The quantity of dry soil and dispersing agent is taken as double of pipette which is 500 ml.

Toughness index (It) is determined by ratio of plasticity index to flow index: It=IP/If.

The size D10 is sometimes called as effective size or effective diameter.

The constant value of unit weight of water/liquid is taken as ?w=9.81 kn/m².

The largest aperture sieve being kept at top and smallest aperture sieve is at bottom of assembly filled on a sieve shaking machine.

According to Goldschmidt ory, clay does not become plastic when mixed with liquids of non-polarizing agents like kerosene.

Mixing soil with sufficient distilled water and making it pasty enough prevents forming air bubbles in shrinking dish.

Concept:

Toughness Index: 

• Toughness index is defined as ratio of plasticity index (I_P) of soil to flow index (I_F) of soil.

$\begin{array}{l}Toughessindex=\frac{Plasticityindex}{Flowindex}\end{array}$

• This gives us an idea of shear strength of soil at its plastic limit. 
• The toughness index varies between 0 to 3. If If is more, rate of loss of shear strength is more. Hence, toughness index is less.
• When toughness index is less than 1, soil is said to be friable, which means it can be easily crushed at plastic limit.

According to derived equation of hydrometer equation is
R = Rh? + Cm ± CL ? Cd.

For calibration of cylinder, weight of sand required to fill pouring cone of cylinder is needed. Uniformly graded, dry, clean sand passing a 600micron sieve and retained on 300micron IS sieve is used.