Reference page

Bentor, Yinon. "Chemical Element.com - Thallium." On-line. 1 Feb. 2000.
        <http://www.chemicalelements.com/elements/tl.html>.

British Columbia Institute of Technology. "Thallium." On-line. 1 Feb. 2000. 
        <http://nobel.scas.bcit.bc.ca/resource/ptable/tl.htm.>

Heiserman, David. Exploring Chemical Elements and their Compounds. New York: Tab
        Books, 1992

Hsu, David. "Chemicool Periodic Table- Thallium." 1996-97. On-line. 1 Feb. 2000.
        <http://www.chemicool.com/elements/thallium.html>.

Winter, Mark. "Periodic Table- Web Elements: Thallium." 16. Dec.1999. On-line. 1 Feb. 2000.
        <http://www.webelements.com/webelements/elements/text/index/Tl.html.>