Answers to Questions: 1. What is the purpose of hydrometer hydrometer analysis? On which physical principles is hydrometer found? A hydrometer hydrometer analysis analysis is the process process by which which fine-grained fine-grained soils, silts silts and clays clays are graded. graded. Hydrometer analysis is performed if the grain sizes are too small for the sieve analysis, thus soils smaller than 75 micrometers. The principle of hydrometer anal ysis is based on Stoke’s law, it assumes that dispersed soil particles of various shapes and sizes fall in water under their own weight as non-interacting spheres. 2. Does hydrometer analysis determine the size of of soil particles exactly? Yes, the hydrometer analysis determines the size of soil particles exactly. This is because in this experiment the large particles will settle quickly followed by the smaller particles. So every time interval on checking the hydrometer reading, the maximum diameter size of soil remained suspended can be computed. 3.
Why do you correct the distance of fall of particles during hydrometer analysis?
During hydrometer analysis, the distance of fall of particles is being corrected as the reading varies due to certain factors. This will affect the accuracy of the results. 4. What physical quantity is read on the stem of the hydrometer 152 H? In what unit is this quantity expressed? On the stem of a 152 H hydrometer, the mass density is given, and this is expressed in g/l or grams per liter. 5. What corrections are made on the hydrometer reading? Three corrections are applied to the hydrometer reading: the meniscus correction, the temperature correction, and the dispersing agent correction.
6. What modifications would be required if one wanted to carry out a hydrometer analysis in a 200ml cylinder instead of a 100ml cylinder? If one wanted to carry out a hydrometer analysis in a 200ml cylinder instead of a 100ml cylinder, on the temperature requires modification. 7. Does the hydrometer go up or down during the sedimentation of soil particles? In the results, the hydrometer reading decreases as time passes by. So, the apparatus goes down during the sedimentation of soil particles. 8. What is the purpose of the dispersing agent? Does its use require a correction? A dispersing agent is added to all samples to prevent grains from flocculating. Then the addition of this water increases the liquid density. Yes, this requires a correction. It is always positive and should be subtracted from the corrected hydromet er reading R’ when calculating percent by weight finer. 9. Is there a correction for the specific gravity of soil particles when one uses a 152 H hydrometer? When one uses a 152 H hydrometer, the meniscus correction is used. This helps to calculate the grain size and percent by weight finer. 10. What physical quantity does the hydrometer measure? At what location does it measure? The hydrometer measures the specific gravity of solids and this measurement is located in the graduated cylinder. 11. Why do you measure the water temperature during the hydrometer analysis? During the hydrometer analysis, the water temperature is measured because temperature changes of the soil suspension will affect the test results. It influences the hydrometer volume and the density of the solution. This is caused by the thermal expansion or contraction, and thus the density reading.
12. What is the purpose of the hydrometer calibration? What quantities does it relate? The purpose of the hydrometer calibration is to be able to read the measurement correctly at the surface of transparent liquid? 13. Why does the meniscus correction always have the same sign? What is this sign? The meniscus correction always has the same sign to acquire and insure the correctness of the hydrometer reading. The sign for this is positive. 14. For what reason do you agitate the suspension at the beginning of the hydrometer test? At the beginning of the hydrometer test, the suspension should be agitated to loosen the sediment at the bottom of the cylinder. 15. What is the usual duration of the hydrometer analysis? Why does the sedimentation part take so much time? The hydrometer analysis experiment usually takes one hour. The sedimentation takes so much time as the dispersion of the mixture of soil in water with chemical needs time for It to settle due to their chemical properties.
Sample Calculations: Formula:
= +0.02( −68) 30 − ) = √ 980( = 100 Time: 0.5 min
= 16+0.02(73.4−68) = 16.108 ) 7 = √ 980(2.30(0.605−0.0938)(13. 9976)(0.5) = 0.069 = 16.50108 100 = 32.22 Time: 2 min
= 15+0.02(71.6−68) = 15.072 ) 30(0.605−0. 0961)(13. 8 = √ 980(2. 9978)(2) = 0.035 = 16.50072 100 = 30.14
Introduction:
Principles of the Experiment: The hydrometer analysis is done to determine the grain size distribution of the fine – grained soils having particles size smaller than 75 micrometers. If soil samples have particle sizes ranging from sand to silt or clay, sieving and sedimentation analysis are combined. The principle of hydrometer analysis is based on Stroke’s law. It assum es that dispersed soil particles of carious shapes and sized fall in water under their own weight as non-interacting spheres. Falling spheres in a viscous fluid in which the terminal velocity of fall depends on the grain diameter and the densities of the grain in suspension and of the fluid. The grain diameter thus can be calculated from a knowledge of the distance and time of fall. The hydrometer also determines the specific gravity or density of the suspension, and this enables the percentage of particles of a certain equivalent particle diameter to be calculated.
Interpretation of Results: To get the results needed in the experiment, we submerged a hydrometer and a thermometer on a graduated cylinder with soil that is retained or passed through sieve 100 and 200. We recorded the hydrometer reading for 30 secs, 1 min., 2 min., 5 min., 15 min., 30 mins., and 60 min. mark. Based on the results of experiment, we were able to get a hydrometer reading of 16, 15, 15, 15, 14 ,13, and 13 respectively. Based on the equation given we were able to get the % of soil in suspension for each time mark. We were also able to observe that finer soil solid particles stay suspended longer than the bigger soil solid particles.
Application: Grain-size analysis of soil—Hydrometer Method falls under ASTM D-422. Soils with small grain sized cannot generally be analyzed using sieves because of the very small size of sieve opening
that would be required and the difficulty of getting such small particles to pass through. Grain-size analysis for these soils is done by a sedimentation process using a hydrometer. The hydrometer method is based on Stoke’s law, which states that the larger the grain size, the greater its settling velocity in a fluid. The distribution of different grain sizes affects the engineering properties of soil. Grain size analysis shows size distribution, and it is required in classifying the soil.
Conclusion: In this experiment, distribution of soil particles having sizes less than 75 micron were determined by a sedimentation process using a hydrometer to obtain the necessary data such as the borderline between clay and silt. Using this test, the GSD or grain size distribution for soils containing appreciable amount of fines was obtained. Based on the results of the experiment, the time increases while the hydrometer decreases. It is related with the dispersion of the mixture which are soil; water and dispersing agent. Thus, the time is indirectly proportional to the hydrometer reading. The temperature decreases as well because the liquid is exposed to the atmosphere and this affects the temperature of the mixture. As time passes by the maximum grain diameter in suspension decreases, as the soil particles goes down at the bottom of the cylinder. The larger particles settle quickly thus the maximum grain diameter in suspension decreases. There were three corrections applied to the hydrometer reading: the meniscus correction, the temperature correction and the dispersing agent correction. It was advised to get these values because certain factors affect the hydrometer reading. Some possible sources of error would be the performance of the experiment. Incorrect measurement of hydrometer reading. Sample left in the open having the tendency of acquiring dust or any other small particles from the surroundings, sample was not mixed properly or simply wrong
steps in performing the experiment, are just some possible sources of error. Lastly, wrong computation will definitely give inaccurate results.
References Das, B. M. (2006). Principles of Geotechnical Engineering. Stamford: Cengage Learning. Lu, N., Ristow, G. H., & Likos, W. J. (2000). The Accuracy of Hydrometer Analysis for Fine-Grained Clay Particles. Geotechnical Testing Engineering , 487-495. Murthy, V. N. (n.d.). Geotechnical Engineering: Principles and Practices of Soil Mechanics and Foundation Engineering. New York : Marcel Dekker . Mylonakis, G. (2008, September 29). L3a Hydrometer Analysis. Retrieved from The City College of New York - Dept. of Civil Engineering: wwwce.engr.ccny.cuny.edu/Courses/CE345/L3b%20Hydrometer%20Analysis.doc Prakash, K., Sridharan, A., Thejas, H. K., & H.M., S. (2012). A Simplified Approach of Determining the Specific Gravity of Soil Solids. Geotechnical and Geological Engineering , 1063-1067. Rahman, F. U. (2009, March 19). Particle Size Distribution. Retrieved from The Constructor: https://theconstructor.org/geotechnical/particle-size-distribution-of-soil-hydrometermethod/2775/ Suryakanta. (2015, November 18). Civilblog.org . Retrieved from Hydrometer: What, Why, and How?: http://civilblog.org/2015/11/18/hydrometer-analysis-of-soil-what-why-how/
