464 
NOTE  ON  OZONE. 
trical  sparks,  is  erroneous.  In  repeated  trials,  with  tubes  of 
every  form  and  size,  the  authors  found  that  not  more  than 
part  of  the  oxygen  could  thus  be  changed  into  ozone.  A  greater 
effect  was,  it  is  true,  produced  by  the  silent  discharge  between 
fine  platina  points ;  but  this  also  had  its  limit.  In  order  to 
carry  on  the  process,  it  is  necessary  to  introduce  into  the  appa- 
ratus some  substance,  such  as  a  solution  of  iodide  of  potassium, 
which  has  the  property  of  taking  up,  in  the  form  of  oxygen,  the 
ozone  as  it  is  produced.  After  many  trials,  an  apparatus  was 
contrived  in  the  form  of  a  double  U,  having  a  solution  of  iodide 
of  potassium  in  one  end,  and  a  column  of  fragments  of  fused 
chloride  of  calcium  interposed  between  this  solution  and  the  part 
of  the  tube  where  the  electrical  discharge  was  passed.  The 
chloride  of  calcium  allowed  the  ozone  to  pass,  but  arrested  the 
vapor  of  water;  so  that,  while  the  discharge  always  took  place 
in  dry  oxygen,  the  ozone  was  gradually  absorbed.  The  experi- 
ment is  not  yet  finished,  but  already  one-fourth  of  the  gas  in  a 
tube  of  the  capacity  of  10  cubic  centimetres  has  disappeared. 
To  produce  this  effect,  the  discharge  from  a  machine  in  excellent 
order  has  been  passed  through  the  tube  for  twenty-four  hours. 
When  oxygen  is  thus  converted  into  ozone,  a  diminution  of 
volume  takes  place.  The  greatest  contraction  occurs  with  the 
silent  discharge,  and  amounts  to  about  ~  of  the  volume  of  the 
gas.  The  passage  of  sparks  has  less  effect  than  the  silent  dis- 
charge, and  will  even  destroy  a  part  of  the  contraction  obtained 
by  means  of  the  latter.  If  the  apparatus  be  exposed  for  a  short 
time  to  the  temperature  of  250°  C,  so  as  to  destroy  the  ozone, 
it  will  be  found  that  the  gas  on  cooling  has  recovered  exactly 
its  original  volume.  This  observation  proves,  unequivocally, 
that  if  ozone  be  oxygen  in  an  allotropic  condition,  its  density  is 
greater  than  that  of  oxygen.  Experiments  still  in  progress  in- 
dicate that  the  density  of  ozone  obtained  by  the  electrical  dis- 
charge must,  on  the  above  assumption,  be  represented  by  even  a 
higher  number  than  that  deduced  by  the  authors  from  their  ex- 
periments on  ozone  prepared  by  electrolysis. 
When  mercury  is  brought  into  contact  with  dry  oxygen,  in 
which  ozone  has  been  formed  by  the  electrical  discharge,  it  loses 
to  a  great  extent  its  mobility,  and  maybe  made  to  cover  the  in- 
terior of  the  tube  with  a  fine  reflecting  surface  resembling  that 
