628  Detection  of  Higher  Alcohols.  {^D^iSIf™" 
cient  water  is  added  to  redissolve  the  salt  that  is  precipitated,  and 
then  60  to  70  cc.  of  carbon  bisulphide,  and  the  mixture  is  well 
agitated.  After  a  short  time,  the  bisulphide  is  transferred  to  a 
smaller  similar  vessel,  and  the  extraction  is  repeated  a  second  and 
third  time  with  similar  quantities  of  carbon  bisulphide,  the  whole  of 
the  latter  being  transferred  to  the  second  vessel.  In  order  to 
separate  the  alcohols  from  the  bisulphide,  the  latter  is  mixed  with 
sufficient  concentrated  sulphuric  acid  (about  2  cc.)  to  form  a  heavier 
layer  at  the  bottom  of  the  vessel,  and,  after  vigorous  agitation,  the 
acid  is  transferred  to  a  smaller  vessel.  The  extraction  is  repeated 
several  times  with  I  cc.  of  acid  each  time,  and  the  various  quantities 
of  acid  are  mixed,  heated  at  50-600,  and  a  current  of  air  passed 
over  the  surface  of  the  liquid  until  all  the  bisulphide  is  expelled.  An 
equal  volume  of  glacial  acetic  acid  is  then  added,  and  the  mixture 
heated  on  a  water-bath  at  about  1000  for  a  quarter  of  an  hour,  the 
flask  being  fitted  with  a  reflux  condenser.  When  the  action  is 
complete,  the  contents  of  the  flask  are  poured  into  100  cc.  of 
saturated  salt  solution  If  higher  alcohols  were  originally  present* 
the  corresponding  acetates  separate  and  form  an  upper  layer,  the 
volume  of  which  can  be  measured  by  any  of  the  usual  methods,  the 
liquid  being  previously  cooled  to  150.  The  number  of  cubic  centi- 
metres of  acetates  multiplied  by  0-8  gives  the  percentage  of  higher 
alcohols  in  the  alcohol  examined. 
If  in  the  preliminary  test  an  oily  upper  iayer  separates,  only  25  cc. 
of  the  alcohol  should  be  taken  and  mixed  with  1 00  cc  of  saturated 
salt  solution  and  8  to  10  cc.  of  water.  The  quantity  of  carbon 
bisulphide,  however,  ought  not  to  be  reduced,  and  all  the  other 
operations  are  conducted  in  the  manner  described. 
The  carbon  bisulphide  dissolves  only  butyl  and  amyl  alcohols,  and 
if  propyl  alcohol  is  sought  for,  the  salt  solution  that  has  been  extracted 
with  bisulphide  is  filtered  and  distilled  until  an  alcoholometer  in  the 
receiver  marks  500.  The  quantity  of  propyl  alcohol  in  the  distillate 
is  estimated  by  titration  with  permanganate  (Barbet)  or  by  Gossart's 
method. 
Alcohol  in  the  distillery  residues  known  as  "  essential  oils  "  may 
be  determined  by  a  modification  of  this  method.  500  cc.  is  agitated 
with  an  equal  volume  of  salt  solution,  and  the  latter  is  extracted  with 
three  successive  quantities  of  carbon  bisulphide  and  afterwards  dis- 
tilled.   The  alcoholic  strength  of  the  distillate,  corrected,  if  neces- 
