Determination of Magnetic Susceptibility by Faraday's Method
In this method, a very small volume of the magnetic sample is packed in a quartz ampoule and suspended from a sensitive balance is placed in a region of fairly strong magnetic field. In this situation, the product H(dH/dx), where dH/dx is the field gradient, is constant over the volume of the sample. The whole set-up is housed in an enclosure which can be flushed with nitrogen or helium. The ampoule has an internal diameter of ~1 mm and the balance used is a quartz fibre torsion balance. The region of uniform H(dH/dx) is determined by placing a small volume of a calibrant of mass m and of known magnetic susceptibility at different point along the field. The value of H(dH/dx) is obtained from the relation:
dF = mχgH(dH/dx) -----Equation:1
or, H(dH/dx) = dF/mχg -----Equation:2
Where dF is the force experienced by the sample due to the magnetic field and is measured using a cathetometer. With the help of the measurements first with calibrant and then with the sample, we can write the relation-
χs = χcds/dc mc/ms -----Equation:3
Here χs and χc are the gram susceptibilities of the sample and calibrant, ms mc are the respective masses and ds and dc are the respective deflections at constant H(dH/dx).
In the above equation:3, all the parameters on the right hand side are known, and hence gram susceptibility χs of sample can be calculated easily.
Advantages of Faraday's Method
✍︎ It requires small amount of sample compared to Goy method.
✍︎ Good sensitivity is additional advantage of this technique.
Disadvantages of Faraday's Method
✍︎ Delicate equipment, fragile suspension devices, constructional difficulty, inconvenient solution measurements and small weight changes are some of the disadvantages of this technique.
Source: R.C.Maurya Inorganic Chemistry
Determination of Magnetic Susceptibility by Gouy Method
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