Neumann-Kopp’s rule

Several simplifications can, however, be made if some quantities are not available. If the heat capacity of the crystalline compound A B is not known, it can be estimated in the first approximation using the Neumann-Kopp s rule... 

Y = MF, M2SO4, or M3FSO4 (Af sCp(M3FS04) according to Neumann-Kopp s rule). Estimated values (c.f. Table 4.1.). 

As it follows from Table 4.1, the estimated heats of fusion of Na3pS04 and K3FSO4 are lower than the measured values and the error in the estimation lies within the range 7-13%. This difference is probably due to the limited validity of the Neumann-Kopp s rule, which in most cases, yield higher values of heat capacities of crystalline AB compounds in Eq. (4.19). 

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