Quinke’s method

EXPERIMENT-1

To find out the susceptibility of FeCl3 by Quinke’s method.

APPARATUS

An electromagnet capable of producing field of the order of 104 oersted, power supply unit,

travelling microscope or cathodometer, FeCl3, U-tube, water, funnel 100 cc cylinder,

weighting bottle, weight box, flux meter connected with search oil.

DEFINITION

The magnetic susceptibility K of a material corresponds to the ease with which a material can

be magnetized using a given magnetic field intensity. So it may be defined as the ratio of

intensity of magnetization I produced to the magnetic field intensity H. So we may have K =

I/H and since I corresponds to magnetic moment/unit volume, the susceptibility thus defined

is also called volume susceptibility.

PRINCIPLE

If a paramagnetic salt solution (like manganese chloride) or ferromagnetic salt (like ferric

chloride) is put in a tube and placed between the poles a magnet then there is a liquid level. If

the rise in liquid level is measured accurately, then the susceptibility of the solution can be

found.

THEORY

As the magnetic field between the wedge shaped poles pieces varies along the vertical

direction, so the force on the solution will be vertical.

Now the force on a substance of volume V which is situated in a nonuniform magnetic field

at a place where H is the magnetic field strength is given by

Quinke’s method

Where K is magnetic susceptibility of substance and Ko is the magnetic susceptibility of the

surrounding medium.If the surrounding medium is air, the Ko

(1)

Quinke’s method

From figure let D be the level of solution in funnel and A that in the narrow tube before the

application of the field. Let C and B be new levels respectively with the application of the

field. Let the rise in narrow tube corresponding to AB be denoted by h.

Let a and a’ be the cross-sectional areas of the funnel and the tube respectively.

As is clear from Figure, the level in funnel has to sink from D to C, so B will be at a higher

than the level of the liquid in the funnel.

Let d be the level to which liquid has sink in funnel, then a’.d = a.h or d = ah/a’.

Now as h is the rise in level of the solution in a narrow tube and d the fall in level in the

funnel the corrected height may be written as (1 + a/a’)h. This will correspond to the height

of the liquid column supported by the forces due to magnetic field.

Let h be the density of the solution and g the acceleration due to gravity then the wt. of the

column above the point P is given by

(1 + a/a’) = h ρ g a (2)

Let us consider that at the section P the magnetic field is negligible. Let x be the vertical co-

ordinate above P, then the force on a liquid element of volume a.dx above the point P is

given by

(3) [From eq. (1)]

The force on the entire liquid above the point P is thereby given as

(4)

Where H1 is field intensity at upper level and this force balances the weight (1+ a/a’) h ρ g a

of the liquid column. So from eqns. (2) and (4) we have

Quinke’s method

If a <<a’ the a/a’ may be neglected as compared to 1.

Or (5)

This corresponds to the s of the solution is given by

s = K/ρ = 2g (h/ ) e.m.u./gm (6)

Now since susceptibility depends on the concentration of salt, we can study the variation of

with concentration.

Let m be the mass of anhydrous FeCl3 in solution per c.c then a straight line will be obtained

in the graph between and m. The straight line does not pass through origin but cuts the

axis m = 0 at a finite (through negative) value of . It is because of the contribution of

susceptibility of the solution due to water, which in other words, means that the numerical

value of the intercept gives the mass susceptibility of water ( .

Let be the mass susceptibility of the anhydrous crystals of FeCl3 then we have,

(7)

Let M be the molecular wt. of anhydrous FeCl3, then molecular susceptibility is given by,

(8)

The molecule’s susceptibility is the sum of ionic molecule’s susceptibilities of Fe +++ and Cl-

ions, i.e.,

(9)

Where = 25.1 x 10-6e.m.u. This expression can be used to find the molecular

susceptibility of Fe+++ ion.

Quinke’s method

The magnetic moment of Fe+++ ions in terms of the Bohr magneton is given by

Where k = Boltzman constant = 1.3805 x 10-23 J/K

No =Avogadro Number = 6.0234 x 1023

β = Bohr magneton = 9.27 x 10-21 e.m.u.

T = Temperature in absolute degrees = ……oK

PROCEDURE

1. Calibration of flux meter: make the connections as shown and level the flux meter

with the help of screws provided at the base and place the search coil at the centre of

the space fluxmeter. The flux meter is calibrated to measure deflection in terms of

Maxwell turns. The variations of current can be done by rheostat Rh and the

corresponding value noted by ammeter A. Let be the deflection of the flux meter

pointer for a current I and let b correspond to one division deflection in flux meter.

Let N be the no. of tubes of search coil and A be its mean area. Then the magnetic

field strength of the field in search coil is given by

Since different values of current I will give different values of, , so the

corresponding values of H, can be found from above equation.

2. Fill a U-tube which is thoroughly cleaned with a solution of FeCl3 in water containing

25 gm of a hydrated salt (FeCl3.6H2O) per cc for the solution.

3. Now insert the narrow limb of U-tube vertically between the pole pieces of the

electromagnet and adjust the funnel limb so that when the magnet is energized the

meniscus is in the central region of the uniform magnetic field. Illuminate the

meniscus with an electric lamp and view it through a travelling microscope or a

Quinke’s method

cathetometer. Bring the horizontal crosswire of microscope on the meniscus and note

the reading. Also note the corresponding current in the ammeter.

4. Switch off the current and again bring the cross-wire on the meniscus and take a

reading. Note the fall in height h of the meniscus for a particular current. Repeat the

experiment values of magnetizing current.

5. Repeat the experiment by changing the concentration of the solution.

OBSERVATIONS

(a) For calibration of fluxmeter.

No. of turns of search coil, N = ………….

Mean area of search coil A = …………….

No. of Maxwell turns/division b = ……….

Sr. No. Current i Deflection of

flux meter

Magnetic field,

Plot a curve between current and magnetic field H1, it will be a straight line, it will be

a calibrated curve of fluxmeter because it gives the value of magnetic field H1

corresponding to any value of given current.

(b) For Mass Susceptibility of Solution s

Molecular wt. of FeCl3, M = (56 + 3x35.5) = 162.5 gm

Molecular wt. of hydrous salt = 162.5 + 6(2+16) = 270.5 gm

Quinke’s method

Room temp. T = ……….oK

Mass of weighting bottle = m1g

Mass of bottle + FeCl3 = m1 gm

Mass of FeCl3 = (m2- m1) gm = 20 gm (say)

Volume of solution = 100 cc

Mass of hydrated salt/c.c = 0.20 gm/cc

Calculation for Concentration m

270.5 gm of FeCl3.6H2O contains 162.5 gm of FeCl3

Therefore, 0.20 gm/c.c of FeCl3.6H2O will contain = (162.5 x 0.20)/270.5 gm/cc

Therefore, Concentration m = 162.5 x 0.20)/270.5 = ………..gm/cc

Sr. No. Current

(i)

Corresponding

field H from

graph H1

H12

Initial

position

of the

meniscus

(cm)

Final

position

of the

meniscus

(cm)

Fall in

height

(cm)

Quinke’s method

Plot a curve between H12 and h, which will give a straight line from the graph.

Mass susceptibility of the solution is given by

s = 2.g h/H12 = 2g PQ/OQ

Take similar observations for different amounts of hydrated salt in the same volume

of solution.

Calculate the concentration m and susceptibility s for each set.

(c ) Mass susceptibility of water w

Tabulate the above observations

Sr. No.

Concentration m in gm/cc Susceptibility s e.m.u. /gm

Quinke’s method

From the graph

w = Po = ………e.m.u. /gm = 0.72 x 10-4 at 20oC

(d) Mass susceptibility of anhydrous FeCl 3

Where and m are substituted for a particular set.

(e) Molecular susceptibility of Fe+++ ion

We have

Also we have

Magnetic moment of Fe+++ ion using the relation

Quinke’s method

Where k = 1.3805 x 10-23 J/K

No = 6.0234 x 1023

β = 9.27 x 10-21 e.m.u.

T = ……oK

PRECAUTIONS

1. Check the joints between rubbers and glass tube so that there is no leakage of solution

2. Choose only the prescribed values of magnetizing currents

3. Solution should be prepared carefully so that salt is dissolved uniformly.

SOURCES OF ERROR

1. Due to evaporation of water the results obtained are slightly less than the actual

values.

2. Due to non-uniformity of the narrow limb bore, error due to surface tension may

occur.

3. Since the bore is very narrow, so there may be deformation of the liquid in the

tube due to application of magnetic field and so the rise or fall of the liquid

meniscus may be read wrongly.

ADVANTAGE

In this case no correction for susceptibility of dust particles present in the solution is

required.

Quinke’s method

Oral Questions:

Q.1What are magnetic materials?

Q.2 What are paramagnetic and ferromagnetic materials?

Q.3 Why is Ferromagnetism found in soilds only and not in fluids?

Q.4 What is magnetic moment?

Q.5 What is magnetic susceptibility?

Q.6 What is Quinke’s method?