134 
Determination  of  Alcohol. 
(Am.  Jour.  Pharixl. 
\      March,  1909. 
necessary  a  second  time  with  petroleum  and  then  drawn  off  into  a  distillation 
flask.  Meanwhile  the  petroleum  layers  are  washed  successively  with  25  c.c. 
of  saturated  common  salt  solution,  and  the  washings  added  to  the  main  bulk, 
which  is  neutralized  if  necessary,  and  then  distilled  and  the  distillate  made 
up  to  100  c.c. 
In  the  foregoing  method  it  will  be  noted  that  the  objectionable 
ether,  chloroform,  oils,  etc.,  are  removed  before  the  sample  is  sub- 
jected to  distillation.  In  the  following  method  taken  from  the 
"  Bericht  der  technischen  Priifungstelle  des  Reichsschatzamtes  iiber 
technische  Arbeiten  auf  dem  Gebiete  der  Branntweinsteuer-Befrei- 
ungsordnung,"  for  October  I,  1905,  to  September  30,  1907,  the 
interfering  substances  are  removed  from  the  distillate.  An  outline 
of  this  method  follows : 
One  hundred  grammes  of  the  preparation  are  mixed  with  100  Gm.  of 
water  and  distilled  until  about  150  Gm.  of  distillate  have  been  obtained.  The 
distillate  is  collected  in  a  special  "  burette,"  the  condenser  rinsed  with 
10  c.c.  of  water  which  is  added  to  the  contents  of  the  burette,  and  the  united 
liquids  shaken  in  the  burette  for  three  minutes  with  50  c.c.  of  petroleum 
benzine  of  a  boiling-point  of  from  1600  to  1800  and  a  gravity  of  from  0.785 
to  0.790.  After  separation  of  the  layers,  the  lower  aqueous  layer  which  con- 
tains the  alcohol  is  run  out  into  a  300  c.c.  flask.  The  benzine  layer  in  the 
burette  is  shaken  out  three  times  with  40  c.c.  water  and  the  aqueous  wash- 
ings added  to  the  liquid  in  the  flask. 
The  burette  is  next  emptied  and  cleaned,  and  the  united  liquids  in  the 
flask  returned  to  the  burette,  rinsing  the  flask  out  once  with  water  into  the 
burette.  The  contents  are  again  shaken  for  three  minutes  with  30  c.c.  of 
the  petroleum  benzine.  Should  the  layers  separate  with  more  difficulty,  the 
separation  may  be  assisted  by  the  introduction  of  some  more  water.  After 
separation  again,  the  lower  aqueous  layer  is  run  off  into  a  tared  dry  300  c.c. 
flask,  the  residual  liquid  washed  out  twice  more  with  20  c.c,  water,  the  wash- 
ings returned  to  the  flask,  and  the  weight  of  the  united  liquids  determined. 
By  the  addition  of  water,  this  weight  is  brought  up  to  a  round  number. 
After  shaking,  and  filtering  through  a  dry  filter,  the  alcoholic  content  of 
100  Gm.  is  determined  by  means  of  an  alcoholometer,  and  the  amount  cal- 
culated for  the  entire  liquid,  and  hence  for  the  100  Gm.  of  original  prepara- 
tion taken. 
Example:  After  distillation  and  treatment  twice  with  petroleum  benzine, 
the  liquid  weighs  236  Gm.  It  is  brought  up  to  240  Gm.  with  water,  shaken, 
filtered,  and  30  Gm.  of  alcohol  found  in  100  Gm.  by  means  of  the  alcohol- 
ometer. 
24°  X30    _  y2^  tj_,e  per  cent  ]3y  weight  of  alcohol  in  the  preparation. 
100 
We  now  come  to  the  second  great  difficulty,  namely,  the  mechan- 
ical or  physical  one,  consisting  in  the  tendency  of  the  solution  to 
