A variety of minerals are referred to as salts and provide sea water with its characteristic qualities. Outside of laboratory experiments, it is commonly measured by aquarium enthusiasts, and by farmers who are interested in understanding the presence of any salt clusters in the soil. While there are several tools that can be used to measure salinity, the correct salinity level mostly depends on your specific purpose. Consult an aquarium manual for instructions, or information regarding a particular crop, to find out which salinity level is best for you.
Steps
Method 1 of 3: Using a Portable Refractometer
Step 1. Use this tool to accurately measure salinity in liquids
Refractometers measure how much light bends, or refracts, as it passes through liquid. The more salt or other particles are present in the water, the more resistance the light will encounter, and it will curve more.
- For a cheaper, but somewhat less accurate method, try a hydrometer.
- If you need to measure salinity in soil, use a conductivity meter.
Step 2. Choose a reflectometer suitable for the liquid you are measuring on
Different liquids already refract light differently, so to accurately measure additional salinity (or other solid content), use a refractometer designed specifically for the liquid you need to analyze. If the liquid is not explicitly specified on the package, the refractometer is probably designed to measure the salinity of water.
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Note:
Salt refractometers are used to measure the sodium chloride present in water. Seawater refractometers are used to measure a mixture of salts that are usually found in seawater or saltwater aquariums. Using the wrong one could cause a 5% error, which may be acceptable for non-laboratory results.
- Refractometers are also designed to compensate for the expansion of different materials depending on the temperature.
Step 3. Open the plate near the angled end of the refractometer
A portable refractometer has a round end, open to look through it, and an angled end. Hold the refractometer so that the angled part is on top of the device, and find the small plate near this end that can be slid to the side.
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Note:
If you haven't used a refractometer yet, you should calibrate it first to get a better reading accuracy. This process is explained at the end of this section, but you should read these steps first so that you are familiar with how it works.
Step 4. Add a couple of drops of the liquid to the exposed prism
Take the liquid you would like to measure, and use a dropper to take a few drops. Transfer them to the translucent prism that is revealed by moving the plate. Add enough liquid to cover the bottom of the prism with a thin layer.
Step 5. Close the dish carefully
Cover the prism again by gently returning the plate to its initial position. The pieces of the refractometer can be small and delicate, so try not to force too much even if they appear slightly stuck. Instead, swipe the platter back and forth until it moves easily again.
Step 6. Look through the device to take the salinity reading
Look through the rounded end of the device. There should be one or more numbered scales visible. The salinity scale is probably indicated with 0/00 which means "parts per thousand", and ranges from 0 to at least 50 at the end of the scale at the top. Measure the salinity corresponding to the point where the white and blue areas meet..
Step 7. Clean the prism with a soft cloth
Once you have the measurement, use a soft and slightly damp cloth to clean the prism until it is free of water droplets. Leaving water in the refractometer or immersing it in water can cause damage..
A damp paper towel may also be fine if you don't have a cloth that is flexible enough to reach every spot before
Step 8. Calibrate the refractometer periodically
Periodically calibrate the refractometer using distilled water. Add water to the prism as you would for any liquid, and check if the salinity reading is "0." If not, use a small screwdriver to calibrate the calibration screw, which is usually found under a small shield at one end of the device, until the reading is "0."
- A new, high-quality refractometer may require calibration just every couple of weeks or months. A cheaper or older refractometer must be calibrated before each reading.
- Your refractometer may have been sold to you with instructions that indicate the optimal water temperature for calibration. If there is no such thing, use distilled water at room temperature.
Method 2 of 3: Use a Hydrometer
Step 1. You can use this inexpensive tool to make fairly accurate measurements on water
A hydrometer measures the specific gravity of water, or its density compared with H.2Or pure. Since practically all salts are denser than water, a hydrometer reading can tell you how much salt is present. It is accurate enough for almost any purpose, such as measuring salinity in an aquarium, but many hydrometer models are not accurate or difficult to use correctly.
- This method cannot be used with solid materials. If you want to measure soil salinity, switch to the conductivity meter method.
- For a more accurate measurement, use the economical method of evaporation, the fastest method of the refractometer.
Step 2. Narrow down your hydrometer options
Hydrometers, also called specific gravity meters, are sold online or in aquarium stores, in many different formats. Glass hydrometers that float in water are usually the most accurate, but often do not have precise measurements listed (one decimal part longer). Plastic hydrometers with a rotating arm may be cheaper and more robust, but tend to become less accurate over time.
Step 3. Choose a hydrometer that contains a list of standard temperatures
Since different materials tend to expand or contract differently depending on the temperature, knowing the temperature at which the hydrometer has been calibrated is important for accurate measurements. Choose a hydrometer that has the temperature specified on the package. It may be easier to use hydrometers calibrated at 15.6ºC or 25ºC, as they are the most usual for measurement standards. You could use a hydrometer with a different calibration if it has a table for converting temperatures to salinity.
Step 4. Take a water sample
Transfer some of the water you want to analyze on a flat transparent container. The container must be large enough to contain the hydrometer, and the water must be deep enough to immerse it. Make sure the container is not dirty or contains traces of soap or other materials.
Step 5. Measure the temperature of the water sample
Use a thermometer to measure the water temperature. Once you know the water temperature and the one at which the hydrometer has been calibrated, you can calculate the salinity.
For a slightly more accurate reading, you could bring the water you are measuring to the temperature at which the hydrometer was calibrated. Be careful not to heat the water too much, since the vapors or boiling can significantly alter the salinity
Step 6. Clean the hydrometer if necessary
Clean the hydrometer to remove any dirt on the surface. Rinse the hydrometer in fresh water if it has previously been immersed in salt water, since the salt could have deposited on the surface.
Step 7. Gently place the hydrometer in the water sample
Glass hydrometers can be partially submerged in water, then released to float on their own. Hydrometers with movable arm do not float, and are usually sold with a small handle that allows you to place them in the water without getting your hands wet.
Do not completely immerse the glass hydrometer, as this can cause problems with the reading
Step 8. Gently shake it to remove bubbles
If there are air bubbles on the surface of the hydrometer, they can cause variations in density. Gently shake the hydrometer to remove bubbles, then wait for the water turbulence to vanish.
Step 9. Read the measurement on an arm hydrometer
Keep the boom hydrometer completely horizontal, with no inclination in one direction. The arm points to the measured specific gravity.
Step 10. Read the measurement on a glass hydrometer
In a glass hydrometer, read the measurement where the surface of the water meets the hydrometer. If the surface of the water bends slightly in contact with the hydrometer, ignore that curve and read the measurement at the level of the flat surface of the water.
The water curve is called the meniscus, and is a phenomenon caused by surface tension, not by salinity
Step 11. Convert the result of the specific gravity measurement to a salinity measurement if necessary
Many aquariums report specific gravity, usually measured between 0.998 and 1.031, so you don't have to convert to salinity, usually between 0 and 40 parts per thousand (ppt). However, if it only reports salinity, you will need to convert. If your hydrometer does not have a specific table to do this, look online or in an aquarium care book for a "specific gravity to salinity conversion" table or rule. Make sure you are using those that are suitable for the standard temperatures indicated on your hydrometer, or you may get the wrong result.
- This table can be used for a hydrometer calibrated at 15.6ºC.
- This table can be used for a hydrometer calibrated at 25ºC.
- These tables or rules also vary according to the liquid, but most are related to salt water.
Method 3 of 3: Use a conductivity meter
Step 1. Use this method to measure the salinity of the soil or water
A conductivity meter is the only commonly used instrument that can be used to measure the salinity of the soil. It can also be used to measure the salinity of water, but a high-quality conductivity meter can be much more expensive than a refractometer or hydrometer of equal efficiency.
Some aquarium enthusiasts prefer to use, in addition to one of the two previous methods, also a conductivity meter, to confirm their measurements
Step 2. Choose a conductivity meter
These devices make current flow through materials, and measure how much a material resists the current crossing. The more salt there is in the water or soil, the higher the conductivity level. In order to get good measurements on common types of water and soil, choose a conductivity meter that can measure at least up to 19.99 mS / cm (19.99 dS / m).
Step 3. If you have to measure the soil, mixed with distilled water
Mix one part of soil with five parts of distilled water, shaking it for a long time. Let the mixture sit for at least two minutes before continuing. Since distilled water does not contain electrolytic salts, the measurement you will get will reflect the concentration of the latter within the soil.
Under laboratory conditions, you may be required to let the mixture sit for thirty minutes. This is rarely done outside the laboratory, and the method we describe is accurate nonetheless
Step 4. Immerse the conductivity meter deprived of a protective capsule in the water up to the necessary level
Remove the protection covering the end of the conductivity meter. Immerse it up to the indicated level, or at least until the probe that is to carry out the measurement is completely immersed, if there is no indicated level. Many conductivity meters are not water resistant above a certain level, so do not let it fall into the water.
Step 5. Gently rock the conductivity meter up and down
This movement removes the air bubbles that may have formed during the dive. Do not shake it vigorously, as this could cause the water to escape from the probe.
Step 6. Adjust the temperature according to what is described on the conductivity meter
Some conductivity meters automatically correct themselves based on liquid temperature, which can have an impact on conductivity. Wait at least thirty seconds for the conductivity meter to make this adjustment, or longer if the water is particularly hot or cold. Other conductivity meters have dials that can be used to manually adjust the temperature.
If your conductivity meter does not have either of these two instruments, it may have a table in the package that allows you to make the necessary conversions
Step 7. Read the screen
The screen is usually digital, and may provide you with measurements in mS / cm, dS / m, or mmhos / cm. Fortunately, these three units are equal in size, so you don't have to convert from one to the other.
Respectively these units stand for milliSiemens per centimeter, deciSiemens per meter, or millimho per centimeter. The mho (reverse of an ohm) is an antiquated name for Siemens, but is still used by some industry
Step 8. Determine if the soil salinity is suitable for your plants
Using the method just described, readings of 4 or greater indicate a hazard. Sensitive plants such as mango or banana can be damaged by salinity as low as 2, while tolerant plants such as coconut can resist up to 8-10.
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Note:
When checking specific ranges for certain plants, try to understand the method used in that case to measure salinity. If the soil is diluted with two parts of water, or simply with enough water to form a paste, instead of the 1: 5 proportions described by us, the number can be significantly different.
Step 9. Calibrate the conductivity meter periodically
Between each use, calibrate the conductivity meter by measuring "the conductivity meter calibration solution," which must be purchased for this purpose. If the measurement does not match the conductivity of this solution, use a small screwdriver to turn the calibration screw until the measurement is correct.
