88 
ON  PYROXYLIN. 
At  Bouchet  the  cotton  is  steeped  in  vessels  containing  only 
2  litres  of  mixture  for  200  grammes  of  cotton,  and  the  steep- 
ing is  considered  complete  at  the  end  of  an  hour. 
About  70  per  cent,  of  non-combined  acids  are  pressed  out,  the 
cotton  being  then  watched  for  one  or  two  hours  in  the  river, 
freed  from  most  of  the  water  by  strong  pressure,  and  left  for 
twenty-four  hours  in  an  alkaline  ley  to  neutralise  the  last  traces 
of  acids.  Withdrawn  from  this,  it  is  a  second  time  washed 
in  the  river,  then  pressed,  and  finally  dried  on  a  light  canvas, 
through  which  a  ventilator  forces  cold  air. 
Soluble  glass  has  not  been  tried  at  Bouchet,  but  we  are  about 
to  show  that  it  is  not  so  beneficial  as  it  is  supposed  to  be  by  Gen- 
eral Lenk. 
Quantity  of  Pyroxylin  produced  by  a  given  quantity  of  Cel- 
lulose.— A  German  report  signed  by  MM.  Redtenbacher, 
Schrotter,  and  Schneider  gives  to  Lenk's  pyroxylin  the  form- 
ula— 
C12H707.3N05  or  C12H,3(NO4)O10, 
equivalent  to  the  following  composition  : — 
Carbon   24-24 
Hydrogen    .....  2-36 
Oxygen       .....  59-26 
Nitrogen   14-14 
100-00 
The  reaction  may  be  explained  in  two  ways  :  — 
1.  By  admitting  that  by  contact  with  the  mixture  of  nitric 
and  sulphuric  acids  the  cotton  loses  the  water,  which  is  re- 
placed by  the  first  of  these  acids — 
C12H10O10+3NO6=CJ3H7O7.3NO5+3HG. 
2.  By  supposing  that  the  hydrogen  of  the  cellulose  is  re- 
placed by  an  equal  number  of  equivalents  of  hyponitric  acid — 
C12H10O10+3NO-=C12H,3(NO4)O10+3HO. 
According  to  this  100  parts  of  cotton  ought  to  produce  183  . 
of  pyroxylin ;  but  though  in  more  than  100  experiments  we 
have  varied  the  proportions  of  the  bodies  producing  this  explo- 
