506 
PurijiGidion  of  Commercial  AkohoL 
Am.  Jour.  Pliarm 
( >ct.,  1882. 
ration  of  the  cupric  solution  marks  the  completion  of  the  precipitation 
of  the  copper  in  a  pulverulent  state  upon  the  zinc  cuttings,  and  the 
couple  is  then  ready  for  work.  The  resulting  solution  of  sulphate  of 
zinc  is  run  otf,  and  the  vat  is  filled  with  the  distillate  to  be  purified. 
By  a  special  arrangement,  the  alcohol  is  kept  circulating  in  the  vat^ 
but  the  time  required  for  it  to  remain  in  contact  with  the  couple  is  not 
always  the  same.  This  necessarily  depends  upon  the  degree  of  contam- 
ination in  the  product  to  be  purified,  the  temperature  at  which  the 
hydrogenation  takes  place,  and  the  condition  of  the  couple.  Tempera- 
ture, especially,  has  a  considerable  influence  upon  the  rapidity  of  the 
reaction  ;  for  instance,  a  sheet  of  zinc  covered  with  precipitated  copper 
gave  in  one  hour  at  2-2°C.  1'2  cc.  of  hydrogen,  and  at  98°C.  in  the 
same  time  528  cc.  The  temperature  of  the  liquor  in  the  vat  is  controlled 
by  a  worm  through  which  hot  water  or  steam  can  be  passed.  When 
the  liydrogenation  is  completed,  the  distillate  is  passed  on  to  the  recti- 
fying column. 
The  hydrogenating  action  of  metallic  couples  is  generally  sufficient 
for  the  entire  purification  of  the  distillate,  and  in  the  case  of  distillates 
from  grain  and  beet  molasses,  the  increase  in  the  yield  of  good 
flavored  alcohol  in  the  first  runnings  is  25  to  30  per  cent. 
But  this  treatment,  although  sufficient  for  many  distillates,  does  not 
sufficiently  improve  those  obtained  directly  from  beet,  and  in  these 
cases  M.  Naudin  completes  the  action  by  electrolysis  by  means  of 
electric  machines.  The  distillate  from  the  beet  is  first  left  in  contact 
with  the  copper-zinc  couple  a  sufficient  time  (two  days  or  more)  to 
ensure  its  complete  hydrogenation  and  then,  nearly  purified,  but 
having  still  a  slight  flavor  of  its  origin,  it  is  acidulated  by  means  of 
sulphuric  acid  and  sent  into  a  special  arrangement  of  voltameters. 
The  number  of  voltameters  coupled  varies  with  the  intensity  of  the 
action  required,  and  the  quantity  of  distillate  to  be  purified.  In 
practice,  in  a  factory  running  6,000  or  7,000  gallons  daily,  twelve 
voltameters  are  in  couple,  and  the  electrolytic  action  is  regulated  by 
disconnecting  or  placing  in  circuit  the  required  number.  It  is  evident 
that  in  this  operation  there  must  be  some  oxidizing  action,  and  to  this 
extent  it  would  appear  to  be  open  to  the  same  objection  as  the  proces- 
ses based  upon  oxidation. 
M.  Pictet  has  recently  announced  that  he  effects  the  purification  of 
alcohol  by  rectification  carried  on  at  a  low  temperature,  and  that  this 
operation  is  carried  on  in  a  large  scale  in  Paris.    The  distillates,  or 
