360  CONTRIBUTIONS  TO  THE  THEORY  OF  DYEING. 
fact  that  the  amorphous  cotton-gelatine  precipitated  from  its 
solution  in  cuprate  of  ammonia  (see  this  Journal  [2],  xxvii.  118) 
may  be  mordanted  and  dyed  like  ordinary  cotton.  In  like  man- 
ner, sulphate  of  baryta  and  other  pulverulent  mineral  bodies  may 
be  mordanted  and  dyed  with  decoctions  of  dyewoods. 
With  regard  to  the  nature  of  the  force  which  binds  the  color- 
ing matter  to  the  fibre — whether  or  no  it  be  chemical  attraction? 
Bolley  concludes  that  there  is  no  sufficient  reason  for  accepting 
the  view,  principally  developed  by  Chevreul  [and  by  Kuhlmann, 
Comptes  Rendus,  tomes  xlii.  xliii.  et  xliv.]  that  dyeing  is  a  di- 
rect consequence  of  chemical  affinity.  He  believes  that  the 
power  possessed  by  fibres  of  attracting  certain  bodies — whether 
salts  or  coloring  matters  or  both — from  their  solutions,  belongs 
to  that  class  of  phenomena  which  results  from  the  action  of  fine- 
ly divided  mineral  or  organic  bodies  (charcoal  or  bone  black  for 
example,)  on  such  solutions.  The  distinction  between  the  action 
of  charcoal  and  of  fibres  in  thus  removing  saline  matters,  or 
dyes,  from  their  solutions  is  one  of  degree  only,  the  nature  of  the 
operation  being  identical  in  either  case. 
A  given  weight  of  well  prepared  animal  charcoal  can,  as  a 
rule,  deprive  a  larger  quantity  of  liquid  of  its  color  than  an 
equal  weight  of  wool  or  silk.  Neither  wool  or  silk  can  remove 
all  the  color  from  a  solution  as  charcoal  can,  their  effect  extend- 
ing only  to  a  certain  degree  of  dilution  beyond  which  the  parti- 
cles of  coloring  matter  resist  their  attraction.  Dyes  which  may 
have  been  taken  up  without  a  mordant  by  wool,  or,  especially, 
by  silk,  may  be  removed  again  by  long  washing  in  water,  a  fact 
which  is  not  true  in  the  case  of  charcoal,  or  only  to  a  very  slight 
extent.  The  attraction  of  coloring  matters  for  water  is  there- 
fore more  completely  overcome  by  charcoal  than  by  animal  fibre ; 
but  even  the  cleanest  vegetable  fibres,  as  unmordanted  and 
completely  bleached  cotton,  possess  a  certain  power  of  attracting 
coloring  matter.  That  cotton  should  have  less  effect  in  this  mat- 
ter than  wool  or  silk  is  not  surprising  in  view  of  the  great  differ- 
ence in  the  structure  of  cotton  fibre  as  compared  with  that  of 
the  two  substances  last  mentioned.  It  is  well  known  that  wool 
and  silk  in  consequence  of  their  physical  constitution  belong  to 
the  class  of  strongly  absorbent  or  hygroscopic  substances,  i.  e* 
in  consequence  of  a  certain  porosity  or  looseness  of  their  parti- 
