Am.  Jour.  Pharm.) 
February,  1920.) 
Ionic  Dissociation. 
89 
as  the  product  of  the  original  concentrations.  This  is  in  accord 
with  the  so-called  "law  of  mass  action." 
This  behavior  of  the  ions  may  be  likened  to  a  social  party  at- 
tended by  men  and  women  going  there  in  couples  and  "dissociating" 
as  soon  as  they  come  together  in  the  place  where  the  party  is  being 
held.  The  number  of  chances  each  man  has  of  meeting  a  different 
woman  is  one  multiplied  by  the  number  of  women,  and  the  total 
number  of  chances  of  meetings,  differing  as  to  the  personnel  of  the 
people  concerned,  is  determined  by  multiplying  the  number  of  men 
by  the  number  of  women.  Let  us  suppose  there  are  four  couples 
in  the  party — four  men  and  four  women.  The  number  of  different 
meetings  possible  will  be  4  times  4,  or  16.  Now  let  us  suppose  that 
the  party  is  increased  by  the  appearance  of  six  other  women  each 
carrying  a  dog,  and  that  two  of  the  first  four  women  (who  do  not 
like  dogs)  take  their  escorts  and  go  home.  There  will  be  left  2 
men  and  8  women  and  the  different  combinations  possible  will  be 
2  times  8,  or  16,  as  before.  The  number  of  couples  will  have  been 
reduced  from  four  to  two,  the  man  concentration  decreased  by  half, 
and  the  woman  concentration  increased. 
Now,  let  us  substitute  four  molecules  of  dissociated  water  in  a 
given  volume  for  the  four  couples,  and  we  will  have  four  H  ions  and 
four  OH  ions.  If  we  add  to  the  water  sufficient  sodium  hydroxide 
to  give  us  six  molecules  of  dissociated  NaOH  we  will  be  introducing 
six  Na  ions  and  six  OH  ions,  and  two  molecules  of  water  will  be 
formed  from  two  ions  each  of  H  and  OH,  leaving  only  two  of  the 
original  H  ions.  The  solution  will  now  be  alkaline  from  the  excess 
of  OH  ions,  but  its  strength  may  be  stated  in  terms  of  hydrogen- 
ion  concentration  (acidity),  being  relatively  less  acid  than  water, 
through  having  in  it  fewer  H  ions  (the  cause  of  acidity)  than  originally. 
The  following  table  shows  various  methods  in  use  for  stating  the 
strength  of  solutions  of  acids  and  alkalies  in  terms  of  normality  and 
hydrogen-ion  concentration.  A  normal  solution  of  an  acid  repre- 
sents one  gram  of  H  ions  in  one  liter,  while  a  normal  solution  of  an 
alkali  represents  seventeen  grams  of  OH  ions  in  one  liter.  In  the 
table  the  first  three  columns  show  the  common  fraction  and  deci- 
mal fraction  methods,  respectively,  for  indicating  strengths,  the  third 
column  numbers  being  abbreviated  forms  of  those  in  the  second 
column,  while  the  fourth  and  fifth  columns  show  two  forms  in  use 
for  expressing  the  H-ion  concentrations. 
