The contents of a lime kiln excavated in 1976 in Switzerland by H. Spycher is examined. Three main compounds were found: grey lime, slaked lime and white lime. Electron microscopy, differential thermo-analysis, x-ray diffraction, specific gravity and micro- and macro-porosity were used. The malm line consisted of Ca carbonate, the slaked lime of Ca hydroxide of two types and the white lime of CaCO3, and Ca(OH)2 and MgCO3. The chemical and physical action of increasing burn temperature is discussed.