ADecImber,Pi9i3?' }  Preservation  of  Hydrogen  Peroxide.  539 
hydrogen  peroxide  in  sufficient  quantity  for  experimental  work. 
From  a  study  of  the  behavior  of  such  a  solution  we  are  able  to 
arrive  at  very  definite  and  indisputable  conclusions  concerning  the 
effects  of  various  impurities  and  of  acetanilide  upon  the  peroxide. 
Preparation  of  Pure  Hydrogen  Peroxide. 
Commercial  hydrogen  peroxide,  about  3  per  cent,  in  strength,  was 
concentrated  by  distillation  in  vacuo  until  a  strength  of  about  20 
per  cent,  was  obtained.  When  a  sufficient  quantity  of  this  20  per 
cent,  product  had  been  prepared,  it  was  carefully  subjected  to  further 
distillation  and  the  distillate  reserved ;  this  distillation  was  continued 
until  the  residue  showed  a  strength  of  from  35  per  cent,  to  40  per 
cent.  At  this  point,  distilled  water  was  added,  sufficient  in  amount  to 
dilute  the  residue  to  20  per  cent,  and  the  distillation  continued. 
This  process  was  repeated  until  the  desired  amount  of  distillate  was 
obtained.  In  the  above  distillation  the  flask  was  immersed  in  a 
bath  maintained  at  500  and  the  temperature  of  the  liquid  in  the  flask 
never  exceeded  400.  The  vapor  was  condensed  by  means  of  an 
ordinary  Liebig's  condenser  and  the  combined  distillate  contained 
over  1  per  cent,  of  hydrogen  peroxide.  When  a  sufficient  quantity 
of  distillate  was  obtained,  it  was  concentrated  by  distillation  in  vacuo, 
the  temperature  of  the  bath  being  maintained  at  400  and  that  of  the 
distilling  liquid  not  exceeding  280. 
Procedure. 
For  each  series  of  experiments  described,  a  separately  prepared 
lot  of  peroxide  was  used,  the  purity  of  which  had  been  assured  by 
analysis.  In  all  cases  the  total  residue  and  the  acidity  of  the  prepara- 
tions were  negligible.  The  strength  of  the  solution  in  hydrogen 
peroxide  was  determined  by  means  of  potassium  iodide  and  thiosul- 
phate  and  as  given  in  the  tables  is  represented  by  c.c.  of  n/io  thio- 
sulphate.  The  strength  in  which  the  different  substances  were  added 
is  indicated  in  the  tables  by  a  fraction  which  is  the  ratio  of  the  weight 
of  substance  to  the  volume  of  solution.  In  series  III  the  acidity  is 
expressed  in  terms  of  a  normal  solution.  The  solutions  were  pre- 
served in  4  oz.  bottles  of  amber-colored  glass  which  had  been  thor- 
oughly cleaned  and  dried  in  vacuo.  Sixty  to  75  c.c.  of  solution  were 
used  in  each  experiment.  The  bottles  were  well  stoppered  and  placed 
in  a  closet,  the  corks  of  the  less  stable  solutions  being  removed  from 
time  to  time  in  order  to  relieve  the  pressure. 
