160  IRON  ALUM. 
Series  of  Alums  described  by  different  Authors, 
General  formula  M2  08,  3  S03  +  MO,  S03  +  24  Aq. 
Common  Alum. 
With  Potash  Al2  03,  3  S03  +  KO,  S03  +  24  Aq. 
"   Soda  Al2  03,  3  S08  +  NaO,  S03  +24  Aq. 
"    Ammonia  Al2  03,  3  S03  +  NH40,  S03+  24  Aq. 
"    Magnesia  Al2  03,  3  S03  +  Mg  O,  S03  +24  Aq. 
"    Lithia  Al2  03,  3  S03  +  Li  0,  S03  +  24  Aq. 
"    Manganese  Al2  03,  3  S03  +  Mn  O,  S03  +  24  Aq. 
"    Iron  Ala  03,  3  S03  +  Fe  0,  S03  +  24  Aq. 
Iron  Alum. 
With  Potash  Fe2  03,  3  S03  +  KO,  S03  +  24  Aq. 
"    Soda  Fe2  03,  3  S03  +  NaO,  S03  +  24  Aq. 
"    Ammonia  Fe2  03,  3  S03  +  NH40,  S08  +  24  Aq. 
Chrome  Alum. 
With  Potash  Cr2  08,  3  S03  +  KO,  S03  +  24  Aq. 
"    Soda  Cr2  08f  3  S03  +  Na  0,  S03  +  24  Aq. 
"    Ammonia  Cr2  03,  3  S03  +  NH4  0,  S03  +  24  Aq. 
Manganese  Alum. 
With  Potash  Mn2  03}  3  SO,  +  KO,  S03  +  24  Aq. 
"    Soda  Mn2  03,  3  S03  +  Na  0,  S03  +  24  Aq. 
«    Ammonia  Mn2  03,  3  S03  +  NH4  O,  S03  +24  Aq. 
It  would  be  seen  from  this  table  that  many  of  the  salts  to  which 
the  term  alum,  in  its  most  comprehensive  sense,  was  applied,  and 
including  the  iron  alum  in  question,  contain  no  alumina.  He  had 
been  principally  induced  to  bring  the  subject  under  the  notice  of 
the  meeting  in  consequence  of  some  doubt  and  misapprehension 
having  existed  among  Pharmaceutists  to  whom  prescriptions  or- 
dering iron  alum  had  been  taken,  as  to  the  salt  intended  to  be  in- 
dicated by  that  term.  As  already  stated,  the  salt  now  used  at  St. 
Mary's  Hospital  is  the  double  sulphate  of  peroxide  of  iron  and 
potash.  It  is  prepared  either  by  dissolving  peroxide  of  iron  in 
sulphuric  acid,  or  by  peroxidizing  protosulphate  of  iron  with  ni- 
tric acid,  and  adding  an  equivalent  of  sulphate  of  potash.  If  the 
salt  with  ammonia  be  required,  sulphate  of  ammonia  is  added  in- 
stead of  sulphate  of  potash.  The  solution,  with  excess  of  sulphu- 
ric acid,  is  to  be  evaporated  until  crystals  are  formed  on  cooling. 
