anyway to identify which gas is in this cylinder?

[sandman2234]

There are gases that are put in bottles that will kill you upon inhalation of them! I happened upon 5 bottles that I could have just for hauling off, and had (just barely) enough sense to figure out what the gas was. It was something that would kill you with 3 parts per million if inhaled. I left them, and stayed clear of that place.

The outside condition of the bottle has very little to do with the condition of the bottle itself as far as passing a test. They should remove the valve, inspect the interior of the bottle, and pressure test the bottle, noting how much it fails to return to its original size before pressurizing. The amount it displaces in water volume and how much it fails to return to original shape are the criteria.
As far as the valve threads condition, you should probably make sure that the threads are clean and not damaged. If you find that there was an issue, it probably doesn't mean you ruined a regulator, because those stems on the regulator are replaceable. I have quite a supply of them stashed. I was recently working with a acetylene/oxygen torch, when the diaphragm in oxygen regulator went out. Changed to a brand new (but 20 years old) regulator and it went out immediately. I grabbed a Hydrogen regulator, swapped out the stem and put it into service as an oxygen regulator. (regulator was new, never used).
Got to love having a bunch of spares when you have limited time to do most of your work, and always on the weekends when nobody is open to get repair parts!
Just for the record, never use a regulator for oxygen that has been used for other gases unless you know that there are no residuals, especially oil or grease in any amount!

David from jax

 

[ning]

Since you're playing with balloons:

1. weigh empty balloon (gram scale)
2. fill it
3. weigh full balloon
4. submerge it & note the volume difference

(#3 - #1) ÷ #4 = density

In order to do #4, you may first want to assume that you're going to be getting your hands in the water while submerging the balloon (because you'll have to hold it under the water), so "tare" the water level with your hands in the water to some specific level (maybe put a rubber band around your wrists) -- have a helper fill the container with water to a particular level with your wrists at that same level, so that when the water is at that known level it includes the volume of your wrists. Then, when you submerge the balloon, measure the new water level with your hands submerged to the same line as before; mark the container at the "tare" line and at the includes-submerged-balloon line, and then measure how much water you have to add to get between one and the other.

Using the density, you can figure out what the gas is; CO2 has a density of 1.96 g/L; Ar 1.78 g/L; Acetylene 1.1772 g/L. The density of air is about 1.29 g/L, so you need to take the measured density and add the air density (because the measured weight of a balloon full of air is the same as the weight of an empty balloon, because the air inside essentially doesn't count - imagine a water balloon with a gallon (8.34#) in a swimming pool - it feels weightless). If you calculated 0.67g/L from the scale weight divided by the volume, that's CO2 (0.67 + 1.29 = 1.96).

In order to be able to actually get a weight for the full balloon that's measurably different than the weight of the empty balloon, you either need a really accurate (milligram) scale, or a gram scale and a balloon filled as big as you can manage - a balloon about 8" across would be about 4L, which would give less than 1g difference between CO2 and Argon; 12" across would be ~14L (4/3*πr³)