Am^Ximrm  }   Analysis  of  Coal  Tar  Preparations.  487 
This  process  affords  an  approximate  idea  of  the  composition  of 
the  tar  oil,  but  it  maybe  still  further  extended  without  much  increase 
of  manipulative  details,  so  as  to  give  a  fuller  idea  of  the  disinfectant 
value  of  the  product,  in  a  manner  that  has  proved  extremely  useful 
to  us  in  the  examination  of  Jeyes'  Fluid  and  other  coal-tar  prepara- 
tions. We  refer  to  the  more  complete  isolation  of  the  constituents 
by  a  repetition  of  the  above  processes,  submitting  the  hydrocarbons 
and  tar  acids  to  fractional  distillation  and  weighing  the  different 
fractions. 
Determination  of  Hydrocarbons. — For  the  analysis  of  a  very  con- 
centrated coal  tar  preparation  like  Jeyes'  Fluid  50  grammes  suffices 
for  examination,  but  of  course  more  dilute  preparations  that  contain 
comparatively  small  quantities  of  the  disinfectant  principles  require 
that  a  larger  quantity  should  be  taken  to  obtain  equally  reliable 
results.  After  determination  of  the  specific  gravity  and  alkalinity 
of  the  preparation  a  weighed  quantity  is  diluted  with  an  equal  or 
even  with  the  double  volume  of  ordinary  ether,  and  then  extracted 
several  times  with  10  per  cent,  caustic  soda  solution.  The  amount 
of  soda  solution  employed  for  the  above  quantity  should  be  about 
100  cc.  for  the  first  shaking,  the  alkaline  liquor  then  run  ofT,  and  the 
ethereal  layer  containing  the  hydrocarbons  and  bases  again  shaken 
repeatedly  with  successive  portions  of  50  cc.  soda  solution  until 
nothing  further  is  removed.  This  stage  is  shown  by  the  colorless- 
ness  of  the  alkaline  layer,  or  by  the  absence  of  any  tar  acids  sepa- 
rating when  the  alkaline  liquor  is  acidified,  four  or  five  shakings 
generally  effecting  the  required  separation. 
The  ethereal  layer  is  further  washed  once  or  twice  with  water  to 
remove  the  greater  part  of  the  adherent  alkali,  and  the  alkaline 
liquors  and  washings  mixed  and  again  shaken  once  with  ether  to 
remove  any  naphtalene  or  other  hydrocarbons  that  may  have  been 
dissolved-in  the  alkaline  liquor,  or  rather  in  the  ether  dissolved  by 
the  water.  This  quantity  is  appreciable,  although  not  sufficient  to 
seriously  affect  the  analytical  results,  so  that  this  operation  may  be 
left  out,  although  a  fairly  liberal  use  of  ether  tends  to  increase  the 
accuracy  of  the  results. 
The  ethereal  solution  of  the  hydrocarbons  is  then  extracted  three 
or  four  times  with  about  20  cc.  of  dilute  (1:4)  sulphuric  acid  to 
remove  the  bases,  washed  with  water  to  remove  the  excess  of  acid, 
.and  then  dried  by  the  introduction  of  a  few  pieces  of  calcium 
