:318  Lithim  Citras.  {'^""iine'isss*'''"' 
There  are  two  sources  : — 
1st.  The  carbonate  of  lithium. 
2d.  The  citric  acid. 
The  chief  impurities  in  the  carbonate  are  calcium,  potassium,  and 
sodium  chlorides. 
The  citric  acid  may  contain  tartaric  acid,  salts  of  potassium  and 
calcium,  together  with  iron,  lead  and  copper.^ 
The  mineral  lepidolite,  a  silicate  of  aluminium,  potassium  and 
iithium. 
Petalite,  a  silicate  of  aluminium,  sodium  and  lithium. 
Triphyline,  a  phosphate  of  iron,  manganese,  sodium,  and  lithium, 
mid 
Spodumene,  another  silicate  of  aluminium,  sodium  and  lithium,  are 
the  principal  sources  whence  the  lithium  carbonate  of  commerce  is 
derived. 
A  description  of  two  of  the  processes  by  which  the  carbonate  of 
lithium  is  prepared  from  lepidolite,  etc.,  may  be  interesting,  as  show- 
ing how  the  impurities  before  alluded  to  come  to  be  present  in  the 
<;arbonate. 
1.  Schering's  process  for  obtaining  lithium  carbonate  from  lepido- 
lite, which  is  the  greatest  source  of  the  lithium. — The  lepidolite  is 
ground  up,  treated  with  strong  sulphuric  acid.  It  is  heated  with  con- 
stant stirring  until  it  gains  consistency  enough  to  be  made  into  balls, 
which  are  then  introduced  into  a  reverberatory  furnace.  The  slight 
excess  of  sulphuric  acid  is  driven  off  at  a  gentle  heat,  the  temperature 
is  then  raised,  and  the  pieces,  while  still  hot,  are  treated  with  water  in 
vessels  lined  with  lead.  Silica  is  then  removed  by  filtration,  and  to 
the  lye  sufficient  carbonate  of  potassium  is  added  to  convert  all  the 
alumina  present  into  alum,  as  lithium  does  not  replace  potassium  in 
alum.  The  alum  meal  separating  on  boiling  is  removed,  and  the  small 
remaining  quantity  of  alum  is  precipitated  by  milk  of  lime ;  all  the 
lyes  are  united,  the  salts  converted  into  chlorides  by  treatment  with 
barium  chloride,  the  liquid  is  evaporated  to  dryness,  and  the  lithium 
and  calcium  chlorides  are  extracted  with  absolute  alcohol  in  order  to 
separate  them  from  the  barium,  sodium  and  potassium  chlorides  pre- 
sent. The  calcium  is  separated  by  ammonium  oxalate.  Any  heavy 
metals  w^hich  may  happen  to  be  present  are  got  rid  of  by  ammonium 
sulphide.    The  lithium  chloride  is  evaporated  to  dryness  in  a  large 
^  A.  H.  Allen,  Chem.  News,  xxxi.,  277. 
