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Ionic  Dissociation. 
(Am.  Jour.  Pharm. 
\     February,  1920. 
constants  for  the  pure  solvent.  The  conductivity  method  is  the 
one  most  used,  though  results  calculated  from  all  agree  closely  in 
practice. 
A  tabular  arrangement  of  some  of  the  common  acids,  bases  and 
salts,  with  data  showing  the  degree  to  which  they  ionize  under  simi- 
lar conditions  is  instructive.  The  figures  given  show  percentages 
of  dissociation  at  i8°  C,  and,  except  where  otherwise  indicted,  are 
for  normal  {N / 1)  aqueous  solutions: 
Substance.  Per  Cent.  Dissociated. 
Nitric  Acid  (62%)   9.0 
Nitric  Acid  (6.3%)   83.0 
Sulphuric  Acid  (  5%)   0.7 
Sulphuric  Acid  (iV/i )   51.0 
Hydrofluoric  Acid  •  •  •  •      7  0 
Acetic  Acid   9.4 
Potassium  Hydroxide   77  0 
Sodium  Hydroxide   73  •  o 
Ammonium  Hydroxide   0.4 
Disodium  Phosphate  (A/32)   83.0 
Ammonium  Chloride   74  •  o 
Sodium  Chloride   67.6 
Sodium  Sulphate   44  -5 
Zinc  Sulphate   24.0 
Copper  Sulphate   22.0 
Mercuric  Chloride   i .  o 
Carbonic  Acid  (A/ 10)   0.17 
Phosphoric  Acid  (A/2)   0.17 
Boric  Acid  (A/io)   o.oi 
Calcium  Hydroxide  (saturated  solution)   90.0 
Most  chemical  action,  possibly  all  chemical  action,  is  between 
ions  and  not  molecules. 
Hydrion  holds  its  charge  less  firmly  than  most  cations  of  bases. 
This  explains  the  action  of  acids  on  metals  where  hydrogen  gas  is 
liberated  as  the  metal  goes  into  solution.  Hydrion  loses  its  charge 
and  becomes  free  hydrogen  while  the  metal  takes  the  charge,  be- 
comes ionic  and  passes  into  solution. 
Example:    Zn  +  H+  +  H+  +  SO4—  =  Zn++  +  H2  +  SO4— . 
Hydroxidion  0H~  holds  its  charge  less  firmly  than  almost  any 
other  anion  except  chloridion  (Cl~),  bromidion  (Br~),  iodidion 
(I~)  and  their  like. 
Highly  concentrated  acids,  even  the  so-called  "strong"  acids — 
hydrochloric,  nitric  and  sulphuric — have  little  or  no  action  on  metals 
