Am.  Jour.  Pharm. 
May,  1902. 
Atomic  Weight  Tables. 
233 
exclusively  to  oxygen,  hydrogen,  nitrogen  and  carbon,  and  compare 
the  atomic  weights  as  used  at  the  present  time,  or  those  used 
twenty  years  ago,  we  will  find  that  they  differ  but  little  from  those 
given  in  the  O-16  column.  Or,  if  we  confine  ourselves  to  what  is 
directly  of  interest  to  the  working  pharmacist,  and  admit  that  a 
large  amount  of  the  available  chemical  work  has  been  done  on  the 
basis  of  the  atomic  weights  as  given  in  the  Pharmacopoeia  for  1880, 
and  then  compare  such  common  and  important  elements  as  carbon, 
oxygen,  nitrogen,  bromine,  chlorine,  iodine  phosphorus,  sulphur, 
potassium,  sodium,  calcium,  magnesium,  iron,  lead,  mercury  and 
arsenic  we  will  find  that  the  weights  given  in  the  list  for  1880  cor- 
respond very  closely  with  those  given  in  the  O-16  column.  This  is 
true  of  all  the  elements  enumerated  above,  with  the  single  exception 
of  magnesium,  the  atomic  weight  of  which  has  been  recalculated 
within  the  past  twenty  years. 
But  what  is  perhaps  even  more  astonishing  to  the  ordinary  indi- 
vidual is  that  the  atomic  weights  given  in  the  Pharmacopoeia  of 
1890  on  the  basis  of  H-i  correspond  more  closely  to  those  of  the 
O-16  series  than  they  do  to  the  revised  H-i  tables.  This  is,  of 
course,  due  to  the  fact  that  Morley,  in  1898,  showed  that  the  proper 
relation  of  oxygen  and  hydrogen  is  as  1  to  15-875  instead  of  1  to 
15-96  as  suggested  by  Lothar  Meyer. 
But  there  are  still  other  reasons  why  we  should,  from  a  practical 
point  of  view,  adopt  O-16,  and  retain  approximately  the  same 
molecular  weights  that  have  been  used  for  upwards  of  thirty  years. 
Among  these  are  the  facts  that  both  the  German  and  Swedish  Phar- 
macopoeias have  already  adopted  the  O-16  standard,  and  that  if  we 
should  vary  as  much  as  we  necessarily  would,  by  retaining  the  H-i 
standard,  all  of  the  new  work  done  in  these  countries  would  not  be 
available  for  us  without  elaborate  recalculation. 
Another  interesting  factor  is  found  in  the  fact  that  the  total  deci- 
mals of  all  of  the  elements  given  in  the  table  of  atomic  weights  as 
published  in  the  German  Pharmacopoeia  is  33,  while  the  correspond- 
ing elements  in  our  own  Pharmacopoeia,  or  in  the  H-i  column,  have 
43,  a  difference  of  more  than  thirty  per  cent.  To  the  ordinary 
mortal  a  saving  of  one-third  in  the  necessary  amount  of  extra  calcu- 
lation would  appeal  as  being  a  matter  of  considerable  moment. 
After  all,  would  it  perhaps  not  be  better  to  admit  that  chemistry 
is,  as  yet,  not  an  exact  science,  but  an  experimental  one,  in  which 
