Naphtha
Naphtha ( or ) is a flammable liquid hydrocarbon mixture. Generally, it is a fraction of crude oil, but it can also be produced from natural gas condensates, petroleum distillates, and the fractional distillation of coal tar and peat.  In some industries and regions, the name naphtha refers to crude oil or refined petroleum products such as kerosene.
Nephi and naphthar are sometimes used as synonyms. It is also known as Shellite in Australia.

Etymology
The word naphtha is from Latin and Ancient Greek (νάφθα), derived from Middle Persian naft ("wet", "naphtha"), the latter meaning of which was an assimilation from the Akkadian napṭu (see Semitic relatives such as Arabic نَفْط nafṭ ["petroleum"], Syriac ܢܰܦܬܳܐ naftā, and Hebrew נֵפְט neft, meaning petroleum).

Antiquity
The book of II Maccabees (2nd cent. BC) tells how a "thick water" was put on a sacrifice at the time of Nehemiah and when the sun shone it caught fire. It adds that "those around Nehemiah termed this 'Nephthar', which means Purification, but it is called Nephthaei by the many." This same substance is mentioned in the Mishnah as one of the generally permitted oils for lamps on Shabbat, although Rabbi Tarfon permits only olive oil (Mishnah Shabbat 2). 
In Ancient Greek, it was used to refer to any sort of petroleum or pitch. The Greek word νάφθα designates one of the materials used to stoke the fiery furnace in the Song of the Three Children (possibly 1st or 2nd cent. BC).  The translation of Charles Brenton renders this as "rosin."
The naptha of antiquity is explained to be a "highly flammable light fraction of petroleum, an extremely volatile, strong-smelling, gaseous liquid, common in oil deposits of the Near East"; it was a chief ingredient in incendiary devices described by Latin authors of the Roman period.

Modern period
Since the 19th century, Solvent naphtha has denoted a product (xylene or trimethylbenzenes) derived by fractional distillation from petroleum; these mineral spirits, also known as "Stoddard Solvent", was originally the main active ingredient in Fels Naptha laundry soap.The usage of the term "naphtha" during this time typically implies petroleum naphtha, a colorless liquid with a similar odor to gasoline. However, "coal tar naphtha", a reddish brown liquid that is a mixture of hydrocarbons (toluene, xylene, and cumene, etc.), could also be intended in some contexts.

Petroleum
In older usage, "naphtha" simply meant crude oil, but this usage is now obsolete in English. There are a number of cognates to the word in different modern languages, typically signifying "petroleum" or "crude oil".
The Ukrainian and Belarusian word нафта (nafta), Lithuanian, Latvian and Estonian "nafta" and the Persian naft (نفت) mean "crude oil". The Russian word нефть (neft') means "crude oil", but нафта (nafta) is a synonym of ligroin. Also, in Albania, Bosnia and Herzegovina, Bulgaria, Croatia, Finland, Italy, Serbia, Slovenia, Macedonia nafta (нафта in Cyrillic) is colloquially used to indicate diesel fuel and crude oil. In the Czech Republic and Slovakia, nafta was historically used for both diesel fuel and crude oil, but its use for crude oil is now obsolete and it generally indicates diesel fuel. In Bulgarian, nafta means diesel fuel, while neft, as well as petrol (петрол in Cyrillic), means crude oil. Nafta is also used in everyday parlance in Argentina, Paraguay and Uruguay to refer to gasoline/petrol. In Poland, the word nafta means kerosene, and colloquially crude oil (technical name for crude oil is ropa naftowa, also colloquially used for diesel fuel as ropa). In Flemish, the word naft(e) is used colloquially for gasoline.

Types
Various qualifiers have been added to the term "naphtha" by different sources in an effort to make it more specific:
One source distinguishes by boiling point:

Light naphtha is the fraction boiling between 30 °C and 90 °C and consists of molecules with 5–6 carbon atoms. Heavy naphtha boils between 90 °C and 200 °C and consists of molecules with 6–12 carbon atoms.
Another source which differentiates light and heavy comments on the hydrocarbon structure, but offers a less precise dividing line:

Light [is] a mixture consisting mainly of straight-chained and cyclic aliphatic hydrocarbons having from five to six carbon atoms per molecule. Heavy [is] a mixture consisting mainly of straight-chained and cyclic aliphatic hydrocarbons having from seven to nine carbon atoms per molecule.
Both of these are useful definitions, but they are incompatible with one another and the latter does not provide for mixes containing both six and seven carbon atoms per molecule. These terms are also sufficiently broad that they are not widely useful.

Uses
Heavy crude oil dilution
Naphtha is used to dilute heavy crude oil to reduce its viscosity and enable/facilitate transport; undiluted heavy crude cannot normally be transported by pipeline, and may also be difficult to pump onto oil tankers. Other common dilutants include natural-gas condensate and light crude. However, naphtha is a particularly efficient dilutant and can be recycled from diluted heavy crude after transport and processing. The importance of oil dilutants has increased as global production of lighter crude oils has fallen and shifted to exploitation of heavier reserves.

Fuel
Light naphtha is used as a fuel in some commercial applications. One notable example is wick-based cigarette lighters, such as the Zippo, which draw “lighter fluid”—naphtha—into a wick from a reservoir to be ignited using the flint and wheel.
It is also a fuel for camping stoves and oil lanterns, known as “white gas”, where naphtha’s low boiling point makes it easy to ignite. Naphtha is sometimes preferred over kerosene as it clogs fuel lines less. The outdoor equipment manufacturer MSR published a list of trade names and translations to help outdoor enthusiasts obtain the correct products in various countries.Naptha was also historically used as a fuel in some small launch boats where steam technology was impractical; most were built to circumvent safety laws relating to traditional steam launches.

Plastics
Naphtha is a crucial component in the production of plastics.

Health and safety considerations
The safety data sheets (SDSs) from various naphtha vendors indicate various hazards such as flammable mixture of hydrocarbons: flammability, carcinogenicity, skin and airway irritation, etc.Humans can be exposed to naphtha in the workplace by inhalation, ingestion, dermal contact, and eye contact. The US Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit for naphtha in the workplace as 100 ppm (400 mg/m3) over an 8-hour workday. The US National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 100 ppm (400 mg/m3) over an 8-hour workday. At levels of 1000 ppm, which equates to 10 times the lower exposure limit, naphtha is immediately dangerous to life and health.Fels-Naptha is an American brand of laundry soap manufactured by Summit Brands. It originally included the ingredient naphtha, effective for cleaning laundry and urushiol, an oil contained in poison ivy. Naphtha was later removed as a cancer risk.

See also
Coleman fuel
Fels-Naptha
Fractional distillation
Fluid catalytic cracking
Greek fire
Hydrocarbon
Kerosene
Mineral spirits
Naphtha launch
Oil refinery
Petroleum distillation
Petroleum naphtha
Tar

References
External links
 The dictionary definition of naphtha at Wiktionary
 Media related to Naphtha at Wikimedia Commons