AMiy?;iP873RM*}    Value  of  Certain  Salts  of  Iron,  etc.  215 
is  as  unyielding  as  it  is  unstable  :  when  you  have  combined  it  with 
strong  acids  you  can  go  no  further  with  its  salts :  you  can  do  nothing 
with  them,  not  even  an  alum.  Sesquioxide  of  iron,  on  the  contrary, 
is  a  perfect  Proteus  ;  sometimes  a  base,  sometimes  an  acid,  it  is  al- 
ways ready  to  enter  into  some  combination  or  other  on  the  slightest 
provocation. 
In  a  paper  published  some  time  ago  I  demonstrated  that  nearly  all 
the  insoluble  sesqui-salts  of  iron  could  be  combined  with  the  alkaline 
citrates,  forming  soluble  and  tasteless  compounds,  to  which  I  gave  the 
name  of  quadruple  citrates. 
Since  then,  further  experiments  have  shown  me  that  other  vege- 
table salts,  besides  the  citrates,  possessed  also  the  same  property,  and 
that  not  only  the  insoluble  but  also  the  soluble  sesqui-salts  of  iron 
could  form  similar  combinations. 
In  other  words,  I  may  lay  down  this  rule  :  All  the  salts  of  sesqui- 
oxide of  iron,  without  exception,  soluble  or  insoluble,  form  combinations 
with  all  the  alkaline  citrates,  tartrates  and  oxalates.  Such  combinations 
are  invariably  green,  whatever  may  be  the  color  of  the  iron  salt ;  they 
are  all  soluble  in  water,  nearly  insoluble  in  alcohol ;  they  are  all  free 
from  ferruginous  taste,  all  perfectly  stable,  and  miscible  with  prepa- 
rations of  Peruvian  bark  without  decomposition.  In  all  of  them  the 
presence  of  iron  is  so  disguised  as  not  to  be  detected  by  chemical 
reagents,  unless  after  the  addition  of  strong  acids  or  sulphuretted 
hydrogen,  both  of  which  destroy  the  combination. 
In  other  papers  I  have  described  the  soluble  compounds  obtained 
in  combining  the  phosphate,  hypophosphate,  valerianate  and  arseniate 
of  iron  with  the  alkaline  citrates.  In  this  I  will  merely  describe  the 
tasteless  combinations  of  the  alkaline  citrates  with  iodide,  chloride, 
sulphate  and  nitrate  of  iron. 
Tasteless  Iodide  of  Iron. 
This  is,  no  doubt,  the  most  important  of  the  whole  series,  both 
therapeutically  and  chemically ;  therapeutically,  because  iodide  of 
iron  is  admitted  to  be  the  best  of  all  iron  combinations ;  chemically, 
because  all  the  reactions  happening  during  its  preparation  are  so  re- 
markable and  so  easy  to  follow  with  accuracy  as  to  be  likely  to  give 
a  key  to  the  real  composition  of  the  rest  of  the  series — a  result  which 
can  hardly  be  obtained  with  any  of  the  other  similar  combinations. 
The  salt  is  obtained  in  the  following  manner:  126,3  grs.  (1  eq.)  of 
