JeT;8^75r™' }    Development  of  the  Chemical  Arts.  555 
Concerning  the  nature  of  ozone,  opinion  fluctuated  for  a  long  time. 
More  than  one  eminent  chemist  held  that  it  contained  hydrogen. 
Marignac  and  De  la  Rive  maintaimed  the  opposite  view,  w^hich  was 
finally  demonstrated  by  Soret  in  1863.  The  reason  of  the  difference 
between  ozone  and  ordinary  oxygen  became  gradually  intelligible.  The 
first  step  was  furnished  by  the  observation  of  Andrews  and  Tait,  that 
ozonized  oxygen,  if  heated  to  270°,  was  converted  into  common  oxygen, 
increasing  at  the  same  time  in  volume,  and  that  ordinary  oxygen,  if 
ozonized  by  silent  electric  discharge,  decreased  in  volume.  This  de- 
crease in  bulk  corresponds  to  the  quantity  of  the  active  oxygen  ab- 
sorbed by  potassium-iodide,  so  that  if  the  volume,  on  ozonization,  is 
I  I 
decreased  by  -  ,  then  -  of  the  ozonized  oxygen  is  absorbed  by  solu- 
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tion  of  potassium-iodide.  Ozone,  therefore,  appears  indubitably  as 
condensed  oxygen.  Odling's  hypothesis,  that  this  condensation  amounts 
to  one-third,  and  that  the  molecule  of  ozone  is  larger  by  the  half  than 
that  of  ordinary  oxygen,  its  molecular  weight  being  O3  =  48,  that  of 
common  ozygen  being  O2  =  32,  was  approximately  proved  by  Soret 
in  1865,  and  decidedly  demonstrated  by  Brodie  in  1871.*  Soret  added 
the  discovery  that  ethereal  oils,  especially  oils  of  turpentine  and  of 
cinnamon,  absorbed  the  whole  amount  of  the  ozone  formed  ;  conse- 
I  3 
quently,  not       but  -. 
n  n 
Ozone  has  never  been  obtained  in  a  state  of  purity. 
All  chemical  methods,  as  well  as  the  electrolysis  of  water,  yield  it 
only  very  sparingly,  since  not  merely  reducing  agents,  but  even  oxidi- 
sers,  all  super-oxides  for  instance,  re  convert  ozone  into  ordinary 
oxygen.  The  example  of  barium  super-oxide  shows  this  in  the  follow- 
ing equation  : — 03+Ba02=2024-BaO. 
Connections  of  cork  and  caoutchouc  cannot  be  used  in  an  ozone 
apparatus,  on  account  of  their  oxidisability.  The  electric  spark  has 
also  a  destructive  action  upon  ozone.  The  best  procedure  for  its  pre- 
paration is,  therefore,  silent  discharge  with  the  aid  of  a  Ruhmkorff''s 
apparatus  in  induction-tubes,  filled  with  oxygen.  The  greatest  contrac- 
tion which  Andrews  and  Tait  observed  in  oxygen  thus  treated  was  one 
■'^"Brodie,  "  Proceedings  of  the  Royal  Society,"  vol.  xx,  p.  472,  1872;  Odling, 
*'  History  of  Ozone," — Proceedings  of  the  Royal  Institution^  1872. 
