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?
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.
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."
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,
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.
