526        EMPLOYMENT  OF  NITROGLYCERINE  IN  QUARRIES. 
bad  headaches.  Its  vapor  produces  similar  effects,  and  this  rea- 
son might  well  prove  an  objection  to  its  use  in  the  subterranean 
galleries  of  mines,  where  its  vapors  cannot  disperse  as  they  do  in 
open-air  quarries. 
Nitroglycerine  is  not,  properly  speaking,  a  nitrated  body,  such 
as  nitro-  or  binitro-benzol,  or  mono-  bi-  and  trinitro-phenisic 
acids.  Indeed,  under  the  influence  of  reducing  bodies,  such  as 
nascent  hydrogen,  sulphuretted  hydrogen,  &c,  the  glycerine  -is 
set  at  liberty,  and  the  caustic  alkalies  decompose  the  nitroglyce- 
rine into  nitrates  and  glycerine. 
III.  Modes  of  employing  Nitroglycerine. — Suppose  the  object 
is  to  detach  a  stratum  of  rocks.  At  2*50  to  3  metres  distance 
from  the  exterior  border  sink  a  mining  hole  about  5  or  6  centi- 
metres in  diameter  and  2  or  3  metres  in  depth. 
After  having  thoroughly  cleared  all  mud,  water  and  sand  out 
of  the  hole,  pour  into  it,  through  a  funnel,  from  1500  to  2000 
grammes  of  nitroglycerine.,  Then  immerse  in  it  a  little 
cylinder  of  wood,  pasteboard,  or  tin,  about  four  centimetres 
in  diameter,  and  from  five  to  six  centimetres  in  height,  and 
filled  with  ordinary  powder.  This  cylinder  is  fixed  to  an  ordi- 
nary mining  fuse,  which  goes  down  a  certain  depth  to  insure  the 
combustion  of  the  powder.  The  cylinder  is  lowered  by  means  of 
the  wick  or  fuse ;  the  moment  the  cylinder  reaches  the  surface 
of  the  nitroglycerine  may  easily  be  known  by  the  touch.  When 
it  touches  the  surface,  hold  it  perfectly  still,  and  pour  sand  into 
the  hole  until  it  is  quite  full ;  there  is  no  need  to  compress  or 
plug  the  sand.  Cut  the  wick  some  centimetres  from  the  orifice 
of  the  hole,  and  then  set  fire  to  it.  In  about  eight  or  ten  minutes 
the  match  burns  down  to  the  powder  and  fires  it.  Then  ensues 
a  violent  shock,  which  immediately  causes  the  detonation  of  the 
nitroglycerine.  The  explosion  is  so  sudden  that  the  sand  is  not 
even  projected. 
The  whole  mass  of  the  rock  rises,  is  displaced,  then  resettles 
without  any  projection ;  only  a  dull  detonation  is  heard. 
Only  on  examining  the  spot  can  an  idea  be  formed  of  the 
power  of  the  force  developed  by  the  explosion.  Formidable 
masses  of  rock  are  slightly  displaced  and  rent  in  every  direction, 
and  ready  to  be  removed  mechanically. 
