256 
ON  THE  UTILIZATION  OF  CHROME  ALUM. 
parative  trials,  it  is  not  only  essential  to  have  all  the  experi- 
ments conducted  on  the  same  principle,  as  regards  detail,  but  it 
is  also  of  the  greatest  importance  that  the  surface  of  the  liquid 
and  the  taper  used  in  catching  the  exact  point  at  which  the 
vapor  explodes,  shall  be  at  an  equal  distance  in  each  case.  This 
point  is  of  the  first  importance  to  all  who  test  the  igniting  point 
of  vapors ;  and  to  explain  this  statement  more  clearly,  I  have 
printed  on  the  table  the  results  of  experiments  made  on  the  same 
commercial  samples,  keeping  the  lighted  taper  IJ  inches  from 
the  surface  of  the  liquid,  in  one  case,  and  in  the  other  at  only 
half  an  inch  from  the  surface  of  the  sample  under  trial.  The 
results  are  as  expected — when  the  vapor  has  to  diffuse  and  mix 
with  atmospheric  air  through  a  space  of  IJ  inches,  it  is  found 
that  a  greater  temperature  is  required  in  order  to  evolve  the 
larger  quantity  of  vapor,  than  in  the  experiments  of  only  half 
an  inch  between  the  lighted  taper  and  sample  ;  and  this  is  ex- 
plained by  the  circumstance  that  the  vapor,  immediately  on 
being  liberated,  mixes  with  the  small  volume  of  atmospheric  air 
in  the  experimental  basin,  forming  with  it  a  mixture  which,  on 
meeting  a  light,  explodes.  In  the  other  set  of  experiments,  a 
greater  temperature  is  required  to  disengage  a  larger  volume  of 
vapor  to  mix  with  the  greater  proportion  of  air. — Chem.  News^ 
Jan.  1869. 
NOTE  ON  THE  UTILIZATION  OF  CHROME  ALUM. 
By  M.  F.  Jean. 
The  manufacture  of  aniline  green  and  violet,  and  of  valerianic 
acid,  gives  abundant  residues  of  chrome  alum.  These  residues 
cannot  be  utilized  as  mordants,  because,  when  calcined,  they  are 
insoluble  in  water,  and  therefore  do  not  find  a  sufficient  market, 
thereby  considerably  augmenting  the  net  price  of  products  pre- 
pared with  bichromate  of  potash.  Whilst  endeavoring  to  turn 
these  residues  to  account,  I  discovered  that  when  chrome  alum, 
previously  mixed  with  three  equivalents  of  carbon,  is  heated  to 
redness,  decomposition  takes  place  as  follows  : — 
S03KO,3S03Cr203-f3C:=3S02+S03KO+Cr203+3CO. 
If,  on  the  other  hand,  chrome  alum  be  decomposed  with  seven 
