The Chemistry of Powder and Explosives - Sciencemadness Dot Org

120 PYROTECHNICS
potassium, sodium, or ammonium thiocyanate to a solution of
mercuric nitrate, a ferric chloride or ferrie alum indicator being
used to indicate by a red color when enough of the former solution
has been added. This is necessary since mercuric thiocyanate
is soluble in an excess of either of the reagents by the interaction
of which it is produced. The precipitate is collected, washed,
dried, powdered, moistened with gum-arabic water in which a
little potassium nitrate is dissolved, and made into small pellets
by means of a device like a star board or by a pelleting machine.
The small pellets are known as Pharaoh's serpent's eggs.
Snakes-in-the-grass, volcano snakes, etc., depend upon the use
of ammonium dichromate. If this material in the form of a powder
is made into a conical heap, and a flame applied to the top
of it, a visible but not violent "combustion" proceeds through
the mass, which "boils up" to form a large volume of green material
resembling tea leaves.
(NH4)2Cr207 > N2 + 4H2O + Cr2O3
In practice, more flame is desired than ammonium dichromate
alone will give. Weingart 54 recommends a mixture of 2 parts of
ammonium dichromate with 1 of potassium nitrate and 1 of dextrin.
Tinfoil cones are made from circles of tinfoil shaped on a
former, and are introduced by means of the former into conical
cavities in a block of wood; they are then about half filled with
the powdered mixture, a Pharaoh's serpent's egg is pressed in,
and the edges of the tinfoil are turned down upon it to form the
base of the cone.
While the fumes from burning mercuric thiocyanate are offensive
because of their sulfur dioxide, the small amount of mercury
vapor which they contain probably presents no serious danger.
The possibility, however, that children may swallow the pellets,
with fatal consequences, is a real hazard. For this reason, the sale
of mercury snakes has been forbidden by law in many states,
and black non-mercury snakes, which are essentially non-poisonous,
have come into general use.
Black Non-Mercury Snakes 55
These are used in the form of barrel snakes, hat snakes (black
84 Op. cit., p. 152.
55 Davis, loc. cit.