Re: Re: Why should the chemical Tris be spelled with a capital T?

Whenever you have any question on how to give name to a chemical compound,
the first place you must look at is the IUPAC [1]. This is the
international organization for chemists to agree on the rules to be
followed all over the world, so scientists from any country can make sure
they are talking about the same thing or not. 

The IUPAC organize the information in different "coloured" books:

Blue for organic chemistry [2]
Gold for combined glossary [3]
Green for physical chemistry [4]
Orange for analytical chemistry [5]
Purple for macromolecular chemistry [6]
Red for inorganic chemistry [7]
Silver for clinical chemistry [8]
and White for biochemical chemistry [9]

On regards to your question, the term "tris" corresponds to the numerical
indexing of complex features (e.g. substituted substituents), which are
named "-kis" after the corresponding numerical prefix, except for one
(obviously), two (bis) and three (tris) [10, 11].

I have found no further rules about the spelling of this particle so I
think low case should be used when not at the beginning of the sentence.

But you could be talking about the common, non systematic, name given to
the 2-amino-2-hydroxymethyl-propane-1,3-diol. 

Image of the compound: http://en.wikipedia.org/wiki/File:Tris.png

This is also known as Tris buffer, Tris base or just TRIS, and it can be
found in Sigma-Aldrich catalogue as Trizma(TM) [12]. As these are not the
systematic names of the compound and they may lead to confusion with the
numerical index it is important to show the difference. So for the sake of
clarity and ease of communication, the more common way of naming this
compound, and the first step to a final global agreement, is TRIS, written
in capital letters.

References
[1] http://www.iupac.org/ and http://www.chem.qmul.ac.uk/iupac/index.html
[2] Nomenclature of Organic Chemistry, Sections A, B, C, D, E, F, and H,
Pergamon Press, 1979. Edited by J Rigaudy and S P Klesney. [ISBN 0-08-022369-9]
[3] Compendium of Chemical Terminology, Blackwell Scientific Publications,
1987. Edited by V Gold, K L Loening, A D McNaught and P Sehmi. [ISBN
0-632-01765-1; 0-632-01767-8 (pbk)] Second edition, 1997. Edited by A D
McNaught and A Wilkinson [ISBN 0-8-654-26848].
[4] Quantities, Units and Symbols in Physical Chemistry, 3rd edition, RSC
Publishing, 2007. Edited by I Mills. [ISBN 9780-85404-433-7]
[5] Compendium of Analytical Nomenclature, 3rd edition, edited by J
Inczedy, Blackwell Scientific Publications, 1998. [ISBN 0-86542-615-5]
[6]  Compendium of Macromolecular Nomenclature, Blackwell Scientific
Publications, 1991. Edited by W V Metanomski. [ISBN 0-632-02846-7;
0-632-02847-5 (pbk)]
[7] Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005, Royal
Society of Chemistry, 2005. Edited by N G Connelly and T Damhus (with R M
Hartshorn and A T Hutton) [ISBN 0-85404-438-8].
[8] Compendium of Terminology and Nomenclature of Properties in Clinical
Laboratory Sciences, Blackwell Science, 1995. Edited by J C Rigg, S S
Brown, R Dybkaer and H Olesen. [ISBN 0-865-426120]
[9] Biochemical Nomenclature and Related Documents, 2nd edition, Portland
Press, 1992. Edited C Liébecq. [ISBN 1-85578-005-4]
[10] N. Lozac'h Pure Appl. Chem., 1986, 58, 1693-1696.
[11] http://www.chem.qmul.ac.uk/iupac/misc/numb.html
[12] http://www.chemindustry.com/chemicals/657845.html