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In over drying method for determination of water content the sample is kept at which temperature for 24 hours?
<80┬░C
100тИТ110┬░C
>200┬░C
None of these
100тИТ110┬░C
The oven-drying method is the most accurate laboratory technique for determining the water content of soil. The soil sample is dried in a thermostatic oven maintained at a constant temperature of 105┬░C to 110┬░C for a period of 24 hours to ensure complete removal of free water.
The oven-drying method is the most accurate laboratory technique for determining the water content of soil. The soil sample is dried in a thermostatic oven maintained at a constant temperature of 105┬░C to 110┬░C for a period of 24 hours to ensure complete removal of free water.
w=WsтАЛWwтАЛтАЛ├Ч100% тАФ Definition of water content as a percentage
WwтАЛ=WwetтАЛтИТWdryтАЛ тАФ Calculation of water weight lost during drying
The principle relies on the evaporation of pore water within the soil matrix without causing structural damage to the mineral particles. Maintaining the temperature between 105┬░C and 110┬░C is critical because temperatures below 100┬░C may fail to evaporate all water, while temperatures significantly above 110┬░C may lead to the loss of chemically bound water or structural water in certain minerals like gypsum or organic matter.
Standard drying duration is 24 hours.
Temperature range 105тИТ110┬░C is IS code (IS: 2720 Part II) specified.
For organic soils, lower temperatures (60┬░C) are sometimes used to prevent oxidation.
The process removes adsorbed water and capillary water but not structural water.
Provides the most accurate and reliable results.
Simple procedure that is easy to execute in a laboratory.
Time-consuming as it requires 24 hours for completion.
Not suitable for soils containing significant organic matter or gypsum.
Standard reference method for soil index properties.
Calibration of rapid field methods like calcium carbide or pycnometer methods.
IS: 2720 (Part 2) is the Indian Standard for determination of water content.
If the temperature exceeds 110┬░C, organic matter may burn, leading to erroneous results.
Samples should be cooled in a desiccator before weighing to prevent moisture re-absorption.
B is correct тАФ The standard laboratory oven-drying method requires the soil sample to be maintained at a temperature between 105┬░C and 110┬░C for 24 hours to ensure complete dehydration.
Always remember that for soils with high gypsum content, the temperature should be limited to 80┬░C to avoid loss of water of crystallization, which is a favorite 'trap' question in competitive exams.
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