Black snake and Pharaoh's serpent are two similar types of outdoor firework.

After lighting the small tablet, both fireworks start smoking and an ash resembling a snake is created via intumescent

Intumescent

An intumescent is a substance which swells as a result of heat exposure, thus increasing in volume, and decreasing in density. Intumescents are typically used in passive fire protection and, in America, require listing and approval use and compliance in their installed configurations in order to...

 reaction. They stay on the ground and do not emit sparks, flares, any form of projectiles, or any sound, but may release smoke.

Sodium bicarbonate

Sodium bicarbonate

Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula Na HCO3. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder. It has a slightly salty, alkaline taste resembling that of washing soda . The natural mineral form is...

 which produces carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 gas and sugar

Sugar

Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...

 forming carbon containing ash, are common chemicals used for creating black snake. Other sources report the contents as "a nitrated mixture of linseed oil

Linseed oil

Linseed oil, also known as flaxseed oil, is a clear to yellowish oil obtained from the dried ripe seeds of the flax plant . The oil is obtained by cold pressing, sometimes followed by solvent extraction...

 and naphthalene

Naphthalene

Naphthalene is an organic compound with formula . It is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings...

s".

The traditional "Pharaoh's serpent" version of this firework produced a more impressive snake, but its operation depended upon mercury thiocyanate

Mercury(II) thiocyanate

Mercury thiocyanate is an inorganic chemical compound, the salt of Hg2+ and the thiocyanate anion. It is a stable solid at room temperature that has the appearance of white powder with chunks; it can also be grey in color, depending on purity. Mercury compounds are extremely toxic and protective...

, which is no longer used because of its toxicity.