Displacement in a Graduated Cylinder
Finding the volume of a regular solid simply requires measurement of the sides and employing the appropriate mathematical formula. However, when measuring the volume of irregular solids the ruler may be retired and the graduated cylinder employed. Displacement in a graduated cylinder is an effective measure of volume since the object's volume remains unchanged since it is submerged, producing an equivalent increase in the sum of the object and surrounding liquid.
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The Graduated Cylinder
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The graduated cylinder is a common piece of laboratory equipment used to measure volume. The graduated cylinder consists of a cylindrical glass or plastic tube closed at one end with graduated markings along the side of the cylinder. Graduated cylinders are available in different sizes with markings relative to the overall volume of the cylinder. For example, 100 mL graduated cylinders typically have markings in 1 mL increments and 10 mL graduated cylinders are marked in 0.1 mL increments.
Measuring Volume of Liquids
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Liquids poured into a graduated cylinder form an inverted bulge at the top of the liquid. This inverted bulge is higher along the sides and lowest in the center, which is referred to as the meniscus. The volume of a liquid within the graduated cylinder is measured with the marking closest to the meniscus.
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Displacement in a Graduated Cylinder
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Submerging an object within a graduated cylinder will cause a rise in the volume equal to the volume of the submerged object. Agitating the object while submerged reduces the amount of trapped air in the object, allowing for a more accurate measurement. By subtracting the volume of the liquid with the object from the volume of the liquid without the object, the volume of the object may be calculated.
Limitations
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Water is normally used as the liquid for measuring volume by displacement. However, many substances dissolve in water and some will even react with water. In both instances, a different liquid should be selected for the measurement. Another problem arises if the object is of relatively low density, leading the object to float.
Advantages
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The major advantage of using displacement is in quickly and easily measuring the volume of an irregular solid, again providing that the object is more dense than the liquid, insoluble in the liquid, and not reactive with the liquid. As long as the previous issues are addressed, this nondestructive test allows for other measurements to be performed on the object.
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