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<p>[QUOTE=&quot;Richard M. Renneboog, post: 2851801, member: 89693&quot;]Kentucky, you are almost right. The chlorine atoms are bound by sigma bonds to carbon atoms in the molecular skeleton. BUT the carbon-chlorine bonds are &quot;photochemically labile&quot;, which means that they can be dissociated by ultraviolet light to liberate free chlorine atoms to a measurable degree. In fluorescent lights and otherwise normal white light there is enough of an ultraviolet component to initiate that process. The carbon-chlorine bond can immediately reform, of course, but for a finite amount of time there will be a free chlorine atom or three in the material. These can do things other than reform a C-Cl bond. They can pull off a hydrogen atom from the carbon atom next door to produce HCl (aka hydrochloric acid) or another chlorine atom to produce molecular chlorine (Cl2), both of which are anathema to metals. That, btw, is one of the actual processes by which PVC degrades. If you study material structure at the molecular level, you will find that there is a lot of empty space between the atoms and molecules in what we tend to think of as solid materials, so there is ample room for atoms to move about and do things like tarnish coins, discolour the casing material, and so on. Maybe I should write up an ebook for coin aficionados explaining the whole chemistry thing...[/QUOTE]</p><p><br /></p>

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