COMMERCIAL  VALUE  OF  MANGANESE. 
73 
Another  . difficult j  occurred  in  effecting  the  solution  of  the  oxide 
of  manganese  in  the  arsenical  solution,  as  in  proportion  to  the  ele- 
vation of  temperature  does  the  loss  of  terchloride  of  arsenic  in- 
crease. This  source  of  error  is  prevented  by  employing  a  dilute 
acid  solution  of  arsenious  acid,  and  adapting  one  of  Will's  nitro- 
gen bulbs,  containing  a  solution  of  potash,  to  the  flask  in  which 
the  oxide  of  manganese  is  dissolved.  Any  terchloride  of  arsenic 
which  may  pass  over  is  there  effectually  retained,  provided  solution 
be  effected  at  a  low  temperature.  The  normal  solution  of  arsenious 
acid  is  made  by  dissolving  113.53  grs.  of  arsenious  acid,  corres- 
ponding to  100  grs.  of  peroxide  of  manganese,  in  a  solution  of 
potash,  and  then  adding  hydrochloric  acid  until  the  solution  occu- 
pies 100  measures. 
A  standard  solution  of  hypermanganate  of  potash  is  obtained  by 
diluting,  for  example,  5  measures  of  the  normal  solution  of  ar- 
senious acid,  corresponding  to  5  grs.  of  peroxide  of  manganese, 
and  then  determining  the  number  of  measures  of  the  solution  of 
hypermanganate  of  potash  that  are  required  to  transform  the  ar- 
senious acid  therein  contained  into  arsenic  acid. 
These  two  solutions  being  obtained,  an  estimation  of  the  value 
of  a  specimen  of  oxide  of  manganese  may  be  expeditiously  and  ac- 
curately made. 
Ten,  or  any  number  of  grains  of  the  specimen  under  examina- 
tion, are  placed  in  a  small  flask,  to  which  10  or  more  measures  of 
the  normal  arsenical  solution  are  added,  and  to  the  flask  is  adapted 
one  of  Will's  nitrogen  apparatus,  containing  a  solution  of  potash. 
The  flask  is  then  placed  in  a  water-bath,  or  a  gentle  heat  is  ap- 
plied until  solution  is  effected.  The  contents  of  the  flask,  after 
having  been  allowed  to  cool,  are,  together  with  the  solution  of 
potash,  transferred  to  a  larger  flask,  and  diluted  with  water.  The 
amount  of  arsenious  acid  remaining  unchanged  is  then  determined 
by  the  addition  of  the  standard  solution  of  hypermanganate  of  pot- 
ash, and  the  quantity  thus-indicated  being  deducted  from  the  num- 
ber of  grains  of  arsenious  acid  employed  in  the  first  instance,  will 
give  the  value  of  the  specimen  submitted  to  analysis. 
In  order  to  obtain  correct  results  by  this  method,  it  is  of  course 
necessary  that  the  hydrochloric  acid  and  the  potash  employed 
should  be  free  from  sulphurous  or  nitric  acid,  or  any  other  reducing 
or  oxidizing  impurities. — Chem.  Gazette,  JVoVo  1,  1853. 
