""juirtSTr''-}      Oarholic  Acid  in  Powder  Form.  297 
The  powder  used  by  me  is  quite  dry,  has  very  little  coherence,  is 
light  and  porous,  little  inclined  to  form  lumps  by  exposure  to  moist- 
ure, and  contains  about  20  per  cent,  of  the  mixed  tar  acids,  which 
gradually  and  slowly  volatilize  when  the  powder  is  exposed  to  the 
atmosphere. 
That  the  corrosive  qualities  of  the  acid  are  considerably  modified 
by  this  mode  of  dilution,  and  therefore  an  objectionable  feature  of 
the  common  solution  obviated,  without  sacrificing  any  valuable  prop- 
erty, I  convinced  myself  by  the  following  experiments  : 
A  number  of  shrubs  and  flowers  in  my  garden  had  become  infested 
by  swarms  of  various  parasites,  green  and  black  lice,  aphides  of 
larger  kind,  &c.  To  destroy  them,  or  at  least  drive  them  away,  I  used 
a  spray  syringe  charged  with  water  containing  crude  carbolic  acid  in 
various  amounts.  I  began  with  J  per  cent.,  and  gradually  increased 
the  quantity.  A  rose-bush  was  first  selected,  on  which  thousands  of 
green  insects  were  preying. 
The  weaker  applications  proved  entirely  unsuccessful,  until  above 
4  per  cent,  of  acid  were  used,  when  some  of  the  animals  died,  but  at 
the  same  time  the  rose-bush  began  to  Avither,  and  after  a  few  weeks  of 
sickly  existence  perished. 
Similar  results  were  obtained  with  a  number  of  other  plants  sub- 
jected to  a  like  treatment,  some  of  them  resisting  larger  amounts  of 
acid,  but  all  being  materially  injured  or  killed  before  all  the  animals 
were  destroyed. 
The  powder  containing  about  20  per  cent,  of  the  acid  was  next 
sprinkled  slightly  over  different  plants.  On  the  first  day  neither 
plants  nor  insects  appeared  to  be  affected.  After  three  days  but  very 
few  parasites  remained  on  the  plants,  while  no  damage  whatever  had 
resulted  to  vegetable  life,  the  plants  remaining  quite  healthy  and  con- 
tinuing to  grow  thriftily  while  under  observation  for  some  time  after. 
A  continuous  and  regular  exhalation  of  the  acid  vapor  from  the 
finely  divided  surface  of  the  powder  appears  to  be  preferable  to  the 
more  irregular  .diffusion  resulting  from  evaporation  of  an  aqueous 
solution,  and,  so  far  as  safety  in  the  hands  of  the  inexperienced  is 
concerned,  I  do  not  hesitate  to  give  the  powder  form  a  decided  prefer- 
ence over  that  of  solution  in  liquids. 
It  would  be  well  if  during  the  revision  of  the  U.  S.  Pharmacopoeia 
now  going  on,  the  Committee  would  give  some  attention  to  this  mode 
of  dispensing  the  acid  for  general  use,  and  would  incorporate  a  pre- 
