Content

• To step
• Method 1 of 4: Determine porosity theoretically by volume
• Method 4 of 4: Calculate porosity in the field by taking core samples
• Tips
• Warnings
• Necessities

Porosity, or porosity, is the value used to describe how much empty space is present in a given sample. This characteristic is usually measured with respect to the soil, as the correct degree of porosity is necessary for the growth of the plants. Porosity can be theoretically calculated using equations and given values, which is the case when dealing with exam questions. Porosity can also be determined by finding the values ​​needed to solve the equations experimentally, either in the laboratory or in the field.

To step

Method 1 of 4: Determine porosity theoretically by volume

1. Extract useful values ​​from the given information. When calculating the porosity theoretically, you get an example situation that contains some of the values ​​you need. Read your question carefully and look for values ​​such as total volume (${ displaystyle Vt}$Draw up the correct equation. By definition, porosity (${ displaystyle Pt}$Find values ​​for your volume variables. It's helpful to keep that in mind ${ displaystyle Vt}$Apply the known volume variables to the porosity equation. Once you have a value for it ${ displaystyle Vp}$Solve the equation to determine the porosity. Now that your equation is complete and you have the correct values, you can solve it with a simple calculation. It might help to have a calculator on hand for this part.
   • Since porosity is often expressed as a percentage, it is common to multiply this value by 100% once you find the decimal value.
   • Using the same values ​​from the examples above, your equation will look something like this:
     • ${ displaystyle Pt}$Assume that the particle density (P.d{ displaystyle Pd}Use the relationship between volume and density to derive your equation. Since density is defined as mass per volume, and porosity is a comparison of pore volume to total volume, it is possible to express porosity in terms of density as well. The result is the comparison${ displaystyle Pt}$Determine the value of P.b{ displaystyle Pb}Solve the equation by inserting the correct density values. Now you have the values ​​for ${ displaystyle Pb}$With the volume of your sample. You can measure the volume directly if your sample exactly fills a container with a known volume. You can also transfer the sample to a bottle or cup, such as a measuring cup, to measure the volume. If you cannot measure the volume directly, you can calculate the volume mathematically.
       • Note that transferring the sample from one container to another can affect the porosity by disturbing the material.
     • Measure out a volume of water. It is not important exactly how much water you measure. The two things that are important in this step are measuring more water than you need to saturate your sample, and recording the amount of water you started with. This is the only way you can know how much you have used.
     • Saturate the test sample with water. This is an easy step, but can be tricky. You must add enough water to fill all the pores in your sample, but you should not add too much water. While it is important to get as close to saturating the sample as possible, there will be some margin of error. Get the water level as close to the surface of your fixed sample level as possible.
     • Record the volume of the water used. Subtract the amount of water that remains from the amount of water you started with. This way you are left with the volume of water that has been drained. The volume of water you use is (approximately) equal to the pore volume of your sample.
     • Set up the equation to calculate porosity with a known volume. Now that you have the volume of your sample (${ displaystyle Vs}$Do the calculations to find the porosity of your sample. Enter the correct values ​​into the equation. Make sure to keep track of your units and make sure they are properly canceled as porosity is a unitless value. A calculator can also be useful at this step.

Method 4 of 4: Calculate porosity in the field by taking core samples

1. Saturate the area you want to sample. A good way to do this is to place a steel ring of known weight (such as a ring with a diameter of 7 cm and a height of 10 cm) on the ground where you want to take a sample and fill it with water. Let the water sit in the ring overnight, or until it is absorbed by the soil, this will make it easier to collect your sample.
   • You can find fixed weight steel rings at home improvement stores and online.
2. Push the steel ring into the ground. Work the ring into the ground with a block of wood and a hammer. The soil within the ring is called a core or core sample. The ring protects the core sample from disturbance during collection.
3. Dig around the steel ring. Carefully dig around the steel ring with a shovel and other digging tools. You don't want to disturb the ground in the ring. Trim away any roots from the bottom of the ring.
4. Remove the ring. Once you've cleared the soil around the ring, you can get the ring and monster out of the hole. Keep the core sample inside the ring and do not disturb it. Be careful not to lose monsters while moving.
5. Record the saturated mass of your sample. Place the ring in a large, clear container. Add water until the sample in the ring is completely saturated and cannot contain any more water. Weigh the sample in the steel ring. Subtract the mass of the steel ring from that value. This leaves the saturated mass of the sample.
6. Record the volume of your sample. The volume of your sample will be the same as the volume of your ring. Since your ring is a cylinder, to calculate the volume, you are going to multiply the height of the cylinder by the radius squared (the radius is the distance from the center of the circle to the edge), then multiply that by pi (often rounded to 3.14).If you don't know the radius, you can measure the top of the cylinder at its widest point and divide it in half.
7. Move the soil to a container suitable for the oven. Make sure you weigh the container beforehand and the mass (${ displaystyle mc}$Dry your sample. If you are using a microwave, 10 minutes should be high enough to dry your sample. This ensures that all pores in the sample are cleared of water. You can also dry the sample in a conventional oven at 105 degrees Celsius for at least two hours. Although it is still full of air, it will not affect the sample's mass.
8. Weigh your dried sample in the dish to get the total mass (mt{ displaystyle mt}Pull up mc{ displaystyle mc}Calculate the mass of the water in the saturated sample. Subtract the dry mass (${ displaystyle md}$Convert the mass of the water to the pore volume of your sample. By definition, one gram of water equals one cubic centimeter of water. This means that the mass of your water in grams is equal to the volume of the water in cubic centimeters. Since the sample is saturated, all pores are filled with water, so the pore volume is equal to the volume of water in the saturated sample.
9. Divide the pore volume by the total volume of your sample. This returns a decimal number that is less than one. Multiply that number by 100%. The result is the porosity of your sample as a percentage.

Tips

• Take multiple samples in the field. This will help minimize errors in your readings.
• If you are transferring the sample from the field to another location for analysis, seal it in a plastic bag.
• There are also software programs such as RESRAD that can help determine porosity, but they are beyond the scope of this article.
• Bulk density and particle density can also be found experimentally to calculate porosity. Bulk density is found by dividing the dry mass by the sample volume. The particle density is often 2.66 g / cm ^ 3.

Warnings

• The instruments used to take measurements also affect the margin of error of the measurement. The finer an instrument is tuned, the smaller the margin of error. However, keep in mind that all instruments have their limitations.
• Human error is present to some extent in all experimental measurements.
• Disruption of the test sample can cause a change in the porosity of the sample due to the compaction or separation of particles. Proceed with caution.

Necessities

• Theoretical calculation of porosity to volumes
  • Calculator
• Experimental calculation of porosity to saturation
  • Sample
  • Container for test samples
  • Water
  • Water container
• Calculation of porosity in the field by taking core samples
  • Steel ring
  • Hammer and block
  • Shovel
  • Scale
  • Oven or microwave