Sentence:  The cathode consisted of a 1/4 '' diameter thoriated tungsten rod attached to a water cooled <WSD>copper</WSD> tube . 
Meaning of the word marked with <WSD> tags:  a ductile malleable reddish-brown corrosion-resistant diamagnetic metallic element; occurs in various minerals but is the only metal that occurs abundantly in large masses; used as an electrical and thermal conductor