256 
PREPARATION  OF  ROCHELLE  SALTS. 
a  flame.  But  as  Magnus  has  shown  by  a  very  simple,  but  in- 
teresting experiment,  it  may  be  made  combustible  in  a  high  de- 
gree if  it  is  magnetized.  If  a  magnet  approaches  that  delicate 
powder,  this  is  attracted  and  held  up  by  the  magnetic  poles,  and 
if  now  a  burning  splint  is  neared,  the  iron  powder  takes  fire 
which  rapidly  spreads,  and  if  the  magnet  is  shaken,  many  sparks 
are  falling  down,  being  the  burning  particles  of  iron. — Buchners 
Neues  Bepertorium,  1858,  472.  J.  M.  M. 
ON  THE  PREPARATION  OF  ROCHELLE  SALT. 
By  Rebltng. 
The  author,  after  noticing  the  difficulties  and  the  loss  sus- 
tained in  the  attempt  of  freeing  this  salt  of  tartrate  of  lime, 
states  that  he  has  succeeded  in  preparing  it  from  the  crude  and 
the  depurated  commercial  cream  of  tartar,  and  also  from  tar- 
trate of  lime.    The  following  embraces  his  directions  : — 
From  tartrate  of  lime — Take  of  tartrate  of  lime  10  parts, 
purified  soda  6  parts,  purified  potash  2f  parts  ;  boil  with  twenty 
to  twenty-four  parts  of  water  for  half  an  hour,  stirring  occa- 
sionally until  a  filtered  sample  is  not  rendered  turbid  by  carbo- 
nate of  soda  when  heated  to  boiling  ;  after  setting  aside  for  a 
quarter  of  an  hour  to  allow  the  carbonate  of  lime  to  settle,  the 
liquid  is  poured  through  a  porous  paper  filter,  the  residual  lime 
is  twice  washed  with  water,  and  is  afterwards  thrown  on  the 
filter  for  the  tartrate  to  be  entirely  washed  out.  Tartrate  of 
lime  yields  a  little  above  its  own  weight  of  Rochelle  salt. 
From  commercial  cream  of  tartar. — Cream  of  tartar  generally 
contains  8 — at  most  10  per  ct.  of  tartrate  of  lime,  which  must  be 
decomposed  into  bitartrate  of  potassa,  in  order  to  obtain  all  tar- 
taric acid  as  Rochelle  salt.  Take  of  finely  powdered  cream  of 
tartar  16  oz.,  crystallized  soda  14  oz.,  purified  potash  J-  oz., 
water  44  oz.  ;  boil  for  half  an  hour,  until  a  filtered  portion  is 
not  precipitated  by  soda ;  then  filter  and  crystallize.  Almost 
the  whole  of  the  mother  liquor  will  furnish  clear  crystals  ;  when 
they  cease  to  form,  the  liquor  may  be  precipitated  by  muriatic 
acid  to  obtain  cream  of  tartar,  or  it  may  be  neutralized  with 
pure  bitartrate  of  potassa,  when  even  the  soda,  which  had  been 
