A^'ctJoror;r9hitm'}       Identification  of  Artificial  Silks.  475 
few  drops  of  reagent  No.  2.  In  the  second  dish  put  some  of  the 
fibre  and  a  small  amount  of  reagent  No.  3,  and  note  carefully  what 
changes  in  color,  if  any,  take  place.  If  both  samples  show  a  dis- 
tinct yellow  coloration,  the  silk  is  Acetate  Silk. 
On  the  other  hand,  if  the  coloration  is  blue,  the  silk  may  be 
either  collodium,  cellulose  or  viscose  silk,  which  is  confirmed  if  the 
coloration  shown  in  the  second  dish  is  reddish-violet.  To  differen- 
tiate between  these  three  silks  just  mentioned,  place  a  small  tuft  of 
the  fibres  in  a  dry  dish  and  pour  upon  it  a  small  amount  of  cold 
concentrated  sulphuric  acid  (No.  4).  If  the  silk  dissolves  rapidly, 
the  specimen  is  either  collodium  or  viscose  silk ;  cellulose  silk,  i.e., 
Pauly,  Fremery,  etc.,  dissolves  slowly. 
Confirmatory  tests  are  made  in  test-tubes  with  the  chromic  acid 
solution  (No.  5)  in  the  cold,  when  these  three  silks  dissolve  grad- 
ually, and  upon  the  tube  being  heated,  dissolve  quickly.  When 
treated  in  the  same  manner  with  warm  caustic  potash  solution 
(No.  6)  these  three  silks,  together  with  the  acetate  silk  show  a  dis- 
tinct swelling,  while  gelatin  silk  dissolves  rapidly  and  completely. 
The  copper  oxide  ammonia  test  (No.  7)  when  applied  in  a  test- 
tube  first  causes  a  swelling  and  dissolves  collodium  and  viscose  silks, 
but  acetate  silk  swells  without  dissolving,  and  gelatin  silk  takes 
a  bluish-violet  coloration  without  dissolving. 
The  nickel-oxide-ammonia  reagent  (No.  8),  when  applied  both 
cold  and  warm  to  a  sample  of  artificial  silk  in  the  test-tube,  causes 
a  swelling  of  the  fibres  but  without  dissolving  them.  This  applies 
to  collodium,  cellulose,  viscose,  and  acetate  silk,  but  not  to  gelatin 
silk,  which  latter  takes  a  brown  coloration  without  dissolving. 
The  alkaline-copper-glycerin  solution  (No.  9)  has  no  action  even 
after  long  boiling  upon  the  first  four  silks  above  mentioned,  but 
gelatin  silk  dissolves  after  a  short  time. 
A  convenient  reagent  for  artificial  silk  is  the  concentrated 
sulphuric  acid-diphenylamine  solution  (No.  10)  which  has  been 
extolled  as  the  one  reagent  for  this  class  of  work,  but  as  a  matter 
of  fact  its  usefulness  is  limited  exclusively  to  differentiate  only  the 
nitro  silks  from  the  others.  With  nitro  silks  of  the  Chardonnet 
type,  it  causes  a  distinct  blue  coloration,  while  the  other  silks 
remain  uncolored.  This  diphenylamine  reaction  lasts  but  a  com- 
paratively short  time,  reaching  its  maximum  intensity  within  five 
minutes  after  adding  the  reagent,  when  it  gradually  disappears. 
In  order  to  be  in  the  position  where  one  can  absolutely  and 
