32  Laboratory  Notes.  {^"^'i^Z'S^s-^^' 
tity  of  dry  oxalate  produced  is  30  grammes.  To  convert  into  carbon- 
ate project  the  oxalate  little  by  little  into  a  platinum  capsule  over  a 
good-sized  Bunsen  burner  3  after  being  strongly  heated,  the  oxalate  is 
decomposed  into  the  carbonate,  and,  if  heated  high  enough  to  be  fused, 
will  furnish  about  23  grammes  of  fused  carbonate  of  soda ;  fused  or 
not,  dissolve  in  water,  filter,  evaporate  to  dryness,  dehydrate  over  a 
naked  flame,  and  granulate  it  by  stirring  when  hot. 
Double  or  quadruple  the  quantities  above  given  may  be  operated  upon 
at  once  with  similar  results.  The  carbonate  of  soda  thus  made  is  per- 
fectly free  from  chlorine,  sulphuric  acid,  silica,  or  other  impurity  that 
will  interfere  with  its  use  in  analysis. 
Pure  Carbonate  of  Potash. — It  may  be  wrong  to  use  the  word  pure  in 
connection  with  the  preparation  of  this  substance  in  the  manner  to  be 
described,  as  it  may  contain  at  the  end  of  the  operation  a  trace  of 
nitrate  of  potash.    The  starting  point  is  pure  nitre,  which  is  a  cheap 
potash  salt,  and  can  be  readily  purified  by  repeated  crystallization  ;  the 
other  is  oxalic  acid,  the  commercial  acid  crystallized  once  or  twice  ;  50 
grammes  of  pure  nitre  and  100  grammes  oxalic  acid  are  placed  in  a 
platinum  capsule  ;  to  this  is  added  a  small  quantity  of  water,  and  heated 
over  a  gas  burner  ;  before  the  mixture  is  entirely  dry,  a  second  portion 
of  water  is  added  and  the  heat  continued  until  the  mass  is  brought  to 
dryness,  at  which  time  nearly  all  the  nitric  acid  of  the  nitre  is  expelled ; 
the  heat  is  now  continued,  and  the  whole  mass  brought  to  redness, 
breaking  up  the  lumps  with  an  iron  rod,  when  the  oxalate  of  potash 
formed  will  be  decomposed  into  the  carbonate  ;  the  mass  is  treated  with 
water,  filtered,  dried  and  granulated  over  the  flame  ;  this  furnishes  about 
31  grammes  of  carbonate  of  potash  which,  as  I  have  already  said,  may 
contain  a  little  nitre,  but  this  in  no  way  interferes  with  the  ordinary  use 
of  carbonate  of  potash  in  making  fusions.    For  this  purpose,  I  com- 
monlv  mix  equal  parts  of  carbonates  of  soda  and  potash  at  the  time 
thev  are  required  for  use. 
Absolute  Alcohol. — This  substance,  as  obtained  in  commerce,  very 
seldom  marks  more  than  98  or  99  per  cent.  It  is,  however,  not  unfre- 
quently  made  in  our  laboratories,  and  when  this  is  done  the  usual  method 
is  emploved  of  pouring  strong  alcohol  on  lime  until  the  lumps  of  lime 
are  covered.  This  method  of  proceeding  gives  a  thick  magma  which; 
when  heated  over  a  water-bath,  allows  the  alcohol  to  pass  over  but 
slowly,  and  much  of  the  alcohol  is  lost  from  the  impossibility  of  the 
heat  penetrating  the  thick  mass.    The  method  I  follow  differs  from 
