10 Average Questions about Elementary, My Dear Watson

Answer: Battery

Lithium is the lightest and least dense of all metals, and the third lightest of all the elements. Lithium was discovered in a mineral called petalite in 1817, but the pure metal was not isolated until 1821. Its name comes the Greek word "lithos," meaning "stone." Its first use came when it was discovered that certain lithium compounds could be used to treat some mental disorders. Lithium and its compounds have many uses, but one of the most common applications is in batteries. Lithium batteries are small and last a long time. Chances are that if you are wearing a wristwatch, it's powered by a lithium battery.

Answer: Your smoke detector

With an atomic number of 95, Americium is usually obtained by extracting it from spent nuclear reactor fuel. There are many isotopes of Americium, but the one used in smoke detectors is usually Americium-241. Americium-241 has a half-life of 432.2 years, and decays by emitting highly-highly charged but harmless alpha particles.

In a smoke detector, the alpha particles pass through an ionization chamber, and allow an electric current to pass and complete a circuit. If smoke enters the chamber, the ionization process is interrupted, causing the circuit to fail and an alarm to sound.

Although Americium is toxic and highly radioactive, the amounts used in smoke detectors are so small - about 0.28 micrograms - that it does not pose a health hazard.

Some people have raised questions about the dangers of disposing of used smoke detectors in landfills, however.

Answer: An old fountain pen

Iridium has the distinction of being one of the rarest elements found in the Earth's crust; it is also one of the densest. Like most very dense metals, most of Earth's iridium probably sank into the core during the early stages of planetary formation. Iridium is much more abundant in meteorites; in fact, it is the high levels of iridium in the so-called K-T boundary that led to the theory that an asteroid was responsible for the extinction of the dinosaurs some 65 million years ago.

Pure iridium is hard and brittle, but extremely resistant to corrosion, even more so than gold. An alloy of platinum and iridium was used to make the first international meter and kilogram standards for the International Bureau of Weights and Measures. Iridium also has some applications in electronics and jewelry, but its first significant industrial use was in alloys to used to tip fountain pen nibs. Because iridium is very expensive, only the finest pens used these nibs. The nib itself was made of gold, but gold is too soft to withstand prolonged use, so the the tiny ball at the end of the nib that came into contact with the paper was made of an alloy of ruthenium and iridium. Most modern fountain pen nibs, even those labeled "iridium," don't contain any of the scarce element, but a few manufacturers continue to use it on their high-end models.

Answer: Your medicine cabinet

Iodine, atomic number 53, belongs to that group of elements called halogens. It is quite reactive, and forms compounds readily. The name iodine comes from the Greek word "ioeidēs," meaning "purple."

Iodine is an element essential to life, and a shortage of iodine in the diet can lead to a swelling of the thyroid gland called a goiter; for this reason, traces of potassium iodide is often added to table salt to combat iodine deficiencies in the diet. But the most common place to find a significant amount of iodine in your home is in your medicine cabinet. Tincture of iodine has been used as an antiseptic for over 100 years, and is still popular for treating minor cuts and abrasions. Tincture of iodine contains 2% to 7% elemental iodine, along with potassium iodide or sodium iodide, dissolved in a mixture of alcohol and water. It is one of the most effective topical antiseptics available, and many people still keep a bottle in their home to treat minor cuts and scrapes.

Answer: An incandescent light bulb

Tungsten is a hard metal that has the highest melting point, 6,192 degrees Fahrenheit (3422 °C), of any element. It is mostly used to harden alloys, and as an abrasive in the form of tungsten carbide. But the most common place to find nearly pure tungsten in your home is in the filament of an incandescent light bulb. Tungsten has many properties that make it ideal as a light bulb filament.

It is a relatively poor conductor of electricity compared to most metals, so it heats up rapidly when an electric current is passed through it, but its high melting point prevents it from melting.

It also does not expand or contract much when subjected to heat, nor does it evaporate readily. The interior of the light bulb is filled with argon, an inert gas that does not react with the hot tungsten, and further inhibits the evaporation of the filament.

It will eventually evaporate, however, and the bulb will need to be replaced. The reason a burned out light bulb often looks dark or black is the elemental tungsten that evaporates and then condenses on the inner surfaces of the bulb.

Answer: A disposable cigarette lighter

Rare earth metals are a series of metals that have similar physical and chemical properties; there are 17 in all. The most abundant of them is cerium, which was identified as an element in 1803; it was named after the asteroid Ceres, which had been discovered in 1801. One of the most common commercial applications of cerium is in an alloy called ferrocerium, which is used to make the "flints" in cigarette lighters. Cerium has a very low ignition temperature, and burns readily in air.

In a cigarette lighter, a spring holds a small cylinder of ferrocerium against a wheel of hardened steel with a rough surface. Spinning the wheel causes small particles of the ferrocerium to be rubbed off, which are ignited by friction, and appear as sparks. Ferrocerium not only contains cerium, it also contains three other elements you probably didn't know were in your home: lanthanum, neodymium, and praseodymium.

Answer: In your mouth

Mercury, also known as quicksilver, is the only metal that is liquid at room temperature. Mercury and its compounds are very toxic to humans, so you don't see many mercury thermometers in the home any more. If, however, like most people, you have one or more fillings in your teeth, you may be carrying around quite a bit of it in your mouth.

Mercury readily forms alloys, called amalgams, with many other metals. The silver fillings in your teeth are made from an amalgam consisting of 50% mercury, with the remainder being silver, tin, and copper. Dental amalgam is a good material for filling teeth, as it is soft and pliable when first made, but hardens rapidly, and lasts a very long time. Small amounts of mercury may leach out of the fillings over time, but the amount is so small that it represents no health risk. Nevertheless, some countries have begun placing restrictions on the use of dental fillings containing mercury, citing both health and environmental concerns.

Answer: Your computer

Yes, there's gold in them thar computers - about a gram in many models. There's also gold in your television, your cell phone, your VCR and in almost every kind of electronic equipment. Gold's ability to conduct electricity with little resistance, and the fact that it is not subject to corrosion, means that it is used extensively in switches, wires, connectors, etc. That's the good news.

The bad news is that while there are many companies that recover gold from used or broken electronic equipment, doing so yourself is not a practical idea, even when the price of gold is very high.

The process of recovering gold from electronic scrap requires chemicals that are both expensive and dangerous.

Answer: Your china cabinet

Naturally occurring uranium is not highly radioactive, and is less chemically toxic than many other heavy metals, but it's still not something most people would be comfortable being around. But there could be some in your house. From 1880 until about 1940, uranium oxide was added to glass to produce a light yellow-green color. It was called "vaseline glass," and contained between 2% and 25% uranium by weight. It is distinguishable from other types of green glass by the fact that it fluoresces under UV light.

And there was another source of uranium that could be found in your house. For many years, the Homer Laughlin China Company produced a popular pattern of dishes called "Fiestaware." It was available in a variety of colors. Red Fiestaware was colored with a glaze containing high amounts of uranium oxide. In 1943, the United States government ordered the Homer Laughlin company to stop producing red Fiestaware, and seized its stock of uranium oxide for the war effort. They began producing it again after the war, and continued to use uranium in their red glaze until 1972. Fiestaware produced after that date does not contain any uranium.

An even more surprising possible source of uranium might be lurking in your mouth. Up until the 1980s, it was a common practice to add uranium compounds to the porcelain used to make false teeth, to make them whiter and shinier!

Answer: Stop looking - you won't find any

As we've seen, you can find almost any element in the periodic table somewhere in your house, but you won't find astatine. In fact, you won't find it anywhere outside of a laboratory or a hospital. Astatine, atomic number 85, is the rarest naturally occurring element. It is estimated that there is less than one gram in the entire Earth's crust.

The reason for this is simple. There are six naturally occurring isotopes of astatine, but the most stable one has a radioactive half-life of only 56 seconds. Almost soon as it is formed by the decay of heavier elements, it's gone.

Many of the properties of astatine remain unknown, because scientists have not been able to manufacture enough of it to study it properly. Nevertheless, experiments are ongoing in an attempt to use astatine-211, a man-made isotope with a half-life of 7.21 hours, in various cancer treatments.