^'^AuZ'Zt'''^' }    ^development  of  the  Chemical  Arts.  365 
set  free,  which  he  (as  also  Susini)  chiefly  condensed  by  a  pressure  of 
three  atmospheres,  and  removed  the  rest  by  passage  through  milk  of 
lime.  A  manufactory  on  this  principle,  established  at  Paris,  had  but  a 
short  career.*  The  very  high  temperature  required  is  evidently  a 
hindrance.  Probably  the  oldest  source  of  oxygen,  saltpetre,  had  not 
been  used  for  the  preparation  of  the  gas,  for  two  reasons.  On  the 
one  hand,  the  product  is  largely  mixed  with  nitrogen,  and  on  the  other, 
the  temperature  required  for  its  decomposition  augments  the  cost  of 
preparation.  Websterf  overcame  the  latter  difficulty  by  adding  to  the 
nitre  oxide  of  zinc.  20  lbs.  of  soda-saltpetre  and  4  lbs.  of  crude  oxide 
of  zinc  yielded  in  his  hands  94'676  cubic  feet  of  a  mixture  of  59  per 
cent,  of  oxygen  and  41  per  cent,  of  nitrogen,  the  residue  being  chiefly 
oxide  of  zinc  and  caustic  soda.  In  this  mixture,  which  is  useful  for 
many  purposes,  the  oxygen  cost  2*32  francs  per  cubic  metre  if  the 
solid  residue  be  neglected  ;  but,  if  the  latter  be  utilized,  the  expense  of 
the  oxygen  falls  to  0*78  francs. J 
In  all  these  methods,  one  of  the  leading  ideas  of  modern  industry, 
the  regeneration  of  residues,  has  been  neglected.  The  following  pro- 
posals are,  in  this  respect,  happier,  and  have,  therefore,  been  partially 
more  successful.  To  combine  the  oxygen  of  the  atmosphere  chem- 
ically with  some  substance  which  shall  readily  give  off  the  combined 
gas,  and  be  again  able  to  take  up  and  give  off  fresh  quantities  of  oxygen, 
as  is  done  by  the  mercury  in  mercuric  oxide  ;  this  is  the  problem  which 
has  been  solved  in  the  last  few  years.  As  early  as  1829,  Dingier, 
Junior,||  observed  that  both  oxide  of  copper  and  the  peroxides  of  nickel 
and  cobalt,  with  an  excess  of  chloride  of  lime,  gave  off  oxygen,  con- 
verting the  latter  substance  into  chloride  of  calcium.  In  1845,  Mit- 
scherlich§  made  known  the  fact  that  various  other  metallic  oxides, 
peroxide  of  manganese,  hydrated  peroxide  of  iron,  &c.,  if  added  to  a 
solution  of  chloride  of  lime,  occasioned  a  plentiful  liberation  of  oxygen. 
In  1865,  these  observations  were  renewed  by  T.  H.  Fleitmann,T[  with 
especial  reference  to  recently  prepared  sesquioxide,  small  quantities  of 
which  sufficed  to  decompose  completely  a  concentrated  solution  of  chlo- 
Wagner,  "  Jahresberichte,"  1867,  ^''S- 
t  Pepper,  "Chemical  News,"  1862,  218. 
X  Dupre,  "Comptes  Rendus,"  Iv,  736. 
II  "  Dinglef  s  Polyt.  Journ.,"  xxvi,  231. 
^  Mitscherlich,  "  Pogg.  Ann.,"  Iviii,  471 
\  "Ann.  Chem.  Pharm.,"  cxxxiv,  64. 
