The terms “coal oil” and “kerosene” have often been used interchangeably, creating a common misunderstanding about whether they are the same substance. Both played a significant historical role as illuminants, providing light before the widespread adoption of electricity. This article clarifies the differences and similarities between coal oil and kerosene, exploring their origins, evolving usage, and present-day definitions.
Understanding Coal Oil
Historically, “coal oil” referred to a liquid fuel derived from coal, oil shale, or other bituminous materials through destructive distillation. This method involved heating these organic substances without oxygen, breaking them down into various components, including a combustible oil.
Before petroleum-derived fuels, coal oil provided an important, though sometimes smoky, light source. Scottish chemist James Young pioneered a cleaner-burning coal oil in 1850, allowing it to compete with whale oil for indoor illumination. This early product, often extracted from cannel coal, improved artificial lighting.
Understanding Kerosene
Kerosene, in its refined form, is a combustible hydrocarbon liquid primarily derived from petroleum. The process involves fractional distillation of crude oil, separating it into components based on boiling points, with kerosene typically comprising hydrocarbon chains from 6 to 16 carbon atoms. This refining yields a clear, oily liquid known for burning with a bright, smokeless flame.
Canadian geologist Abraham Gesner discovered and commercialized a process for distilling kerosene in 1846, initially from coal and later from oil shale. He coined the name “kerosene,” from the Greek “keroselaion” meaning “wax-oil.” Kerosene quickly gained popularity, largely replacing whale oil due to its lower cost and superior burning characteristics.
The Historical Overlap and Evolution of Terms
The historical overlap of “coal oil” and “kerosene” stems from their functional similarity as lamp fuels and evolving production sources. Initially, Abraham Gesner’s patented “kerosene” was distilled from coal and oil shale. This meant his early “kerosene” was essentially coal oil. This direct link contributed to the interchangeable use of the terms.
As petroleum deposits were discovered, particularly in Pennsylvania in 1859, illuminating oil production shifted from coal to more abundant crude oil. Despite this feedstock change, the name “kerosene” persisted for the petroleum-derived product. In many regions, especially the United States, “coal oil” continued to be used colloquially for this new petroleum-based kerosene into the 20th century.
This terminological overlap was fueled by their chemical similarities. Both consist mainly of alkane series hydrocarbons with similar carbon chain lengths (typically 10 to 16 atoms) and comparable boiling points. Despite distinct sources—coal via destructive distillation and petroleum via fractional distillation—their similar chemical properties and use as lamp fuels maintained “coal oil” as a synonym for kerosene.
Modern Distinctions and Safety Considerations
In contemporary usage, “kerosene” almost exclusively refers to petroleum-derived fuel. It serves various applications today, including aviation fuel (jet fuel), heating oil, and cooking and lighting fuel worldwide. The term “coal oil,” as a distinct fuel product, is largely historical. While coal can still be converted into liquid fuels, this is typically for different industrial applications, not for direct illumination as in the 19th century.
The distinction between petroleum distillates, including various grades of kerosene, carries safety implications. Different fuels possess distinct flash points—the lowest temperature at which their vapors ignite when exposed to an open flame. Accurate fuel identification is important because using a product with an unsuitable flash point can lead to fires or explosions. Modern kerosene is refined to have a flash point suitable for its intended uses, ensuring safe operation in lamps, heaters, and engines when handled correctly.