Thursday, August 27, 2009

On ice

Between my last post on politics and drinking 2 liters of Halflytely, I've exposed enough poop for one day, and I want to get back to science.




I have an ice maker I have been afraid to use--the refrigerator line is hooked up to a 1/2" copper pipe in the basement via a saddle valve, and all you need to know about saddle valves is that sooner or later they leak. No, gentle reader, this will not be a treatise on plumbing (though that would be a wonderful way to explain voltage and amperage).

While snooping around plumbing sites on how best to bypass the saddle valve, I stumbled upon a wonderful debate in the ice maker universe--should you attach the ice maker to the cold or hot water pipe?

On first blush, the answer seems obvious--put it on the cold line, why waste energy cooling down hot water. Leaving aside the Mpemba effect, in which hot water can freeze faster than cold water under some circumstances, turns out that by the time the water gets into the freezer, it will be at ambient temperature.

Still, some old-timers will insist that you tap your ice line into the hot water pipe, and they have a good reason.*

Boil some water, then put it in an ice cube tray. (If you're a young'un whose never seen an ice tray, just use a paper cup.) Pour the same amount of cold water from the tap into a similar receptacle.

Put them both in the freezer under the same conditions, yadda yadda. Wait a few hours, then take them out.

The ice made from the previously boiled water will be much clearer than the ice from the cold tap water. Plumbers know this, and most could probably tell you why, too, if you bothered to ask.

Can you figure it out (without using Google)?

There's an elegant, uncomplicated lab exercise at the Teachers' Lounge website that gives a huge hint--don't peek until you've given this some thought.


*A lot of folks worry about lead and other particles coming out of the hot water heater, and do not want their ice coming from there--I am not enough of a plumber to know how much a concern this is. Do not take plumbing advice from strangers on the internet.....


The ice delivery photograph is from the National Achives, taken in 1918.

5 comments:

John Spencer said...

Your posts on science make me feel ignorant . . . but in a good way.

Kathryn J said...

The link about the Mpemba effect didn't take me anywhere but I found a useful article at http://math.ucr.edu/home/baez/physics/General/hot_water.html

This could be a very interesting way to introduce students to several aspects of science including the debate about an explanation for observed phenomenon including the lack of acceptance until theoretical calculations support that explantion. It is also cool that Mpemba was a high school student when he "discovered" this.

BTW I knew it was dissolved gases. That said, we do not have an icemaker hooked to either water line because of the leaky valve issue. We just make ice the old fashioned way - well not like the picture but with trays.

doyle said...

Dear John,

We're all ignorant--revel in the process!

Dear Kathryn,

Link fixed, but glad to have the new one as well--I have a physics link from the post I think I now linked correctly.

The Mpemba story is wonderful--he stuck to observations despite a lot of pressure from his teacher and his classmates.

ertzeid said...

Who cares about a bit of cloudy ice? Even if it's dissolved gases. The more important part is that it's a bit of a waste of energy to heat up water that you're just going to freeze.

doyle said...

Dear Amanda,

Shoot, you're rgiht!

Every time I think we are completely fubared Kerry or you or Ben or one of a whole class of "kids" reminds me that we have a generation of bright folks who care.

Thanks for the reminder.