AmASt,w<&m'}       The  U.S. P.  Inorganic  Chemicals.  389 
with  phenolphthalein  as  indicator  ;  methyl-orange  gives  lower  results, 
namely,  81-17  per  cent. 
Sulfurous  Acid. — The  extemporaneous  preparation  of  small  quan- 
tities of  sulfurous  acid  after  the  U.S.P.  1890  formula  is  usually 
attended  with  variable  success.  A  number  of  experiments  were 
made  with  the  view  of  modifying  the  process  so  that  the  resulting 
product  might  be  more  uniform  in  strength.    The  following  is  a 
summary  of  our  results. 
Per  cent. 
so2 
(1)  U.S.P.  method  ('90)  with  500  c.c.  water,  not  cooled  ....  1*35 
(2)  "  "       "       "       "  "       ice  cold  2*24 
(3)  "  "       "       *'  "  "   3-oo 
(4)  Charcoal  10  grammes. 
H2S04  50  c.c. 
Water,  cold,  500  c.c.  in  2^  hours  6*4 
(5)  Charcoal  10  grammes. 
H2S04  80  c.c. 
Water,  cold,  500  c.c.  in  2%  hours  6'6 
(6)  Charcoal  20  grammes. 
H2S04  60  c.c. 
Water,  cold,  500  c.c.  in  3^  hours  7*4 
(7)  Copper  60  grammes. 
H2S04  80  c.c. 
Water,  cold,  500  c.c.  in  1  hour   .  6*2 
(8)  Copper  75  grammes. 
H2S04  160  c.c. 
Water,  cold,  1000  c.c.  in  i]/z  hours  4.3 
(9)  Copper  30  grammes. 
H2SO,  80  c.c. 
Water,  cold,  500  c.c.  in  1  hour   4.45 
(10)  Copper  20  grammes. 
H2S04  60  c.c. 
Water,  cold,  500  c.c.  in  1  hour  2.5 
In  experiments  1,  2  and  3  the  requirements  of  the  U.S.P.  '90  were 
closely  followed,  using  500  c.c.  of  water  in  the  receiver  in  place  of 
IOOO  c.c.  as  directed.  In  all  other  experiments  the  solution  of 
sodium  carbonate  was  dispensed  with,  for  when  used,  the  greater 
portion  of  the  sulfurous  acid  was  found  in  the  last  receiver  and  but 
little  in  the  first,  where  it  would  be  expected.  In  order  to  obtain 
a  saturated  solution  of  the  gas,  there  must  be  a  slight  back-pressure 
exerted  in  the  absorption  flask.  This  cannot  be  brought  about  by 
the  use  of  an  alkali  solution  in  the  second  flask,  owing  to  the  readi- 
ness with  which  the  gas  is  absorbed.    In  order  to  free  the  sulfurous 
