Abstract: A process for purification of crude glyceride oil compositions which comprises diluting a crude glyceride oil composition containing gum material and wax as main components of impurities with an organic solvent, bringing the diluted crude glyceride oil composition into contact with a semipermeable membrane composed of polyimide consisting essentially of a repeating unit represented by the general formula: ##STR1## wherein R.sup.1 represents a divalent organic group, under pressure to obtain a semipermeable membrane permeable liquid in which the gum material in the glyceride oil after removal of said organic solvent is 100 ppm or less, carrying out bleaching of the glyceride oil obtained from said semipermeable membrane permeable liquid with at least one kind of an adsorbent selected from the group consisting of clay, activated clay, activated carbon and bone black, and then carrying out deodorizing to obtain a purified glyceride oil.

Abstract: A wire electrical discharge machining apparatus which cuts to a desired shape a workpiece placed on a workpiece table, using a discharge phenomenon occurring between the workpiece and a wire electrode opposite to the workpiece with a machining fluid in a space therebetween, characterized in that the workpiece table is made of cast iron having a coefficient of thermal expansion of less than 6.times.10.sup.-6 /.degree.C. and that a surface layer is provided on the workpiece table on which a workpiece is placed, the surface layer having corrosion resistance to the machining fluid and having a hardness higher than that of the material constituting the workpiece table.