42 
Notes  on  Aluminium  Flares. 
Am.  Jour.  Pharm. 
January,  1920. 
cinol  and  to  make  a  determination  of  pentosans  in  a  much  shorter 
time. 
Oklahoma  Agricultural  Experiment  Station, 
Stillwater,  Oklahoma. 
NOTES  ON  ALUMINIUM  FLARES.^ 
By  Ernest  H.  Brittain. 
The  use  of  magnesium  ribbon  and  powder  in  flashlight  photog- 
raphy is  famiUar  to  every  chemist,  but  it  is  not  so  generally  known 
that  aluminium  is  more  frequently  used  in  the  various  signal  lights, 
rocket  stars,  ground  flares,  etc.,  which  became  so  familar  during  the 
great  war.  Aluminium  is  used  in  the  form  of  fine  powder  similar 
to  the  aluminium  bronze  used  in  making  aluminium  paints,  etc., 
and  for  pyrotechnic  purposes  is  compounded  with  barium  or  potas- 
sium nitrate  and  other  ingredients  in  varying  proportions,  accord- 
ing to  the  specific  purpose  for  which  the  flare  may  be  required. 
Sometimes  a  mixture  of  aluminium  and  magnesium  is  used,  as  in 
the  "star  compositions"  used  in  signal  rockets.  The  aluminium 
powder  should  be  very  fine,  capable  of  passing  through  a  120-mesh 
sieve,  and  should  be  as  free  from  oil,  grease,  or  soap  as  possible.  It 
must  also  be  free  from  grit,  sand,  or  other  impurities.  There  are 
two  kinds  of  aluminium  powder  on  the  market — a  dull  grey  variety 
and  a  bright,  lustrous,  silvery  kind  (but  every  gradation  between 
is  also  made).  The  lustrous  kind  is  used  for  aluminium  paints  on 
account  of  this  property,  and  its  luster  is  due  to  the  use  of  oil  or 
grease  in  manufacture.  This  kind  is  not  so  suitable  for  pyrotech- 
nical  purposes  as  the  dull  grey,  since  it  is  more  dangerous  when 
compounded.  Even  dull  aluminium  powders  frequently  contain 
considerable  percentages  of  oil,  oil  being  used  by  the  manufacturer 
as  a  safety  precaution.  The  powdering  of  aluminium  is  a  dangerous 
business,  as  spontaneous  combustion  is  not  infrequent,  and  with 
the  intense  heat  of  burning  aluminium,  to  say  nothing  of  the  explo- 
sive violence  of  such  conflagrations,  any  measure  of  precaution  is 
welcomed  by  the  manufacturer.  The  exact  cause  of  these  spon- 
taneous ignitions  is  unknown,  but  the  use  of  oil  in  powdering  seems 
to  prevent  them  to  a  considerable  extent.  Even  then  the  mills 
are  operated  in  the  open,  or  only  under  rough  sheds,  and  left  unat- 
^  From  The  Chemist  and  Druggist,  November  22,  1919. 
