56         ON  THE  REVISION  OF  THE  U.  S  PHARMACOPOEIA. 
the  circumstance  of  the  color  of  this  preparation  being  better 
when  the  solution  is  filtered  into  syrup,  from  which  the  air  has 
been  expelled  by  the  heat  in  making  it,  as  confirmation  of  the 
fact  that  there  is  far  less  air  contact  and  far  less  consequent  de- 
composition when  the  syrup  is  made  beforehand. 
When  solutions  of  chloride,  iodide  or  bromide  of  iron,  with 
the  chlorine,  iodine  or  bromine,  in  minimum  combining  propor- 
tions, are  brought  in  contact  with  organic  matter,  a  portion  of 
the  haloid  salt  is  always  decomposed  with  separation  of  sesqui- 
oxide  of  iron.  The  extent  of  the  decomposition  is  determined 
chiefly  by  the  presence  of  oxygen  or  air,  but  also  by  the  extent 
of  the  contact,  by  the  dilution  of  the  solution,  and  by  the  tem- 
perature of  the  reacting  substances.  Hence  the  writer  would 
have  as  small  a  quantity  of  solution  to  filter  as  possible, — would 
filter  this  through  as  small  a  filter  as  possible, — would  filter  it 
cold,  or  cool,  and  with  the  least  possible  exposure  to  the  air, — 
and  would  abstain  from  washing  the  last  portions  out  of  the 
filter.  This  last  portion,  if  washed  through,  is  always  of  a  brown 
color,  and  if  washed  through  with  water  containing  the  usual 
proportion  of  air,  is  very  brown. 
Fortunately,  the  solution,  when  not  embarrassed  by  the  de- 
bris of  a  large  excess  of  iron  passes  through  a  filter  very  readily, 
and  very  rapidly  ;  so  that  by  ordinary  care  and  precaution,  a 
very  perfect,  and  so  to  speak,  a  very  chemical  preparation  may 
be  easily  obtained,  in  which  the  beginnings  of  evil  have  been 
successfully  opposed. 
The  writer  is  disposed  to  resume  or  re-incorporate  the  direc- 
tion to  preserve  this  preparation  from  the  light,  since  by  long  ex- 
posure to  light  it  loses  its  fine  pale-green  color  and  becomes  color- 
less, with  probably  a  material  change  of  composition,  and  possi- 
bly of  medicinal  effect.  Indeed,  as  a  general  rule,  medicinal 
substances  should  be  excluded  from  light  to  a  far  greater  de- 
gree than  at  present  obtains  in  practice  ;  and  it  would  be  an 
important  step  in  the  right  direction,  to  have  some  of  the  white 
painted  shelves  of  dispensing  establishments  replaced  by  closets. 
Concentrated  ether,  exposed  to  sunlight  for  an  hour  of  each  day, 
soon  acquires  a  strong,  disagreeable,  pungent,  and  often  empy- 
reumatic  odor,  becomes  acid,  and  altogether  unfit  for  use, 
through  partial  decomposition.    Chloroform,  under  similar  cir- 
