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Old 10-27-2019, 09:25 AM
Unclenick Unclenick is offline
Join Date: Nov 2010
Posts: 1,078


1., Yes. I was thinking only of compound molecules. The other fun aspect of helium that affects tire testing is its mean velocity in Brownian motion is about three times faster than air, so it tries to get out of leaks three times more frequently than the average air molecule does. We used to use it to speed evacuation of vacuum insulation core materials by back-filling with it and re-evacuating. Not only did that cut the time in half, despite the extra step, it swept some larger "slug" solvent molecules out of the way, so the final vacuum held up better. I understand there is a shortage of it currently.

2. The Arrhenius function is not uniform across all reactions. Most chemical reactions and atomic interractions double approximately every 10C, particularly for reactants that are gasses, as Boltzman's constant is involved in determining the molecular collision rate, but you will notice that number doesn't have a lot of decimal places after it as it will for actual individual reactions. There is a distribution around it that makes it close, for the most part, but it isn't too unusual to run into experimental reactions where it doesn't do a very exact job. In the case of powder, I calculated the doubling rate based on the Navy experimental deterioration time and safe storage time at bunker temperature, and also in a declassified army study of stabilizer deterioration done at elevated temperatures that I found on the web. It won't be exact, though, and I should have left the last decimal place off.

For an extreme example of the Arrhenius calculation giving an odd result, I was recently looking in some detail at annealing brass and found recrystallization rates for brass stressed to nearly the point of splitting will double about every 24C once it initiates. Brass that is only about 50% work-hardened actually has a bend in that curve at higher temperatures, where the rate changes. I suspect the rate differs from the 10C number because of the time needed for atomic dislocations to move back into place in the crystal lattice. The world is a funny place sometimes.

3. It's actually nitric acid smell. If you ever have occasion to work with nitric acid, it is acrid, like vinegar, so its scent has that similarity, but it doesn't smell exactly the same. Unfortunately, with odors, as is often the case with testing the nose of wines, description fails me. But if you ever get a chance to waft some HNO3 toward your nose, you will remember it as distinct. Same for the more commonly encountered HCl (muriatic acid). Acrid, like vinegar, but with unique qualities that will let you identify it as separate from vinegar.

In addition to smell, a good test for some powders is to shake a little out on a sheet of white paper, then slide it off and look for reddish rust-colored particles to be left behind. It's an early indicator where it happens, but it doesn't happen with all powders. Oilyness or clumping are the other indications.

You are sure correct about there being no such thing as partly bad powder. Depending on the degree of deterioration, it can either produce a wimp load or overpressure due to burning too fast, as the Navy tests found. A moderator at another board lost his left hand when an old shotgun shell burst his gun. Made the local papers near him. Good guy with a lot of experience, but a momentary lapse in consideration of what he was doing. I know there are guys who've fired 30-06 made in the 1920's and got away with it, but there have also been photos of a Garand destroyed, including blowing off the receiver ring, by some 1947 surplus. I pulled down my 1953 AP after reading about that one. It's not worth the risk in my opinion.

Here's an example of the corrosion it can cause. I had a small sample I was given of this powder sitting on a shelf, obscured by other things for 20 years when I discovered it. The 'powder' itself had fused to a solid lump. Rinsing the bottle with water, the water came out yellow-colored (another deterioration test you can make with a powder sample).


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Last edited by Unclenick; 10-27-2019 at 09:28 AM.
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Old 11-04-2019, 06:46 AM
mac1911 mac1911 is offline
Join Date: Oct 2009
Posts: 2,915

No idea how they will hold long term but I picked up a few of these. Inexpensive enough and the stack pretty well. When stacking with the tray its a tad weak on the notches but for the price I can over look that.
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