PERMANGANATE  OF  POTASSA. 
391 
a  very  small  quantity,  the  addition  of  the  binoxide  causes  trouble- 
some spitting,  and  the  little  drops  thrown  out  are  liable  to  burn 
the  hands  and  face  of  the  operator,  or  fly  in  his  eyes.  The 
aspersion  with  water  requires  care  and  skill  to  get  the  whole 
mass  quickly  moistened  with  the  least  possible  loss  by  the  ex- 
plosive flying  off"  of  the  finer  particles.  There  is  always  much 
loss  from  this  cause,  and  the  portion  lost  is  the  most  soluble 
and  valuable  portion  of  the  whole.  When  finally  heated  ready 
for  dissolving  out  the  soluble  portion,  the  whole  mass  weighs 
within  100  grains  of  three  pounds,  whilst  the  sum  of  the 
weights  of  the  binoxide  and  potassa  would  give  four  pounds. 
This  loss  is  doubtless  in  great  part  water  from  the  potassa,  but 
cannot  all  be  accounted  for  in  this  way,  even  when  the  loss  by 
dust  is  added.  In  dissolving  out  the  salt  from  the  insoluble 
residue,  long  boiling  should  be  avoided,  because  any  lower 
oxides  of  manganese  that  may  have  been  formed  would  be  ox- 
idized at  the  expense  of  the  permanganate.  The  insoluble  re- 
sidue should  not  be  washed  farther  than  is  indicated  in  the  pro- 
cess, because  the  quantity  remaining  in  the  residue  is  insignifi- 
cant, and  does  not  repay  the  loss  from  additional  evaporation. 
The  exhausted  residue  weighs  a  few  grains  less  than  twenty- 
eight  ounces.  Then  as  the  two  pounds  of  binoxide  contained 
about  71  per  cent.,  or  nearly  twenty-three  ounces  of  pure  bin- 
oxide, the  loss  of  four  ounces  of  this  would  be  a  little  over  one- 
sixth,  or  between  16  and  17  per  cent.,  and  this  quantity  would 
represent  about  seven  ounces  of  permanganate  of  potassa,  and 
would  indicate  about  950  grains  as  the  quantity  of  potassa  re- 
ally utilized  or  combined  in  the  process,  all  the  remainder  be- 
ing excess  ;  and,  in  practice,  without  such  excess,  the  product 
is  very  small.  This  is  a  curious  and  unaccountable  feature  in 
the  process.  The  calculated  yield  of  seven  ounces  of  perman- 
ganate is,  however,  never  realized,  but  oftener  four  or  four  and  a 
half  ounces.  What  it  might  be  upon  a  larger  scale  is  as  yet 
undetermined,  but  the  probability  is  that  it  would  not  be  better. 
It  would  doubtless  increase  a  little  by  accumulation  as  the  pro- 
cess was  continued,  since  the  mother  liquor,  being  continually 
passed  on,  would  carry  a  portion  of  the  salt  with  it.  In  making 
the  process  a  continuous  one,  the  proportion  of  potassa  would 
finally  be  reduced  to  about  three  or  four  ounces  to  the  two 
