May 05, 2016 at 02:06AM

Today I Learned: 1) ...what's up with halogen bulbs. Halogen bulbs are distinct from normal incandescent bulbs by having halogen gasses (usually iodine, bromine, or some mix of the two) mixed in the otherwise inert air in the bulb. Halogens are pretty darned reactive gasses -- why have them in a bulb? The answer has to do with bulb failure. Normally what happens in an incandescent bulb is that the heat of the bulb slowly causes the tungsten filament to vaporize. This causes two problems: 1) tungsten gas will adhere to the side of the bulb, eventually building up a a dark film that makes the bulb less bright; 2) as the filament loses mass and gets thinner, it becomes more succeptible to snapping when the bulb is rapidly heated, as happens whenever the light is turned on. Halogens in the bulb combat tungsten evaporation by quickly reacting with tungsten gas to form a tungsten halide that apparently either doesn't deposit on glass or does so reversibly (so that the halogens strip tungsten off the glass). At high temperatures, the tungsten halide will actually deposit *back on the filament*, preventing pretty much any filament loss over time. This makes halogen bulbs last longer than their incandescent counterparts. Perhaps more importantly, halogen bulbs don't dim over time, which is why they're used in laboratory equipment where even and predictable lighting is important (also stage lighting, though I'm not sure why it's important there....). Best of all, nothing in the bulb is particularly hazardous. Iodine and bromine aren't particularly *nice*, but they're not terribly toxic and they're relatively easy to dispose of. The major downside to halogen bulbs is that bit about re-depositing of tungsten only happening *at high temperatures*. Halogen bulbs run much, much hotter than their incandescent counterparts, which makes them a moderate-to-major fire hazard. 2) Vegemite is basically flavored, low-salt LB broth (yeast extract). 3) ...why my RNA cleanups have been failing (specifically, not yielding much in the way of RNA) -- I was accidentally skipping a step in the extraction, so my RNA was just falling right through the column. Also, ethanol contamination is a big problem with the kit I'm using. I'll have to take steps to keep ethanol out in future attempts.