Amsiptr;iS2arm'}  Analysis  of  Coa,  Tar  Preparations.  489 
character  that  they  dissolve  in  not  too  dilute  solutions  of  alkalies. 
For  their  determination  the  alkaline  liquors  removed  from  the  hydro- 
carbons in  the  previous  experiment  are  subjected  to  further  treat- 
ment. Without  driving  off  the  ether  dissolved  in  the  liquors  they 
are  made  decidedly  acid  with  sulphuric  acid,  and  the  liberated  tar 
acids  that  rise  to  the  top  of  the  solution  are  removed  in  a  separat- 
ing funnel.  The  acid  liquor  is  then  shaken  twice  with  small  quanti- 
ties of  ether, and  the  ethereal  solution  added  to  the  remainder  of  the 
tar  acids.  The  acid  liquor  now  only  contains  inorganic  bodies, 
either  originally  present  in  the  preparation  or  introduced  during  its 
analysis,  and  traces  of  bases  that  owing  to  their  solubility  in  water 
were  not  entirely  removed  from  the  solution  by  ether  when 
alkaline. 
The  ether  is  distilled  off  on  the  water-bath  from  the  tar  acids 
after  they  have  been  washed  with  water  and  dried  with  calcium 
chloride.  The  residual  acids  are  then  introduced  into  a  weighed 
fractionating  flask  of  suitable  size  with  the  aid  of  ether,  and  sub 
jected  to  distillation  in  the  same  way  as  the  hydrocarbons.  Carbolic 
acid  boils  at  1830  C,  whilst  the  three  homologous  cresols  which 
constitute  the  chief  constituents  of  cresylic  acid  boil,  respectively, 
about  1850,  1950  and  2000  C.  As  soon  as  the  last  traces  of  ether 
have  been  distilled  off,  the  temperature  rapidly  rises  above  1800  C, 
when  the  phenols  commence  to  distil  over,  although,  owing  to  the 
proximity  of  their  boiling  points,  it  is  impossible  to  separate  them 
to  any  extent  by  fractional  distillation. 
As  carbolic  acid  possesses  very  dangerous  toxic  properties,  whilst 
the  homologous  cresols  are  equally  or  even  more  efficient  as  disin 
fectants,  and  at  the  same  time  comparatively  innocuous  to  the  human 
system,  it  is  preferable  that  carbolic  acid  should  not  be  included  to 
any  great  extent  in  the  acid  constituents  of  coal-tar  preparations. 
As  it  is  stated  that  Jeyes'  Fluid,  which  contains  about  40  per 
cent,  of  acid  constituents,  and  may  therefore  be  regarded  as  possess 
ing  very  high  disinfectant  properties,  is  free  from  carbolic  acid,  we 
endeavored  to  determine  whether  it  was  possible  to  detect  small 
quantities  of  this  substance  in  a  mixture  of  cresols  and  analogous 
compounds.  Operating  upon  small  quantities  this  is  impossible,  as 
the  ordinary  color  tests  for  carbolic  acid  and  the  formation  of  an 
insoluble  bromine  compound  are  useless,  since  the  same  reactions 
occur  with  the  higher  phenols. 
