goTenna Mesh community

Is there a chemist among you?

Some of the semi-commercial postings I’ve seen in these fora of late got me thinking (yikes!). Last fall, when we were down in the Gold Butte Monument (Nevada), we were doing some hikes that got us split up. I was able to connect us somewhat using GTM, but adjacent to our fabulous campsite we had a 30-foot rock formation in the direction we were mostly headed for our hikes.

It’s the posts about the super-heavy-duty helium kites that got me started. We needed no such thing…just being able to get a GTM up 50 feet or so would have covered the entire area. A GTM weighs 48 grams. I’ve purchased a few PVC 36" diameter balllons (which would be reusable, fairly impervious to gas passign through the walls). Those work out to holding about 1/2 cubic meter of gas, so will lift a bit over 500 grams. The balloons weigh 32g. I have 400-pound test line that weighs under 0.5g foot. So filled with helium, one of those balloons would lift itself, a GTM (in optional water-tight baggie) and 100 foot or that cord and have 300g or so of lift left. Could reel it back it at dusk, swap GTMs, put it back up the next morning. Coolsville.

Helium has gotten spendy. The gas to fill one of those balloons would run about $30. Plus hauling/buying a tank, regulator, etc. A 40 cu ft tank would just fill such a balloon three times…and would run $80 just for the gas.

But hydrogen…I’d only be doing this outdoors, away from flame. There are tons of videos online of folks filling balloons with hydrogen by combining sodium hydroxide (cheap), water (really cheap) and aluminum (pretty cheap) in a bottle/tank whatever, and stretching the balloon mouth over the mouth of the mixing vessel. A lot of them are filling 3-4 small balloons…like 12"…so not much gas required. But I’d need about 400 liters of gas per fill. H2 isn’t quite an ideal gas, so a gram-molecular-weight is about 24 liters at standard-temperature-pressure. More like 26-27 in any conditions I’d be doing this in. So roughly 15 g-m-w of H2 should do it.

The reaction is: 2Al(s) + 2NaOH(aq) + 6H2O  2Na+(aq) + 2[Al(OH)4]- + 3H2(g). So 2 g-m-w of aluminum, 2 g-m-w of sodium hydroxide, and 6 g-m-w of water will produce 3 g-m-w of H2. That works out to:

Water: 615/3 * 18g/g-m-w => 540g (or 540ml)
Aluminum: 2
15/3 * 27g/g-m-w => 270g
NaOH: 2*15/3 * 40g/g-m-w => 400g

It wouldn’t quite fit in a 750ml bottle, a shame, as we generally encounter (create) a few empties on camping trips. But it would certainly fit in a liter bottle. It’d be pretty easy to pre-measure the non-water reagents and bag them. The water is a non-issue. I’m just wondering if the 50+ years of rust on my chemistry classes is getting me to the wrong answer through the wonder of math. My reagent amounts seem large compared to what folks were using in videos on the web.

For some of you thinking about being able to deploy an elevated relay on short notice with cheap materials, this might be worth a thought. Could be useful in an emergency that didn’t entail sustained high winds.

–Richard

I wish a professional chemist could instruct us on how to do this safely with minimal component parts.

It’s hydrogen…so “safe” will always be relative. I have the reagents, a wine bottle, a balloon filler wine cap I designed and 3D-printed. Have been waiting for weather to get steady enough to do this with a PVC balloon outdoors…no way we’re doing the hydrogen two-step inside! Will do a test run with baking soda and vinegar, just to make sure I’ve got a good seal at the balloon neck, and that it doesn’t require keeping my hand cinching it the whole time it fills. This week’s weather is good…a little too good…so getting the irrigation repaired and online comes first. But soon…