* H. YURTSEVEN*, Department of Physics, Middle East Technical University, Ankara, 06531 - Turkey.

We establish here the modified Pippard relations by relating the specific heat C_{p} to the frequency shifts \frac1
\left( \frac\partial
\partial T \right)_{P} and also the thermal expansivity
_{p} to the \frac1
\left( \frac\partial
\partial P \right)_{T} for the
(140 cm^{-1}) Raman mode of NH_{4}Br close to its phase I- phase II transition. From our linear plots of C_{p} vs. \frac1
\left( \frac\partial
\partial T \right)_{P} and
_{p} vs.
_{p} to the \frac1
\left( \frac\partial
\partial P \right)_{T} , we extract the values of the slope DP/dT, which are close to the experimental value of 28.2 bar/^{o}C near the phase I-phase II transition in NH_{4}Br.