laster's  method  op  preparing  sulph.  of  manganese.  175 
the  case  directly  after  the  heat  has  reached  redness,  and  there 
should  be  no  elimination  of  free  oxygen,  as  takes  place  when 
the  heat  becomes  full  red ;  consequently  we  may  know  from 
these  phenomena  that  there  is  loss  of  acid  from  its  decomposi- 
tion, also  a  loss  of  sulphate  of  manganese,  because  at  the  high 
temperature  the  sulphate  is  decomposed  into  protosesquioxide  of 
manganese,  sulphurous  and  sulphuric  acids,  thus  (3  MnO  S03)= 
SO2,  2  S03-fMn304,  and  whatever  be  the  proportions  of  sulphate 
or  binoxide  used  in  this  process  there  will  be  an  excess  of  proto- 
sesquioxide of  manganese.  The  mass,  after  cooling,  is  to  be 
subjected  to  the  action  of  water,  which  removes  the  sulphate  of 
manganese,  which  is  freed  from  iron  by  the  usual  process.  This 
method  of  preparing  the  above  sulphate  is  the  most  laborious, 
and  the  results  generally  unsatisfactory. 
A  second  method  is  to  heat  binoxide  of  manganese  with  sul- 
phuric acid,  and  after  the  mass  has  cooled,  again  treating  with 
sulphuric  acid,  the  moistened  mass  is  to  be  again  heated  ;  the 
portion  of  sulphate  of  manganese  formed  is  -to  be  removed  and 
treated  as  in  the  first  process.  Operating  *in  this  manner  we 
not  only  use  an  excess  of  sulphuric  acid,  which  is  driven  off  at 
the  high  temperature,  but  we  have  the  bin,  or  as  Mr.  Laster 
more  properly  expresses  it,  the  compound  Mn304,  which  event- 
ually changes  to  binoxide  eveloping  in  excess  the  sulphate 
formed. 
The  admirable  process  introduced  by  Mr.  Laster  enables  the 
pharmaceutist  to  overcome  these  difficulties,  and  is  thus  briefly 
stated  by  him : 
"  Take  of   Binoxide  of  Manganese,  40  parts, 
Hydrochloric  Acid  (Commercial),  200  parts. 
Dissolve  the  binoxide  in  the  acid,  beneath  a  chimney  flue,  and 
when  solution  is  complete  and  chlorine  no  longer  evolved,  mix 
very  gradually  sulphuric  acid  (53)  parts  with  the  reddish  liquid ; 
continue  the  evaporation  beneath  the  flue  until  acid  vapor  is  no 
longer  driven  off,  and  the  mass  becomes  dry.  Dissolve  this  mass 
in  water  (350  parts)  heated  to  the  boiling  point.  Treat  this  so- 
lution with  carbonate  of  manganese  until  it  becomes  rose  red, 
filter  or  decant,  evaporate  and  crystallize." 
Unlike  the  objectionable  article  of  the  U.  S.  Pharmacopoeia, 
