208      PHYSICAL  CHARACTERISTICS  OF  OFFICINAL  POWDERS. 
large  proportion  of  a  fine  dust  which  will  pass  through  the  No. 
80  sieve.  If  the  whole  had  been  subjected  to  contusion  until  it 
would  pass  the  coarsest  sieve,  a  still  larger  proportion  of  the 
finer  grades  would  have  been  contained  in  the  resulting  powder. 
The  ordinary  method  was,  however,  adopted  in  this  as  in  the 
other  experiments,  the  finer  particles  being  three  times  separated 
as  the  contusion  proceeded.  Wild  cherry  gives  nearly  the  same 
difference,  more  of  the  finest  powder  being  produced  by  contu- 
sion at  the  expense  of  the  coarsest,  the  intermediate  grades  dif- 
fering but  little  in  relative  weight. 
Ginger,  by  contusion,  seems  to  increase  in  the  proportion  of 
No.  50  and  No.  60  powder  ;  its  starchy  character  probably  being 
unfavorable  to  its  ready  reduction  to  "  very  fine  powder."  The 
loss  in  ginger  is  greater  than  in  any  of  the  other  experiments, 
chiefly  from  the  fibre,  a  portion  of  which  failed  to  pass  the 
coarsest  sieve,  and  may  be  called  "gruffs." 
Ergot,  which  has  a  corneous  and  oily  character  unfavorable  to 
breaking  up  into  fine  dust,  gives  nearly  uniform  results  by  either 
method,  the  proportion  of  fine  powder  being  very  small,  espe- 
cially in  the  triturated  specimen. 
Gentian,  of  which  the  average  of  several  experiments  is  given, 
furnishes  decided  evidence  of  the  general  fact  that  the  pestle  and 
mortar  are  more  favorable  to  the  production  of  the  finer  grades 
of  powders  than  the  mill.  In  the  single  experiment  tried  with 
Swift's  mill  the  No.  40  and  No.  50  powders  were  in  larger  pro- 
portion than  when  the  small  mill  was  used,  but  the  No.  60  and 
No.  80  powders  are  nearly  in  the  same  proportion  and  decidedly 
less  than  the  results  of  contusion. 
The  Swift's  mill  is  not  well  adapted  to  use  with  so  small  a 
quantity  of  material,  on  account  of  the  great  extent  of  the  rough 
grinding  surfaces. 
These  experiments,  though  only  conclusive  upon  the  one  point 
of  the  relative  preponderance  of  the  finer  powders  as  the  result 
of  contusion,  tend  to  show  the  great  diversity  of  results  by  the 
different  means  of  mechanical  division,  even  when  applied  to  the 
same  drug,  and  especially  when  applied  to  drugs  of  different 
structure,  and  prove  that  the  grades  of  powder  indicated  by  the 
