What is the density measurement device typically used to find the specific gravity of oil?

The device specifically designed for measuring the density of liquids, which allows for the determination of specific gravity, is the hydrometer. A hydrometer consists of a glass tube with a weighted bottom that floats in the liquid being measured. The level at which the hydrometer floats correlates to the density of the liquid.

For oils, the hydrometer can be calibrated to provide readings directly related to specific gravity, which is the ratio of the density of the oil to the density of water. This is particularly useful in various applications, such as in the petroleum industry, where understanding the specific gravity of different oils is essential for processing and handling.

Other devices mentioned do not fulfill this purpose: a thermometer measures temperature, a barometer measures atmospheric pressure, and a psychrometer is used for measuring humidity. These instruments serve distinct functions and are not suitable for determining the specific gravity of liquids.