42 
Ferrous  Citrate  and  Double  Salts. 
f  Am.  Jour.  Pharm. 
I      Jan.,  1883. 
cases  where  compound  molecules  of  saturated  valence  still  continue  to 
combine  and  where  elementary  molecules  coalesce  with  seemingly 
abnormal  capacities.  In  the  opposite  direction  we  also  find  that  many 
elements  most  usually  do  not  exert  their  full  atomic  power.  Such 
instances  are  termed  apparent  valence.  This  important  condition  is 
most  thoroughly  representative  of  chemism  at  its  climax.  Apparent 
valence  generally  gives  rise  to  compounds  of  the  greatest  stability  owing 
to  the  fact  that  the  intra-molecular  affinities  have  been  subjected  to 
fewer  subdivisions  than  in  the  states  of  higher  atomicity.  In  chemical 
notation  some  difficulty  is  experienced  in  expressing  the  formulas  of 
compounds  containing  the  same  element  in  different  degrees  of  valence. 
Although  the  atomicity  is  most  usually  noted  by  indices,  a  much  more 
striking  and  definite  notation  would  be  acceptable.  To  illustrate  a 
change  in  that  direction  the  ferrous  condition  might  be  indicated  by 
Fo,  the  ferric  by  Fi,  and  the  ferrate  by  Fa.  Other  elements  of  vary- 
ing atomicity  could  be  similarly  treated.  In  course  of  time  ultra- 
valence  will  probably  command  commensurate  notice.  The  chemical 
notation  used  in  pharmacy  is  often  conveniently  abbreviated,  especially 
to  avoid  writing  out  in  full  the  complicated  formulas  of  the  acids  of 
carbon.  But  the  system  employed  is  not  only  confusing,  but  erroneous. 
The  abbreviation  for  citric  acid,  for  instance,  was  written  Ci,  and  in  its 
combinations  it  still  appeared  as  Ci.  Now  the  proper  and  consistent 
l^lan  is  to  designate  the  radicles  only  in  shortened  forms,  and  hence 
citric  acid  may  be  written  HgCi. 
On  a  former  occasion  when  treating  of  ferro-ferric  or  ferroic  citrate 
the  writer  obtained  the  formula  for  ferrous  citrate  from  a  faulty  source, 
stating  it  to  be  a  triferrous  salt,  thus,  Fe32Ci.  When  recently  operat- 
ing on  definite  quantities  of  material  the  writer,  however,  found  that 
it  is  a  diferrous  citrate,  thus,  Fe2H2Ci2  or  FeHCi,  that  is,  in  fact,  a 
double  citrate  of  iron  and  hydrogen,  or  properly,  a  hydroferrous  citrate. 
Correctly  speaking,  a  double,  triple,  etc.,  salt  is  invariably  derived  from 
a  single  acid  by  substitution  of  the  basic  hydrogen  by  one  or  more 
basic  radicles  partially,  or  by  more  than  one  basic  radicle  wholly.  But 
when  the  conditions  are  reversed,  that  is,  when  one  basic  radicle  unites 
with  more  than  one  acid  radicle  secondary,  tertiary,  etc.,  salts  are 
formed.  Yet  further,  when  a  multiplicity  of  both  acid  and  basic 
radicles  converge  to  form  a  compound  molecule  then  secondary  double 
salts,  tertiary  triple  salts,  etc.,  are  produced. 
Ferrous  citrate,  when  prepared  by  boiling  citric  acid  with  metallic 
