Arsenic

Arsenic (As) is the 33rd element in the periodic table. It is also one of the deadliest. It is beautiful and mysterious, at once a coquette and a killer. It is one of the few elements that doesn’t have a liquid state at atmospheric pressure; it sublimates when heated thoroughly. (That means that much like dry ice, which is much safer, it goes directly from a solid state to a gaseous state or vice-versa.)

The Bronze Age
Way back before our ancestors discovered how to make bronze out of copper and tin, a few of them discovered that you could make a pretty formidable alloy out of copper and arsenic, called The practice didn't catch on worldwide, though — probably because of all that arsenic vapor released in the smelting process.

"Destroys household pests"

 * Arsenic is a key component in some pesticides, herbicides, and insecticides.
 * It was used in older pressure-treated wood; it poses a health hazard if burned or if someone picks up splinters from it.
 * It was also used as embalming fluid until its danger to embalmers was discovered.
 * It is supposedly very effective when used as a cure in homeopathy.
 * According to traditional Chinese medicine, non-homeopathic arsenic taken internally is very good for intestinal parasites, sore throats, and (when applied externally) for "swelling, abscesses, itching, rashes, and other skin disorders." (We wish we were making this up.)
 * Arsenic is also used in Ayurvedic medicine, and about 20% of Ayurvedic herbs sold on the Internet (by both Indian and American companies) contain dangerous amounts of substances such as lead, arsenic, and mercury.
 * Inorganic arsenic is also carcinogenic to humans by inhalation and water routes. Certain areas of the world have naturally high levels of arsenic and have increased the risk of cancer among people who consume said water (e.g., Taiwan and Bangladesh).
 * Arsenic compounds were often 'useful' (most often as arsenic sesquioxide, As2O3, often referred to as "inheritance powder") to people seeking to hasten the collection of an inheritance by hastening the demise of a not-so-dearly-beloved relative. This method of collecting an inheritance was literal murder, but unlike other means of poisoning it imparted no taste upon a food or drink in which it was introduced. Until methods of detecting arsenic in dead bodies became reliable, people literally got away with murder. Symptoms of arsenic poisoning are similar to those of cholera, a once-commonplace disease caused by germs. The Marsh test detects arsenic and related antimony very well, often resulting in the detection of a murderer and the retraction of any inheritance.
 * Paris green was a toxic pigment made with copper and arsenic that was widely used for coloring wallpaper and clothing during the Victorian era. Eventually, doctors realized it was toxic when entire families would get sick with a mysterious illness but their neighbors who used a different wallpaper were perfectly fine. Paris green would later find a new use as a pesticide, and the resulting stigma against arsenic-based pigments is a large reason that green is still associated with poison to this day.

Murder
Arsenic poisoning was a popular method of committing murder in the 1800s and is still being used as murder weapon. In 2004, Indonesia's best known human rights activist was murdered by arsenic poisoning on a Garuda airlines flight from Singapore to the Netherlands by a deadheading Garuda pilot who was acting on behalf of a conspiracy of Garuda executives and the Indonesia State Intelligence Agency (BIN). Garuda refused to pay compensation to the widow despite two court orders.

Ministry of silly molecule names

 * Arsole (C4H5As) is, as one might wager, a heterocyclic aromatic compound &mdash; colloquially you'd call it a ring.
 * Cacodyl (C4H12As2) stinks like, well, caca.
 * Arsine (AsH3), used in mass quantities by fabricators of gallium arsenide semiconductors, is a very nasty flammable and lethally toxic gas, definitely not something that one would want to be arsing around with.

Historical uses
Although we now know that arsenic is not the sort of thing to eat, historically it has been used in a wide range of beauty products, medicines, and other purposes.
 * Skincare: pills or wafers containing arsenic were used in the late 19th century to remove freckles, pimples, and other skin blemishes. The Pure Food and Drug Act of 1906 helped stop this in the US.
 * Rouge: arsenic was used as a beauty product due to its ability to promote red cheeks, which it does by damaging capillaries.
 * Arsenic was actually one of the first major cures for syphilis, with Paul Ehrlich and Sahachiro Hata's preparation discovered in 1909. A form of arsenic trioxide is sold under the trade name Trisenox as a treatment for leukemia, and is on the World Health Organization's List of Essential Medicines, however.
 * Pigment: A cupric compound known as was formerly used as pigment in the 18th to 19th centuries in wallpaper, paints, wax candles, and even on some children's toys. It was also used to dye cotton and linen. We all know what happened afterwards to those who were exposed to it, Napoleon being a possible casualty due to the presence of Scheele's green on the wallpaper used in his house in St. Helena where he was exiled. A later pigment called  (also known as emerald green) was invented in an attempt to improve upon Scheele's green's durability, though its use was later relegated as a pesticide well into the mid 20th century until it was supplanted with equally toxic safer alternatives such as DDT. One shrewd doctor named Robert C. Kedzie compiled bolts of arsenic-laced wallpaper to a book entitled , which only served to drive the point home more than it need to be, as the book itself was made from the aforementioned toxic wallpaper whose arsenical content is far too dangerous for any sane person to even handle–the shock value from the book alone served to dissuade consumers from buying potentially unsafe wallpaper and pressured manufacturers to use safer pigments. All but four copies of the book were destroyed for obvious reasons, and those that remain were either sealed in plastic for patrons to be able to browse the book safely or digitised, neither of which were an easy task again for fairly obvious reasons.