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Halide

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January 26, 2005, 19:13
<Asa Lovejoy>
Halide
Here's another rant from grumpy old Asa on a chemical theme: In today's paper there was an article on cracked "halide" light bulbs causing sunburn. OK, fine. But my issue is WHICH *(!@#)&%$ halide!?!? Back in the days when only Lucas in England and Marchal in France sold such lamps, they were called "quartz-iodine" lamps, since the halide in question was - you guessed it - iodine, contained in a pure quartz envelope. But there are other halides such as bromine, chlorine, flourine, et al. Are we to assume that the particular halogen is irrelevant? Somehow I don't think so. What am I missing - or what is the newspaper ignorant of?
January 27, 2005, 05:50
Graham Nice
No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No! No!

Iodine is a halogen, not a halide. There is an enormous difference.

Try putting chlorine on your chips, giving bromine to frustrated prisoners or putting fluorine in drinking water - then you will see the difference: halogens are not halides.
January 27, 2005, 06:08
<Asa Lovejoy>
So how about more explanation, Graham? I assume that "halogen" is a salt-forming element, and "halide" is an ion, but please clear up why in the old days they referred to those lights as "quartz-iodine" and now as "halide."
January 27, 2005, 13:49
neveu
quote:
Originally posted by Asa Lovejoy:
So how about more explanation, Graham? I assume that "halogen" is a salt-forming element, and "halide" is an ion, but please clear up why in the old days they referred to those lights as "quartz-iodine" and now as "halide."

Halogens are elements (Group VII or VIIa) and halides are binary compounds with one halogen atom.

Metal-halide lamps produce light by creating an arc in a tube of conductive gas formed by the vaporization of mercury-halide amalgam. Possibly the quartz-iodine lamps you speak of were the first of these (the quartz part is the tube; the arc would melt ordinary glass).

This message has been edited. Last edited by: neveu,
January 27, 2005, 14:21
tinman
Here's what Wikipedia has to say about halides. Any one want to contribute to the article?

Tinman
January 27, 2005, 15:21
neveu
quote:
Are we to assume that the particular halogen is irrelevant? Somehow I don't think so. What am I missing - or what is the newspaper ignorant of?

I think it is largely irrelevant. I think main issue is the mercury vapor the halogen is mixed with. They all produce a lot of ultraviolet that needs to be blocked or converted to visible light.