Evans balance

[5] The original design was later modified, with assistance from Johnson Matthey, to place two pairs of magnets within an H-frame.

When a sample tube would be introduced between the magnets, the torsional force would be counterbalanced by the current passing through the coil, providing a reading on the display instead of using a potentiometer.

[5] The Evans balance is capable of measuring within a range of 0.001 x 10−7 to 1.99 x 10−7 CGS volume susceptibility units.

[7] The original model demonstrated an accuracy within 1% of literature values for diamagnetic solutions and within 2% for paramagnetic solids.

A commonly used calibration compound is mercury cobalt thiocyanate, HgCo(NCS)4, which has a susceptibility of 16.44×10−6 (±0.5%) CGS at 20°C.

[9] To calculate the volume magnetic susceptibility (χ) for a liquid sample, the equation would include the V term in the numerator and divide by the density (d) of the solution instead of the mass (m).