Mass sampling of temperature is required in many types of earth science problems. An accurate, precise, and economical technique for mean temperature determination in soil, water or air is afforded by the Pallmann solution method, which relies on the irreversible breakdown of sucrose sugar into the simpler forms, d glucose and d(−) fructose. These sugars are optically active, thus, changes in their concentration result in measurable changes in the optical properties of the solution. Since optical rotation ratios are proportional to chemical concentration ratios, one may determine the reaction velocity coefficient, which in turn depends on temperature according to the van't Hoff-Arrhenius Law. Thus, if an acidified, buffered sucrose solution is exposed over a known time period and if its optical properties are measured before exposure, at the time of interest and at the end point of the reaction, then the mean temperature to which the solution was exposed during that period can be determined. Sensor analysis is accomplished with apparatus commonly found in a well-equipped organic chemistry laboratory. A highly successful field test of the method, applied to mean soil temperature determination, was conducted in the Mo-hawk River Valley west of Schenectady, New York, during the winter of 1968–1969.