A^r'Xt™" }    development  of  the  Chemical  Arts,  367 
Thus,  one  part  of  the  above-stated  problem  is  solved,  and  the  devel- 
oper of  oxygen  is  re-formed  by  the  very  act  of  developing  oxygen. 
Still  the  oxygen  is  obtained,  not  from  the  atmosphere,  but  from  the 
chloride  of  lime.  The  solution  of  chloride  of  calcium  formed  must  be 
removed,  and  replaced  by  milk  of  lime.  The  process,  therefore,  is 
not  continuous,  and  in  this  respect  there  is  still  room  for  economic  sim- 
plification. 
This,  also,  has  been  achieved,  and  by  means  of  experiments  which  • 
lead  us  back  from  the  moist  to  the  dry  vv^ay.  Since  1851,"^  Boussin- 
gault  has  brought  baryta  into  use  as  a  bearer  of  oxygen,  heating  it  to 
redness  in  porcelain  tubes,  and  treating  it  with  moist  air  free  from  car- 
bonic acid,  by  which  it  is  converted  into  peroxide  of  barium.  By 
means  of  a  current  of  watery  vapor,  it  is  re-converted  into  hydrate  of 
baryta,  and  oxygen  is  liberated.  An  addition  of  lime  or  magnesia  pre- 
vents any  incipient  fusion,  and  75  grms.  of  baryta  yield  on  each  opera- 
tion 4  to  5  litres  of  oxygen.  Gondolof  improved  this  method  in  1868^ 
replacing  the  porcelain  tubes  with  iron  ones,  protected  by  magnesia 
within  and  by  asbestos  without,  and  laid  in  suitable  furnaces,  whose 
temperature  was  regulated  by  dampers,  and  adding  to  the  baryta  a  little 
manganate  of  potash  as  well  as  lime  and  magnesia.  In  this  manner  as 
many  as  122  alternate  oxidations  and  deoxidations  were  conducted  in 
the  same  tube.  Whether,  however,  it  be  due  to  the  high  temperature^ 
or  to  other  drawbacks  which  stand  in  the  way  of  the  industrial  applica- 
tions of  this  method,  it  has  not  yet  found  its  way  into  actual  practice,  j 
Attention  was  directed  to  more  sensitive  transferrers  of  oxygen 
than  baryta,  and  in  the  first  place  to  chloride  of  copper.  Its  property^ 
on  exposure  to  the  air  to  pass  into  oxychlorides  of  various  composition^ 
lies  at  the  root  of  the  manufacture  of  a  well-known  pigment,  Bruns- 
wick green.  In  1855,  Vogel  proposed  the  action  of  hydrochloric  acid 
upon  oxychlorides  of  copper  as  a  source  of  chlorine. ||  Mallet§  exam- 
ined these  bodies  more  closely,  and  in  1867  and  1868  proposed  a  method 
for  the  industrial  preparation  of  chlorine  and  oxygen.  He  found  that 
cuprous  chloride  is  converted  into  oxychloride  by  a  current  of  steam  at 
from  100°  to  200°  C,  which,  in  contact  with  hydrochloric  acid,  is  im- 
*  Boussingault,  "  Comptes  Rendus,"  xxxiii,  261  and  821. 
f  Gondolo,  *'  Comptes  Rendus,"  Ixvi,  488. 
X  Robbin,  "  Pogg.  Ann.,"  cxxii,  256. 
II  Vogel,  Wagner,  "  Jahresberichte,"  1861,  177. 
I  Mallet,  "Comptes  Rendus,"  Ixiv,  286,  and  Ixvl,  349. 
