Which substance was initially in high demand for lighting homes in the mid-19th century?

In the mid-19th century, whale oil was in high demand for lighting homes, particularly before the widespread adoption of kerosene and electric lighting. The oil extracted from sperm whales and other species was burned in lamps and provided a bright, steady light that was preferable to the alternatives available at the time. This led to a significant whaling industry, as the demand for whale oil surged to meet the needs of households seeking more effective illumination.

During this period, whale oil became a staple in many American homes, especially as urban areas began to grow and industrialize. Although gasoline started to gain traction with the rise of the automobile in the late 19th and early 20th centuries, it was not a primary source for lighting in the specified timeframe. Similarly, coal was primarily used for heating and powering steam engines rather than for household lighting. Electricity would not become a common lighting source until later, following the advancements in electrical infrastructure in the late 1800s and early 1900s. Therefore, whale oil stands out as the correct answer for this question, given its essential role in lighting during that era.