524        EMPLOYMENT  OF  NITROGLYCERINE  IN  QUARRIES. 
From  the  first  we  have  considered  that  the  nitroglycerine 
should  be  prepared  on  the  spot ;  it  always  seemed  to  us  the 
transport  of  an  explosive  compound  of  such  frightful  power 
ought  not  to  be  allowed  either  by  land  or  water.  The  terrible 
accidents  which  have  happened  at  Aspinwall  and  at  San  Fran- 
cisco, justify  these  fears,  and  the  transport  of  nitroglycerine 
should  be  positively  forbidden. 
After  having,  with  M.  Keller's  assistance,  studied  in  my  la- 
boratory the  different  processes  of  the  preparation  of  nitroglyce- 
rine (mixtures  of  glycerine  with  concentrated  sulphuric  acid  and 
nitrates  of  potash  and  soda  or  with  nitric  acids  of  different  con- 
centrations), we  have  determined  on  the  following  method  of 
manufacture,  which  is  performed  in  a  wood  cabin,  constructed 
in  one  of  the  quarries. 
1.  Preparation  of  Nitroglycerine. — We  begin  by  mixing  in  an 
earthenware  vessel  placed  in  cold  water  some  fuming  nitric  acid 
at  49°  or  50°  Baume  (1*51 — 1*53)  with  twice  its  weight  of  the 
strongest  sulphuric  acid.  These  acids  are  purposely  prepared  at 
Dieuze,  and  sent  on  to  Saverne.  At  the  same  time  we  evaporate 
in  a  pot  some  commercial  glycerine  free  from  both  lime  and  lead, 
until  it  makes  30°  or  31°  Baume  (1-26— 1-27).  This  concen- 
trated glycerine  should,  after  cooling,  have  a  syrupy  consist- 
ence. 
The  workman  then  throws  3300  grammes  of  a  mixture  of  sul- 
phuric and  nitric  acids  well  cooled  into  a  glass  flask  (a  pot  of 
earthenware  or  a  capsule  of  porcelain  might  equally  be  employed) 
placed  in  a  trough  of  cold  water,  and  then  he  slowly  pours  into 
it,  stirring  it  continually,  500  grammes  of  glycerine.  The  thing 
to  be  observed  is  the  avoidance  of  any  sensible  heating  of  the 
mixture,  which  would  determine  a  tumultuous  oxidization  of  the 
glycerine  and  the  production  of  oxalic  acid.  For  this  reason  it 
is  that  the  vessel  in  which  the  transformation  of  the  glycerine 
into  nitroglycerine  takes  place,  should  be  constantly  cooled  ex- 
ternally by  cold  water. 
When  the  materials  are  thoroughly  mixed,  the  whole  must  be 
left  for  five  or  ten  minutes  ;  then  pour  the  mixture  into  five  or 
six  times  its  volume  of  cold  water,  to  which  a  rotatory  movement 
must  first  be  imparted.    The  nitroglycerine  precipitates  very 
