"^""MaTxs^or™ }         Diffusive  Properties  of  Iron.  27 1 
3.  Potassio-  Tartrate  of  Iron^  Tartarated  Iron. — This  salt,  which,  until 
the  adoption  of  the  process  now  given  in  our  Pharmacopoeia,  was  com- 
monly supplied  in  the  form  of  an  imperfectly  soluble  powder,  is  now 
produced  in  soluble  transparent  scales.  But,  as  it  is  more  susceptible 
of  change  from  slight  variation  of  the  conditions  to  which  it  is  sub- 
jected, it  is  less  uniform  in  composition  and  properties  than  the  salt 
previously  referred  to — the  ammonio-citrate.  Several  samples  of  potas- 
sio tartrate  of  iron  were  submitted  to  dialysis. 
(3,  a.) — A  10  per  cent,  solution  of  potassio-tartrate  containing  31  "09 
per  cent,  of  Fe203  was  put  into  the  dialyzer.  In  two  days  94*02  grains 
or  47  01  per  cent,  of  the  salt  had  diffused,  containing  ii'^j  per  cent, 
•of  P'e203.  In  four  days  more  a  further  quantity  of  25*99  gi'^ins,  or 
I2'99  per  cent,  of  the  whole  was  obtained,  containmg  32*97  per  cent, 
of  Fe203.  Only  slight  diffusion  took  place  beyond  this.  The  residue 
left  in  the  dialyzer  at  the  end  of  ten  days  contained  65*36  per  cent,  of 
Fe,03. 
(3,  Z*.) — A  10  percent,  solution  of  potassio-tartrate,  containing  36.25 
per  cent,  of  Fe203,  submitted  to  dialysis,  gave  in  two  days  a  diftusate 
from  which  53'0i  grains,  or  26*5  per  cent,  of  a  salt  containing  8'82 
per  cent,  of  Fe203  was  obtained.  In  four  days  more  another  product 
of  22*32  grains,  or  ii*i6  per  cent,  of  the  whole,  and  containing  7*03 
per  cent,  of  Fe203  was  obtained.  The  residue  left  in  the  dialyzer 
contained  62*70  per  cent,  of  Fe203. 
(3,  c.) — A  10  per  cent,  solution,  the  same  as  the  last,  but  rendered 
alkaline  with  potash,  after  being  dialyzed  for  two  days  gave  a  diffusate 
containing  79*83  grains,  or  39*91  per  cent,  of  dry  salt,  with  12*31  per 
cent,  of  Fe203.  In  another  four  days  33*7  grains  or  16  85  per  cent,  of 
the  salt  had  diffused,  containing  10*71  per  cent,  of  Fe203.  The  resi- 
due in  the  dialyzer  contained  60*30  per  cent,  of  Fe203. 
The  following  table  gives  the  principal  results  of  the  preceding  three 
experiments  : 
Ten  per  cent.  Solutions  (200  grains  Potassio-  Tartrate  of  Iron  in  2,000  grains 
of  Solution)  Dialyzed for  Six  Days. 
Amount  of  salt    Per  cent,  of  salt    Per  cent,  of  FeoOs    Diffusion  on      Per  cent,  of  FeoO.j 
diffused.  diffused.  in  diffusate.        tne  sixth  day.   in  salt  n^t  diffused. 
(3,  a)  120  0  6o'o  24*9  not  ended  65  36 
(3,  b)  75*33  37  66  8-2  not  ende-d  62-70 
(3,  ii3'53  56*76  II-8  not  ended  60*30 
It  thus  appears  that  the  potassio-tartrate  of  iron  is  a  less  diffusable 
salt  than  the  ammonio-citrate,  and  this  especially  applies  to  the  iron  as 
