I just dropped my expensive color thermometer and now have separations in the "mercury" column. Any way of fixing this ...or did I just blow $70.00?
Thanks,
-Michael
I just dropped my expensive color thermometer and now have separations in the "mercury" column. Any way of fixing this ...or did I just blow $70.00?
Thanks,
-Michael
Sometimes you can shake the mercury down, with repeated vigorous motion. If That doesn't work heat the thermometer in boiling water until the mercury merges. When it cools it will stay together.
Last edited by Ron Marshall; 15-Aug-2006 at 08:31.
Thanks, Ron. The hot water did it. Whew!
Do watch closely when doing that, though; I used to have a Delta floating thermometer (alcohol type) that accidentally got exposed to water about 20-30 degrees F hotter than its scale covered, and it popped the top off the capillary. Needless to say, I couldn't fix that one...Originally Posted by poco
If a contact print at arm's length is too small to see, you need a bigger camera. :D
Yeah, I know the dangers of overheating a thermometer. When I was a kid the rule was "no staying home from school without a high temperature." That's how I learned that thermometers and hot light bulbs don't mix ...was finding mercury pellets in my bed for a week.
Never use a light bulb on a thrememeter to stay home from school. Your mother will not believe you have a 125f fever! Just rub the bulb quickley on the sheets, you can raise it a couple degrees at a time. My kids realy hate it when I know the tricks.
My brother used to hold it in front of the heat register. Which did absolutely nothing, after we got the wood stove and the furnace wouldn't run at all overnight...
If a contact print at arm's length is too small to see, you need a bigger camera. :D
A Kodak process control thermometer has a fairly limited range, and it may be possible to easily and safely fix a column separation by placing it in a deep freeze for a few hours. The temperature corresponding to the transition from bulb to stem is well above freezer temperature, so all of the mercury gets sucked down into the bulb, to re-emerge as a solid column on warming. Worked for me, anyway.
There's nothing quite like an etched-stem thermometer as a reliable basic reference, arguments for mercury-free electronic devices notwithstanding. Dial-type thermometers can suddenly develop errors of a few degrees, and I once bought a new one that was off by some eleven or twelve degrees. An electronic thermometer may or may not be better, but without a known-good reference, how would you know?
It's at least fairly simple to verify the electronic thermometer within a couple degrees F if you know you local elevation; all you need to do is boil some distilled water in your microwave (preferably in a clean glass graduate or beaker, to ensure a minimum of dissolved impurities that can change the boiling point, though Visions, Pyrex or Corningware cookware is a good substitute), then keep it barely boiling on a lab type hot plate or similar and measure the temperature of the water. Knowing the local elevation and, if you're *really* after precision, the barometer reading will let you calculate what the boiling temperature should be within a fraction of a degree F.
You can calibrate the other end of the scale with ice water -- again, if you start with distilled water for both the liquid and the ice and use a clean, non-metallic container, you can pretty confidently know the correct temperature to a fraction of a degree F.
No exotic equipment needed, and the tests can be repeated in half an hour, any time you feel like it.
OTOH, I'm not a big fan of equipment that needs a battery, if non-electronic stuff will do the same job. When I was in high school, we made simple air/gravity thermometers with capillary tubing fire polished shut on one end, tiny droplets of mercury drawn in by heating the tube and letting the cooling air draw in a short column, and the air trapped in the tube. Measuring the height of the air column at a known angle (where the weight of the mercury supplied a fixed gauge pressure) and correcting for barometer reading allowed simple calculation of ambient temperature using Boyle's law. Don't know where I'd find mercury to make one of those now, but the first place I'd look would be in the house thermostats, if I needed one...
If a contact print at arm's length is too small to see, you need a bigger camera. :D
Donald--
While this is hardly the place to debate the niceties of experimental technique, I would like to point out that I once thought that ice and boiling points would be good, easily reproducible calibrations also. When my NBS-traceable platinum resistance thermometer disagreed, my colleagues at the time (at Hewlett-Packard Laboratories, back when the company was still very much an instrumentation outfit) gently pointed out that issues of superheating and stirring conspire to make fixed point measurements a lot harder than they look. Getting to within a degree or two is not so hard; getting down to fractional degrees (even if you have an instrument with that much resolution, rare for consumer electronics) is a lot tougher.
Certainly, the boiling/freezing points will tell you if your thermometer has gone seriously out of whack, which is all one needs for most photographic work. Thanks for pointing out the "kitchen physics" solution.
Regards,
Harold
Posting Permissions
Reply With Quote
Bookmarks