How did Justus von Liebig help identify the ethyl radical?

Justus von Liebig’s identification of the ethyl radical in 1834 was a significant outcome of his intensive investigations into organic chemistry during the 1830s.1

Following his development of an improved method for organic analysis—which allowed for the precise determination of carbon content by burning compounds with copper oxide and weighing the resulting products—Liebig conducted a decade of rigorous research. This analytical breakthrough enabled him to publish numerous papers annually, among which the identification of the ethyl radical was a notable achievement.1

It is important to clarify that Liebig’s work on radicals, such as his earlier collaborative research with Friedrich Wöhler on the "benzoyl" radical, was grounded in the radical theory of the time. This approach sought to classify organic compounds based on common constituent groups, a method that provided the necessary background for his subsequent analytical successes. While the modern understanding of free radicals as transient, highly reactive species differs from the 19th-century concept of stable radicals, Liebig’s systematic application of his combustion analysis technique was the essential factor that facilitated his identification of the ethyl radical.12