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Several bulk mixed crystals of KCl-KBr have been measured by means of their infrared reflectance at $300\circ K,200\circ K$ and $100\circ K$ from $25-250cm-1$. Only one major restrrahlen peak was observed in each case which shifted linearly with concentration. It is apparent that other modes are present and contribute to the broad reststrahlen band but their oscillator strengths are small compared with the main lattice vibration. The reflectivity curves were analyzed by means of a Kramers-Kronig transformation and a classical oscillator model to provide the oscillator strengths and damping constants. Transmission measurements of thin evaporated films and of the materials in polyethylene matrices were in good agreement with the reflection data.