224 
ON  PYROXYLIN. 
heat,  that  in  some  cases  it  detonates,  and  in  others  apparently 
identical  it  is  destroyed  without  combustion.  Why  should  it 
not  be  the  same  at  a  low  temperature  ?  Why  should  we  not 
add  to  the  instances  of  simple  decomposition  those  of  detonation  ? 
The  analogy  is  so  evident  that  we  need  not  have  recourse  to 
the  supposition  of  imperfect  washing  to  explain  the  combustion 
of  pyroxylin. 
The  Hirtenberg  pyroxylin  itself  exploded  in  the  magazine  at 
Simmering,  and  in  the  investigation  made  July  31,  1862,  it  was 
merely  decided  that  the  accident  was  due  to  spontaneous  com- 
bustion. It  has  also  been  attributed  to  the  ordinary  powder 
also  contained  in  the  magazine,  but  this  supposition  is  in- 
admissible, as  for  several  centuries  there  has  been  no  known 
instance  of  spontaneous  combustion  of  gunpowder.  We  must 
not,  of  course,  as  was  done  in  an  Austrian  paper,  confound 
accidents  during  manufacture,  carelessness  of  workmen,  or 
faulty  mechanism,  with  the  explosions  produced  by  no  other 
cause  than  the  reactions  among  the  elements  of  the  compound. 
Comparison  of  Lenk's  Pyroxylin  with  those  of  Bouchet  rela- 
tive to  their  Propulsive  and  Blasting  Qualities. — It  remains  for 
us  to  give  the  results  of  the  experiments  made  with  Navet's 
pendulum  to  compare  the  propelling  powers  of  these  two  kinds 
of  gun-cotton.  Twenty-five  charges  were  fired  with  Lenk's  py- 
roxylin, fifteen  with  those  of  Bouchet,  three  grammes  for  each 
charge,  and  round  balls  weighing  each  25  gr.  50. 
Taking  first  the  medium  velocity  of  the  balls,  and  then  the 
greatest  and  the  least,  we  have— . 
Gun-cotton. 
Hirtenberg.  Bouchet. 
m.  m. 
Medium  velocity,  .  .  .  385*36  394-32 
Greatest    "  ...     441-53  485-94 
Least       "  ...     357-63        357  63 
Differences  much  greater  than  those  presented  by  the  above 
figures  are  sometimes  found  in  firing  from  the  same  specimen. 
For  instance,  the  pyroxylin  brought  from  Austria  by  General 
Lenk  was  fired  twice,  giving — 
m. 
On  February  17,  ....  374*40 
"  March  8,  .....  408-40 
