By Timothy Banas, Updated Aug 30, 2022
Water and other liquids evaporate at rates that vary with temperature, humidity, airflow, and exposed surface area. While the rate can shift with conditions, the relative speed between different liquids remains constant—for example, ethanol always evaporates faster than water under identical conditions.
Begin by noting the surroundings where you’ll perform the test. Are you indoors or outdoors? What is the time, temperature, barometric pressure, and relative humidity? How fast is the wind, and is the sky clear or cloudy? Conducting the experiment indoors lets you control these variables.
Fill a 500 mL graduated cylinder with the liquid you’re testing. Start a stopwatch once the cylinder is filled to the 500 mL mark.
Periodically check the liquid level. When a measurable drop is observed, stop the stopwatch and record both the elapsed time and the new cylinder reading. For instance, after one hour the level might read 495 mL.
Subtract the final reading from the initial 500 mL. In the example, 500 mL – 495 mL = 5 mL of liquid has evaporated.
Divide the volume lost by the elapsed time. In this case, 5 mL evaporated in one hour, yielding an evaporation rate of 5 mL / hour.
Remember that the calculated rate is context‑specific; it will vary with environmental changes.
