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Nyrin t1_j92f707 wrote

You know how salt has historically been used as a de-icer? That's because salt water has a lower freezing point than normal water, meaning it has to get colder to freeze.

When it gets cold enough anyway, salt water forms something with the cool name of a "eutectic frigorific mixture," which establishes crystals of high-heat-transfer ice crystals on skin at much, much lower temperatures than normal ice. That means really bad frostburn with no sensitivity to know you're even being burned.

This has apparently been idiotically embraced as an "internet challenge" enough to merit a Wikipedia page: https://en.m.wikipedia.org/wiki/Salt_and_ice_challenge

>The mixture of ice and salt create eutectic frigorific mixture which can get as cold as −18 °C (0 °F).[3]

>The salt and ice challenge can quickly cause second- and third-degree injuries similar to frostbite or being burnt with the metal end of a lighter, as well as causing painful open sores to form on the skin. Due to the numbing sensation of the cold and possible nerve damage during the stunt, participants are often unaware of the extent of any injuries sustained during the challenge, only feeling pain once the salt on their skin enters lesions created during the challenge. Skin discoloration from the challenge may remain after the challenge has been attempted.[4][5][6]

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Chemomechanics t1_j92t5vz wrote

The origin is freezing point depression. Broadly, salty water - and the water can come from skin moisture alone - has a lower water concentration (<100% water) than pure ice (100% water), so water tends to move to the area of lower concentration. (This is equivalent to the equilibrium melting point going down.) But this movement requires melting, which absorbs substantial energy corresponding to the latent heat and makes the system and the surroundings much colder. This translates into much more severe freezing of tissue than with ice alone. Make sense?

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lemlurker t1_j934hqv wrote

ice doesnt traditionally remove temperature from your body well as its a solid and needs a phase change to do so so the temperature of the surface is usually around 0c where it contacts the skin.

salt lowers the freexzing temperature so that the ice melts at a lower temp and so when it touches skin it melts at -5 or -10 or colder, now that surface is so far below freezing it can quickly freeze cells in your skin causing ruptures just like burning as your cells arent filled with salt to stop them freezing

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akeean t1_j937lot wrote

Replying to Nyrin (#1,859,989)

You can use this effect to chill some cans of soda or beer very quickly. Put just enough cold tap water to submerge your cans+ice cube+salt in a bowl and slowly stir with a long spoon until the cubes *melt.Wait a minute & give the can a short wash under cold tapwater (to wash off the saltwater)

Edit: Non-native English speaker here. I used molten there since it is interchangable in German 'geschmolzen' as incorrect past tense of 'melt' for describing the phase change of a substance from solid to liquid. The German term works with glaciers, ice cubes, rock and steel. I see it makes no sense in English like this. Thanks for correcting me. Must be painful to browse reddit, lol.

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BrightCharlie t1_j93b1jl wrote

Replying to Nyrin (#1,859,989)

And in case you're wondering where the water comes from in rock salt, remember that sodium chloride is a powerful desiccant, it'll literally remove water from the air and turn it into salt water -- which is also why it's used as a food preservative, because it very thoroughly dries it (and any bacteria it might have, too)

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ramriot t1_j93eitm wrote

So, outside of some small scale salt mining in the himalayan range it turns out that Himalayan salt is mostly not mined from the Himalayan mountain range but from the Pothohar Plateau in Pakistan where the climate appears to be continental and arid, changing from tropic to subtropic.

With only a short polar cold period in winter.

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Recipe-Jaded t1_j93fb67 wrote

Replying to lemlurker (#1,862,133)

thank you. In highschool, I asked my physics teacher this question and she said, "because the salt lowers the freezing temperature of the ice". She left it at that, but you filled in the remainder.

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monsieurkaizer t1_j93pgtj wrote

Replying to LogicalMeerkat (#1,863,501)

It is because they can't be molten. Molten means liquefied by heat. Cheese can be molten, because it exists as cheese and melted cheese. Ice cubes just melt into water. So they're no longer cubes, and maybe that's why it irks you.

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ParanoidMaron t1_j93q0ce wrote

Replying to monsieurkaizer (#1,864,010)

>Molten means liquefied by heat.

... Ice melts thanks to heat.. into liquid water, ice is just solid water. Ergo, ice can become molten, as water and ice are the same material, just the same as aluminium is the same material molten or not.

It sounds wrong. It is not, technically speaking, wrong.

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Interesting-Month-56 t1_j93ro1k wrote

Replying to Recipe-Jaded (#1,863,029)

Just to add to this, not only is there less no convection with a solid (ice), it has a lower thermal conductivity (though not by much), and the surface area of water in contact with your skin is much higher.

Conductive heat transfer efficiency at an interface will be a function of the total area of contact between the two surfaces. Add in convection, where the heat is rapidly moved away from the skin by mixing of the water and water is a much better coolant than solid ice.

If you further add things like evaporative cooling into the mix, wet skin can be really dangerous.

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Reliv3 t1_j93s6hd wrote

Replying to ParanoidMaron (#1,864,055)

Yeah, I think molten is actually fine here. People are just used to using molten when describing melting materials which are solid at higher temperatures. Ice is a solid at much lower temperatures, so a state one may describe as "molten" will also exist at a much lower temperature.

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EBtwopoint3 t1_j93tgsd wrote

Replying to mschweini (#1,863,375)

The salt itself doesn’t make the water any colder. It just lets the water get colder before freezing, and increases the rate of heat transfer. For sweat, if it’s not much below freezing it’s really no different than being wet. With that said, sweating when it’s really cold out actually is dangerous.

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seanbrockest t1_j940qb8 wrote

Canadian Potash (potassium chloride instead of sodium chloride) mine here. Our mine is roughly 76% NaCl and 22% KCl. What we mine is then refined. Our mine is dry, so I've never experienced salt burns, but if you have other questions I'd be happy to answer them.

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seanbrockest t1_j945b43 wrote

Replying to PyroDesu (#1,865,284)

Mostly true, but there are wet mines. My company used to have one on the East Coast of Canada that literally went out underneath the Atlantic Ocean. They were under the ocean!

The rock was very cool, so all humidity coming in on the fresh air formed as condensation on the walls, creating a wet mine.

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Patsastus t1_j946f5s wrote

Replying to Reliv3 (#1,864,258)

It's more that "molten" is an extra descriptor used for the liquid state of something that's usually solid. So molten ice sounds fine, molten water sounds weird and tautological, because of the assumption that you mean liquid water the majority of the time you say "water"

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DeftTurnOfPhrase t1_j94a0xa wrote

Replying to [deleted] (#1,865,649)

This basically does happen in places with high humidity. It doesn't become "full" of water, but the salt clumps together enough to become impossible to shake out of the container. One remedy is to mix the salt with dry rice, which is either more of a desiccant than salt or has a mechanical effect that breaks up the clumps.

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[deleted] t1_j94dnn2 wrote

Replying to monsieurkaizer (#1,864,010)

Molten is only really used with things that are hot and will solidify again at room temp.

For example there is molten chocolate and there is liquid chocolate(sauce). They have clear definitions and are straight up never used interchangeably. Its like a rectangle and square.

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DieFlavourMouse t1_j94sroa wrote

Replying to Nyrin (#1,859,989)

Thank you, there's a lot of great information I your response. "eutectic frigorific mixture" is quite a fascinating concept. But can you explain a bit more of what you meant by "... frostburn with no sensitivity to know you're even being burned"? Why do we sense this phenomenon differently than other types of burns?

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redd-zeppelin t1_j94u582 wrote

Replying to ramriot (#1,862,965)

https://en.m.wikipedia.org/wiki/Tibet%E2%80%93Nepal_salt_trade_route

"Throughout history, Nepalis and Tibetans have traded with each other via a number of mountain passes.[1] Two of the most important goods traded were salt from the lakes of Tibet (e.g. Namtso), and rice from the Middle Hills of Nepal.[2][3] For centuries, the barter of grain and other agricultural products from Nepal with salt and wool from Tibet formed the basis of a trade that has traditionally been in the hands of various, mostly Tibetan-speaking communities.[4]"

Salt mining has been a part of the traditional Tibetan economy for centuries, which I believe is what OP is talking about. I do know there is also a large industry in Pakistan now.

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InevitableSignUp t1_j9621ra wrote

Replying to Nyrin (#1,859,989)

I hate to sound silly, but where does the extra cold come from? Is this assuming the ice/salt mixture is still in a sub-freezing environment? How does putting salt on ice and then onto your skin make the ice colder? Colder enough to cause such damage?

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AnnoyedPanther t1_j96qxqb wrote

Replying to EsUnTiro (#1,867,977)

As a Sufferer of Secondary Non Focalized Hyperhidrosis I can attest to that. I sweat excessively because of medications I'm on. Unlike most people who will sweat out of focalized point in the body first ie; armpits, forehead, etc. I sweat all over my body at once with minimal effort. My body and the clothes I'm in become soaked. Just the wet skin alone whether it is +30 or -10 degrees triggers cold shock. Your muscles clench, you gasp for air, your heart rate skyrockets, your skin STINGS all over your body and it HURTS. You sweat more because your anxious and it hurts. You just want to curl in a ball and sleep you become so exhausted and quickly. I'ts extremely debilitating.

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rational_american t1_j97epu7 wrote

Replying to freshmountainbreeze (#1,867,625)

Where would this be? That sounds like variations in temperature are causing condensation. I have lived on a literal island in the ocean, 500 meters from the pounding waves, and have had my salt clump a bit, but never dissolve itself into salt water in the container, even though dew and condensation was on everything at least some part of almost every day.

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