490  Analysis  of  Coal  Tar  Preparations.  {Ava^ttmtm- 
The  only  method  found  practicable  consisted  of  an  adaptation  of 
the  commercial  process  for  the  separation  of  phenols,  by  fractionally 
precipitating  the  alkaline  solution  of  the  tar  acids  with  small  quan- 
tities of  mineral  acid,  in  which  case  the  carbolic  acid  is  concentrated 
in  the  first  fraction,  and,  if  necessary,  the  treatment  repeated. 
Necessarily  the  results  obtained  increase  in  accuracy  with  the  quan- 
tity of  tar  acids  treated  and  by  operating  on  2Q0  grams  of  the  acids 
in  this  way  we  convinced  ourselves  that  the  above  preparation  con- 
tained less  than  one-quarter  per  cent,  carbolic  acid. 
Higher  homologues  of  phenol  than  the  cresols  are  not  found  in 
any  quantity  in  most  of  the  commercial  preparations,  and  the  tem- 
perature therefore  again  rapidly  rises  above  210°  C.  This  fraction 
should  therefore  be  collected  separately  and  weighed.  If  any  con- 
siderable quantity  still  remains  in  the  distillation  flask,  it  generally 
consists  of  resin  acids  and  their  anhydrides  derived  from  resin  soap 
added  for  purposes  of  emulsification.  These  commence  to  distil 
about  2500  C,  but  the  greater  part  passes  over  at  a  temperature 
above  that  registered  by  a  mercurial  thermometer,  and  hardens 
again  to  a  resin-like  mass  on  cooling.  From  the  analytical  as  well 
as  the  disinfectant  point  of  view  this  emulsifying  agent  is  far  prefer- 
able to  other  bodies,  like  gelatine  and  saponin,  that  are  employed 
ior  a  similar  purpose  in  some  preparations,  since  the  latter  form 
emulsions  in  the  analytical  processes  that  make  the  separation  of 
the  ethereal  layer  very  tedious,  and  considerably  increase  the  diffi- 
culties of  the  analyst. 
Determination  of  Bases. — The  basic  constituents  of  coal-tar  pre- 
parations are  extracted  from  the  hydrocarbons  with  dilute  sulphuric 
acid  in  the  manner  above  described,  after  the  removal  of  the  acid 
constituents.  They  include  pyridine  and  chinoline  and  their  homo- 
logues, the  separation  of  which  would  prove  a  difficult  and  unneces- 
sary task.  Two  methods  may  be  employed  for  their  estimation, 
either  of  which,  however,  only  gives  an  approximate  value,  the  titra- 
tion of  the  acid  solution  of  the  bases  with  a  standard  alkaloidal 
reagent  or  of  the  alcoholic  solution  with  standard  acid,  calculating 
the  amount  of  bases  from  an  empirical  combining  weight,  or  the 
formation  and  direct  weighing  of  their  neutral  salts.  We  adopted 
the  latter  process  as  the  simplest  and  as  affording  perhaps  the  most 
reliable  results,  the  sulphate  of  the  bases  being  prepared  in  prefer- 
ence to  the  hydrochlorides  as  recommended  in  some  text-books, 
