alt=A closed structure of black bricks Contrary to popular belief, pencil<unk> s in wooden pencils have never been made from<unk> . When the pencil originated as a wrapped graphite writing tool, the particular type of graphite used was named plumbago (literally, act for<unk>  or<unk>  mockup). Elemental form<unk>  metal has several useful mechanical properties, including high density, low melting point, ductility, and relative inertness. Many metals are superior to<unk>  in some of these aspects but are generally less common and more difficult to extract from parent ores.<unk> 's toxicity has led to its phasing out for some uses.<unk>  has been used for bullets since their invention in the Middle Ages. It is inexpensive; its low melting point means small arms ammunition and shotgun pellets can be cast with minimal technical equipment; and it is denser than other common metals, which allows for better retention of velocity. It remains the main material for bullets, alloyed with other metals as hardeners. Concerns have been raised that<unk>  bullets used for hunting can damage the environment.<unk> 's high density and resistance to corrosion have been exploited in a number of related applications. It is used as ballast in sailboat keels; its density allows it to take up a small volume and minimize water resistance, thus counterbalancing the heeling effect of wind on the sails. It is used in scuba diving weight belts to counteract the diver's buoyancy. In 1993, the base of the Leaning Tower of Pisa was stabilized with 600 tonnes of<unk> . Because of its corrosion resistance,<unk>  is used as a protective sheath for underwater cables. A 17th-century gold-coated<unk>  sculpture<unk>  has many uses in the construction industry;<unk>  sheets are used as architectural metals in roofing material, cladding, flashing, gutters and gutter joints, and on roof parapets.<unk>  is still used in statues and sculptures, including for armatures. In the past it was often used to balance the wheels of cars; for environmental reasons this use is being phased out in favor of other materials.<unk>  is added to copper alloys, such as brass and bronze, to improve machinability and for its lubricating qualities. Being practically insoluble in copper the<unk>  forms solid globules in imperfections throughout the alloy, such as grain boundaries. In low concentrations, as well as acting as a lubricant, the globules hinder the formation of swarf as the alloy is worked, thereby improving machinability. Copper alloys with larger concentrations of<unk>  are used in bearings. The<unk>  provides lubrication, and the copper provides the load-bearing support.<unk> 's high density, atomic number, and formability form the basis for use of<unk>  as a barrier that absorbs sound, vibration, and radiation.<unk>  has no natural resonance frequencies; as a result, sheet-lead is used as a sound deadening layer in the walls, floors, and ceilings of sound studios. Organ pipes are often made from a<unk>  alloy, mixed with various amounts of tin to control the tone of each pipe.<unk>  is an established shielding material from radiation in nuclear science and in X-ray rooms due to its denseness and high attenuation coefficient. Molten<unk>  has been used as a coolant for<unk> -cooled fast reactors. The largest use of<unk>  in the early 21st century is in<unk> –acid batteries. The<unk>  in batteries undergoes no direct contact with humans, so there are fewer toxicity concerns. People who work in<unk>  battery production plants may be exposed to<unk>  dust and inhale it.} The reactions in the battery between<unk> ,<unk>  dioxide, and sulfuric acid provide a reliable source of voltage. Supercapacitors incorporating<unk> –acid batteries have been installed in kilowatt and megawatt scale applications in Australia, Japan, and the United States in frequency regulation, solar smoothing and shifting, wind smoothing, and other applications. These batteries have lower energy density and charge-discharge efficiency than lithium-ion batteries, but are significantly cheaper.<unk>  is used in high voltage power cables as sheathing material to prevent water diffusion into insulation; this use is decreasing as<unk>  is being phased out. Its use in solder for electronics is also being phased out by some countries to reduce the amount of environmentally hazardous waste.<unk>  is one of three metals used in the Oddy test for museum materials, helping detect organic acids, aldehydes, and acidic gases. Compounds left In addition to being the main application for<unk>  metal,<unk> -acid batteries are also the main consumer of<unk>  compounds. The energy storage/release reaction used in these devices involves<unk>  sulfate and<unk>  dioxide: :(s) + (s) + 2(aq) → 2(s) + 2(l) Other applications of<unk>  compounds are very specialized and often fading.<unk> -based coloring agents are used in ceramic glazes and glass, especially for red and yellow shades. While<unk>  paints are phased out in Europe and North America, they remain in use in less developed countries such as China, India, or Indonesia.<unk>  tetraacetate and<unk>  dioxide are used as oxidizing agents in organic chemistry.<unk>  is frequently used in the polyvinyl chloride coating of electrical cords. It can be used to treat candle wicks to ensure a longer, more even burn. Because of its toxicity, European and North American manufacturers use alternatives such as zinc.<unk>  glass is composed of 12–28%<unk>  oxide, changing its optical characteristics and reducing the transmission of ionizing radiation, a property used in old TVs and computer monitors with cathode-ray tubes.<unk> -based semiconductors such as<unk>  telluride and<unk>  selenide are used in photovoltaic cells and infrared detectors.
Lead
Basilicon
Mercury
Arsenic
Metaldehyde
Sybil 
Vinyl chloride
Lindane