390 
PERMANGANATE  OF  POTASSA. 
Then  set  it  aside  over  night  to  cool  and  crystallize.  Put  the 
whole  into  a  funnel,  the  lower  part  of  which  is  obstructed  by 
broken  glass,  and  allow  the  solution  to  drain  off  from  the  crys- 
tals. Return  this  solution  to  the  basin,  placed  over  the  fire  as 
at  first,  and  having  added  to  it  one  pound  of  the  potassa,  evap- 
orate the  mixture  until  it  begins  to  froth  and  thicken  ;  then 
add  to  it  two  pounds  of  the  binoxide  of  manganese,  and  repeat 
the  entire  process  as  with  the  first  two  pounds ;  and,  finally, 
proceed  in  precisely  the  same  manner  with  the  remaining  two 
pounds  of  the  binoxide.  (And,  should  the  making  be  continued 
farther,  the  proportion  of  potassa  may  be  reduced  to  half  a 
pound  for  each  two  pounds  of  the  binoxide.)  Displace  the 
mother  liquid  contained  in  the  accumulated  crystals  in  the  fun- 
nel, with  distilled  water,  and  dissolve  the  crystals  in  about  six 
pints  of  boiling  distilled  water ;  allow  the  solution  to  settle  for 
half  an  hour,  and  then  pour  the  clear  portion  off  for  crystalli- 
zation. After  twenty-four  hours'  standing,  drain  the  crystals  in 
a  funnel,  wash  them  with  a  fluid-ounce  of  cold  distilled  water,  and 
dry  them  on  a  delf  plate  at  ordinary  temperatures,  protected 
from  dust  and  laboratory  vapors.  Finally,  concentrate  the 
mother  liquors,  and  obtain  one  more  crop  of  crystals,  to  be 
treated  as  the  first,  and  then  add  the  remaining  mother  liquor 
to  that  first  separated  from  the  crude  crystals,  to  be  reserved 
with  it  for  the  next  making,  where  it  may  be  taken  to  repre- 
sent one  and  a  half  pounds  of  potassa.  The  yield  of  finished 
crystals  under  good  management  will  be  20  to  25  per  cent,  of 
the  weight  of  the  oxide  used,  but  under  ordinary  management 
will  not  be  over  16  to  18  per  cent. 
The  residuary  oxide  of  manganese  directed  to  be  thrown 
away,  when  assayed  by  the  method  of  Fresenius  and  Will, 
gives  about  60  per  cent,  of  the  binoxide,  and  therefore  may  be 
reserved  for  making  chlorine,  or  possibly  to  be  used  over  again 
in  this  process. 
Half  of  the  above  quantities  in  a  basin  half  the  size  indicated, 
have  been  repeatedly  used  over  a  good  gas  flame,  but  the  yield 
is  not  proportionally  as  good,  while  the  time  and  labor  is  about 
the  same. 
In  drying  the  mixture  of  binoxide  and  potassa  in  the  first 
step  of  the  process,  if  the  solution  of  potassa  be  not  evaporated  to 
