596 
Weight  by  Measure. 
Am.  Jour.  Pharm. 
Dec,  1883 
comparison  formulae  expressed  in  weights,  and  those  in  which  volumes 
are  employed,  as  at  present  in  the  British  Pharmacopoeia.  A  ready- 
means  of  making  such  comparisons  and  translations,  is  an  acknow- 
ledged desideratum.  The  Committee  charged  with  the  revision  of  the 
Pharmacopoeia,  found  it  impossible,  in  the  limited  time  at  their  dis- 
posal to  supply  it.  The  table  herewith  furnished  may  serve  tempo- 
rarily to  meet  the  want. 
The  table  includes  the  more  important  officinal  liquids,  especially 
those  frequently  occurring  in  officinal  and  private  formulae.  Its  uses 
will  be  too  obvious  to  require  elucidation. 
In  computing  the  table  I  have  assumed  that  all  specific  gravities 
are  to  be  referred  to  water  at  its  maximum  density  as  a  standard  of 
comparison.  The  U.  S.  Pharmacopoeia  does  not  state  that  that  stand- 
ard is  uniformly  adopted,  and  it  is  evident  in  looking  over  its  tables 
of  specific  gravities,  that  in  some  instances  water  at  a  temperature  of 
68°  or  60°  F.  has  been  taken  as  the  standard.  This  is  notably  the 
case  in  the  very  elaborate  alcoholometric  table  given,  after  Hehner.  In 
the  existing  confusion  on  this  point,  I  have  thought  it  best  to  accept, 
provisionally,  the  figures  of  the  Pharmacopoeia,  referring  them,  except 
in  the  case  of  alcohol,  to  a  single  unit,  and  I  have  adopted  that  which 
is  employed  in  the  majority  of  the  tables  now  in  use,  although  per- 
sonally, I  am  in  favor,  tor  practical  purposes,  of  adopting  as  a  standard 
water  at  the  same  temperature  as  that  at  which  the  weighing  is  made. 
No  doubt  a  considerable  number  of  the  figures  given  in  the  Pharma- 
copoeia have  bet  n  actually  obtained  by  the  use  of  such  a  standard,  and 
the  corresponding  values  given  in  the  table,  are  therefore  subject  to  a 
correction,  practically  unimportant  however,  on  this  score.  The  figures 
relating  to  alcohol  assume,  exceptionally,  as  a  standard  water  at  60  °F. 
Again  I  found  some  difficulty  in  deciding  what  figure  ta 
adopt  for  the  weight  of  a  pint  of  water  at  maximum  density. 
The  U.  S.  Pharmacopoeia  indeed  gives  a  value,  which  perhaps 
in  the  formulae  of  that  work  must  be  considered  authoritative,  but 
it  is  inconsistent  with  other  values,  which  must  equally  be  accepted 
as  authoritative.  It  is  impossible  to  reconcile  the  value  given  for  a 
minim  (0-0616  gram),  with  that  for  a  pint  (7291-2  grains  at  60°  F.  or 
7297*46  grains  at  maximum  density).  It  is  equally  impossible  to 
reconcile  the  values  commonly  given  for  the  length  of  the  metre  in 
inches,  and  the  weight  of  a  cubic  inch  of  water  in  grains  with  the 
fundamental  ratio  in  the  metric  system  of  kilogramme  to  litre.  With- 
