The Chemistry of Powder and Explosives - Sciencemadness Dot Org

68 PYROTECHNICS
has been inserted and fixed in place by a blob of paste of meal
powder with gum-arabic water.
Aluminum and Magnesium Flares
When barium and strontium nitrates are used in colored lights,
these substances serve the twofold purpose of coloring the flame
and of supplying oxygen for its maintenance. The materials which
combine with the oxygen to yield the flame, in the compositions
which have been described, have been sulfur and carbonaceous
matter. If, now, part or all of these materials is substituted by
magnesium or aluminum powder or flakes, the resulting composition
is one which burns with an intensely bright light. A mixture
of potassium perchlorate 7 parts, mixed aluminum powder and
flakes 5 parts, and powdered sulfur 2 parts burns with a brilliant
light having a lilac cast. A balanced mixture of barium and
strontium nitrates, that is, of green and red, gives a light which is
practically white. Such lights are used in parade torches and
signals, but are so bright as to be trying to the eyes. They find
important use in aviation for signaling and for illuminating landing
fields and military objectives.
Magnesium is attacked fairly rapidly by moisture, and pyrotechnic
mixtures containing this metal do not keep well unless
the particles of magnesium are first coated with a protecting
layer of linseed oil or similar material. Aluminum does not have
the same defect and is more widely used. An excellent magnesium
light, suitable for illumination, is described in a patent recently
granted to George J. Schladt. 22 It consists of a mixture of 36 to
40 per cent barium nitrate, 6 to 8 per cent strontium nitrate, 50
to 54 per cent flake magnesium coated with linseed oil, and 1 to 4
per cent of a mixture of linseed and castor oils.
The airplane wing-tip flares which were used for signaling
during the first World War are good examples 23 of aluminum
compositions. They were loaded in cylindrical paper cases 414
inches in length and 1% inches in internal diameter. The white
light composition consisted of ^l parts of barium nitrate, 13 of
flake aluminum, and 5 of sulfur intimately mixed and secured by
a binder of shellac, and burned in the cases mentioned, for 1
22 U. S. Pat. 2,149,314, March 7, 1939.
28 Faber, op. cit., Vol. 2, pp. 223, 225-227.