Salt ice for cooler

[MYTraveler]

Originally Posted by hellsop

If you isolate the salt ice from fresh ice (a la milk jug method), the phase change in the salt ice will happen first and help keep the fresh ice from melting. The TOTAL amount of time that your cooler stays cool doesn't change, though.

That is true, but does it really matter which ice melts first?

[COLINFLTENG]

Bottom line is I will try salt ice!

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[jeanathon]

Just found out adding salt to fresh water ice actually removes heat since the salt uses energy to dissolve.

[Dave Lochner]

Originally Posted by jeanathon

Just found out adding salt to fresh water ice actually removes heat since the salt uses energy to dissolve.

Were you listening to Science Friday too?

Yes some salts (Sodium Chloride) use energy when they dissolve and thus lower the temperature of the water and others (like Calcium Chloride) give off energy when dissolved thus raising the temperature of the water.

That's why CaCl will melt ice when it is very cold and NaCL won't.

[RaymondR]

I agree Gatorade has suger not salt

I think you will find that any of these drinks which claim an electrolyte replacement capability have salts of some sort in them.

[RaymondR]

Yes some salts (Sodium Chloride) use energy when they dissolve and thus lower the temperature of the water and others (like Calcium Chloride) give off energy when dissolved thus raising the temperature of the water

I think it used to be called "the latent heat of fusion".

Is Calcium Chloride a salt?

[Dave Lochner]

Originally Posted by RaymondR

I think it used to be called "the latent heat of fusion".

Is Calcium Chloride a salt?

Yes.

https://en.wikipedia.org/wiki/Calcium_chloride

[RaymondR]

I recall that numbers of calcium compounds generate heat as they hydrate, are two processes occurring, the hydration of the calcium compound and it's dissolution as a salt, and is the heat from the hydration masking the latent heat from the dissolution of the salt?

[jeanathon]

Originally Posted by Dave Lochner

Were you listening to Science Friday too?

Yes some salts (Sodium Chloride) use energy when they dissolve and thus lower the temperature of the water and others (like Calcium Chloride) give off energy when dissolved thus raising the temperature of the water.

That's why CaCl will melt ice when it is very cold and NaCL won't.

Yes I was! Love Science Friday!

[Captain Bill]

If you've ever made ice cream it's pretty clear that by putting salt on fresh water ice you can lower the temperature. It's how you get the ice cream to freeze since Ice cream does not freeze at 32 f or 0 C. Since the salt in salt ice is already dissolved one does not get this advantage. As to the calories of heat it takes to melt a pound or kilo of salt Ice, I think you will find it is not significantly different than the calories required to melt the same amount of fresh water ice. The difference is primarily The temperature at which the two ices undergo a phase change. It takes 84 calories/gram of ice to turn it into a gram of water. It gets this heat from warmer things in its environment. This can be from heat that passes through the insulation or that beer that you just put in. If you have enough salt in the water you can depress the freezing point to 0 F. That means that the salt ice will absorb heat from anything warmer than 0 f. This may or may not be important to you. If you are trying to chill a beer it's probably not worth much, but if you are trying to keep meat or ice cream frozen then it makes a big difference since neither meat or ice cream freeze at 32 F. Salt ice with enough salt in it will do that, fresh water ice will not. In theory, a sealed container of salt ice will not rise above it's phase change temperature until all the ice in the container has melted. In reality, this is only true in a well stirred slush, but it's close enough for practical purposes. This basically the way cold plate refrigeration systems work, though the working chemical is not salt water. The other issue is that to make the " milk jug" of salt ice you have to get the temperature below the phase change point of the salt solution in that jug which may mean you need a "subzero" freezer. I once bought an 8 lb chunk of dry ice and put it in a medium size ice chest along with 2 10 lb bags of ice and a bunch of food I wanted to keep frozen. The water ice did not even start to melt for 10 days. Admittedly this was in the winter in Fl and the Bahamas, so temps were not extreme. One day we put some soft drinks in there to give them a quick chill and promptly got distracted and forgot about them two hours later a couple of muffled thumps caught our attention as the soft drinks froze and the cans split open, so be careful as you will have to treat your ice chest like a deep freeze rather than a refrigerator. Also you could have driven nails with the steaks we put in there and they took for ever to thaw.