Am  Jour.  Pharm.  ) 
July,  1878.  / 
Editorial. 
365 
1.  — TO  EXPRESS  QUANTITIES  BY  WEIGHT  OF  THE  APOTHECARIES'  SYSTEM  IN 
METRIC  TERMS,  OR  TO  WRITE  MEDICAL  PRESCRIPTIONS  IN  METRIC  WEIGHTS. 
Rule  A. — Reduce  each  quantity  to  grains ;  then  divide  the  number  by  10,  (or  move  the  decimal 
point  one  place  to  the  left,)  and  from  the  quotient  subtract  one-third.  The  remainder  is  in  each  case 
the  number  of  grammes  representing  (nearly)  the  same  quantity.  Or, 
Rule  B. — Reduce  each  quantity  to  drachms,  and  multiply  the  number  by  4.  The  product  is  in 
each  case  the  number  of  grammes  representing  (nearly)  the  same  quantity.  Or, 
Rule  C. — Reduce  each  quantity  to  ounces,  and  multiply  the  mimber  by  32.  The  product  is  in  each 
case  the  number  of  grammes  representing  (nearly)  the  same  quantity. 
One  gramme  is  equal  to  i5"43234874  troy  grains  {Professor  Miller). — In  preparing  the  above  rules 
the  fraction  has  been  ignored,  as  for  medical  and  pharmacal  purposes  one  gramme  and  15  troy  grains  may 
be  safely  considered  as  equal  quantities.  In  rule  A,  therefore,  a  division  of  15  may,  if  preferred,  be 
substituted  for  the  division  by  10,  followed  by  a  subtraction  of  one-third  from  the  quotient,  with  the  same 
result.  The  difference  between  15  and  15*43234874  is  2-882+  per  cent.,  and  hence  the  deviation  from 
exactness  in  the  answer  arrived  at  by  either  of  the  above  rules  corresponds  to  an  excess  of  28-82+  grains 
for  every  1,000  grains,  or  about  14  grains  for  every  ounce. 
To  insure  greater  accuracy,  if  in  any  case  deemed  necessary,  three  per  cent,  maybe  deducted  from 
the  answer  arrived  at  by  either  of  the  Rules  A,  B  and  C.  The  deviation  from  exactness  will  then  be 
reduced  to  one-fifth  of  one  per  cent  ,  the  remainder  being  less  than  the  exact  equivalent  sought  by  only 
2*04  grains  for  every  1,000  grains,  or  about  one  grain  for  every  ounce. 
2.  — TO  EXPRESS  QUANTITIES  BY  MEASURE  OF  THE  APOTHECARIES'  SYSTEM 
IN  METRIC  TERMS,  OR  TO  WRITE  MEDICAL  PRESCRIPTIONS  IN  METRIC  CUBIC 
MEASURES. 
Rule  D. — Reduce  each  quantity  to  minims  ;  then  divide  the  number  by  10,  (or  move  the  decimal 
point  one  place  to  the  left),  and  from  the  quotient  subtract  one-third.  The  remainder  is  in  each  case 
the  number  of  cubic  centimetres  representing  (nearly)  the  same  quantity.  Or, 
Rule  E — Reduce  each  quantity  to  fluid  drachms,  and  multiply  the  number  by  4..  The  product  is 
in  each  case  the  number  of  cubic  centimetres  representing  (nearly)  the  same  quantity.  Or, 
Rule  F '.—Reduce  each  quantity  to  fluidounces,  and  multiply  the  number  by  32.  The  product  is 
in  each  case  the  number  of  cubic  centimetres  representing  (nearly)  the  same  quantity. 
One  metre  is  equal  to  39  370432  inches  {Captain  Clarke). — Hence  one  cubic  centimetre  is  equal  to 
0.0610253868  —  cubic  inches,  or  to  16*2311678  +  minims,  (there  being  61,440  minims  in  each  wine-gallon  of 
231  cubic  inches).  In  preparing  the  above  rules  1  cubic  centimetre  and  15  minims  have  been  considered 
as  equal  quantities,  which,  for  medical  and  pharmacal  purposes,  is  deemed  sufficiently  accurate.  In 
Rule  D,  therefore,  a  division  by  15  may,  if  preferred,  be  substituted  for  the  divis:on  by  10,  followed  by  a 
subtraction  of  one-third  from  the  quotient,  with  the  same  result.  The  difference  between  15  and 
16-2311678+  is  8  208— per  cent.,  and  hence  the  deviation  from  exactness  in  the  answer  arrived  at  by  either 
of  the  above  rules  corresponds  to  an  excess  of  82*08 — minims  for  every  1,000  minims,  or  about  41  minims 
for  every  fluidounce. 
To  insure  greater  accuracy,  if  in  any  case  deemed  necessary,  8  per  cent,  may  be  deducted  from  the 
answer  arrived  at  by  either  of  the  Rules  D,  E  and  F.  The  deviation  from  exactness  will  then  be  reduced 
to  less  than  one-half  of  one  per  cent.,  the  remainder  being  less  than  the  exact  equivalent  sought  by  only 
4*49 — minims  for  every  1,000  minims,  or  less  than  2^  minims  for  every  fluidounce. 
We  are  pleased  that  official  sanction  has  been  given  to  this  very  simple  method  of 
familiarizing  physicians  with  the  use  of  the  metric  system,  and  thus  set  at  rest  the 
groundless  fears  of  dangerous  inaccuracy  occurring  in  consequence  of  the  conversion 
of  old  values  into  their  approximate  metric  equivalents.  It  will  also  be  observed  that 
for  liquids  of  the  spec,  grav-  of  water  weights  may  be  substituted  for  measures,  since 
1  gram=i  cubic  centimeter.  It  would  seem  then  as  if  there  was  but  little  if  any 
difficulty  of  abandoning  measures  altogether  in  prescriptions  in  favor  of  weights,  as 
we  have  repeatedly  taken  occasion  to  advocate.  It  affords  us  pleasure  to  refer  to  a 
paper,  by  Dr.  E.  Wigglesworth,  which  was  recently  published  in  the  "  Boston 
Medical  and  Surgical  Journal,"  and  strongly  urges  the  course  indicated.  There  is 
a  slight  inaccuracy  in  that  paper,  which,  however,  does  not  detract  from  the  value 
of  the  argument  j  the  author  has  overlooked  the  fact  that  the  apothecaries'  grains, 
