Am^^em'} Relation  of  Specific  Gravity  to  Atomic  Weight,  483 
THE  RELATION  OF  SPECIFIC  GRAVITY  TO  ATOMIC 
WEIGHT. 
By  A.  N.  Doerschuk^" 
Read  before  the  Missouri  State  Pharmaceutical  Association. 
Since  the  study  of  Chemistry  by  beginners  and  amateurs  is  so 
often  hampered  by  apparently  logical  theories  and  conclusions  which 
seem  perfectly  correct  to  the  undeveloped  eye,  which  has  not  been 
associated  with  the  fundamental  truths  and  underlying  principles  of 
this  acute  science,  and,  since  views  obtained  from  these  theories  and 
conclusions  often  cost  much  labor,  time  and  many  ungrounded  mis- 
givings, we  ask  your  most  worthy  attention  for  a  few  moments  while 
we  explain  one  of  these  theories  which  so  often  worry  the  beginner 
in  Chemistry,  and  for  which  very  few  if  any  satisfactory  explanations 
are  given. 
The  problem  generally  presents  itself  in  this  shape : 
"  Why  is  the  sp.  gr.  of  Iron  (7*84),  to  the  sp.  gr.  of  aluminium 
(2-56)  not  proportionate  to  the  atomic  weight  of  iron  (55  9)  to  the 
atomic  weight  of  aluminium  (27)  ?"  Or  "  Why  is  the  sp.  gr.  of 
iron  to  the  sp.  gr.  of  aluminium  not  proportionate  to  the  molecular 
weight  of  iron  to  the  molecular  weight  of  aluminium  ?"  Or  "  Why  is 
it  that  the  sp.  gr.  of  a  body,  in  a  proportion  to  the  sp.  gr.  of  water, 
or  (1),  is  not  the  same  as  the  proportion  formed  by  the  molecular 
weight  of  that  body  and  the  molecular  weight  of  water  or  (18)  ?" 
To  get  a  clear  idea  of  this  matter,  we  must  first  know  that  the  sp. 
gr.  of  a  body  is  a  "  purely  nominal  value  "  and  is  "  the  relative 
weight  of  equal  bulks  of  different  bodies."  From  observation  we 
know  that  a  material  difference  exists  in  the  "  bulk  or  volume"  of 
the  same  weights  of  different  bodies,  while  the  molecular  weights  of 
these  bodies  are  nearly  the  same ;  therefore,  density  is  as  great  a 
factor  in  determining  the  sp.  gr.  of  a  body,  as  is  the  intrinsic  value 
of  the  element  or  elements  contained  in  that  body  compared  to  a 
standard  of  weight.  Physical  research  has  taught  that  molecules 
are  never  in  absolute  contact ;  in  fact,  the  density  of  a  substance  is 
entirely  dependent  upon  molecular  affinity  and  the  pressure  and 
heat  to  which  it  is  subjected.  Let  us  take,  for  instance,  a  body  the 
sp.  gr.  of  which  is  -5,  sp.  volume  2,  and  its  bulk  twice  as  great  as 
that  of  an  equal  weight  of  water.  Now,  if  in  the  space  between 
the  molecules  of  this  body  we  would  place  the  same  number  of  mol- 
ecules of  the  same  construction  as  are  in  the  body,  then  its  sp.  gr. 
