98  Analysis  of  Coal-tar  Coloring  Matters.  { Am  ^ig?rm' 
them.  The  object  of  Mr.  Green's  paper  was  to  submit  a  scheme  of 
analysis  formulated  into  tables,  such  as  are  used  in  qualitative  inor- 
ganic analysis.  Unfortunately,  his  MS.  and  proofs  of  the  paper  had 
miscarried,  and  he  was  compelled  to  give  a  resume  of  the  commu- 
nication. Taking  Weingartner's  scheme  as  the  basis,  Mr.  Green 
showed  that  we  may  first  divide  the  different  colors  according  to  their 
solubility  or  insolubility  in  water;  then  taking  those  which  are  solu- 
ble the  addition  of  10  per  cent,  aqueous  solution  of  tannin  determines 
whether  the  color  is  acid  or  basic,  the  latter  affording  a  precipitate 
and  the  former  none.  Next,  the  behavior  of  the  color  with  zinc 
dust,  plus  a  sufficiency  of  hydrochloric  acid  or  ammonia,  furnishes 
another  separation  into  three  classes,  viz.,  those  which  are  readily, 
or  slowly,  or  not  at  all,  reduced.  Again,  taking  those  which  are 
reduced,  we  may  separate  them  into  other  three  groups  :  {a)  those 
which  are  completely  reduced  and  cannot  be  reoxidized  ;  {b)  those 
which  by  means  of  chromic  acid  are  brought  back  to  their  original 
state,  or  something  like  it ;  and  (V)  those  which  spontaneously  reox- 
idize  in  the  air.  Azo  colors  may  also  be  divided  into  those  which 
do  or  do  not  dye  cotton. 
Water  insoluble  colors  may  be  divided  into  those  which  are  or 
are  not  soluble  in  caustic  soda  solution,  and  in  regard  to  their 
behavior  towards  zinc  dust. 
Mr.  Green  then  showed  the  meeting  some  of  the  reactions.  Tak- 
ing three  blues — a  thiocyanin,  a  roseaniline  derivative,  and  an  azo 
blue — he  showed  that  all  were  reduced  by  zinc  and  hydrochloric 
acid,  the  thiocyanin  color  reoxidizing  quickly,  as  was  evident  when 
some  of  the  solution  was  placed  on  a  piece  of  filtering  paper  ;  the 
roseaniline  color  was  seen  to  be  a  faint  yellow  ;  and  the  azo  color 
had  a  red  shade.  On  moistening  with  chromic  acid  the  roseaniline 
was  still  unchanged,  but  ammonia  vapor  brought  back  the  blue, 
wrhereas  with  the  same  oxidizer  the  azo  stain  was  changed  to  a 
secondary  color  not  affected  by  ammonia.  Similar  experiments 
were  shown  with  three  red  colors,  and  again  distinctive  reactions 
resulted. 
It  was  next  stated  that  sulphuric  acid  distinguishes  between 
coloring  matters  chemically  different,  although  belonging  to  the 
same  group.  That  was  shown  by  treating  three  scarlets  (alike  in 
shade  when  dissolved  in  water) — xylenene  dissolved  red  in  the 
acid,  crocein  brown-black,  and  Biebrich's  scarlet  gave  a  deep  blue. 
