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Sodium acetate is the chemical in the reusable handwarmers.

You can coat a reactive chemical in a protective coating, then like popping a balloon, the pressure breaks the coating and triggers the reaction. The easiest example of this is putting an oxidizer and a reductant in the same bag.

There are lots of exothermic crystallization reactions where the pressure nucleates a crystal in supersaturated solution. You can control that pressure using engineering of the container, but it's not unique to the actual chemical.

Yes, the kidney will retain bicarbonate, but unfortunately, under normal conditions the kidney already reabsorbs close to 100% of bicarbonate. So unfortunately this mechanism cannot be increased enough to fully compensate for respiratory acidosis.

The kidney has other methods to indirectly raise the pH, like excreting ammonium (which would otherwise be reacted with bicarbonate in the liver). Other acids can also be excreted. However, renal compensation for respiratory acidosis takes days. The lungs are much faster at removing acid from the body than the kidney is.

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Rubber "corrosion" is similar to iron rust. More corrosion makes even more corrosion. You need to keep removing any hard or corroded segments to keep the underlying material good.

Storage environment is one of the biggest factors for lifetime of rubber seals. Some will fail via getting harder and others fail by getting softer.

Some of the types of rubber are degrading from the day they are manufactured. It can be trace amount of metal catalysts, free radicals or simply environmental oxygen, moisture, stress.

Failing soft. The way elastomers are made involves a chemical method called polymerisation. It's kind of a special type of zipper - it zips closed to make the elastomer but it can be triggered to unzip back to starting materials. That's where rubbers can fail soft.

Failing hard: A rubber when looked at under a microscope is like lots of little hairs all aligned. When it is sitting there static, some of those hairs will start to cross-link (e.g. you get a knot in your hair or some loose cables in your junk drawer form a knot). This can be residual free radicals (or oxygen induced radicals) that grab hold of the nearest neighbouring strand to make themselves stable. But similar to a relay race, that free radical never goes away, it just gets passed along the chain to the next open spot - then that crosslinks to another strand. Once you have too many knots in your hair or your Christmas lights are tangled up, it turns into a hard non-elastomeric mess.

Using the rubber gasket does involve mechanical/thermal stresses. It will be getting pushed or pulled. Any tiny hard sections will be ground away like a sacrificial layer. It keeps the majority of the seal elastomeric. Unfortunately, leave it static too long and those hard sections will get large.

Other places you see rubber degrading: knife handles getting sticky, plastic toys yellowing with age, shoe soles cracking when not worn, rubber car tyres softening in storage sheds, latex / synthetic clothing turning brittle in the back of your cupboard unworn. A gasket is no different.

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> What's the point of submerging in water if we're just going to let it dry? What's happening there?

You really want to avoid sudden temperature shocks that can cause cracking, which is why you first soak the earthenware in water. The water acts like a buffer for the temperature changes as the water in the clay will never exceed boiling point of 100°C. The thin layer of oil on the surface will get hotter, then polymerise and make the pot more hydrophobic, less likely to stain, prevent the unpleasant taste of raw clay, etc.

> When seasoning cast iron,

The metal expands when it's hot. Oil can diffuse into the gaps. When the pan cools the metal will shrink and grab onto the polymerized layer. Overall the heating/cooling is like scrunching up / unfolding paper.

You want the metal pan to be as hot as possible for the maximum amount of expansion, which is going to result in at least smoky oil, if not burnt carbon. Domestic oven / burner can't really get hot enough (it's fine, but people still have problems with the seasoning cracking or failing to adhere), however, a gas BBQ outside is much hotter. You can get a much better seasoning by really getting the pan hot before adding the seasoning oil.

Earthenware has a very different expansion/contraction issue compared to metal. Earthenware is already porous, so lots of little handhold grips for the seasoning to adhere into, no need for expansion/heating. The temperature only needs to be hot enough for the oil to polymerise, but not too hot or too long otherwise the earthenware will dry out and crack.

> Is there any logic behind using olive oil besides "authenticity"?

No logic. Other people use animal fats or other vegetable oils.

You can play around with using a drying oil such as linseed to form a hard, tough polymer film. Or you can use a non-drying oil such as olive and it's just fine.

Extra virgin olive oil isn't the best. It contains lots of non-oil stuff like proteins that make it tasty, but will also prevent it forming a nice tough barrier. You want to use "refined olive oil" or any other refined food oil.

> why the manufacturer would ship this tagine uncured and unseasoned?

Cost and time. It's tradition to season it yourself so you get that local family flavour, so manufacturer will allow for that and save money on an additional step.

Mold and rancid oils. The manufacturer has no idea how long the product will sit unsold on the shelf. Any residual water + oil = microbe food.

If you throw a rock very hard at some dry sand on a beach, it’ll make a disturbance in the sand. If you throw it hard enough, the disturbance in the sand will be a circle. The circular craters on the moon form for similar (though slightly different) reasons.

We have only recently figured out safe viral gene therapies (usually called lentiviral therapies)- the FDA approved the first two of them in 2022 [1]. I agree that to actually cure HIV, we'd need a system that can hunt down and correct the rogue DNA in our cells, but the technology is not yet there. First of all, to my knowledge, current lentiviral therapies aren't very good at targeting where in the genome they insert. That would be important to correct the implanted HIV sequence. However, our CRISPR DNA engineering systems are good at this. Understandably, there is work underway to combine the two [2], but academia tends to lead actual therapies by quite a bit. In the cases of both potential therapies, they wouldn't come close to screening / inserting into every potentially infected cell with our current technology. There's a lot of interest in improving this issue in pharma, though. Maybe it'll be possible some day, but not before a lot of work in the field.

I think about this specific question in the shower a lot, and am kind of stoked that somebody asked it.

[1]: https://asgct.org/publications/news/september-2022/eli-cel-second-lentiviral-vector-gene-therapy

[2]: https://pubmed.ncbi.nlm.nih.gov/34372494/

The self-diffusion coefficient of neat water is:

• 2.3·10−9 m2·s−1 at 25 °C (room temperature, or close enough), and

• 1.3·10−9 m2·s−1 at 4 °C (inside the fridge).

You can play around with equations for diffusion towards a target (on average a straight line velocity), diffusion over a certain distance (e.g. how long to randomly move from one wall to the opposite side), or collision frequency.

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Yes. The laws of physics are always working on the larger scale and the smaller scale. There's a lot of reasons why a car works, internal combustion engine, friction of the tires, blah blah blah, but ultimately it's fundamental physics.

Physical chemistry is the hardest undergraduate level class. There's a lot more to it than oil and water. But oil and water is the reason cell membranes exist.

This is remarkable to me. I don't know why this isn't talked about more. Every inch of us is composed of cells - yet the function of these cells (you could almost say the function of "you") is entirely a chemical process based on random interactions. The spindle emerging and grabbing hold of chromosomes and arranging them in the middle and splitting them into different sides - this intelligent looking process is fundamentally the same as pouring oil into water. Do I have that right?

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Your question is more accurately a chemistry question than a biology question. More specifically physical chemistry. It is entirely a matter of molecules bumping into each other. Molecules have different types of surface area made up of different atom types --your carbon, oxygen and nitrogen mostly in biology. There are either favorable "sticky" interactions or unfavorable repulsive interactions with the surface types of other molecules.

Most intuitive example is how oil and water don't mix, that's unfavorable thermodynamics. But sugar and water do mix, that's favorable thermodynamics.

Evolution used these rules to build cells that function. If two molecules need to find each other to function, they evolved "sticky" parts that lock together.

The information in the DNA is what contains the instructions for our body, correct? Does the DNA also contain instructions for how the cell works? Or is this a separately evolved system that works based on molecules bumping into each other? Can I conceive of the cell as almost a separate life form that exists inside of me?

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I think on a certain level everything happens this way. A virus has no neurological system but it is replicated by a series of chemical reactions. If it doesn’t work it doesn’t continue to exist. Same for cell division. When it doesn’t work the cell dies - or becomes cancer and kills the host.

It is hard to conceive of the fact that this system has evolved by these chemicals literally bumping into each other for billions of years.