| http://www.w3.org/ns/prov#value | - Referring to the drawings, a vacuum chamber 5, the walls of which may be made of aluminum or other suitable material is preferably rectangular in form and may be supported on a framework 6. -This framework includes ribs or bars 7 extending upward along the sides and across the top of the chamber and which may be cast integral with the chamber walls, to give sufficient strength and rigidity to the
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