Abstract: A drilling jig has a pyramidal tip, a cylindrical portion, and a proximal end. The pyramidal tip is formed like a polygonal pyramid and each pyramidal face is provided with a concave. The cylindrical portion connecting with the pyramidal tip is formed like a prism and the proximal end is made of a flat plate functioning as a stopper. The drilling jig makes it possible to efficiently recover sodium from a spent NaS cell without greatly damaging the structure of the cell.

Abstract: A filter apparatus comprises a plurality of ceramic porous filter elements each having a number of through-apertures in parallel with each other whose front and rear ends are alternately closed, filter element casings arranging therein one of the filter elements, respectively, and piled one above the other with the filter elements received therein being spaced apart from each other and the front ends of the filter elements upward directing, raw liquid supply means for supplying a raw liquid to be filtered to the front ends of the filter elements, raw liquid supply chambers located between the filter elements for receiving the raw liquid from the raw liquid supply means, filtrate exhaust chambers located between the filter elements for receiving filtrate which has passed through the filter elements, and filtrate exhaust means for exhausting the filtrate from the filtrate exhaust chambers out of the apparatus.