Recent experimental work on the negative thermal expansion material Zn(CN)2 has shown that the elastic stiffness is anomalously reduced on compression. That is, if B is the bulk modulus, the derivative dB/dP is negative. From our molecular dynamics simulations of this system we have predicted that the dB/dP has a striking temperature-dependence, namely with positive value at low temperature, then quickly falling to a maximal negative value before slowly tending towards zero at high temperature. The purpose of this proposal is to test this prediction using powder diffraction and performing measurements across the two-dimensional space of both pressure and temperature. The experiment will be performed on Polaris using the gas cell pressure device within a cryostat.