What is the name of the device that measures the specific gravity of a liquid?

The device designed specifically to measure the specific gravity of a liquid is known as a hydrometer. A hydrometer operates based on the principle of buoyancy, where it floats in the liquid to provide a reading based on the level at which it floats. This level corresponds to the density or specific gravity of the liquid being tested.

Specific gravity is a measure of the density of a liquid relative to the density of water, and since hydrometers are calibrated for this purpose, they are particularly useful for determining the concentration of solutions, such as sugar or alcohol, as well as other applications in various industries.

The other devices listed serve different purposes; for instance, a barometer measures atmospheric pressure, an osmometer measures the osmotic pressure of solutions (which relates to the concentration of solutes), and a manometer measures the pressure of gases. Each device has its unique application, which underscores the specific function of a hydrometer in measuring liquid densities.