Magnetic Susceptibility

length of the fishing line. (NOTE: When measuring solutions, the solution only fills the top halfof the Gouy tube. In order to get good measurements, the bottom of the solution should be wherethe field is the strongest (center of the poles) and the top where it is weakest (at or above thepoles). Make these adjustments now and then use the same Gouy tube for all measurements.)b) Stop the tube from swinging then press the “Tare” button (right side of the long bar). Thebalance should read 0.0000 g fairly steadily. You may need to press it again.c) Turn on the magnet and wait for the weight to stop changing. This may take about a minute.Record this value and turn the magnet off.d) Wait a minute or two and repeat these steps. Do this for a total of three times. If you do not get areasonably consistent reading, repeat again.e) IMPORTANT: Anytime that you move the balance, you need to re-determine the response of theempty tube.3) The TA will provide you with solutions of all of the complex ions to be studied except for ferrousammonium sulfate. You will also be given the density of these solutions.4) Measuring the sample:a) Using a pasteur pipette rinse the Gouy tube with distilled water. Then rinse the tube with severalportions of the solution to be analyzed, putting the wash solution into the waste containerprovided. Finally, carefully fill the tube to the mark with the solution. Secure the top with therubberbands and hang the tube from the line.b) Check the position and remember that if you have to shift the balance you need to re-determinethe response of the empty tube to the field.c) Make sure that the tube is not swinging. Tare the balance. Turn on the magnetic field. Wait forthe weight to stabilize and record the value.d) Turn off the magnet.e) Do the above in triplicate, checking for reproducibility.f) Empty the tube using a pasteur pipette and put the solution into the waste container provided.II. Evans MethodUsing the Gouy method, the electromagnet is stationary and the sample is pulled into or pushed out of themagnet when the magnetic field is turned on. The force that the magnet exerts on the sample is measuredby the analytical balance. The portable magnetic susceptibility balance uses the same configuration as theGouy method but the sample is stationary and the magnet is suspended. The equal and opposite forcewhich the sample exerts on a suspended permanent magnet is measured.Pairs of magnets are fixed at opposite ends of a beam which is balanced on a fulcrum. Without a sample,the system is in balance. Introduction of a sample between the poles of one pair of magnets produces adeflection of the beam. The extent that it tips depends upon the magnetic susceptibility of the sample.The deflection is registered by means of photodiodes. A current passes through a coil mounted betweenthe poles of the second pair of magnets in such a way as to return the system to equilibrium. Atequilibrium, the current through the coil is proportional to the force exerted by the sample and can bemeasured as a voltage drop.2