Salt water in a bottle in the water bucket. A trial.

[saysfaa]

Three containers, each with exactly 10 cups of cold tap water.

Three bottles:

• One with 1 cup of cold tap water.
• One with 1 cup of cold tap water and one cup of salt, shaken to dissolve all the salt that will dissolve..
• One with cold tap water filled to the level of the salt water - about 1 and a half cups.

I ran the tap long enough to be sure the temperature is even before filling everything quickly enough for it to stay even.

The three set out on the deck at the same time in temperature of about 15 F which is about -9.5 C.

I'm looking for an obvious difference in ice formation or the timing of ice formation.

 

[saysfaa]

There is an identical film of ice across the top of the water in each of the three buckets.

 

[saysfaa]

One hour later, the ice in the bucket with the salt water bottle is about twice as thick as the ice in each of the other two buckets. It is a matter of a 2 mm vs 1 mm.

My best guess is the plastic bottles in the other two buckets sit at more of an angle because the salt weighs down one end of the salt water bottle. And that means the plastic bottles are insulating the surface a little bit.

The bottle of salt water is gradually becomeing more upright. I think it is because the water can dissolve less salt as the temperature drops. The salt settles to the bottom of the bottle.

I stirred all three buckets throughly because I couldn't be sure I broke the ice evenly in each when I checked how thick the ice is.

 

[saysfaa]

End results: 11 hours after setting the buckets out.

I broke the ice, pulled the bottles out, poured the water into a measured cup and weighed the remaining ice.

The bucket with 1 cup of water bottle:
6 cups (1420 ml) plus 400 ml of water
826 g of ice

The bucket with 1 cup of water and 1 cup of salt bottle:
6 cups (1420 ml) plus 350 ml of water
833 g of ice of ice

The bucket with 1 1/2 cups of water bottle:
6 cups (1420 ml) plus 200 ml of water
861 g of ice

The math is off (if you calculate the weight of ten cups of water compared to the weight of the water poured off plus the weight of the ice) because I didn't decide to measure the ice until I was on the third bucket (the one with 1 1/2 c of water in the bottle). I didn't keep all the shards of ice from the first two.

Edit to add:
The math is also off because I didn't tare the buckets. They weigh: 9.7 oz (275 g), 9.3 oz (263 g), and 9.7 oz (276 g).

I didn't keep track of which bucket held which bottle or notice that one bucket weighs a bit less than the others - maybe we bought two at one time and one a couple of years later.

I don't think it matters for this experiment. Putting a bottle of salt water in a waterer is not a useful way to keep the water from freezing.

 

[saysfaa]

In case anyone wonders, the temps stayed in the teens F (about -8 C ) and the buckets were between the house and a snowbank that curved around two of the other sides so no wind. They were not in a sunny spot at any time.