A.m.  Jour.  Pharm. 
October.  1897. 
Powdered  Vegetable  Drugs. 
531 
(b)  While  these  ocular  micrometers  ruled  in  square  millimeters 
are  easily  made,  still  the  makers  of  microscopical  accessories  charge 
such  a  very  high  price  for  the  same  that  it  has  been  found  desira- 
ble to  devise  another  way  for  doing  the  same  kind  of  work.  An 
ordinary  ocular  micrometer  divided  into  tenths  of  millimeters  is 
taken,  and  the  number  of  elements  between  the  outer  portions,  ruled 
to  a  less  number  of  divisions  (as  those  marked  X,  Fig.  4.),  are 
counted. 
It  is  better,  when  using  this  ocular  micrometer,  to  turn  the  latter 
around  1800  after  counting  in  the  one  direction,  and  counting  again. 
In  other  words,  an  additional  count  is  made,  i.  e.y  ten  are  made  upon 
each  mount. 
(V)  There  are  some  cases  when  it  is  not  desirable  to  use  either  (a) 
or  as  when  the  elements  or  tissues  are  so  large  that  it  is  more 
practicable  to  exclude  the  ocular  micrometers,  and  to  count  all  of  the 
tissues  or  constituents  as  they  appear  in  the  whole  field  of  view  of 
X  in  Fig.  1. 
The  low  power       to  y2  inch)  may  be  used  sometimes,  as  in  the 
X 
X 
X 
X 
X 
x, 
X 
X 
X 
X 
X 
X 
X 
X 
x 
X 
X 
X 
X 
Fig.  3. 
estimation  of  cinchona,  quillaja,  glycyrrhiza,  etc.,  while  in  other 
drugs,  as  Hyoscyami  folia,  Belladonnae  folia,  etc.,  a  higher  power 
(t  to  i) ls  used- 
(10)  The  number  of  mounts  to  be  made  of  the  standard  and  the 
powder  under  examination  should  generally  not  be  less  than  twelve 
each.  But  as  two  to  three  mounts  can  be  made  upon  the  same  slide, 
from  four  to  six  slides  only  are  necessary  for  each  powder. 
(1 1)  If  the  powder  is  found  to  be  a  mixture,  a  similar  compound, 
representing  the  proportions  found,  should  be  made  up,  and  the 
powder  under  investigation  be  compared  with  it. 
(12)  It  is  apparent  that  the  quantitative  results  are  purely  com- 
parisons of  an  unknown  with  a  known  powder.  The  conditions 
must  be  nearly  the  same  in  both.  The  sampling  must  be  done 
similarly ;  the  same  amount  of  powder  must  be  used  in  both,  and 
