What is the maximum water temperature that should not be exceeded during a wash in test method D1140?

The correct answer reflects the protocol defined in test method D1140, which pertains to the wash in tests performed to determine the washability of a soil sample. According to this method, the water used for washing the soil must not exceed a temperature of 32°C or 90°F. Exceeding this temperature could adversely affect the test results by altering the physical properties of the soil or causing changes in its structure, which could lead to inaccurate measurements of the materials' characteristics.

The reason that other temperature options are not suitable is that they either exceed the maximum limit stipulated by the method or do not align with standard practices for soil testing. For instance, temperatures like 50°C (122°F) and 100°C (212°F) are too high, as they can thermally alter the sample and compromise the integrity of the test. On the other hand, a temperature of 25°C (77°F) is acceptable but is below the required maximum, indicating a more conservative approach than necessary. Therefore, adhering to the maximum water temperature of 32°C ensures that the test conditions meet the established guidelines, thereby allowing for reliable and valid testing outcomes.