522 
ON  DROPS. 
flasks,  of  76a  pounds  each,  of  mercury.    The  selling  price  in 
San  Francisco  is,  at  present,  and  has  been  for  some  time  past, 
75  c.  per  pound,  while  in  London  and  New  York  it  has  ranged 
from  40  to  50  c.  per  pound. 
San  Francisco,  May,  1864. 
— Amer.  Jour.  Sci.  and  Arts.  Sept.,  1864. 
DROPS. 
By  Charles  W.  Quin,  F.  C.  S. 
Mr.  Frederic  Guthrie,  Professor  of  Chemistry  and  Physics  at 
the  Royal  College,  Mauritius,  has  lately  brought  before  the 
Royal  Society  the  results  of  some  investigations  recently  made 
by  him  into  the  laws  which  govern  the  formation  of  drops,  an 
account  of  which  cannot  fail  to  interest  our  readers. 
On  turning  to  the  subject  of  drops,  as  treated  of  in  "  Par- 
rish's  Practical  Pharmacy,"  or  any  other  standard  pharmaceu- 
tical work,  we  cannot  help  being  struck  with  the  great  differ- 
ence observable  in  the  relative  size  and  weight  of  the  drops  of 
different  fluids.  Thus,  although  we  are  always  taught  that  a 
fluidrachm  contains  on  an  average  sixty  drops,  each  of  which 
is  equal  to  a  minim  or  a  grain,  we  find  it  stated  in  Parrish,  on 
the  authority  of  Durand,  that  a  fluidrachm  of  distilled  water, 
hydrocyanic  acid,  or  weak  ammonia,  contains  only  forty-five 
drops,  or  in  other  words  that  a  drop  of  either  of  these  sub- 
stances is  one-third  greater  than  it  is  generally  supposed  to  be. 
In  the  case  of  other  fluids  the  discrepancy  is  in  the  opposite 
direction — for  instance,  a  drop  of  crystallizable  acetic  acid,  di- 
luted alcohol,  tincture  of  opium,  and  several  other  liquids  used 
daily  by  the  pharmacist,  is  only  half  the  supposed  size.  A 
patient,  therefore,  who  is  prescribed  acetic  acid  in  drops  gets 
less  than  the  supposed  quantity,  while  the  one  who  is  ordered 
hydrocyanic  acid  by  the  same  measure  would  get  more  than 
the  proper  amount. 
According  to  the  same  authority,  the  bottle  or  measure  from 
which  the  liquid  is  dropped  has  a  great  influence  on  the  size  of 
the  drops.  Thus,  according  to  Parrish's  experiments,  seventy- 
three  drops  of  acetic  acid  dropped  from  a  pint  tincture  bottle 
made  up  a  fluidrachm,  -while  102  drops  were  necessary  when  a 
minim  measure  was  used.    These  differences  seem  to  show  the 
