Putting bottles of salt water inside waterers to keep them from freezing - Anyone done this?

So I found this article a few days: http://www.achickandhergarden.com/chickens-water-from-freezing/

In the article the author fills 20 oz bottles with salt water and puts them inside her waterers to keep them from freezing. I'm skeptical that this would actually work, but its a great idea if it does. I think I might try this during the cold snap that is supposed to hit here later this week.
Has anyone else tried this? Does it work well?

Physically the idea makes no sense. Yes, water with high salinity will have a lower freezing point (arctic ocean water tends to freeze around 28F/-2C), but it will have no effect on the fresh water that the birds drink from. The fresh water will freeze as it normally would around the saline bottles. Once the ice temperature gets cold enough the saline will begin to freeze too.

The person mentions that the water didn't freeze with a "real feel" of -7F. Wind chill, real feel, or whatever you want to call it has no effect on the actual air temperature. If it's 35F outside and the wind chill is 10F, the water won't freeze. If the sun is hitting the waterer it may not even freeze at temps slightly below 32F.

What is the heat capacity of saltwater versus freshwater? It might make difference that way if salt water at a given temperature holds more thermal energy or must release more to freeze.


What makes me think this way is when I make strong salt solution, the water temperature drops.

Saltwater has a slightly lower heat capacity than freshwater. So the saltwater would cool or warm faster. The bottle temperature should track right in line with the freshwater with the obvious caveat that the whole "system" is cooling from the outside-in via conduction.

Freezing (fusion) does give off some heat. Think of it as an energy conservation...the water goes to a lower energy state from liquid to ice so the outside environment gains the energy. In meteorology we call this latent heating of the air. Usually we talk about in terms of condensation (clouds), but it works in this case too. The freshwater would cool and eventually begin to freeze. While under the phase change, it's turning to ice but maintaining a temp near freezing...think ice water bath. When the freshwater completely freezes the saltwater remains liquid. The freshwater ice continues to cool to an ice temp of 28F or so and then the saltwater solution begins to freeze. As the saltwater goes through the phase change, it too will release some latent heat of fusion out to the freshwater ice. My guess is it isn't enough to raise the temp of the freshwater 4-5F to make it melt again. You also still have heat loss to the colder outside air working on the system as well.

If someone wants to try it and prove me wrong that'd be great. It just doesn't make scientific sense to me.

I've heard this used for cattle and horses but you are supposed to fill a milk jug half way with salt water and toss it in the stock tank. I thought this worked primarily because the jug would bob around on the surface and keep the water in the stock tank from freezing as quickly. Additionally, the horses learn that as the water does ice over, they can push the jug down to break the thin layer of ice. At real cold temps the tank is going to freeze regardless though.

Thanks for the comments. The more I thought about this, the more it logically just didn't make sense. I decided to give it a try last week. I filled a plastic bottle with salt water and put it in a one gallon bucket of water, and left it on the porch. Overnight it got down to 6F.
The result: The bottle of salt water had no ice in it at all, however the bucket was nearly frozen solid. So salt water will not freeze in single digit temps, but will not keep waterers from freezing at all.