266 
Diffusive  Properties  of  Iron, 
Am.  jour.  Pharm. 
May,  1E80. 
oxide  of  iron  as  it  exists  in  dialyzed  iron,  and  founded  on  the  observa- 
tion of  these  properties  it  has  been  inferred  that  dialyzed  iron  is  a  very- 
inert  preparation.  The  iron  exists  here  in  u^hat  Graham  has  desig- 
nated the  colloidal  state,  in  which  it  has  a  very  lou^  diffusive  power. 
It  was  observed  by  Graham  that  substances  which  in  solution  possessed 
very  low  diffusive  power  were  characterized  by  the  absence  of  the  crys- 
tallizing property  and  that  they  generally  formed  gelatinous  hydrates^ 
while  substances  of  high  diffusive  power  generally  belonged  to  the  class 
of  crystalline  bodies.  Hence  the  names  colloid  and  crystalloid  applied 
to  these  two  classes  of  substances. 
But  although  substances  of  very  low  diffusive  power  are  always 
found  to  be  uncrystallizable,  it  cannot  be  inferred  that  the  absence  of 
crystalline  property  will  be  necessarily  attended  with  low  diffusive 
power.  I  proved  this  experimentally  many  years  ago,  and  briefly  stated 
the  fact  in  a  communication  made  to  this  Society  on  Dialysis  in  1862* 
Yet  the  opinion  appears  to  be  often  entertained  that  the  diffusive  pro- 
perty of  substances  in  solution  bears  some  relation  to  the  power  they 
possess  of  assuming  a  crystalline  condition  ;  and  as  we  have  now  sev- 
eral preparations  of  iron,  largely  used  and  considered  to  be  efficacious 
medicines,  which  are  entirely  devoid  of  the  power  of  crystallizing,  it 
may  be  of  use  to  show  the  position  which  these  and  some  other  prepa- 
rations occupy  with  regard  to  their,  diffusive  properties. 
If,  as  stated  by  M,  Personne  in  his  recent  communication  to  the 
French  Academy  of  Medicine,  a  notice  of  which  appeared  in  the 
Pharmaceutical  Journal  "  of  last  November,  dialyzed  iron  is  inca- 
pable of  being  absorbed  during  its  passage  through  the  intestinal  canal^ 
and  is  therefore  inactive,  and  if  this  is  due  to  the  colloidal  state  of  the 
iron,  it  might  be  expected  that  other  preparations  of  iron  would,  at  any 
rate  to  some  extent,  owe  their  activity  as  medicinal  agents  to  their  dif- 
fusive properties. 
Now,  among  the  preparations  of  iron  which  have  become  most 
largely  used  in  medicine  are  the  scaled  preparations,  which,  in  com- 
mon with  dialyzed  iron,  are  often  preferred  to  the  crystalline  salts  of 
iron  on  account  of  the  absence  of  the  inky  taste  which  characterizes 
the  latter.  The  absence  of  inky  taste  and  strong  styptic  property  may 
tend  to  induce  a  belief  that  the  scaled  preparations  of  iron  are  either 
colloidal,  like  dialyzed  iron,  or  at  least  that  they  are  deficient  in  diffu- 
sive power,  for  colloids  are  usually  marked  by  absence  or  deficiency  of 
taste. 
