46 
COLORING  MATTERS  FROM  COAL  TAR. 
notice  successively  the  compounds  from  which  the  coloring  mat- 
ters may  be  formed,  and  the  coloring  matters  themselves,  de- 
scribing the  most  advantageous  and  best  known  processes  for 
obtaining  them. 
1.  Aniline, — Unverdorben  first  discovered  aniline  among  the 
products  of  the  dry  distillation  of  indigo,  in  1826.  As  it  formed 
crystallised  salts  with  acids  he  gave  it  the  name  of  crystalline. 
In  1840  Fritsche  made  anthranilic  acid  by  introducing  finely 
powdered  indigo  into  a  hot  and  strongly  concentrated  solution 
of  caustic  potash.  One  of  the  most  remarkable  properties  of 
this  acid  is  its  splitting  up  into  carbonic  acid  and  aniline  when 
distilled  with  quick  lime. 
Ci4H,NO,+2CaO=Ci2H,N+2(C02,CaO) 
Anthranilic  acid.  Aniline. 
Erdmann  first  observed  that  aniline  was  identical  with  the 
crystalline  of  Unverdorben.  Hoffman  afterwards  showed  that 
to  prepare  aniline  it  was  not  necessary  to  make  anthranilic  acid, 
but  that  it  sufficed  to  distil  indigo  directly  with  hydrated  caustic 
potash,  the  aniline  being  formed  in  consequence  of  a  real  oxida- 
tion of  the  indigo. 
Isatine  a  product  of  the  oxidation  of  indigo  by  weak  nitric 
acid  also  furnishes  aniline  on  distillation  with  caustic  potash, 
Runge,  1837,  first  announced  the  existence  of  three  volatile 
bases  in  coal  tar,  which  he  named  respectively  kyanol,  leukol 
and  pyrrhol.  Hoffmann  subsequently  demonstrated  that  kyanol, 
was  identical  with  aniline,  and  later  he  proved  that  leukol  was 
identical  with  quinoline,  a  base  which  Gerhardt  had  obtained  by 
distilling  the  cinchona  alkaloids  with  mineral  alkalies.  Another 
very  remarkable  method  of  forming  aniline  is  based  upon  the 
action  of  reducing  bodies  on  nitrobenzole.    Zinin,  by  saturating 
an  alcoholic  solution  of  nitrobenzole  with  ammonia,  and  then 
passing  sulphuretted  hydrogen  as  long  as  any  deposit  of  sulphur 
was  formed,  obtained  an  organic  alkali  which  he  called  benzidam, 
but  which  was  afterwards  proved  to  be  aniline. 
Ci^H^NO.+GHS  =Ci2H7N+4HO+6S. 
Nitrotenzole. 
