474  Identification  of  Artificial  Silks.       \  A™koZri9um' 
The  apparatus  required  to  make  the  tests  consists  of  a  dozen 
small  plain  white  butter  dishes,  a  dozen  small  test-tubes  of  short 
length  and  not  over  half  an  inch  in  diameter,  and  a  spirit  lamp  or 
Bunsen  burner  to  supply  heat.  There  should  also  be  at  hand  two 
small  bottles  or  tubes  containing  red  and  blue  litmus  paper.  The 
entire  outfit  is  procurable  under  five  dollars. 
There  are  five  kinds  of  artificial  silk  generally  met  with  in  com- 
merce, as  follows: 
Collodium  Silk  (Strictly  nitro  silks). 
Cellulose  Silks. 
Viscose  Silks. 
Acetate  Silks.  '  • 
Gelatin  Silks. 
The  first  important  test  to  make  is  to  determine  whether  the  silk 
under  examination  is  made  from  gelatin  or  not. 
Take  one  of  the  test-tubes,  see  that  it  is  clean  and  dry  inside,  and 
place  at  the  bottom  of  it  a  small  tuft  of  the  silk  about  the  size  of  a 
small  pea  when  rolled  between  the  fingers.  In  the  open  end  of  the 
tube  insert  a  piece  of  red  litmus  paper,  bending  the  end  over  so  that 
the  strip  will  not  slide  down  the  tube. 
With  a  handle  made  of  several  folds  of  paper  around  the  neck 
of  the  tube  so  as  to  permit  one  to  hold  it  comfortably,  place  the  closed 
end  of  the  tube  in  the  flame  of  the  Bunsen  burner  or  spirit  lamp, 
giving  the  tube  a  slight  to  and  fro  motion  until  the  fibres  in  the  tube 
begin  to  char  and  vapors  are  seen  to  arise.  When  these  vapors  are 
observed  to  come  out  of  the  open  end  of  the  test-tube,  note  whether 
the  color  of  the  red  litmus  paper  changes  to  blue.  If  such  a  change 
takes  place  it  is  due  to  the  presence  of  ammonia  gas  resulting  from 
the  charring  of  the  fibres  and  which  could  only  come  from  gelatin 
silk.  These  vapors  may  also  have  the  odor  of  burning  horn  or  hair, 
which  odor  is  further  indicative  of  the  presence  of  gelatin. 
On  the  other  hand,  if  the  litmus  paper  does  not  change  color, 
acid  fumes  may  be  present  and  are  to  be  confirmed  by  repeating 
the  test,  but  using  blue  litmus  paper,  and  upon  it  turning  red, 
indicates  that  the  silk  may  be  any  one  of  the  four  above-named 
makes. 
To  distinguish  finally  between  the  several  artificial  silks  emitting 
acid  fumes  with  heat,  place  two  of  the  butter  dishes  side  by  side ; 
in  one,  place  some  of  the  silk  fibre  and  upon  it  pour  some  of  reagent 
No.  i,  and  let  soak  for  a  few  minutes,  and  then  afterwards  add  a 
