LIQUID VOLUME MEASURING DEVICES : THE GRADUATED CYLINDER AND BURET

Like weighing, measuring liquid volume is a fundamental and frequently encountered lab task. However, liquid volume is frequently measured using either a graduated cylinder or a buret.As the name implies, a graduated cylinder is a cylindrical glass (or plastic) tube sealed at one end with a calibrated scale etched (or marked) on the outside wall. Graduated cylinders come in a range of sizes (volume capacities), and much like a measuring cup, volume is measured by adding liquid to the cylinder and comparing the liquid level to the graduated scale. The measured volume corresponds to the volume of liquid contained in the cylinder. Hence, the graduated cylinder and devices like it (volumetric flasks, Erlenmeyer flasks, and beakers) are classified as to-contain (TC) devices.

The volume of liquid in the graduated cylinder is obtained directly by reading the calibrated scale. In most situations, the liquid will be water or an aqueous solution. The liquid surface is curved (U-shaped) rather than horizontal due to the relatively strong attractive force between water and glass. (The curved surface is called the meniscus.) As a general rule, the bottom of the meniscus is taken as the liquid level in the cylinder (and any other volume measuring device).

The scale divisions on a graduated cylinder are generally determined by its size. For example, the 50-mL graduated cylinder is divided into 1 mL increments. However, the scale of a 10-mL graduated cylinder is divided into 0.1 mL increments, and the scale of a 500-mL graduated cylinder is divided into 5 mL increments. The graduated cylinder scale is a ruled scale, and it is read like a ruler. The scale is read to one digit beyond the smallest scale division by estimating (interpolating) between these divisions. With a 50-mL graduated cylinder, read (and record) the volume to the nearest 0.1 mL. The 10-mL graduated cylinder scale is read to the nearest 0.01 mL and the 500-mL graduated cylinder scale is read to the nearest milliliter (1 mL).

A buret is a scaled cylindrical tube attached to a stopcock (valve). A buret is designed to dispense or transfer a precisely measured volume of liquid to another container. The volume of liquid dispensed is determined by reading and recording the buret scale which corresponds