72 
ON  THE  DESTRUCTION  OF  NOXIOUS  INSECTS. 
any  contact  from  without,  as  is  usually  done  in  pulverizing  drugs 
in  a  laboratory.  The  quantity  to  be  pulverized  should  not  ex- 
ceed a  pound  at  a  time,  thus  avoiding  too  high  a  degree  of  heat, 
which  would  be  injurious  to  the  quality  of  the  powder.  The 
pulverization  being  deemed  sufficient,  the  substance  is  sifted 
through  a  silk  sieve,  and  the  residue,  with  a  new  addition  of 
flowers,  is  put  into  the  mortar  and  pulverized  again. 
This  method  of  preparation  is  so  simple  as  to  be  within  the 
reach  of  all  ;  the  pulverization  by  steam  is  more  rapid  and 
effectual,  but  necessarily  more  expensive.  The  best  receptacles 
for  holding  the  powder  seem  to  be  bottles  ;  these,  if  well  corked, 
will  keep  out  moisture,  which  is  so  injurious  to  the  properties  of 
the  powder.  If  the  powder  is  not  to  be  kept  long,  small  boxes 
will  do  as  well  as  bottles. 
Insects  destroyed  by  the  Powder. — The  principal  insects  to 
which  the  powder  is  destructive  may  be  ranged  under  four 
classes  : — first,  insects  injurious  to  agriculture  and  horticulture  ; 
second,  insects  obnoxious  to  man  and  his  habitation  ;  third,  in- 
sects destructive  to  certain  substances,  as  wool,  furs,  feathers ; 
and,  fourth,  insects  injurious  to  museums  of  animal  and  vege- 
table products,  and  collections  of  natural  history.  We  do  not 
pretend  to  enumerate  all  the  insects  to  which  the  powder  is  de- 
structive ;  it  will  suffice  to  mention  a  few  instances,  which  will 
sufficiently  show  what  applications  may  be  made  of  it.  Our 
domestic  animals, — dogs,  cats,  fowls,  pigeons,  etc., — are  subject 
to  annoyance  from  insects  which  cannot  withstand  the  effects 
of  this  powder.  Of  the  numerous  insects  injurious  to  agriculture 
and  horticulture  we  may  mention  the  following  which  have  been 
destroyed  by  it : — the  weevil,  bark-beetle,  wheat-fly,  maggots, 
cocci,  aphides,  earwigs,  spiders,  ants,  etc.  It  is  evident  that 
not  only  the  perfectly  developed  insects  are  destroyed,  but  also 
the  larvae,  which  in  some  cases  do  greater  injury  than  the  in- 
sects themselves.  Large  depots  where  military  stores  or  navy 
supplies  are  kept,  and  especially  extensive  bakeries,  may  use  the 
powder  with  great  advantage  for  the  destruction  of  weevils,  mid- 
ges, crickets,  cockroaches,  etc.,  the  great  plague  of  those  estab- 
lishments. The  powder  is  equally  efficacious  in  destroying  injects 
which  are  a  constant  source  of  annoyance  to  the  inhabitants  of 
cities  and  the  country.    Gnats  and  mosquitoes  are  banished  ; 
