ON  PYROXYLIN. 
sive  matter,  178  is  the  greatest  yield  we  have  been  able  to  ob- 
tain. 
The  German  report  is  silent  on  the  subject  of  the  yield,  which, 
in  our  opinion,  constitutes  the  most  solid  basis  for  determining 
the  composition  of  pyroxylin.  We  do  not  say  that  the  exact 
determination  of  the  yield  of  cotton  in  pyroxylin  renders  use- 
less the  elementary  analysis  of  the  latter,  but  it  is  necessary 
that  the  analysis  should  agree  with  the  figures  representing  this 
yield. 
Our  experiments  on  the  yields  have  been  made  with  cotton  of 
good  quality,  previously  washed  in  a  boiling  solution  of  carbo- 
nate of  potash  or  soap,  and  then  freed  as  much  as  possible  from 
foreign  bodies,  particularly  from  cotton  seeds.  Before  being 
used  it  was  carefully  dried  in  a  Gay-Lussac  stove,  between  100c 
and  115° 
The  sulphuric  acid  marked  66°  on  the  Baume  'areometer, 
The  nitric  acid  had  a  density  of  1-500  at  9°  ;  it  was  yellow 
and  slightly  nitrous. 
The  relative  proportions  of  the  sulphuric  and  nitric  acids 
were  varied  so  as  to  present— 1.  The  composition  of  Lenk's 
mixture ;  2.  That  of  the  unequal  volumes  of  Bouchet ;  3.  Va- 
rious intermediary  proportions  between  2  and  3  of  sulphuric 
acid  for  1  of  nitric  acid. 
The  relative  proportions  of  acid  mixture  and  the  weight  of 
cotton  were  also  varied,  including  those  formerly  used  at  Bou- 
chet, and  those  indicated  by  General  Lenk,  until  the  weight  of 
the  acids  was  500  times  that  of  the  cotton. 
The  duration  of  the  immersion  of  the  cotton  in  the  acids 
varied  from  1  to  66  hours. 
In  all  these  experiments  the  yields  differed  very  little,  never 
exceeding  178  per  cent,  of  cotton. 
The  yield  in  manufactories  whether  at  Hirtenberg  or  Bouchet 
is  far  from  being  so  large  as  that  obtained  with  small  quantities 
in  the  laboratory.  In  fact,  General  Lenk  says  that  it  requires 
64-500  kils.  of  undried  cotton  to  produce  100  kilogrammes  of 
pyroxylin,  which  corresponds  to  a  yield  of  155.  Supposing  the 
cotton  to  contain  6  to  7  per  cent  of  moisture,  the  yield  of  dry 
cotton  at  Hirtenberg  would  have  been  from  165  to  167  per- 
cent. 
