EXPLOSIVE  FORCE  OF  NITRO-GLYCERIN. 
479 
means  of  a  sieve,  and  the  question  which  is  engaging  attention 
is,  whether  or  not  the  powder  is  damaged  by  being  submitted  to 
this  treatment.  One  writer  suggests  that  glass  powder  is  liable 
to  become  alkaline,  and  therefore  hygroscopic.  Mr.  Hearder 
objects  that  it  may  not  be  possible  to  separate  the  glass  com- 
pletely, and  therefore  the  explosive  force  of  the  powder  must 
be  more  or  less  diminished.  The  Reader  mentions  some  experi- 
ments which  "  seem  to  show  that  the  addition  of  the  protective 
powder  to  ordinary  powder  has  the  effect  of  rendering  the  ex- 
plosion more  gradual" — an  effect  which  would  be  valuable,  if  the 
protective  powder  were  combustible.  We  have  not  seen  any 
notice  of  the  effect  of  the  glass  on  the  glazing  of  the  powder, 
any  interference  with  which  would  seriously  affect  the  quality  of 
the  powder,  particularly  of  the  finer  kinds.  On  the  whole,  we 
must  conclude  that  the  practical  value  of  Mr.  Gale's  invention 
has  yet  to  be  demonstrated.  It  is,  indeed,  very  desirable  to 
have  a  means  of  rendering  gunpowder  combustible  or  non-com- 
bustible, at  will ;  but  to  be  really  available,  the  results  must  be 
accomplished  with  less  trouble  and  risk  than  is  the  case  with 
Mr.  Gale's  process. — London  Chem.  Neivs,  August  18,  1865. 
EXPLOSIVE  FORCE  OF  NITRO-GLYCERIN. 
Experiments  have  been  made  in  the  open  workings  of  the  tin 
mines  of  Altenburg,  in  Saxony,  by  M.  Nabel,  which  prove  that 
the  use  of  nitro-glycerin,  for  blasting  purposes,  is  quite  practic- 
able. Its  chief  advantage  is,  that  it  requires  a  much  smaller 
hole  or  chamber  than  gunpowder  does,  the  strength  of  the  latter 
being  scarcely  one-tenth  of  the  former.  If  the  boring  presents 
fissures,  it  must  first  be  lined  with  clay  to  make  it  watertight  ; 
this  done,  the  nitro-glycerin  is  poured  in,  and  water  after  it, 
which,  being  the  lighter  liquid,  remains  at  the  top.  A  fuse  is 
then  applied  in  the  usual  ma*nner.  In  one  of  the  experiments 
referred  to,  a  bore-hole  one  and  one- third  inch  in  diameter  was 
made  perpendicularly  in  a  dolomitic  rock,  sixty  feet  in  length, 
and  at  a  distance  of  fourteen  feet  from  its  extremity,  which  was 
nearly  vertical.  At  a  depth  of  eight  feet,  a  vault,  filled  with 
clay,  was  found,  in  consequence  of  which,  the  bottom  of  the  hole 
