The reaction between solid Pt and liquid Hg, at temperatures varying from 20 to 153°C, has been investigated using a combination of gravimetric, x ray, and radioactive tracer techniques in an effort to evaluate the suitability of Pt-Hg contacts for Josephson device packages. The reaction product was identified as Hg4Pt with a lattice parameter of 6.2047 Å±0.02%. No penetration of Hg into Pt lattice or grain boundaries has been detected. The kinetic law governing the amalgam formation has been found to be X (cm)=4.48×10-3t exp(-0.52 eV/kT) where X is Pt thickness consumed in the amalgam, t is time in sec, k is Boltzmann constant, and T is temperature. The results indicate that the rate of amalgam formation is controlled by reaction at the Pt-amalgam interface.