Am'/une,' i89oarm" }      Sodium  Carbonate  and  Chlorine.  301 
DIRECT  PRODUCTION  OF  SODIUM  CARBONATE  AND 
CHLORINE  FROM  SODIUM  CHLORIDE.1 
By  W.  Hempel. 
In  the  electrolysis  of  metallic  chlorides,  which  give  readily  solu- 
ble decomposition-products,  the  latter  are  further  decomposed  as 
soon  as  the  quantity  produced  reaches  a  certain  limit.  When, 
however,  the  compound  produced  is  only  sparingly  soluble,  this 
secondary  decomposition  does  not  take  place,  and  the  whole 
strength  of  the  current  is  utilized.  Potassium  chloride  and  sodium 
chloride,  for  example,  can  be  converted  into  the  corresponding 
chlorate ;  calcium  chloride  and  magnesium  chloride  can  be 
decomposed  into  chlorine  and  a  solid  hydroxide,  by  employing  a 
diaphragm. 
Marx  has  shown  that  alkaline  chlorides  can  be  directly  converted 
into  chlorine  and  an  alkaline  hydrogen  carbonate,  by  passing  car- 
bonic anhydride  through  the  solution  during  electrolysis,  metal  and 
liquid  diaphragms  being  employed. 
The  author,  who  has  been  engaged  independently  in  making 
similar  experiments,  describes,  with  the  aid  of  diagrams,  an  appa- 
ratus in  which  sodium  chloride  can  be  directly  converted  into 
chlorine  and  crystalline  carbonate.  The  cathode  is  a  perforated 
iron  disc,  the  anode  a  perforated  carbon  disc,  the  perforations  being 
about  4  mm.  in  diameter,  and  bored  in  an  upward  direction  to  allow 
the  gas  to  escape  freely.  A  disc  of  ordinary  asbestos-paper,  placed 
immediately  between  the  carbon  and  iron  discs,  serves  as  a  diaphragm. 
The  three  discs  are  placed  in  the  centre  of  a  vessel  made  of  porcelain 
and  glass,  which  is  thus  divided  into  two  chambers,  each  of  which 
is  provided  with  a  conducting  tube,  in  one  case  for  carbonic  anhy- 
dride, in  the  other  for  chlorine.  If  sodium  chloride  is  added  from 
time  to  time  through  a  suitable  aperture,  and  the  water  which  is 
removed  with  the  crystalline  carbonate  is  replaced,  the  apparatus 
can  be  worked  continuously,  sodium  carbonate  and  almost  chemi- 
cally pure  chlorine  being  obtained. 
A  tension  of  3-2  volts  is  required  for  decomposing  the  sodium 
chloride,  and  a  tension  of  2-5  volts  to  overcome  the  polarization 
current  ;  but  the  latter  has  only  a  slight  tension  when  both  electrodes 
1Berichte  XXII,  2475-2478.  Reprinted  from  Jour.  Chem.  Society,  January, 
1890,  p.  10. 
