The Kopp–Neumann law, named for Kopp and Franz Ernst Neumann, is a common approach for determining the specific heat C (in J·kg ·K) of compounds using the following equation: C = ∑ ∑ i = 1 N C i f i , where N is the total number of compound constituents, and C i and f i denote the specific heat and mass fraction of the i -th constituent. This law works surprisingly well at room-temperature conditions, but poorly at elevated temperatures.