THE  AMERICAN 
JOURNAL  OF  PHARMACY. 
JULT,  1880. 
ON  THE  EQUIVALENCE  OF  DROPS. 
By  S.  L.  Talbot,  Ph.G. 
[From  an  Inaugural  Essay.) 
The  design  of  the  writer  in  experimenting  upon  this  subject  was  to 
determine,  if  possible,  some  relation  between  the  size  of  the  drop  and 
a  minim  of  the  same  liquid,  and  thus  enable  any  one  to  determine  the 
number  of  drops  of  any  given  liquid  that  should  be  directed,  to  secure 
a  uniform  dose  of  said  liquid. 
The  labor  involved  in  this  endeavor  can  be  judged  of  when  about 
275  different  liquids  were  experimented  with  and  each  one  tested  three 
times.  The  results,  as  summarized,  show  the  general  exactness  which 
characterized  the  work  of  our  former  fellow-member,  Mr.  E.  Durand, 
whose  labors  have  been  carefully  reviewed  by  the  author,  and  demon- 
strate most  fully  that  minims  only  should  be  directed  in  prescribing 
quantities  of  liquids  less  than  half  a  fluidrachm. 
The  whole  experiments  made  show  results  according  with  Durand's 
and  Bernouilli's  statements,  that  the  bulk  of  drops  depends  upon  the 
density  of  the  liquid,  the  cohesion  of  the  constituent  particles  of  it, 
and  also  upon  adhesion,  as  shown  by  the  variation  when  dropped  from 
vessels  of  different  material  or  shape.  They  also  agree,  for  the  most 
part,  with  the  two  general  rules  of  Durand  :  "  First.  That  liquids  with 
SMALL  PROPORTION  of  water  afford  a  small  drop,  and  vice  versa. 
Second.  That  amongst  liquids  containing  a  large  proportion  of  water, 
those  not  charged  with  remedial  substances  give  a  larger  and  heavier  drop 
than  these  same  liquids  having  extraneous  bodies  in  solution.^''  In  his  second 
rule  the  word  ''heavier"  should  be  erased,  as  in  the  officinal  solu- 
tions, in  most  cases,  the  bodies  in  solution  cause  increase  in  weight, 
which  more  than  offsets  or  counterbalances  the  decrease  in  size  ;  and 
the  same  statement  is  true  of  tinctures  made  with  diluted  alcohol.  In 
nearly  all  cases  the  cohesion  seems  to  be  impaired  by  the  interposition 
cf  bodies  in  solution,  and  cohesion  would  seem  to  exert  a  stronger 
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