410  PEROXIDE  OF  HYDROGEN,  NEW  REMEDY  FOR  DIABETES. 
barium,  strontium,  calcium,  potassium  or  sodium  are  decomposed 
with  acids.  It  forms  during  the  electrolysis  of  water  acidulated 
with  sulphuric  acid,  also  in  many  instances  where  slow  oxidation 
is  in  progress,  and  under  conditions  such  as  give  rise  at  the  same 
time  to  the  formation  of  ozone,  as  for  instance  during  the  oxida- 
tion of  phosphorus  in  moist  air. 
Schoenbein  believes  that  in  this  case  the  oxygen  of  the  air  is 
transformed  into  ozone  and  antozone,  its  electrical  opposite,  and 
this  latter  then  combines  with  tiae  water  present  to  form  perox- 
ide of  hydrogen.  In  the  familiar  method  of  exhibiting  the  for- 
mation of  ozone  by  heating  platinum  in  a  vessel  of  air  containing 
also  a  small  quantity  of  water  and  ether,  there  is  formed  an  ap- 
preciable quantity  of  peroxide  of  hydrogen  along  with  ozone. 
Some  chemists  believe  that  in  all  cases  where  oxidation  takes 
place  in  moist  air,  more  or  less  peroxide  of  hydrogen  is  formed, 
as  in  the  rusting  of  metals,  the  decay  of  organic  substances,  or 
the  respiration  of  animals,*  and  that  in  these  processes  it  plays 
an  important  part. 
Notwithstanding  the  many  possible  methods  of  forming  the 
peroxide,  only  those  are  practically  useful  based  upon  the  decom- 
position of  barium  peroxide  by  means  of  an  acid  in  presence  of 
water. 
In  the  original  method  of  Thenard,  hydrochloric  acid  was  em- 
ployed. But  the  purification  and  concentration  is  by  his  method 
very  difficult  and  circumstantial.  Pelouze  employed  hydroflu- 
oric acid,  also  hydrofluosilic  acid.  But  by  far  the  most  satisfac- 
tory method  is  that  of  Balard,  as  modified  by  Duprey.f  A  very 
rapid  current  of  pure  cai'^onic  acid  is  passed  through  distilled 
water,  and  peroxide  of  barium  added  in  small  quantities,  care 
being  taken  to  have  the  acid  always  in  excess.  After  filtration 
the  solution  is  concentrated  under  the  receiver  of  an  air  pump. 
A  very  dilute  solution  of  the  peroxide  may  also  be  obtained  in  the 
following  manner,  which  for  experimental  purpose  is  an  excel- 
lent method,  and  admits  of  execution  sufficiently  rapid  to  be 
suited  for  the  lecture  table :  a  small  amount  of  the  peroxide  of 
potassium  is  prepared  by  melting  the  metal  in  a  test  tube,  and 
*  See  interesting  article  on,  in  Erdman's  Journal,  vol.  89,  p.  323. 
t  Compt.  Rendus,  i,  55,  p.  736. 
