Kopp's law

Kopp's law can refer to either of two relationships discovered by the German chemist Hermann Franz Moritz Kopp (1817–1892).

Kopp found "that the molecular heat capacity of a solid compound is the sum of the atomic heat capacities of the elements composing it; the elements having atomic heat capacities lower than those required by the Dulong–Petit law retain these lower values in their compounds."^[1]
In studying organic compounds, Kopp found a regular relationship between boiling points and the number of CH₂ groups present.^[2]

^ See page 96 of Millard, Earl Bowman (1921). Physical Chemistry for Colleges. New York: McGraw-Hill. p. 96. Kopp's Law.
^ See page 942 of Miller, William Allen (1869). Elements of Chemistry. London: Longmans, Green, Reader, and Dyer.