Am.  Jour.  Pharm.\ 
August,  1896.  J 
Editorial. 
457 
EDITORIAL. 
THE  ELECTROLYTIC  PRODUCTION  OF  ALKAIyl  AND  BLEACHING  POWDER. 
The  problem  of  the  production  of  chlorine  and  caustic  soda  by  the  electro- 
lysis of  the  alkaline  chlorides  has  occupied  the  attention  of  many  experimenters 
during  the  past  ten  years,  and  what  at  first  looked  to  be  a  practical  impossi- 
bility has  now  become  a  commercial  success. 
Two  great  difficulties  had  to  be  overcome  before  this  success  could  be  ob- 
tained. It  is  well  known  that  when  anodes  and  cathodes  are  placed  opposite 
each  other  in  a  solution  of  sodium  chloride,  but  without  being  separated  by  a 
porous  diaphragm,  the  electric  current  gives  rise  to  the  formation  of  hypo- 
chlorite of  sodium.  If,  on  the  other  hand,  you  place  porous  diaphragms 
between  the  positive  and  negative  plates  in  such  a  way  as  to  form  water-tight 
compartments,  chlorine  will  be  generated  in  all  the  positive  compartments, 
and  caustic  soda  in  all  the  negative  ones.  Again,  both  the  chlorine  and  the 
oxygen,  as  evolved,  have  a  powerful  disintegrating  action  on  ordinary  carbons; 
so  that  a  form  of  carbon  had  to  be  sought  that  would  be  capable  of  resisting 
the  action  of  these  elements  for  a  lengthy  period.  Gas  carbon,  specially  pre- 
pared and  highly  heated,  so  as  to  obtain  a  maximum  density,  was  finally  found 
to  work  best.  The  difficulty  with  the  diaphragm  was  a  much  more  persistent 
one,  and  has  not  been  entirely  overcome.  We  have,  however,  at  the  present 
moment  three  promising  industrial  processes  for  the  electrolysis  of  salt  solu- 
tion, which  claim  to  have  substantially  overcome  the  difficulties  just  noted,  and 
a  brief  account  of  these,  abridged  from  the  Engineering  and  Mining  Journal, 
of  June  13  and  20,  1896,  may  be  of  interest  to  our  readers. 
The  first  of  these  is  the  Richardson-Holland  process,  which  is  worked  by  the 
Electro-Chemical  Company,  at  Parr,  near  Widnes,  in  Lancashire,  England.  In 
this  process,  instead  of  porous  partitions,  use  is  made  of  one  non-porous  parti- 
tion which  does  not  quite  reach  to  the  bottom  of  the  tank,  so  that  the  solutions 
in  the  two  compartments  are  not  separated  from  each  other  at  the  bottom  of  the 
electrolyzer.  In  the  electrolyzing  tanks,  the  solution  of  soda  attains  a  maxi- 
mum density  of  14  per  cent.,  but  is  not  wholly  free  from  chlorine,  which  means 
that  there  is  some  loss  of  soda,  as  well  as  chlorine,  due  to  formation  of  hypo- 
chlorite. 
The  plant  erected  promises  to  turn  out  6,400  tons  of  caustic  soda  (of  70  per 
cent,  strength)  and  13,320  tons  of  bleaching  powder  per  annum,  and  the  entire 
production  for  the  current  year  (1896)  has  been  sold  in  advance. 
The  Castner  process  differs  very  materially  from  that  just  described,  and 
seems  to  be  in  all  respects  superior  to  it.  In  this  case  the  diaphragm  consists 
simply  of  a  layer  of  mercury,  which  constantly  oscillates  in  a  compartment 
closed  on  each  side  by  a  non-porous  partition,  the  lower  end  of  which  just 
reaches  the  layer  of  mercury.  No  resistance  is  offered  by  this  diaphragm, 
which  automatically  (in  consequence  of  a  slow  rocking  of  the  tank)  leans  first 
towards  the  cathode  and  then  towards  the  anode,  and  which,  in  coming  alter- 
nately in  contact,  first  with  one  and  then  with  the  other,  absorbs  the  sodium 
liberated,  and  then  at  once  gives  it  up  to  the  water  which  is  over  the  mercury. 
There  seems  to  be  an  entire  absence  of  hypochlorite  formation,  and  the  solu- 
tions of  caustic  soda  formed  in  the  cathode  compartments  have  a  density  of  20 
per  cent.,  and  yield,  on  evaporation,  solid  caustic  soda  of  78  per  cent,  strength 
