Essential oils from plants (terpenes/terpenoids) are hydrogen-rich hydrocarbons and they smell nice. Menthol is an example, with a hydrogen mass fraction of about 12%. For comparison, water has a hydrogen mass fraction of about 11.2%.

If you abandon the "smell nice" constraint, you can get an even higher hydrogen mass fraction. For example, n-pentane has a hydrogen mass fraction of about 16.8% and it's liquid at a pressure of 1 atmosphere and a temperature of 25 degrees Celsius, but it evaporates rapidly, so you need to keep it in a container.

If you don't mind pressurizing the container a bit, you could put ammonia in there, and it has a hydrogen mass fraction of about 17.6%.

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bilsbie 3 days ago | parent | next [-]

I didn’t realize the mass fractions were that low. Is that correct??

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philipkglass 3 days ago | parent [-]

Yes, because hydrogen atoms are so light. It takes 12 hydrogen atoms to equal the mass of a carbon atom and 16 hydrogen atoms to equal the mass of an oxygen atom.

	▲	bilsbie 3 days ago \| parent [-]
		It’s a surprisingly good rocket fuel to be mostly carbon then.

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artemonster 3 days ago | parent | prev [-]

It was a joke about gasoline

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ricardobeat 3 days ago | parent [-]

Smells nice?

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SoftTalker 3 days ago | parent [-]

Some people actually think it does. Especially before it had so much ethanol added. I don't think it smells particularly nice but it is definitely a memory trigger of being a small kid helping my dad get the lawn mower ready to cut the grass.

	▲	toast0 3 days ago \| parent [-]
		Ethanol free gas definitely has a more enjoyable smell than gas with ethanol, but nice is maybe the wrong word.