^^"iv/aTis^"" }        Diffusive  Properties  of  Iron,  267 
The  experiments,  the  results  of  which  1  am  about  to  lay  before  the 
Society,  were  made  for  the  purpose  of  showing  what  the  relative  diffu- 
sive power  of  some  of  the  salts  of  iron  is,  and  to  what  extent  this  is 
connected,  in  such  salts,  with  their  crystalline  or  amorphous  condition. 
The  dyalizer  used  in  the  experiments  consisted  of  a  glass  jar,  the 
membrane  covered  mouth  of  which  was  5 J  inches  in  diameter;  and 
this  rested  in  the  mouth  of  a  wide  earthen  dish.  Two  thousand  grain- 
measures  of  either  a  5  per  cent,  or  a  10  per  cent,  solution  of  the  salt 
used  was  put  into  the  glass  jar,  and  25  ounces  of  water  into  the  dish. 
The  difFusate  was  usually  removed  at  the  expiration  of  two,  but  some- 
times of  three  days,  at  the  commencement  of  an  experiment,  although 
a  longer  time  was  allowed  for  each  separate  diffusion  when  the  action 
became  sluggish  towards  the  end  of  an  experiment. 
I.  Citrate  of  Iron^  Ferric  Citrate. — Some  simple  citrate  of  iron  was- 
made  in  the  usual  way,  by  dissolving  to  saturation  moist,  recently  pre- 
cipitated hydrated  peroxide  of  iron  in  solution  of  citric  acid.  After 
being  scaled  and  dried  at  212°,  it  was  found  to  contain  32*29  per  cent, 
of  ferric  oxide,  FcgOg.  Aided  by  heat,  it  was  perfectly  soluble  in 
water,  the  solution  being  acid  to  test  paper.  200  grains  of  this  salt 
dissolved  in  water  to  make  2,000  grains  (10  per  cent,  solution)  was  put 
into  the  dialyzer.  At  the  expiration  of  two  days  the  diffusate  was 
removed,  evaporated  to  dryness,  and  the  residue  dried  at  2I2°F.  It 
amounted  to  51*26  grains,  or  25*63  per  cent,  of  the  salt,  and  on  being 
incinerated  it  gave  22*45  grains,  or  43*75  per  cent,  of  oxide  of  iron. 
It  thus  appeared  that  the  iron  was  diffusing  more  rapidly  than  the  acid 
with  which  it  had  been  combined.  Fresh  water  having  been  mtro- 
duced  into  the  dish,  the  diffusion  subsequently  went  on  more  slowly^ 
but  the  results  still  showed  that  the  iron  was  diffusing  more  rapidly 
than  the  acid.  At  the  end  of  fifteen  days,  125*59  grains  of  the  salt 
had  passed  through  the  membrane. 
The  results  of  the  experiment  are  given  in  the  following  tabulated 
statement : 
200  grains  of  Citrate^  containing  64*58  grains  of  Yq^O^  in  Dialyzer. 
Amount  of 
Amount  of 
Per  cent,  of 
Per  cent  of 
Days. 
salt 
FeoO.3  in 
salt 
FeoO.-i  in 
diffused. 
diffusate. 
diffused. 
diffusate. 
2 
5i"26 
22-45 
25-63 
4375 
4 
44-81 
19-45 
22-41 
45*63 
4 
20-50 
8-67 
10-25 
42*26 
5 
9*02 
4-10 
4-51 
45*45 
14 
6-37 
3-68 
3-i8 
57-77 
29 
131-96 
58-35 
65-98 
