Am'/u0i^iS7arm'}        Insect  Powders  of  Commerce.  365 
It  will  be  seen  from  the  remarks  made  on  the  toxic  constituents 
of  the  flowers  of  C.  cinerariaefolium  that  the  following  statement 
embraces  the  results  of  my  own  experience  as  well  as  that  of  the 
majority  of  laborers  in  the  same  field: 
That  the  value  of  insect  powder  is  in  direct  proportion  to  the 
combined  amount  of  essential  oil  and  soft  acid  resin,  and  in  inverse 
proportion  to  the  amount  of  chlorophyll,  both  statements  to  be  read 
together. 
Jt  has  not  been  my  good  fortune,  up  to  the  time  of  writing  this, 
to  have  met  with  one  sample  of  <i  foreign-ground  "  insect  powder 
that  was  not  grossly  sophisticated. 
A  perfect  sample  of  insect  powder  should  pass  a  sieve  having  at 
least  eighty  meshes  to  the  linear  inch  ;  the  particles  would  be,  there- 
fore, approximately  T^  of  an  inch  in  greatest  magnitude.  (The 
powder  has  been  passed  through  a  sieve  with  100  meshes  to  a  linear 
inch,  but  90  is  the  more  usual  number.)  The  powder  should  yield 
5-25  per  cent,  of  combined  essential  oil  and  soft  resin ;  chlorophyll 
should  be  absent,  or  present  in  the  merest  trace. 
The  following  simple  method  of  testing  the  value  of  insect  powder 
should  be  adopted  by  all  chemists  who  wish  to  sell  a  genuine  pow- 
der, or,  to  put  the  matter  on  lower  grounds,  who  wish  to  increase 
their  sale  of  this  really  important  commercial  product.  Place  100 
grains  of  the  powder  to  be  tested  in  the  cylinder  of  a  glass  syringe 
(1  oz.).  The  powder  should  be  pressed  down  compactly  on  to  a 
piece  of  absorbent  cotton,  to  act  as  a  filter.  Moisten  with  ether  7-35. 
Close  the  top  of  the  syringe,  and  macerate  for  thirty  minutes ;  perco- 
lation may  then  proceed  ;  the  powder  being  repercolated  with  the 
same  fluid  four  times,  and  finally  washed  through  with  sufficient 
ether  to  make  up  one  fluid  ounce.  The  resulting  percolate  should 
be  of  a  rich  yellow  color ;  if  a  pronounced  green  color  be  the  result, 
the  sample  may  be  discarded  at  once. 
In  the  absence  of  much  green  coloring  matter,  the  fluid  may  be 
carefully  evaporated  (temperature  not  exceeding  200°  F.),  and  the 
residue  weighed  in  a  tared  watch-glass.  The  resulting  soft  mass 
should  not  weigh  less  than  375  grains,  and  in  the  finest  samples 
reaches  5-5  grains,  and  should  have  the  pleasant  and  characteristic 
odor  of  the  flowers.3  At  the  present  time  the  price  of  insect  powder 
3  Exactness  may  require  the  determination  of  the  chlorophyll.  If  an  appre- 
ciable amount  be  present,  this  may  be  done  by  boiling  the  residue  in  dilute  sul- 
