526 
DETECTION  OF  ALCOHOL. 
inches  long,  may  be  slipped  into  it.  Into  this  tray  some  platinum- 
blaek  is  put,  and  at  each  end  of  it  is  placed  a  piece  of  blue 
litmus-paper  moistened  with  distilled  water,  which  must  be  par- 
tially in  contact  with  the  platinum-black.  The  tray  is  now  pushed, 
by  means  of  a  wire  hook,  to  the  place  where  the  neck  of  the 
retort  passes  into  its  belly,  and  the  water-bath  is  heated  by  means 
of  a  spirit-lamp.    The  operation  may  be  facilitated  by  filling  the 
water-bath  with  a  solution  of  chloride  of  calcium  or  sodium, 
instead  of  water.    As  alcohol  boils  at  a  lower  temperature  than 
water,  it  of  course  is  the  first  to  be  driven  off.    As  soon,  there- 
fore, as  the  first  water-drops  begin  to  condense  in  the  neck  of 
the  retort,  that  portion  of  the  litmus-paper  which  is  in  contact 
with  the  platinum-black  becomes  reddened,  whilst  that  portion 
which  is  turned  towards  the  belly  of  the  retort  still  remains  blue, 
and  thus  at  once  shows  that  the  acid  did  not  come  out  of  the 
retort,  but  was  only  formed  in  contact  with  the  platinum-black. 
When  the  heat  has  been  applied  for  some  time,  and  single  drops 
begin  to  run  from  the  neck  of  the  retort,  without  any  reddening 
of  the  litmus-paper,  we  may  conclude  with  certainty  that  no 
trace  of  alcohol  was  contained  in  the  substance  under  examina- 
tion.   But  if,  on  the  contrary,  the  litmus-paper  is  quickly  and 
strongly  reddened,  and  it  is  desired  to  produce  further  proof  of 
the  presence  of  alcohol,  the  tray  is  again  to  be  drawn  out  of  the 
neck  of  the  retort ;  the  latter  is  then  bent  down  a  little  more,  a 
receiver  is  attached  to  it,  and  distillation  is  continued,  until  the 
distillate  amounts  to  several  drachms,  during  which  the  receiver 
is  cooled  by  a  cloth  soaked  in  cold  water.    The  distillate  is  then 
transferred  into  a  small  retort,  and  about  the  same  quantity  of 
fused  chloride  of  calcium  ;  or  if  this  be  not  at  hand,  wTell-dried 
chloride  of  sodium  is  added  to  it.     This  retort  is  then  put  upon 
the  water  bath  in  pure  water,  a  receiver  is  attached  to  it,  and 
distillation  continued  as  long  as  anything  passes  over.     A  few 
drops  of  this  second  distillate  may  now  be  added  to  a  mixture  of 
bichromate  of  potash  and  sulphuric  acid,  to  obtain  the  alcoholic 
reaction.     The  remainder  of  the  distillate  may  be  made  use  of 
to  ascertain  the  specific  gravity ;  but  this,  when  operating  upon 
such  small  quantities,  not  only  requires  fine  apparatus,  but  also 
much  skill,  and  must  consequently  often  remain  undone.    A  por- 
tion of  the  fluid  may  afterwards  be  poured  into  a  metallic  or  por- 
