ON  PYROXYLIN. 
the  Bouchet  pyroxylin,  the  product  of  the  immersion  of  cotton 
in  a  mixture  of  monohydrated  nitric  acid  and  sulphuric  acid  at 
66°.    The  two  methods,  however,  differ  in  several  respects. 
Thus,  the  proportions  of  the  two  acids  are  not  exactly  the 
same,  Lenk's  mixture  being  composed  of  one  part  of  nitric  acid 
to  three  of  sulphuric  acid  ;  that  of  Bouchet,  under  the  name 
of  unequal  volumes,  is  prepared  with  one  part  of  the  first  of 
these  acids  and  two  of  the  second,  equivalent  in  weight  to  1  per 
246.  The  above-mentioned  memoir  gives  as  being  most  suc- 
essful  a  mixture  of  three  volumes  of  nitric  acid  and  seven  of 
sulphuric  acid  (by  weight  1  to  2*86),  proportions  very  nearly 
those  given  by  General  Lenk. 
At  Ilirtenberg  the  cotton  is  steeped  in  portions  of  100  gram- 
mes in  30  kilogrammes  of  the  mixture.  It  is  withdrawn  from 
the  bath  after  being  shaken  in  it  for  an  instant,  and  each  time 
the  quantity  of  mixture  absorbed  by  the  cotton  is  replaced  by  a 
fresh  amount.  These  operations  are  continued  indefinitely,  the 
weight  of  the  mixture  being  always  300  times  that  of  the  cot- 
ton. 
When  the  desired  quantity  of  cotton  has  been  steeped,  it  is 
put  into  a  receiver  and  allowed  to  remain  forty-eight  hours 
impregnated  by  the  acids.  It  is  then  placed  in  a  strainer, 
where  most  of  the  uncombined  acids  are  expelled  in  a  few  min- 
utes. 
It  is  freed  from  the  remainder  in  a  stream  of  water  in  which 
it  is  washed,  and  where  it  remains  immersed  for  six  weeks, 
when  it  is  strained  a  second  time,  boiled  for  two  or  three  min- 
utes in  a  solution  of  carbonate  of  potash  of  2°  Baume.  After 
a  third  and  last  straining  the  cotton  is  dried  in  the  air  if  the 
weather  is  favorable ;  if  not,  in  a  stove  of  which  the  tempera- 
ture is  not  allowed  to  exceed  20°  C. 
General  Lenk  has  latterly  made  use  of  a  solution  of  soluble 
glass  of  12°  Baume\  The  cotton  prepared  as  above  is  soaked 
in  it,  dried,  and  exposed  to  the  air  for  a  sufficient  time  to  allow 
the  carbonic  acid  of  the  atmosphere  to  combine  with  the  soda 
of  the  glass,  which  determines  the  precipitation  of  an  insolu- 
ble silicate,  which,  according  to  General  Lonk,  »  encloses 
the  fibres  of  the  cotton,  and  prevents  the  development  of 
gases." 
