SOLUBILITY  OF  CREAM  OF  TARTAR  IN  ACIDS,  ETC. 
41 
hind  is  very  small,  if  the  washing  is  effected  immediately  after 
digestion  ;  if  the  mixture  is  set  aside  for  24  hours,  it  will  be 
mixed  with  crystals  of  bitartrate  of  potassa  containing  lime, 
which  cannot  be  purified  by  washing. 
Cream  of  tartar  is  obtained  entirely  free  from  lime,  if  the 
acid  mixture  is  completely  dissolved  in  warm  water,  and  the 
solution  then  evaporated  with  constant  stirring  until  it  has 
double  the  weight  of  the  salt  employed,  when  it  is  to  be  rapidly 
washed  out. 
The  requisite  quantity  of  muriatic  acid  depends  on  the 
amount  of  lime  present ;  the  more  of  it  is  employed,  the  easier 
will  be  the  removal  of  the  latter,  but  the  greater  likewise  the 
loss  of  cream  of  tartar ;  for  experiment  3  shows  that  i  oz.  of 
concentrated  muriatic  acid  will  dissolve  274  grs.,  or  somewhat 
more  than  its  own  weight.  A.  quantity  of  muriatic  acid  some- 
what larger  than  just  sufficient  for  the  decomposition  of  the 
limesalt,  will  probably  suffice  in  all  cases.  When  evaporating 
with  larger  quantities,  it  is  for  this  reason  advisable  to  make 
an  estimation  of  the  lime  and  calculate  the  necessary  quantity 
of  muriatic  acid,  1  part  of  which,  to  10  of  cream  of  tartar,  will, 
in  most  instances,  be  more  than  sufficient.  100  carbonate  of 
lime  are  equivalent  to  260  tartrate  of  lime,  and  to  70.8  HOI  or 
212.4  muriatic  acid  sp.  gr.  1.164  of  33.3  per  cent. 
The  use  of  thus  purified  cream  of  tartar  in  preparing  tartrate 
of  potassa,  or  of  potassa  and  soda,  &c,  has  the  advantage 
that  less  water  is  necessary,  that  the  crystallization  is  not  dis- 
turbed by  the  subsiding  pulverulent  tartrate  of  lime,  and  that 
the  iron  and  other  coloring  matters  have  been  completely  re- 
moved by  the  muriatic  acid ;  the  loss  of  cream  of  tartar  is  thus 
compensated  for. 
14ib  cream  of  tartar,  containing  8-8  per  ct.  or  nearly  l^ft> 
tartrate  of  lime,  yielded  by  the  process  of  the  Prussian  Phar- 
macopoeia 12ft)  pure  cream  of  tartar,  showing  a  loss  of  |ft),  or 
5.5  per  ct.,  and  gave  17Jft)  clear  Rochelle  salt.  Of  cream  of 
tartar  containing  lime,  4  parts  yield  usually  4j,  rarely  5  parts 
of  this  double  salt ;  the  above  14ft)  would  consequently  have 
furnished  15.81b  to  17.5ft),  or,  under  the  most  favorable  condi- 
tions, not  more  than  in  this  instance. 
