78     PERMANGANATE  OF  POTASH  AS  AN  OXIDIZING  AGENT. 
filtered.  The  solution  is  then  mixed  with  protopersulphate  of 
iron  and  heated.  It  is  necessary  to  employ  a  spacious  vessel 
for  this  purpose,  as  a  strong  evolution  of  carbonic  acid  takes 
place,  especially  at  the  boiling-point.  The  precipitate  obtained 
is  treated  with  an  excess  of  chemically  pure  muriatic  acid,  when 
the  precipitated  oxide  of  iron  is  dissolved,  leaving  behind  it 
Prussian  blue. 
The  separation  of  the  Prussian  blue  is  facilitated  by  heating 
the  solution  ;  after  filtration  and  complete  washing  with  hot 
water,  and  afterwards  with  alcohol,  it  usually  remains  upon  the 
filter  of  a  dark  blue  color.  If,  however,  it  be  of  a  dingy  green 
color  from  the  presence  of  empyreumatic  constituents  of  the 
tobacco  smoke,  it  must  be  freed  from  this  impurity  by  agitation 
with  ether  and  alcohol,  when  it  always  remains  with  its  charac- 
teristic color. 
It  is  obtained  most  beautiful,  when,  after  it  has  been  washed 
as  much  as  possible  upon  the  filter,  it  is  decomposed  by  solution 
of  potash,  and  a  protopersalt  of  iron  is  added  to  the  solution 
filtered  from  the  peroxide  of  iron,  by  which  it  is  regenerated, 
freed  from  foreign  intermixtures,  after  treatment  with  muriatic 
acid. 
Two  cigars,  weighing  together  10-6  grms.,  furnished  0-018  of 
Prussian  blue  ;  and  two  cigars  of  another  kind,  weighing  together 
8-5  grms.,  gave  0  010  of  Prussian  blue. 
Amongst  all  the  samples  of  tobacco  investigated  in  the  above 
manner  by  the  authors,  there  was  only  one  which  gave  an  im- 
ponderable trace  of  Prussian  blue  from  5  grms.  This  was  a  very 
old  tobacco.  All  the  rest  distinctly  showed  the  presence  of 
Prussian  blue.  The  mode  of  smoking  tobacco,  whether  in  the 
form  of  a  cigar  or  in  a  pipe,  in  fact,  the  mode  of  combustion  in 
general,  appears  to  have  an  influence  upon  the  formation  of 
hydrocyanic  acid  in  the  smoke. — Chem.  G-az.,  Oct.  1858,  from 
Dingier  §  Polyt.  Journal. 
ON  THE  EMPLOYMENT  OF  PERMANGANATE  OF  POTASH  AS 
AN  OXIDIZING  AGENT. 
By  S.  Cloez  and  E.  Guignet. 
To  determine  the  sulphur  contained  in  a  sulphuretted  mate- 
rial, the  most  exact  process  consists  in  converting  the  sulphur 
