The investigation covers two possible areas of application of magnetic fluids, one involving the production of torque by means of rotating magnetic fields and the other the use Of magnetic fluids in the separation of non-magnetic ores on a density basis. The' emphasis-was upon the use of cheap, primitive ferrofluids Le'. non-collOidal suspension of relatively large particles. a Moskowitz and Rosensweig were the first to report electromechanical energy conversion with a rotating magnetic field. Their theory is not confirmed by their experimental results, howevert nor the fact that the fluid can rotate in the opposite direction to the field. This phenomenon has been investigated experimentally for a range of field intensities, wave velocities, particle sizes, volume loading and fluid viscosities. The torque per unit volume has been found to be related linearly to the volume loading but-nonlinearly to the frequency of the supply, field intensity and viscosity. For the primitive ferrofluids the results clearly indicate a combination of saliency and hysteresis torques. No satisfactory explanation for the reverse motion of the fluid has been produced and attempts to quantify the energy transfer have not been successful. Due to the inherently low permeability of the fluid, the torque per unit volume is much smaller than for conventional a. c. machines. Primitive magnetic fluids have also been shown to have potential in the separation of ores according to their densities. The novelty of this work is that the particles, which flocculate in the presence of stationary fields, are kept in suspension by agitation caused by a rotating wave. This agitation also serves to reduce the effective viscosity which at high volume loading can be high at zero field conditions. An effective specific gravity of about 12 has been obtained. The experimental results confirm the theory that the magnetic force in the linear condition is proportional to the magnetic energy - density gradient (in space) but with saturation the force is proportional to the field gradient and independent of body shape. A practical system seems to be feasible.