density determination

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The determination of the density of a substance, using one of several techniques. (a) With a Jolly's spring balance, the sample is first weighed in air, then immersed in water and reweighed, and the density is calculated by comparing the two weights. (b) The Berman balance is a very sensitive torsion balance, used for determining the density of small samples, and is based on the same principle as the Jolly balance. (c) A pycnometer is used to determine the density of soils or powders. It consists of a small bottle fitted with a ground-glass stopper with a capillary opening. The specimen is placed in the pycnometer, weighed, and then the bottle is filled with water and reweighed. (d) Heavy liquids can also be used. Liquids which are relatively dense, such as bromoform (sp. gr. 2.89) and methylene iodide (sp. gr. 3.33), may be mixed with acetone (sp. gr. 0.79) to produce a series of liquids of known density. If a sample is introduced into one of these liquids and it neither rises nor sinks, its density is the same as that of the liquid. These heavy liquids are often toxic, and great care must be taken when using them. Gloves and face masks should always be worn.

Subjects: Earth Sciences and Geography — Ecology and Conservation.

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