Soil composition, layers, examination is described

1. FORENSIC ANALYSIS
OF SOIL
Sivakrishnan.R
MSc. Sem I
Submitted to- Ketan Sir
Shri Vaishnav Institute of Forensic Science

2. INTRODUCTION
Definition :
Soil is the upper layer of earth in which plants grows, a black or
dark brown material typically consist of mixture of minerals,
water, gases, and other organic decaying remains.
•Weathering is the mechanical or chemical process by which rocks
are broken down into smaller pieces.
•As rocks are broken down, they mix with organic materials, which
are those materials that originate from living organisms.
•For example, plants and animals die and decompose, releasing
nutrients back into the soil. Soil is highly heterogeneous in nature
and varies widely from place to place due to the effects of wind,
water, living organisms, mining and agriculture. Thus, Soil from
different places will have different individual characteristics.
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3. TYPES OF SOIL
Soil can be categorised into :
•Sand
•Clay
•Silt
•Peat
•Chalk
•Loam
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4. Sandy soil
Sandy soil are light, warm, dry and tend to be acidic and low in nutrients.
Sandy soils are often known as light soils due to their high proportion of
sand and little clay (clay weighs more than sand).
These soils have quick water drainage and are easy to work with.
The addition of organic matter can help give plants an additional boost of
nutrients by improving the nutrient and water holding capacity of the soil.
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5. Clay soil
 Clay soil are heavy soils that benefit from high nutrients.
 Clay soils remain wet and cold in winter and dry out in summer.
 These soils are made of over 25 percent clay, and because of the spaces found between
clay particles
 clay soils hold a high amount of water. Because these soils drain slowly and take longer
to warm up in summer, combined with drying out and cracking in summer, they can often
test gardeners.
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6. Silt Soil
Silt soil are light and moisture retentive soils with a high fertility rating. As silt soils
compromise of medium sized particles they are well drained and hold moisture well.
As the particles are fine, they can be easily compacted and are prone to washing
away with rain.
By adding organic matter, the silt particles can be bound into more stable clumps.
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7. Peat Soil
Peat soil are high in organic matter and retain a large amount
of moisture.
This type of soil is very rarely found in a garden and often
imported into a garden to provide an optimum soil base for
planting
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8. CHALK SOIL
Chalk soil can be either light or heavy but always highly alkaline due to
the calcium carbonate or lime within its structure.
As these soils are alkaline they will not support the growth of ericaceous
plants that require acidic soils to grow.
If a chalky soil shows signs of visible white lumps then they can’t be
acidified and gardeners should be resigned to only choose plants that
prefer an alkaline soil.
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9. Loam Soil
Loam soil are a mixture sand, silt and clay that are combined to avoid the
negative effects of each type.
These soils are fertile, easy to work e of with and provide good drainage.
Depending on their predominant composition they can be either sandy or
clay loam.
As the soils are a perfect balance of soil particles, they are considered to be a
gardeners best friend, but still benefit from topping up with additional organic
matter.
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10. SOIL HORIZONS
Soil horizons are distinct layers of soil that form naturally in undisturbed soil over
time. The formation of soil horizons is called soil geomorphology and the types of
horizons are indicative of the soil order. Like other natural processes, the age of
the horizon increases with depth.
Soil Horizon Names and Descriptions
O: Decaying plants on or near surface
A : Top Soil, Organic Rich
B : Subsoil, Most Diverse Horizon and the Horizon with the most sub
classifications
C : Weathered/aged parent material
R : Bedrock
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11. METHODOLOGY
• Simple Observations
• Microscopical Observation with Chemical Regents
• Ignition Test
• pH Measurement
• Particle size distribution
• Density distribution
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12. Simple observations
(Stereo-microscope capable with high magnification range.)
Take some soil sample on a clean microscopic slide/ glass plate and make its thin layer.
Place the slide/plate with soil on viewing stage of stereo-microscope and using different
magnifications. take the microscopic observations of soil sample retained in each sieve
during the sample preparation separately in the following manner:
• Observe the colour of soil particles after drying at 105oC.
• Observe the nature of particles as- geometrical shape, black particles (coal dust, black
minerals), red particles (brick dust, red ash, iron oxide or metal oxide), colourless particles
(quarts grains, colourless mineral fragments), green minerals, particles of vegetation
(grass,
leaf fragments, seeds, moulds, fungi, micro-organism etc.
• Find out the traces of foreign materials as -dung cloth fibres, glass fragments, hair,
wooden
particles etc.
• Note every observation and compare with control soil sample.
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13. Microscopical Observation with Chemical Regents
•Place the soil sample on the stage of microscope in the same
manner as described above and
•examine. Moisten a small portion of soil with water and then
add a small drop of concentrated
•hydrochloric acid (HCl) on it. Observe the nature of reaction as-
bubbles and colour.
•Bubbles arising from solid particles indicate insoluble
carbonates such as chalk, dolomite or
•lime stone. Similarly yellowing colour indicates the presence of
soluble iron it can be
•confirmed by appearance of green colour on adding a few
drops of potassium ferrocynide solution to the sample
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14. Ignition Test
Apparatus: Analytical balance with an accuracy 0.0002 gm, Standard
Weights, Alumina crucible (porcelain dish may be used), Muffle
furnace of high temperature range (100014°C),
Method:
•Take an exactly weighed quantity (one gm) of soil sample from sieve
fractions dried at 105°C in a alumina crucible and keep it in a muffle
furnace. Heat it at temperature between 750-800°C for 1 hr.
•And then, cool it to room temperature. Reweigh accurately and record
the loss in weight and change in colour on ignition.
•Calculate the percentage of loss on ignition to the nearest 0.1 and
compare it with a control soil sample.
Calculation:
Initial weight of soil sample taken = Wo g
Weight of soil sample after ignition = W1 g
Weight loss on ignition = (Wo- W1) g
Percent weight loss =(Wo- W1)/ (W0) * 100
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15. pH Measurement of Soil Sample
In order to observe the acid-alkali behaviour of the soil, pH value of soiL
sample can be determined as follow:
Apparatus: a pH-meter with standard electrolytes (buffers) solution of pH 7
and 4.
Method:
 First, standardize the pH-meter with respect to buffers solution of pH 7
and 4
 by using the usual process as it is mentioned in its operating manual.
 Dissolve weighed quantity ( one gm of soil sample in 100 ml distilled
water and stir thoroughly.
 Filter it. Take the filtrate and measure the pH value. Adding 10 ml, 20ml,
30ml, 40ml, and so on successively in solution, measure the pH values
after each dilution and observe their variations.
 Similarly, measure the pH values for control soil sample in the same
conditions and
 compare with suspect soil sample.
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16. Particle size distribution
Requirements :
Set of sieves (ranging in size from ASTM No.5 to 200), Motor-driven
sieve shaker, standard weights.
Procedure:
Take an accurately weighed quantity (50)gm of soil sample.
Arrange all the set of sieve in numerical order and shake the soil.
Collect the soil retained in the each sieve separately and reweight
accurately
calculate its percentage as given below .
Percentage of soil retained on sieve No.=
(Weight of soil retained on sieve) x 100
(Total weight of soil taken)
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17. Density distribution of Soil particles
This analysis depends upon the principle that an object will be suspended in a liquid
of same density. it will sink in a liquid that is less dense and float in a liquid that is
more dense. When two different liquids of different density are mixed together,
they will diffuse into one another and its density will as:
D1 = [(V1d1) + (V2d2)]
(V1) + (V2)
Where:
d1 = density of liquid I (more dense; bromoform)
d2 = density of liquid II ( less dense; xylene)
V1 = volume of liquid I (bromoform) in ml
V2 = volume of liquid II (xylene) in0 ml
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Sivakrishnan.R | MSc. Sem 1

18. Particle size distribution
Requirements :
Set of sieves (ranging in size from ASTM No.5 to 200), Motor-driven
sieve shaker, standard weights.
Procedure:
•Take an accurately weighed quantity (50)gm of soil sample.
•Arrange all the set of sieve in numerical order and shake the soil.
•Collect the soil retained in the each sieve separately and reweight
accurately
•calculate its percentage .
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19. FORENSIC IMPORTANCE
•Soil is a common form of physical evidence found
at the scene of crime such as Hit and Run accidents,
Automobile collisions, Rape and Burglaries.
•A number of physical and chemical methods have
been used for identification of source as well as for
comparison of two soils.
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20. Reference
• Saferstein, Richard, 1978, Criminalistics- An
Introduction to Forensic Science,
• Prentice-Hall of India Pvt. Ltd. New Delhi (INDIA).
• Nicholls, L.C. 1956, The Scientific Investigation of
Crime, Butterworth & Co. (Publishers) Ltd. LONDON.
• Laboratory Procedure Manual- Forensic Physics
• Kirk, Paul, 1960. Crime Investigation, Inter science
Publishers Inc. New York (USA).
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