Am.  Jour.  Pharm.  ) 
Dec.  1,  1871.  J 
071  Citric  Acid,  Etc. 
541 
The  citrate  of  bismuth  and  soda,  and  the  corresponding  potassic 
salt  are  obtained  easily  by  adding  two  equivalents  of  the  caustic  al- 
kali to  one  of  citrate  of  bismuth  suspended  in  water,  moderate  heat 
being  applied.  They  require,  however,  a  little  more  care  than  the 
analogous  ammoniacal  combination,  for  any  excess  of  potassa  or  soda 
is  liable  to  precipitate  oxide  of  bismuth,  a  decomposition  that  ammo- 
nia will  not  effect  under  any  circumstances.  The  double  citrate  of 
bismuth  and  lithia  may  be  prepared  by  adding  two  equivalents  of  car- 
bonate of  lithia  to  one  of  citrate  of  bismuth,  heat  also  being  applied. 
The  following  are  the  formulas  of  these  double  salts  : 
Citrate  Bismuth  and  Potassa  2  KO,  BiOg.  Q^^llfi^^-\-nE.O 
Soda     2  NaO,  BiOg.  Ci2H,0ji+nH0 
Lithia    2  LiO,  BiOg.  Q,,YLfi,,-^nllO 
Not  having  obtained  these  compounds  in  scales  yet,  I  have  not  been 
able  to  determine  the  equivalent  of  water. 
My  study  of  the  citrates  is  far  from  being  completed,  but  I  have 
collected  facts  enough  to  justify  me  in  proposing  to  divide  the  differ- 
ent citrates  in  three  classes. 
In  the  j^rs^  class  I  would  place  all  the  various  simple  citrates,  where 
the  acid  is  combined  with  one,  two  or  three  equivalents  of  one  base. 
These  are  so  well  known,  that  little  need  be  said  about  them. 
The  second  class  would  comprehend  the  double  citrates,  that  is  those 
salts  in  which  one  equivalent  of  citric  acid  is  combined  with  two  equiv- 
alents of  an  alkali  and  one  equivalent  of  another  base,  generally  me- 
tallic. The  simple  citrate  of  that  case  is  always  less  soluble  than  its 
double  citrate.  The  various  double  citrates  of  bismuth  mentioned  in 
this  paper  may  be  considered  as  types  of  the  second  class,  which  con- 
tains a  great  number  of  them.  Many  are  known  and  mentioned, 
such  as  ammonio-citrate  of  bismuth,  of  iron  ;  potassic  citrate  of  zinc, 
magnesia,  etc.;  their  composition,  however,  is  not  stated  anywhere, 
to  my  knowledge. 
The  third  class,  or  quadruple  citrates,  as  I  propose  to  call  them,  is 
not  so  well  known,  the  only  one  being,  I  believe,  the  soluble  pyro- 
phosphate of  iron  discovered  in  1856  by  E.  Bobiquet,  my  old  friend 
and  employer.  These  salts  I  consider  as  a  combination  in  which  an 
alkaline  neutral  citrate  plays  the  part  of  a  base  and  a  peculiar  me- 
tallic salt  the  part  of  an  acid.  I  have  abundant  facts  to  prove  the 
correctness  of  my  theory,  but  I  will  only  mention  that  I  have  already 
discovered  the  following  new  combinations  which  I  place  in  the  third 
