4^2  Dcnitration  of  Pyroxylin.  {^aSg&F* 
Samples  of  ordinary  photographic  collodion  film  and  thin  sheets 
of  celluloid  free  from  coloring  or  mineral  matter,  were  reduced  in 
a  bath  of  ammonium  sulphide. 
It  is  necessary  to  dilute  the  reducing  agent  somewhat  and  keep 
the  bath  cooled  by  immersion  in  water  during  the  early  stages,  or 
the  reduction  takes  place  with  such  rapidity  that  a  very  consider- 
able rise  of  temperature  results,  accompanied  by  a  deposit,  in  and 
on  the  material,  of  finely  divided  sulphur,  which  can  be  removed 
only  by  solvents.  A  too  rapid  reduction  and  consequent  rise  of 
temperature  is  also  not  without  seriously  injurious  effect  on  the 
tenacity  of  the  resulting  cellulose  film. 
After  washing  for  several  hours  in  running  water,  the  material 
is  dried  and  will  now  burn  quietly  like  wood  or  paper.  Analysis 
of  the  material  so  obtained  gave  the  following  result,  a  parallel 
analysis  of  ash-free  filter  paper  being  made  at  the  same  time  for 
comparison  : 
Denitrated  Pyroxylin.  Cellulose  from. 
,  «  ,  Ash-free  Paper. 
C,                                          41*86         42*03          4176  44-00 
H,     .                                        6-14           6*  18           6*07  6-32 
°»                                          50'68         50-47          50-85  49-68 
S,                                                                   -DO                —                     —  — 
Ash,  .                                        72           —          ....  - -  —  .  - 
ioo'oo  —  —  iocroo 
The  sheets  of  cellulose  obtained  by  the  denitrating  process  are 
very  much  reduced  in  area  and  increased  somewhat  in  thickness,  as 
compared  with  the  original  sheet  of  pyroxylin. 
Measurements  were  made  of  a  number  of  sheets  before  and  after 
treatment  to  obtain  figures  expressing  the  approximate  amount  01 
shrinkage. 
The  average  measures  were  : 
Length,       Breadth,  Thickne** 
Inches.        Inches.  Inch. 
Before  treatment,   15*0  io'o  '0057 
After  treatment,  ,  .  .  .  .    11-76  7-5  '007 
The  percentage  decrease  of  area  and  volume  (approx.)  were  as 
follows : 
