Am  junUe^'i89hoarm' }  Microscopical  Examination  o f  Powders.  2 79 
Medium. — For  casual  examination  almost  any  liquid  will  do. 
Besides  the  time-honored  water  and  more  or  less  diluted  glycerin, 
the  writer  finds  sweet  oil,  old  essential  oils  and  especially  liquefied 
carbolic  acid  of  great  service  as  clearing  media ;  a  concentrated 
solution  of  chloral  hydrate  clears  nearly  as  well  as  the  latter  sub- 
stance. 
Mounting. — If  the  powder  is  tolerably  uniform  in  fineness  and 
quite  dry,  so  that  it  does  not  cake,  a  very  cleanly  way  of  mounting 
is  to  follow  Mr.  A.  P.  Brown.  Breathe  upon  a  slide,  press  it  down 
on  the  powder,  and  rap  the  slide  smartly  with  the  edge  on  the 
table  so  as  to  get  rid  of  the  superfluous  powder,  when  the  remainder 
will  be  found  distributed  quite  evenly  on  the  slide.  The  writer 
now  puts  on  the  cover  glass,  places  on  top  a  small  weight  (a  conical 
rifle  bullet,  for  instance),  brushes  off  the  excess  of  powder,  and  adds 
one  or  more  drops  of  the  medium  next  to  the  cover  glass,  when 
the  fluid,  if  not  too  viscid,  will  quickly  run  under  by  capillary 
attraction.  This  does  away  with  the  otherwise  inevitable  "  mess- 
ing," and  comparatively  few  (sometimes  none)  air  bubbles  will  be 
noticed. 
In  order  to  make  a  typical  slide,  since  very  seldom  a  single  slide 
contains  all  the  characteristic  elements,  the  latter  must  be  trans- 
ferred from  several  slides  to  one  of  them,  unless  one  prefers  to  keep 
three  or  four  slides  of  the  same  powder. 
Comparison. — In  order  to  get  a  powder  of  undoubted  purity,  it 
is  certainly  best  to  powder  the  drug  one's  self,  and  since  the  volatile 
parts  are  of  no  consequence  microscopically,  sharp  drying  will  much 
facilitate  the  powdering.  The  pharmaceutical  microscopist  ought 
to  be  sufficiently  familiar  with  the  microscopical  appearance  of  the 
more  important  powdered  drugs  to  be  able  not  only  to  recognize 
them  at  once,  but  also  be  able  to  state  that  such  and  such  other 
elements  (tissues)  do  certainly  not  belong  to  the  drug  in  question. 
Whether  he  is  able  to  tell  what  these  foreign  substances  are,  will 
depend  on  his  familiarity  with  the  usual  impurities  and  adultera- 
tions;  it  is  manifestly  impossible  to  be  acquainted  with  everything 
that  might  be  present  in  a  powder. 
Powdered  Rhubarb. — The  writer  mentioned  the  use  of  essential 
oils  as  media  for  the  examination  of  powders,  because  of  their  clear- 
ing action.    On  examining  a  sample  of  rhubarb  in  oil  of  fennel  seed 
