Sentence:  The desired amounts of inactive chlorine and radioactive <WSD>chlorine</WSD> were likewise condensed in these cells on the vacuum line following which they were frozen down and the manifold as a whole was sealed off . 
Meaning of the word marked with <WSD> tags:  a common nonmetallic element belonging to the halogens; best known as a heavy yellow irritating toxic gas; used to purify water and as a bleaching agent and disinfectant; occurs naturally only as a salt (as in sea water)