182 
Dispensing  by  Drops. 
Am.  Jour.  Pharm. 
April,  1884. 
It  has  been  shown  by  actual  experiments,  that  when  the  growing 
time  is  decreased  below  0*333  second  (coco-nut  oil  was  used  in  this 
instance)  a  continuous  stream  was  the  result,  but  of  course  the  density 
of  the  liquid  regulates  this  to  a  certain  extent.  It  is  also  a  curious 
fact  that  a  stream  so  produced,  delivers  less  in  a  given  time  than  a 
series  of  large  drops. 
This  rapidity  of  dropping  is  one  of  the  greatest  obstacles  to  over- 
come, for  very  few  pharmacists  will  drop  the  same  liquid  in  the  same 
time,  and  if  laws  are  to  be  laid  down,  governing  dropping,  the  time 
certainly  claims  a  large  share  of  attention,  for  the  same  mistake  is  just 
as  likely  if  not  more  so,  to  happen  in  this  instance  than  in  the  pre- 
vious one,  for  a  pharmacist  who  dispenses  100  drops  of  a  liquid  at  the 
rate  of  three  drops  a  second,  will  give  one  half  as  much  again  as 
another  who  measures  the  same  liquid  at  the  rate  of  a  drop  every  second 
and  one  half. 
Prof.  Guthrie  has  shown  the  effect  of  gradually  decreasing  the 
strength  of  saline  solutions.  Dropping,  at  the  rate  of  two  seconds,  he 
found  that  decrease  of  solid  constituents  produced  precisely  the  same 
effect  upon  the  size  of  the  drops,  as  a  decrease  in  the  growth  rate  in 
the  drops  of  homogenous  liquids.  I  find  that  these  facts,  however, 
have  their  greatest  importance  from  a  theoretical  point  of  view,  practi- 
cally there  is  very  little,  if  any,  difference,  although  in  some  instances 
it  does  seem  as  though  the  matter  in  solution  might  be  the  cause  of  the 
decrease  in  size  by  increasing  its  specific  gravity.  The  following  table 
gives  the  result  of  my  experiments,  having  chosen  the  glass  stopper, 
minim  measure  and  lip  of  the  bottle  in  which  the  liquids  are  ordinarily 
kept,  to  drop  from. 
By  comparing  my  table  with  those  of  Prof.  Procter  or  Mr.  Durand, 
it  will  be  noticed,  in  a  number  of  instances,  that  they  vary  very  widely 
about  the  only  way  I  can  account  for  this  is,  that  the  lip  of  the  minim 
measure,  which  I  used,  must  have  been  much  smaller  than  theirs,  but 
even  when  the  same  vessels  are  used,  there  is  such  a  variety  of  results, 
that  to  get  a  medium  size  an  average  is  required  to  be  taken.  This  I 
have  done  in  all  of  the  unimportant  liquids.  How  greatly  they  vary 
maybe  seen  in  the  case  of  Acetum  opii ;  in  the  first  trial  the  result  was 
120  drops  to  a  drachm,  the  second  85,  and  the  third  103. 
There  are  still  other  conditions  which  yield  more  or  less  influence  on 
the  size,  and  one  which  deserves  mention,  is  the  angle  at  which  the 
vessel  is  held.    I  have  already  shown  that  a  cork  may  be  held  so  a 
