..... helium?
I drove past a gas plant today and saw they have a weighbridge.
So if they ship helium, do they see how much less the truck weighs on the way out than on the way in?
I'm more worried about how much extra lead I have to carry when I dive trimix, just to stop me floating off the dock.
Helium is compressed in a cylinder. It is only lighter than air when being released (uncompressed). I think that when the pressure is known and the weight of the cylinder, the amount of Helium can be determined.
In theory, "lighter than air" doesn't mean it has no mass. It has mass and it has weight. It is only hard to measure because of weight by the kilometers of the air above us.
To AWOL, lol ! (but I wonder how many people understand how funny it is).
Helium is not endless by the way. There might be a shortage of Helium in a few decades. However, investing in Helium companies is useless, you have to buy a large amount of the Helium yourself and store it and sell it in 50 years. So when you see a truck with Helium, just remember that people in the future will envy you.
Yup, every time I see a kid's balloon floating away, and I think "some unborn physicist is cursing you!"
(Of course, once we've got fusion, we'll have more helium ash than we know what to do with)
Okay, and 50 years for large scale profitable/commercial fusion should be possible.
It's always been 50 years, for as long as I can remember 
AWOL:
Yup, every time I see a kid's balloon floating away, and I think "some unborn physicist is cursing you!"(Of course, once we've got fusion, we'll have more helium ash than we know what to do with)
We could bury it... 
XD XD XD XD
was helium not abundant on the moon?
robtillaart:
was helium not abundant on the moon?
Lighter gases more easily escape the atmosphere of lighter planets/moons.
Riva:
robtillaart:
was helium not abundant on the moon?Your thinking Helium-3
right 
Peter_n:
Helium is not endless by the way. There might be a shortage of Helium in a few decades. However, investing in Helium companies is useless, you have to buy a large amount of the Helium yourself and store it and sell it in 50 years. So when you see a truck with Helium, just remember that people in the future will envy you.
I thought it was made continuously by radioactive decay in the earths core.
And in the crust. But the easy to get at in volume stuff is mixed in natural gas but not every pocket of NG.
The moon should have more helium-2 than helium-3. The sun doesn't spit out pure heavy isotopes.
And there is another source that won't run out soon, solar wind! You just need really BIG solar sails.
I have an old, now over 90, friend who flew anti-sub blimps in WW2. And then building and flying advertising blimps in post-war Germany, the US and finally Japan (painted like fish, so beautiful!) in the mid-late 70's. I'm not sure if he logged more hours in LTA than fixed wing but he's listed in the Delaware Aviation Hall of Fame.
I asked him if hydrogen would wouldn't lift a lot more weight and it turns out the difference isn't so great.
1000 cubic meters of hydrogen at 0C weighs 89.9 kg
1000 cubic meters of helium at 0C weighs 178.5 kg, 88.6 kg more.
1000 cubic meters of air at 0C weighs 1293 kg.
That's 1114.5 kg more than the helium 1203.1 kg more than hydrogen.
Neither the difference nor the cost are worth the danger of running with hydrogen.
Those antisub blimps were using 10,000+ cubic meters of helium, not like the ones we see now that Lou calls toys.
And BTW, those K ships were tiny compared to the Akron, Macon, and Savannah that carried defensive fighters.
The moon should have more helium-2 than helium-3. The sun doesn't spit out pure heavy isotopes.
Normal Helium is Helium-4. Helium-3 is an unusually LIGHT version of the atom...
As for "how do you weigh?": compress it until it's heavier than air, and then apply Boyle's law.
The difference in mass between compressed gasses and uncompressed gases is quite noticeable. In my day, full SCUBA tanks (at ~2750psi) would sink, while empty ones will float. (I'm not sure if that's held up through the revolution in tank composition (Al, carbon fiber, etc.)
westfw:
The moon should have more helium-2 than helium-3. The sun doesn't spit out pure heavy isotopes.
Normal Helium is Helium-4. Helium-3 is an unusually LIGHT version of the atom...
As for "how do you weigh?": compress it until it's heavier than air, and then apply Boyle's law.
The difference in mass between compressed gasses and uncompressed gases is quite noticeable. In my day, full SCUBA tanks (at ~2750psi) would sink, while empty ones will float. (I'm not sure if that's held up through the revolution in tank composition (Al, carbon fiber, etc.)
Oh that's right 2 protons and 2 neutrons.
2750 psi? That's good for 30 minutes?
We weighed electrons in physics class.
2750 psi? That's good for 30 minutes?
If it's air, and depending on the capacity of your tank and the depth you're going to, it's good for as long as you can make it last.
(I'd be complaining to the fill-station if they only gave me 190 bar)
If it's helium, it's good for about three breaths.
Are sport divers using helium these days?
Im a bit out of touch.
You would have to spend the hours breathing helium+oxygen+CO2 just to get the nitrogen out of your blood before helium in your tank would do you any good.
2750 psi? That's good for 30 minutes?
That was the (old-ish) standard steel tank - 72 ft^2 at 2750psi, about 30 minutes at 30 feet depth (close to an hour at the surface.)
Modern tanks are bigger and higher pressure. 80ft^2 at 3000psi typical for Aluminum, and I see some composite tanks at 4300psi. (hmm. All are negatively buoyant when full and float when empty.) (The SCUBA "big idea" is that you breath gas an ambient pressure. And then exhale as bubbles. 1 Atm additional pressure for every 10m depth, approximately. So at 30m depth, you use up your air three times faster than at the surface.)
You would have to spend the hours breathing helium+oxygen+CO2 just to get the nitrogen out of your blood before helium in your tank would do you any good.
Huh? Nitrogen has several problems:
- At higher pressures, nitrogen starts behaving like an anesthetic. Individual tolerance supposedly varies, but getting "drunk" at 150ft down is "not good."
- Nitrogen dissolves in your blood. At higher pressures, more dissolves, and then it un-dissolves when the pressure is reduced again, resulting in the infamous "bends." The longer you stay in high-pressure situations, the more nitrogen dissolves in your blood, and you have to make "decompression" stops where you wait at various (shallower) depths for the nitrogen to exit via your lungs instead of as bubbles in your circulatory system.
Breathing Helium/oxygen mixtures is considered "Technical diving", which is one step past "Sport diving." I believe it's done mostly to avoid the narcosis issues; my training didn't include any helium decompression info (In the 70s when I took my first class, Helium wasn't available to amateurs. My second class in the early 90s, it was explicitly "not included" in the sport diver training); but I recall reading that helium mixes don't entirely eliminate bends-like problems.
I've never heard of a need to purge atmospheric pressure nitrogen from your system... (although, after diving, even without needing decompression, you are supposed to avoid low-pressure situations (like airplane flights) for quite some time...)
IIRC in a Jacques Cousteau I watched they spent time in a bell purging blood nitrogen for some deep dive.
I have a sinus blockage. Past 20 ft down it gets like a spike driven into my head pain.
I never used a tank except in a 12 ft pool during lifeguard training and yes even just that was neat!
Our instructor talked about some twit turning a 20 ft garden hose into a snorkel.
He said the guy didn't try to breathe through it until he got to depth.
I am limited to snorkelling for the same reason.
I was somewhat jealous recently after a friend brought som amazing pics round after his trip to the truk lagoon.
It was a technical dive based on trimix , not sure of the details of that though.