Am  MJa0yri9^5ain''}    Some  Studies  on  the  Oxy-pinenes.  205 
One  of  the  authors,  C.  Engler,  two  years  later  (Ber.,  vol.  33), 
oxidizes  turpentine  by  oxygen  in  the  presence  of  indigo-sulphuric 
acid  solution  containing  acetic  acid,  and  finds  "  that  half  of  the  total 
oxygen  at  first  absorbed  is  '  active  '  and  is  subsequently  used  for 
oxidizing  other  substances  or  for  intermolecular  oxidation."  This 
rather  perplexing  experience  will  be  quite  clear  when  viewed  in  the 
light  shed  on  the  subject  by  Professor  Harries  and  his  disciples. 
In  the  year  1840  the  eminent  German  chemist,  Schoenbein,  found 
that  oxygen,  like  sulphur,  phosphorus,  carbon,  etc.,  could  exist  in 
different  allotropic  modifications ;  that  ordinarily  the  oxygen  mole- 
cule was  composed  of  two  atoms  of  oxygen  (02),  but  that  under 
some  conditions  it  also  could  form  molecules  containing  three  atoms 
of  oxygen  (03),  and  this  allotropic  modification  of  oxygen  he  called 
ozone. 
This  modification  of  oxygen  naturally  was  very  "  active  "  on 
account  of  its  instability,  and  easily  gave  off  its  third  atom  of  oxygen 
in  the  form  of  nascent  or  atomic  oxygen. 
The  usual  chemical  combination  between  oxygen  and  hydrogen, 
water  (H20),  possesses  only  a  very  feeble  oxidizing  power,  but  in 
the  year  181 8  Thenard  discovered  that  oxygen  and  hydrogen  could 
be  combined  in  the  proportion  H202  (hydrogen  peroxide),  and  in 
this  state  the  oxygen  became  very  active  indeed,  readily  combining 
and  forming  peroxides  with  anything  with  which  it  came  into  contact. 
No  wonder  these  two  substances  were  confused — particularly  as 
the  "  peroxide  of  hydrogen  is  produced  whenever  ozone  is  found  in 
the  presence  of  water"  (E.  Molinari,  "Treatise  on  General  and 
Industrial  Chemistry,"  London,  1913),  and  that  there  was  consider- 
able doubt  about  when  the  active  oxygen  appeared  in  the  form  of 
ozone  or  that  of  hydrogen  peroxide.  This  was,  as  has  before  been 
pointed  out,  particularly  the  case  with  the  oxygen-carrying  tur- 
pentine. 
How  little  was  really  known  about  the  oxidation  of  turpentine 
at  so  recent  a  date  as  1898  may  be  judged  from  an  article  in  Rev.  de 
Chim.  hid.  (vol.  9)  of  that  year  by  R.  Robine.  In  this  he  says  that 
the  only  known  way  to  oxidize  turpentine  "  consists  in  exposing  the 
ordinary  oil  to  the  action  of  the  air  until  a  sufficient  degree  of  oxida- 
tion has  taken  place."  He  admits,  however,  that  the  process  may  be 
hastened  by  "  forcing  air  through  the  oil  under  predetermined  condi- 
tions of  temperature  and  pressure."  He  describes  the  product  ob- 
tained as  "  a  syrupy  liquid  with  the  color  of  honey  and  soluble  in 
