"^'"oc^iS"'"  }        Fiirifieation  of  CommerGial  Ahohol.  505 
conducted  at  the  lowest  possible  temperature.  But  on  a  manufactur- 
ing scale  this  is  impracticable,  because  the  distillatory  columns  are 
heated  strongly  and  for  a  long  time,  so  as  not  to  leave  any  alcohol  in 
the  residues :  at  most  one-third  of  the  product  would  be  alcohol  of 
good  flavor,  and  that  would  be  still  far  from  pure. 
At  the  commencement  of  the  distillation  the  first  runnings  consist  of 
alcohol  having  a  bad  flavor  (mauvais  gout  de  fete)  due  especially  to 
aldehydes  and  alcohols ;  then  the  runnings  become  less  impure  (moyen 
gout  de  fete).  Alcohol  of  good  flavor  is  collected  towards  the  middle  of 
the  operation,  and  the  remainder  constitutes  the  last  runnings  (moyen 
gout  de  queue  and  mauvais  gout  de  queue),  which  contain  the  higher 
alcohols  and  empyreumatic  oils. 
Attempts  have  been  made  to  purify  the  alcohol  by  means  of  wood 
and  animal  charcoal,  but  with  very  imperfect  results.  Oxidation,  both 
by  treatment  with  various  oxidizing  bodies,  and  by  the  action  of  a 
current  of  air  has  also  been  tried,  but  with  indifferent  success,  in  conse- 
quence of  the  loss  of  alcohol.  Considering  the  fact  that  the  most 
active  and  odorous  of  the  contaminating  compounds  are  aldehydes, — 
vinic,  butylic,  amylic,  etc., — M.  Naudin  conceived  the  idea  of  getting 
rid  of  them  by  a  process  of  hydrogenation,  and  this  he  has  carried  out 
practically  by  means  of  the  copper-zinc  couple. 
If  a  plate  of  zinc  be  immersed  in  a  solution  of  a  salt  of  copper  it 
becomes  covered  with  a  metallic  deposit,  and  eventually  constiutes  a 
true  copper-zinc  couple,  in  which  the  copper  exists  in  a  finely  divided 
state.  Thus  prepared  the  couple  is  capable  of  decomposing  pure  water, 
with  evolution  of  hydrogen  and  formation  of  hydrate  of  zinc.  It  can 
consequently  act  freely  in  neutral  liquids,  and  constitutes  a  powerful 
-agent  of  hydrogenation.  If  an  alcoholic  distillate  indicating  40  to  65 
alcohometric  degrees  be  brought  into  contact  with  such  a  couple  in 
action  it  is  found  that  the  hydrogen  evolved  is  absorbed  and  that  the 
odor  and  taste  of  the  distillate  disappear  rather  rapidly.  The  distillates 
of  maize  and  beet  molasses  thus  hydrogenated,  when  rectified  in  the 
ordinary  apparatus,  show  an  augmentation  of  25  to  30  per  cent,  of 
good  flavored  alcohol  over  the  old  yields. 
J;  In  the  apparatus  of  M.  Naudin  zinc  cuttings  are  placed  in  succes- 
sive beds  of  15  to  20  centimeters  in  thickness,  supported  on  wooden 
diaphragms  pierced  with  holes  in  a  vat  made  of  wood,  copper,  or  iron. 
At  the  commencement  of  the  operation  a  suflicient  quantity  of  5  per 
cent,  solution  of  sul])hate  of  copper  is  run  into  the  vat.    The  decolora- 
