544     MANUFACTURE  AND  PROPERTIES  OF  ANILINE  COLORS. 
nitrobenzine  C12H5N04,  distilling  at  213°,  which  by  reducing 
agents  gives  aniline  C12H7N,  distilling  at  182°. 
Toluol,  C14H8,  distils  at  114°;  by  nitric  acid  it  gives  nitrotoluol, 
C14H7N04,  "which  forms  toluidine,  0wH9N,  distilling  at  198°. 
In  this  series  of  homologous  hydrocarbides,  benzol,  toluol, 
xylol,  cumol,  cymol,  the  densities  diminish  in  proportion  as  the 
equivalent  and  the  boiling-point  rise  ;  and  this  law  holds  not  only 
for  hydrocarbides,  but  for  their  nitrogenized  derivatives,  for  the 
alkaloids  derived  from  them,  and  also  for  the  corresponding 
phenols. 
Thus  a  hydrocarbide  distilling  at  80°  will  have  a  density  of 
0*885  ;  of  another,  distilling  at  110°  or  114°,  the  density  will  be 
only  0-870. 
The  density  of  a  nitrobenzol  distilling  at  213°  to  220°  would 
be  1-200  to  1-210,  while  that  of  a  nitrotoluol  distilling  at  220° 
to  230°  would  be  1-180  to  1-190. 
Pure  aniline,  C12H7N,  distilling  at  182°,  would  have  a  density 
of  1*028  ;  pure  toluidine,  C14H9N,  distilling  at  198°,  would  have 
a  density  of  1-001  to  1-002. 
Phenic  phenol,  C12H602,  is  denser  than  cresylic  phenol,  C14H802. 
Neither  pure  aniline  nor  pure  toluidine  produces  coloring 
matter. 
The  best  results,  both  as  to  beauty  and  quantity,  and  with  both 
red  and  violet,  have  been  obtained  with  a  mixture  of  70  per  cent, 
of  toluidine  and  30  per  cent,  of  aniline — that  is  to  say,  2  equiva- 
lents of  the  one,  and  1  equivalent  of  the  other.  These  propor- 
tions agree  perfectly  with  the  formula  ascribed  by  Dr.  Hofmann 
to  rosaniline.  The  object  in  view  is  then  to  obtain  a  commercial 
aniline  thus  composed. 
The  fractional  distillation  of  commercial  aniline  for  this  pur- 
pose is  a  difficult  operation.  The  distillation  of  nitrobenzol  is 
not  only  dangerous,  but  expensive.  It  is  better  to  endeavor  to 
separate  the  hydrocarbides  serving  for  the  fabrication  of  aniline. 
Though  this  is  not  the  usual  operation,  it  appears  to  us  the  only 
rational  one  if  aniline  with  an  unvarying  composition  is  desired. 
The  first  method  of  separating  hydrocarbides  is  due  to  Mans- 
field, who,  in  1848  and  1849,  produced  the  hydrocarbides  of  coal- 
tar  and  their  derivatives,  and  indicated  a  great  many  applica- 
