Salinity, the measurement of salts dissolved in water, is measured in parts per thousand (ppt) using specific instruments. According to the provided reference, these are:
Methods for Measuring Salinity in Parts Per Thousand (ppt)
Salinity can be accurately determined through several methods, each leveraging different physical or electrical properties of the solution. Here's a breakdown of the common techniques:
1. Conductivity Meter
A conductivity meter measures the electrical conductivity of the water. Because salt ions in water facilitate electrical current, higher conductivity indicates higher salinity. The meter translates this electrical conductivity to a salinity reading in ppt.
- How it works: A probe with electrodes is immersed in the water, an electrical current is passed through, and the meter measures how easily the current flows.
- Advantages: Provides rapid and precise readings, often with digital displays.
- Limitations: May require calibration, temperature sensitive.
2. Hydrometer
A hydrometer is a glass instrument that measures the specific gravity of a liquid. Because salt increases the density of water, a hydrometer can indirectly measure salinity. A scale on the hydrometer gives the salinity reading in ppt.
- How it works: The hydrometer is floated in the water, and the depth to which it sinks is measured, indicating density which is then translated to salinity.
- Advantages: Simple and inexpensive to use.
- Limitations: Less precise than other methods, and temperature sensitive.
3. Refractometer
A refractometer measures how light bends as it passes through the water sample. Because salt changes the refractive index of water, this measurement can be translated into salinity. The reading is then presented in ppt.
- How it works: A small water sample is placed on the refractometer prism, and the viewer observes the scale to read salinity in ppt.
- Advantages: Relatively quick, easy, and portable, requires small sample volumes.
- Limitations: Can be influenced by temperature, may require calibration.
Summary of Salinity Measurement Methods
Method | Principle | Advantages | Limitations |
---|---|---|---|
Conductivity Meter | Measures electrical conductivity | Rapid, precise | Requires calibration, temperature sensitive |
Hydrometer | Measures specific gravity | Simple, inexpensive | Less precise, temperature sensitive |
Refractometer | Measures refractive index | Quick, easy, portable | May require calibration, temperature sensitive |
The reference indicates that these are the primary tools for salinity measurement in ppt, each using distinct methods to deduce the salt concentration in water.