tests  for  calcium,  for  chloride,  for  sulphate  and 
for  nitrate. 
Ferri  Oxidum  Hydration  is  still  official,  but  its  name  is  changed  to 
Ferri  Hydroxidum,  which  is  certainly  more  in  accordance  with  our 
present  nomenclature. 
It  is  prepared  as  formerly  by  the  reaction  between  solution  of 
ferric  sulphate  and  ammonia  water,  the  reaction  being  expressed  by 
the  equation  Fe2(S04)3  -f  6NH.OH  =  Fe2(OH)6  +  3(NHJ2S04. 
The  new  process  calls  for  a  larger  quantity  of  ammonia  water,  but 
the  same  quantity  of  ferric  sulphate  solution  as  before ;  the  latter 
is,  however,  2  per  cent,  stronger  than  that  of  the  1890  U.S.P. 
Double  the  quantity  of  water  is  used  for  diluting  the  ammonia  water 
previous  to  the  addition  of  the  iron  solution.  The  directions  for 
making  it  in  haste  when  required  as  an  arsenic  antidote  have  been 
omitted.  There  is  no  pharmacopceial  use  for  the  ferric  hydroxide 
since  emplastrum  ferri  and  trochisci  ferri  have  been  dismissed. 
Attention  is  called  to  the  fact  that  the  new  Pharmacopoeia  gives 
the  chemical  formula  of  ferric  hydroxide  as  Fe(OH)3.  This  assumes 
that  the  atom  of  iron  in  the  ferric  salt  is  trivalent, 
/  O— H 
Fe  —  O  — H 
\0— H 
