Graduated cylinder

A graduated cylinder is a fundamental piece of laboratory equipment used to measure the volume of liquids. It is also frequently called a measuring cylinder or a mixing cylinder. These tools are essential in science because they provide a way to quantify how much space a liquid occupies. While they are very useful, they are not the most precise tools available for all tasks. Scientists typically use them when they need more accuracy than a beaker or a flask can provide. However, for highly exact volumetric analysis, researchers prefer tools like volumetric flasks or pipettes.

The physical structure of a graduated cylinder is designed specifically for measurement. Most traditional cylinders are tall and narrow. This specific shape helps increase the accuracy and precision of the volume readings. They usually feature a base, which acts as a stand or support, and a spout for easy pouring. Some versions are wide and low instead. Mixing cylinders are a special type that feature ground glass joints. These joints allow the cylinder to be closed with a stopper or connected to a manifold. In these cases, the liquid is often removed using a tool called a cannula rather than being poured.

To get an accurate measurement, a scientist must follow a specific process involving the meniscus. A meniscus is the curve seen at the surface of a liquid in a container. This curve forms because molecular forces attract the liquid to the walls of the cylinder. This attraction causes the surface to become either concave, which dips in the middle, or convex, which curves upward. For most liquids, the surface is concave. To read the volume correctly, you must look at the cylinder at eye level. You must always take the reading from the bottom of the concave meniscus.

Accuracy and precision are categorized in several ways in the laboratory. Graduated cylinders are often marked with scales that show three significant digits. For example, a 100 mL cylinder typically has 1 mL grading divisions. A 10 mL cylinder will have smaller 0.1 mL divisions. There are also two distinct classes of accuracy. Class A cylinders are twice as accurate as Class B cylinders. Some cylinders use a single scale to read volume from top to bottom. Other cylinders use a double scale, which allows for both filling and pouring, also known as a reverse scale.

Calibration marks also tell a scientist how the cylinder handles liquid. Some cylinders are marked "TC," which means "to contain." This indicates the volume of liquid held inside the cylinder. Others are marked "TD," which means "to deliver." This means the cylinder accounts for the small traces of liquid left behind after pouring. Today, the international symbols "IN" and "EX" are also commonly used for these purposes. While the tolerances for "to contain" and "to deliver" used to be different, they are now considered the same.

Materials used to build these cylinders vary based on the needs of the lab. Large cylinders are often made of polypropylene, a type of plastic. Polypropylene is chosen because it has excellent chemical resistance. It is also easy to repeatedly autoclave, which is a process used to sterilize equipment. However, if you autoclave polypropylene at temperatures exceeding its specific limit, it can warp or melt. This damage would ruin the accuracy of the tool. Other cylinders are made of polymethylpentene. This material is used because it is transparent, light, and less fragile than glass.

The history of this tool dates back to the late 18th century. Louis Bernard Guyton de Morveau first introduced the graduated cylinder in 1784. He developed it specifically for use in volumetric analysis. Since then, the capacities of these tools have become standardized. Typical capacities now range from 10 mL to 1000 mL. Beyond measuring liquids, these cylinders can also measure the volume of solids indirectly. This is done through displacement, where the solid is placed in the liquid to see how much the level rises.