A laboratory thermometer is a tool used in laboratories to measure temperature with high accuracy. It can be partially or fully immersed in the substance being measured. A laboratory thermometer is recognizable by its long stem with a silver bulb at the end. The silver color in the bulb normally indicates the presence of mercury. Mercury expands as the temperature increases, thus raising the reading, while decreasing temperatures contract the mercury, lowering the reading. Mercury-in-glass thermometers are less used in the 21st century as preference is shifted to other types of thermometers, such as digital, alcohol-filled and organic-based thermometers.