OCR Text |
Show - 1A - a) Isolated temperature measurements with a thermometer, thermoelement, or electrical resistance thermometer. b) Continuous temperature measurement with a thermograph or recording apparatus for thermo- elements. c) Measurement of mean temperature values for short intervals ( hours and days) by the electrolytic method of E. Tamm. ( 3) Isolated temperature values have only limited value for the soil scientist or ecologist. The simultaneious observation of many individual temperatures is either time- consuming or requires a large number of assistants. Automatic temperature recording apparatus is expensive and requires careful maintenance. In recent years a new method of measuring mean temperatures has been evolved ( 4) which is based on chemical principles, and has been given practical field tests during the years 1939 to 194l. It has been demonstrated to be inexpensive, reliable and effective. The temperature sensitive elements hung in the air or buried in the ground consist of small glass ampoules filled with a sterile, buffered sugar solution. Since they have proven to be completely unaffected by the ravages of a mountain climate, they require no maintenance. The effective mean temperature ( eT- value ) can be measured over days, weeks or months. a) The chemico- physical basis of the method Cane sugar ( saccharose, sucrose) dissolved in water is converted into dextrose and fructose by the action of hydrogen ions. The cane sugar is inverted. In a constant concentration of hydrogen ions ( buffered solutionX, this inversion is strongly accelerated by rising temperatures. If one knows the functional relationship between inversion rate and temperature, the mean |