Hydrometer Analysis Introduction:
If the size of the soil particles are smaller than 0.075 mm, it is very difficult to use sieving to separate the particles. Therefore, hydrometer is used for obtaining particle size distribution of soil smaller than 0.075 mm. Settlement of soil particles from a suspension depends on the size of the soil particles. Therefore, settlement of the soil particles from a suspension is used to obtain the particle size distribution. Objectives: •
Determinatio Determination n of the distribution distribution of particle sizes finer finer than 0.075 mm 75 !m" !m" by a sedimentation process using a hydrometer.
Apparatus:
#. $ bal balan ance ce sens sensit itiv ivee to 0.0# 0.0# g. g. %. Stirring Stirring $ppara $pparatus. tus. &ither &ither a mechanically mechanically operated operated stirring stirring device device or an air 'et dispersio dispersion n apparatus. (. )ydr )ydrom omet eter er.. $n $ST* ST* #5# #5# ) or #5% #5% ) or or any any othe otherr stan standa dard rd"" type type hydr hydrom omet eter er graduated to read the grams per litre in suspension and confirming to the re+uirements of the corresponding standard. . Sedimentati Sedimentation on -ylinder. -ylinder. $ glass cylinder cylinder 57 mm in height height and (.5 mm in diameter, diameter, and mar/ed for a volume of #000 ml. 5. Therm Thermom omet eter er accu accura rate te to 0.5 0.50 -. . Dispersing Dispersing $gent. $gent. $ solution solution of Sodium Sodium )eametaphosp )eametaphospate ate shall be used in distilled distilled or demineralised 1ater, at the rate of 0 g of Sodium )eametaphospate2litre of solution.
3igure4# )ydrometer
Procedure:
#. Soil passing 0.%5 mm sieve is used for the test but the sample should not be oven dried. %. Therefore, a portion from the same soil is oven dried to obtain the moisture content of the soil sample. (. Then, the dry 1eight of the sample used for the test is corrected using that moisture content. . $bout 50 g of this soil is accurately 1eighted and #%5 ml of Sodium )eametaphospate solution 0g2litre" is added. 5. *iture is thoroughly 1etted and be allo1ed to soa/ for at least # hours. . The soa/ed sample is transferred to a dispersion cup and sample is further dispersed using a mechanical stirring apparatus after adding a suitable amount of 1ater. 7. $fter dispersion, soil41ater slurry is transferred to a sedimentation cylinder and distilled or demineralised 1ater is added to until the total volume is #000 ml. . 6sing the palm of the hand over the open end of the cylinder, cylinder shall be sha/en vigorously by turning it up side do1n and bac/ for a period of about # minute. . Thereafter the cylinder is placed in a convenient location to ta/e hydrometer readings using a hydrometer sho1n in 3igure4#. #0. 8eadings are ta/en at 0.5 min, # min, % min, min, min, #5 min, (0 min, # hr, % hrs, hrs, hrs, # hrs, and % hrs. ##. The hydrometer should be slo1ly removed after the reading at min, rinsed in 1ater and /ept in a cylinder of distilled or demineralized 1ater. #%. 9hen it is re+uired to ta/e the hydrometer reading, the hydrometer should be carefully inserted about (0 : 5 secs before the reading is due. #(. Immediately after ta/ing the reading, the hydrometer should be carefully removed and placed bac/ in the cylinder 1ith distilled or demineralized 1ater. #. -orrection of hydrometer readings should be carried out. 9hen the hydrometer reading is ta/en, it should be ta/en at the bottom of the meniscus. )o1ever, due to the soil suspension, it is practically not possible to do so. Therefore, the reading of the )ydrometer is ta/en at the top of the meniscus and a meniscus correction - m" is applied as sho1 in 3igure4%.
3igure 5 : *eniscus and dispersing agent correction factors
#5. This correction is obtained by ta/ing the reading at the top and bottom of the meniscus after immersing the hydrometer in an identical solution in cylinder %", 1hich is prepared 1ithout soil. #. The difference bet1een the top and bottom readings is the meniscus correction -m". #7. Similarly, the dispersing agent correction - d" is also obtained by ta/ing the reading in cylinder%. Observation: •
;lease see $nne4#.
Calculations and result: •
8 ) ? 8 )= @ -m The corrected hydrometer reading after application of both corrections may be obtained by> 8 ? 8 ) 4 -d ? 8 )= 4 -d : -m"
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;ercentage of particles remaining in suspensionA The percentage of soil particles remaining in suspension at the level at 1hich the hydrometer is measuring density of the suspension may be calculated asA ; ? 8a #00 B 9 9hereA ; 4 ;ercentage of soil remaining in suspension at the level at 1hich the hydrometer is measuring the density of the suspension. a : -orrection to be applied due to the variation of the specific gravity of the particles. 8 : )ydrometer reading after application of both the corrections. 9 : Cven dry mass of the soil in the suspension after applying the hygroscopic correction.
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Diameter of soil particles
The diameter D" of the particles at the level, 1here hydrometer is measuring density is given by> D? < t 9here : -onstant depending on the temperature of the suspension and the specific gravity of the soil particles.
< : Ealue of < can be obtained from a table provided 1ith the hydrometer. •
-alculations and result for carried out test is given in $nne4#, $nne4% and $nne4(.
Discussion: 1) a. Wat are te reasons !or addin" a dispersin" a"ent !or ydrometer analysis#
b. Discuss a metod to ma$e a lin$ in%bet&een ydrometer analysis and sieve analysis o! a "iven sample.
') a. Discuss te standard conditions to carry out a ydrometer analysis in a "iven soil sample.
b. Discuss te reasons !or per!ormin" a ydrometer analysis in i"&ay projects.
