Am-^.r;1f9h3arn1-}  Analysis  of  Coal-tar  Coloring  Matters.  99 
In  concluding,  Mr.  Green  explained  the  theory  of  the  zinc  dust 
reaction.  Taking  all  these  colors  as  quinone  compounds  he  thought 
that  those  which  reoxidize  readily  are  ortho-derivatives  and  those 
which  reoxidize  slowly  are  para-derivatives :  magenta  (roSeaniline) 
belongs  to  the  latter  and  phosphine  (chrysaniline  derivative)  to  the 
former. 
The  discussion  consisted  mainly  of  questions. 
Dr.  Alder  Wright  asked  how  far  the  scheme  could  be  utilized  for 
mixtures  of  colors.  Mr.  Bevan  wanted  to  know  how  to  proceed  in 
applying  the  reactions  to  colored  fabrics.  Mr.  Blount  asked  if  it 
was  the  case  that  the  majority  of  artificial  blues  are  soluble  in  alco- 
hol, even  when  on  the  fabric,  and  could  this  be  used  as  a  means  of 
distinguishing  between  them  and  indigo. 
The  Chairman  (Mr.  W.  Thorp)  suggested  that  some  indication 
should  be  given  in  the  tables  of  what  the  chemical,  nature  of  the 
colors  is,  as  the  commercial  names  do  not  suffice  for  this. 
Mr.  Green,  in  replying,  said  that  it  was  difficult  to  analyze 
mixtures  of  colors,  and  his  tables  did  not  pretend  to  do  that,  but  it 
was  often  comparatively  easy  to  tell  whether  a  color  was  a 
mixture  or  not.  If  it  be  finely  ground  and  a  little  sprinkled  on  a 
piece  of  wet  filtering  paper,  then  held  up  to  the  light,  it  would  be 
seen  that  the  margins  of  the  particles  differed  in  color  if  there  were 
different  dyes  present.  So  also  in  regard  to  the  behavior  of  the 
mixture  when  a  little  of  it  was  sprinkled  on  sulphuric  acid,  or  when 
the  matter  of  ten  swatches  of  cotton  were  dipped  into  the  dye-bath 
under  different  conditions,  or  whether  wool  and  cotton  behaved 
differently.  These  and  other  methods  could  be  utilized,  but  it  was 
not  possible,  he  thought,  to  deal  more  systematically  with  mixtures. 
Colors  could  be  extracted  from  fabrics  with  alcohol  or  carbonate  of 
soda,  and  the  table  tests  then  applied.  All  basic  blue  colors  could  be 
removed  from  fabrics  by  alcohol,  but  not  the  acid  ones.  It  was 
impossible  to  use  either  formulae  or  constitutional  names  in  the 
tables,  and  on  the  whole  the  commercial  names  were  most  useful  in 
this  instance.  In  reply  to  Mr.  Crowther,  he  stated  that  the  spec- 
troscope was  sometimes  useful  in  this  connection,  and  a  very  simple 
way  of  ascertaining  whether  a  dye  was  a  mixture  or  not  was  to 
allow  a  little  to  soak  up  strips  of  filtering  paper,  when  by  capillarity 
such  a  thing  as  picric  acid,  for  instance,  would  reveal  itself  even  in 
^  roseaniline  solution. 
