132         ACTION  OF  BICHROMATE  OF  POTASSA  IN  DYEING. 
twenty  minutes  to  half  an  hour,  previous  to  its  being  worked 
in  the  dye-bath.  It  is  generally  believed,  that  the  action  of 
this  substance  is  of  an  oxidizing  nature  ;  to  test  the  accuracy 
of  this  opinion  we  had  recourse  to  the  following  experiments  : — 
1st.  A  piece  of  cloth  was  boiled  for  twenty  minutes  in  a  di- 
lute solution  of  permanganate  of  potash — the  solution  became 
green,  proving  the  reduction  of  the  permanganate.  The  cloth 
was  then  well  washed,  and  dyed  with  logwood  and  chloride  of 
tin  (tin  spirits)  in  the  usual  manner — a  color  resulted,  by  no 
means  equal  in  brilliancy,  body  or  tint  to  that  obtained  by 
using  bichromate  of  potash. 
2nd.  A  fresh  piece  of  cloth  was  immersed  in  a  cold  solution 
of  permanganate,  allowing  it  to  stand  until  the  solution  became 
green  ;  but  with  no  better  results  than  in  the  last  experiment. 
3d.  The  same  experiment  as  the  last  substituting  a  cold  so- 
lution of  ferrate  of  potash  for  the  permanganate,  with  similar 
results. 
4th.  The  cloth  was  boiled  in  a  solution  of  pure  chromic  acid, 
previous  to  being  subjected  to  the  dye-bath.  The  color  obtained 
in  this  experiment  more  resembled  a  bronze  than  the  beautiful 
blue  produced  by  bichromate  of  potash.  These  experiments 
show  that  the  cloth  does  not  require  to  be  oxidized  to  prepare  it 
for  taking  on  the  dye ;  indeed,  even  without  the  direct  evidence 
of  experiment,  it  seems  almost  impossible  to  reconcile  the  idea 
of  oxidation  with  bichrome ;  for,  in  dyeing  with  logwood  on  the 
large  scale,  it  is  well  known  that  the  cloth  retains  the  yellow 
color  of  that  salt  and  not  of  the  green  sesqui-oxide  of  chro- 
mium, which  it  would  do,  if  the  bichromate  became  reduced  by 
the  organic  tissue. 
A  piece  of  cloth  was  next  boiled  in  a  solution  of  bichromate 
of  potash,  and  well  scoured,  and  rinsed,  the  cloth  retaining  a 
slight  yellow  color,  after  which  it  was  burnt,  and  the  ashes  sub- 
jected to  chemical  tests  for  the  presence  of  oxide  of  chromium  ; 
formed  by  the  reduction  of  the  chromate  by  the  organic  matter 
at  a  high  temperature.  The  existence  of  this  compound  in  the 
ashes,  together  with  the  fact  of  the  cloth  being  yellow  and  not 
green  after  mordanting  with  bichrome  and  scouring,  gave  abun- 
dant proof  of  the  fact  that  the  bichrome  itself  enters  the  cloth 
and  remains  firmly  fixed  in  the  fibre,  even  after  repeated  wash- 
