Hydrometers are calibrated to measure what type of concentration?

Hydrometers are instruments specifically designed to measure the density of liquids, which can be used to determine the concentration of solutes within that liquid. In the context of water quality, they are commonly employed to measure the percent of salt concentration.

When a hydrometer is placed in a solution, the degree to which it floats or sinks is influenced by the density of the liquid. A more saline (salty) solution is denser than pure water, leading to a higher reading on the hydrometer. This principle allows for the estimation of salt concentration based on the hydrometer's calibrated scale.

In contrast, the other types of concentrations mentioned—dissolved oxygen, turbidity, and sediment concentration—are measured using different methods and instruments. For example, dissolved oxygen is typically measured with specialized probes or meters designed to detect oxygen levels in water, while turbidity is assessed using a turbidity meter or secchi disk to gauge water clarity. Sediment concentration would also require a different analytical approach, such as filtering or centrifuging a water sample. Thus, the specific capabilities of a hydrometer make it suitable for measuring salt concentration in liquid solutions.