Sulfur

Some sulfur is used directly as a fungicide and insecticide, in matches, fireworks, and gunpowder, and in the vulcanization of natural rubber. Most, however, is converted into a multitude of useful compounds.

Sulfur is in group 16 of the periodic table, directly below oxygen. It can form compounds in any one of its three major oxidation states: -2, +4 or +6.

Sulfuric acid is the parent acid of all sulfate compounds. Among the most important sulfates is calcium sulfate (CaSO₄), which occurs naturally as gypsum, alabaster and selenite. Copper sulfate is used as an agricultural insecticide and to kill algae in water supplies. Alums are double sulfates of aluminum and another metal such as potassium, chromium or iron. The most common alum is potassium aluminum sulfate, KAl(SO₄)₂•12H₂O. In water, it makes a gelatinous, goopy precipitate of aluminum hydroxide, Al(OH)₃, which, when it sinks to the bottom, carries along with it all sorts of suspended dirt, leaving behind clear water. Alum is therefore used in water purification.

Hydrogen sulfide is the parent acid of the sulfides, a family of compounds that contain nothing but sulfur and a metal. This family includes many metal ores, including iron pyrites, galena, cinnabar, stibnite and zinc blende, as mentioned above, plus sulfides of copper and silver. Other sulfides are used in leather tanning, as pesticides, and in depilatories—creams that remove "unwanted hair" from the hides of cattle and from people.

Hydrogen sulfide itself is a foul-smelling gas. When eggs and certain other animal matter go rotten and putrefy, the stench is mostly hydrogen sulfide. It is often present in flatus—expelled intestinal gas. Hydrogen sulfide is extremely poisonous, but fortunately, it smells so bad that people don't hang around long enough to be overcome by it. Other very bad-smelling compounds of sulfur are the mercaptans, a family of organic sulfur-containing compounds. A mercaptan is the major ingredient in the aroma of skunks. A tiny amount of a gaseous mercaptan is deliberately added to the natural gas that is used for home heating and cooking, so that dangerous gas leaks can be detected by smell. Natural gas itself is odorless.