366  Development  of  the  Chemical  Arts.  {^"^-p^^^'-J^^'"^' 
ride  of  lime  into  chloride  of  calcium  and  oxygen  gas.  He  recommended, 
in  practice,  a  solution  of  chloride  of  lime  concentrated  as  much  as  possi- 
ble, and  clarified  by  filtation  or  deposition  to  prevent  frothing,  and  then 
mixed  with  o*i  to  0*5  per  cent,  of  its  contents  of  sesquioxide  of 
cobalt,  and  heated  from  70°  to  80°.  On  employing  chloride  of  lime 
at  35  per  cent.,  he  obtained  oxygen  in  a  regular  stream,  to  25  or  30 
times  the  volume  of  the  liquid.  Other  observers,  especially  F.  Var- 
rentrapp,*  confirmed  these  results,  and  recommended  the  industrial 
adoption  of  the  process.  The  sesquioxide  of  cobalt  does  not  require 
to  be  manufactured  in  advance.  Any  salt  of  cobalt  in  solution  serves 
the  same  purpose,  and  the  sesquioxide  settles  to  the  bottom  and  can  be 
used  again  in  fresh  operations. 
For  the  same  reason,  a  cheaper  oxide,  as,  for  instance,  oxide  of  cop- 
per, which  Bottger  proposes,")"  offers  but  little  advantage,  especially  as 
a  higher  temperature  is  required  for  its  decomposition.!  The  trouble 
of  preparing  a  clear  solution  of  chloride  of  lime  may  be  dispensed  with 
if,  as  Stolba  suggests,  a  piece  of  paraffin  of  the  size  of  a  pea  be  added 
to  the  turbid  solution. ||  The  thin  layer  of  oil  upon  the  surface  pre- 
vents frothing.  One  difficulty  yet  remains  to  be  removed.  Chloride 
of  lime  requires  considerable  quantities  of  water  for  solution,  and  large 
vessels  are,  therefore,  required  for  preparing  moderate  quantities  of 
oxygen.  A.  Winkler,§  therefore,  dispensed  with  chloride  of  lime,  by 
using  a  thick  milk  of  lime  with  a  little  salt  of  cobalt,  and  treating  the 
mixture  with  chlorine.  By  means  of  this  modification,  a  larger  volume 
of  oxygen  is  evolved  with  the  same  vessels,  and  all  danger  of  frothing 
over  is  avoided. 
The  part  played  by  the  metallic  oxide  in  these  methods  is  readily 
intelligible.  It  serves  as  a  carrier  of  oxygen,  passing  alternately  to  a 
higher,  readily  decomposable,  stage  of  oxidation,  and  then  returning  to 
its  original  state.  The  hypochlorous  acid  of  the  chloride  of  lime  con- 
verts the  sesquioxide  of  cobalt  into  an  unstable  cobaltic  acid,  which  is 
immediately  resolved  into  sesquioxide  of  cobalt  and  oxygen — 
Co203+3[CaCl(OCl)]--3CaCl2-f2Co03=Co203+03. 
*  "  Mittheilungen  d,  Gewerbe  Vereins  des  Herzogthums  Braunschweig,"  1865- 
66,  72. 
t  Bottger,  "  Journ.  Prakt.  Chem.,"  xcv,  375. 
X  Reinsch,  "  Neues  Jahr.  Pharm.,"  xxiv,  94. 
II  Stolba,  "Journ.  Prakt.  Chem.,"  xcvii,  309. 
I  A.  Winkler,  "  Journ.  Prakt,  Chem.,"  xcviii,  340, 
