Abstract: An appartus for use in the magnetic treatment of liquids in order to reduce precipitation of dissolved materials. In one embodiment the apparatus subjects liquids to magnetic flux by providing an inlet (2) for the liquid, an outlet (3) for the liquid after it has been subjected to magnetic flux, a fluid flow path connecting the inlet and the outlet, a magnetic body, (4), and material (24) for protecting a sensitive part of the magnetic body from the liquid. In this embodiment the magnetic body includes a first magnetic pole (17) made of material which is sensitive to contact with the liquid and a second magnetic pole (25) of opposite polarity to and spaced from the first magnetic pole to define a gap between the poles. The magnetic poles are so disposed that lines of magnetic flux pass between them and, in so doing, traverse at least part of the fluid flow path.