The hydrometer method is a technique employed to evaluate the particle size distribution of fine-grained soils that can pass through a 75 µ sieve. This method relies on the use of a hydrometer, which measures the specific gravity of a soil suspension at the center of its bulb. The specific gravity is influenced by the amount of solids in the suspension, which is in turn affected by the particle size of the soil.
By using the hydrometer method, it becomes possible to determine the particle size distribution of fine-grained soils with a high degree of accuracy. This information is important for a range of applications, including the construction of buildings, roads, and other infrastructure. The method provides valuable insights into the composition of soils and can help engineers and geologists to make informed decisions about how to design and build structures that are safe and effective.
Overall, the hydrometer method is a powerful tool for analyzing fine-grained soils and is widely used in various industries. Its ability to measure specific gravity and particle size distribution allows for accurate and reliable assessments of soil composition, helping to ensure that structures built on these soils are stable and secure.
Soil Particle Size Distribution by Hydrometer Method
Equipments Required
The test procedure requires a specific set of equipment to be used. This includes a hydrometer, glass measuring cylinder (jar) with a capacity of 1000ml, a rubber bung for the cylinder, and a mechanical stirrer. Additionally, a weighing balance with an accuracy of 0.01g, an oven, deflocculating agent, desiccator, evaporating dish, conical flask or beaker with a capacity of 1000ml, stop watch, wash bottle, thermometer, water bath, 75 µ sieve, and a scale are necessary for the test procedure. Each of these pieces of equipment plays an essential role in accurately conducting the test and obtaining reliable results.
Theory of Hydrometer Test
The particle size (D) is given by:
Where
I apologize, but I am unable to find the specific context or reference for the given equation and parameters you have provided. Can you please provide me with more information or context so that I can better understand the question and provide an appropriate response?
Where,
R= corrected hydrometer reading, Ms= mass of dry soil in 1000ml suspension.
Procedure of Hydrometer Test
Part – 1: Calibration of Hydrometer
To conduct this experiment, a measuring cylinder with a capacity of 800ml is required. The initial reading of the water level should be observed after placing the cylinder on a table. Next, the hydrometer should be immersed in the cylinder, and the final reading should be taken after the immersion. The difference between the final and initial readings represents the volume of the hydrometer, which can also be determined by weighing it to the nearest 0.1g. The mass of the hydrometer in grams is approximately equal to its volume in ml.
The area of cross section (A) of the cylinder can be determined by measuring the volume indicated between any two graduations and dividing it by the distance between them, which is measured with an accurate scale.
In addition, the height of the bulb (h) should be measured by determining the distance (H) between the neck and the bottom of the bulb. To determine the effective depth (He) corresponding to each of the marks (Rh) on the hydrometer, the distance (H) between the neck and each mark (Rh) should be measured.
Note:
The first statement is discussing the use of a hydrometer during sedimentation readings. Specifically, it is saying that if the hydrometer is not removed during readings taken at different times after sedimentation has started, the factor VH/A should not be considered.
The second statement is asking for a calibration curve or table to be created between He and Rh. This curve or table would allow for the effective depth He to be determined based on a given reading of Rh.
Fig 1: Hydrometer Method
Fig 2: Hydrometer Calibration Chart
Part – 2 : Meniscus Correction
To measure the density of a liquid using a hydrometer, you first need to insert the hydrometer into a measuring cylinder that contains approximately 700ml of water. Once the hydrometer is in the cylinder, you should take readings at both the top and bottom of the meniscus.
It’s important to determine the meniscus correction, which is the difference between the two readings. The meniscus correction, denoted as Cm, is always positive and remains constant for the hydrometer being used.
To obtain the corrected hydrometer reading, Rh, you need to use the observed hydrometer reading, Rh’. The corrected reading takes into account the meniscus correction and is more accurate. Overall, by following these steps, you can obtain a more precise measurement of the density of the liquid you are analyzing.
Part – 3 : Pretreatment and Dispersion
To begin with, take an air-dried soil sample passing 2mm IS sieve, which is obtained by riffling from the air-dried sample passing 4.75mm IS sieve. Weigh it accurately to the nearest 0.01g, about 50g, and put it in a wide-mouthed conical flask. Add approximately 150ml of hydrogen peroxide to the soil sample in the flask and stir it gently using a glass rod for a few minutes. Cover the flask with a glass plate and leave it overnight.
Next, gently heat the mixture in the conical flask after placing it in an evaporating dish. Stir the contents periodically until vigorous frothing subsides, indicating the reaction is complete. Then, reduce the volume to 50ml by boiling, stop heating and cool the contents. If the soil contains insoluble calcium compounds, add around 50ml of hydrochloric acid to the cooled mixture. Stir the solution with a glass rod for a few minutes and let it stand for about an hour until it has an acid reaction to litmus.
After that, filter the mixture and wash it with warm water until the filtrate shows no acid reaction. Transfer the damp soil on the filter and funnel to an evaporating dish using a jet of distilled water. Use the minimum quantity of distilled water. Place the evaporating dish and its contents in an oven and dry it at 105 to 110 degrees Celsius. Transfer the dish to a desiccator and let it cool. Take the mass of the oven-dried soil after pretreatment and find the loss of mass due to pretreatment.
Then, add 100ml of sodium hexa-metaphosphate solution to the oven-dried soil in the evaporating dish after pretreatment. Warm the mixture gently for about 10 minutes. Transfer the mixture to the cup of a mechanical mixture. Use a jet of distilled water to wash all traces of the soil out of the evaporating dish. Use approximately 150ml of water and stir the mixture for about 15 minutes.
Next, transfer the soil suspension to a 75 µ IS sieve placed on a receiver (pan). Wash the soil on this sieve using a jet of distilled water, using about 500ml of water. Transfer the soil suspension passing 75 µ sieve to a 1000ml measuring cylinder. Add more water to make the volume exactly equal to 1000ml. Finally, collect the material retained on the 75 µ sieve, dry it in an oven, determine its mass and if necessary, perform a sieve analysis of this fraction.
Part – 4 : Sedimentation Test
To determine the density of soil suspension, the following steps should be taken. Firstly, place a rubber bung on the open end of a measuring cylinder containing the soil suspension and shake it vigorously end-over-end to ensure that the suspension is thoroughly mixed. Next, remove the bung and place the measuring cylinder on a table, then start the stop watch.
Gently immerse the hydrometer to a depth slightly below the floating depth and let it float freely. Hydrometer readings (Rh’) should be taken after 1/2, 1, 2, and 4 minutes without removing the hydrometer from the cylinder. The hydrometer should be taken out, rinsed with distilled water, and then floated in another cylinder containing only distilled water at the same temperature as the test cylinder.
After taking readings at 8 minutes, the hydrometer should be removed, rinsed, and placed back in the distilled water. This process should be repeated at 15, 30, 60, 120, and 240-minute intervals. Two readings should be taken after 240 minutes, within 24 hours, and the exact time of reading should be noted. The temperature of the suspension should be recorded during the first 15 minutes and at the time of every subsequent reading.
After the final reading, pour the suspension into an evaporating dish, dry it in an oven, and find its dry mass. Before the test begins and at 30 minutes, 1, 2, and 4 hours, the composite correction should be determined. After each reading, the composite correction should also be determined. To determine the composite correction (C), insert the hydrometer in the comparison cylinder containing 100ml of dispersing agent solution in 1000 ml of distilled water at the same temperature, and take the reading corresponding to the top of the meniscus. The negative of the reading is the composite correction.
Fig 3: Downward Movement of Hydrometer
Data Sheet for Hydrometer Test
Mass of dry soil (Ms)=_______g
Meniscus correction (Cm)= +_______
Specific gravity of solids (G)= ______
Table 1: Observation recording sheet
| Sl. No. | OBSERVATIONS | CALCULATIONS | ||||||||
| Elapsed time | Hydrometer reading | Temperature | Composite correction | Corrected reading Rh=Rh’+Cm | Height (cm) He | Reading R= Rh’+C | Factor M | Particle size D | % Finer | |
| 1 | 1/2min | |||||||||
| 2 | 1 “ | |||||||||
| 3 | 2 “ | |||||||||
| 4 | 4 “ | |||||||||
| 5 | 8 “ | |||||||||
| 6 | 15 “ | |||||||||
| 7 | 30 “ | |||||||||
| 8 | 1 hr. | |||||||||
| 9 | 2 hr. | |||||||||
| 10 | 4 hr. | |||||||||
| 11 | 8 hr. | |||||||||
| 12 | 12 hr. | |||||||||
| 13 | 24 hr. | |||||||||
Result of Hydrometer Test
To plot a particle size distribution curve, two pieces of information are required: particle size and percentage fineness. The curve is a graphical representation of the particle size distribution of a sample, and it shows the percentage of particles that fall within a particular size range. The particle size can be measured using various methods, such as microscopy or laser diffraction, and is usually reported in micrometers (µm). The percentage fineness represents the amount of material that is finer than a particular particle size, and it is expressed as a percentage of the total sample weight. By plotting these two pieces of information on a graph, a particle size distribution curve can be generated, which provides valuable information about the sample’s physical properties.