52  The  Metrical  System  in  Prescriptions.  {Am&Z;*%T 
pharmacist,  Dr.  Blodgett  is  decidedly  in  error.  Says  Dorvault  (p.  543)  : 
"  It  is  frequently  given  as  a  mild  purgative  in  the  dose  of  15  to  60 
grams."  (On  Pemploie  frequemment  commg  purgatif  doux,  a  la  dose 
de  15  a  60  grammes.)  The  fact  is  that  physicians  and  pharmacists^ 
who  study  in  Europe,  are  taught  and  become  acquainted  with  the  doses 
of  all  drugs,  chemical  and  galenical  preparations  by  weight  only,  and 
for  the  former  to  prescribe  by  measures  would  involve  the  same  amount 
of  labor  that  Dr.  Blodgett  objects  to  would  be  entailed  upon  our  phy- 
sicians, if  they  were  to  follow  the  plan  proposed  by  me  in  the  previous 
paper.  But  it  should  be  remembered  that  any  change  of  an  established 
system  will  cause  some  inconvenience,  until  the  new  system  has  gained 
a  firm  foothold,  when  its  use  will  be  found  quite  as  convenient — and 
in  the  case  under  discussion  even  more  so — than  the  one  which  pre- 
ceded it. 
The  greater  convenience  and  correctness  of  weights  have  long  since 
been  recognized  in  the  wholesale  drug  trade.  Acids,  copaiba,  Peril 
balsam,  volatile  oils  and  medicinal  spirits  are  always  sold  by  weight- 
and  within  a  few  years  the  practice  of  selling  castor  oil  by  the  gallon, 
was,  to  the  satisfaction  of  all  dealers,  changed  to  that  by  the  pound. 
Our  "  Pharmacopoeia  "  even  recognizes  the  correctness  of  this  fact  by 
having  changed,  in  the  last  two  revisions,  all  measures  of  the  liquid 
acids,  of  chloroform,  olive  oil  and  honey  into  weights.  If  these  liquids 
are  more  conveniently  and  correctly  handled  by  weight,  why  not  like- 
wise glycerin,  syrups,  tinctures,  ethers,  etc.  ?  And  if  a  change  to  the 
metric  system  is  to  be  made  in  pharmacy  and  medicine,  why  not  make 
it  at  once  far  enough,  instead  of  halting  half  way,  which  would  render 
another  change  in  the  future  necessary  ? 
But  it  might  be  urged  that  chemical  analysis  is  nowadays  more 
extensively  performed  by  the  volumetric  than  by  the  gravimetric 
method.  While  admitting  the  correctness  of  this  preference,  it  should 
be  borne  in  mind  that  the  test  liquids — special  cases  excepted — are  all 
aqueous  solutions,  which  show  a  like  expansion  and  contraction  with 
the  rising  and  falling  variation  from  the  normal  temperature.  Such  is 
not  the  case  with  the  various  liquids  which  are  medicinally  employed  ; 
and  the  relative  weights  of  liquids  entering  into  a  mixture  and  meas- 
ured at  different  temperatures,  must  therefore,  necessarily,  vary,  even 
if  they  had  been  measured  with  instruments  constructed  like  the 
pipettes  and  burettes  employed  in  volumetric  analysis,  instruments 
