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Footbag
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Mpemba effect? Home experiments...
      #6263585 - 12/20/13 11:58 AM

Has anyone done any home experiments of the Mpemba effect?

The Mpemba effect is defined as "There exists a set of initial parameters, and a pair of temperatures, such that given two bodies of water identical in these parameters, and differing only in initial uniform temperatures, the hot one will freeze sooner."

So last night I took two cups of water identical in all ways but their temp. One was 95F, one was 41F. I placed them in my freezer which is 0F. The cold cup clearly had the top freeze up first, but I sampled the temperature at the bottom of both cups every 20m. Within 40m both cups were the same temperature. 32.9F. The cold cup still had a bit more ice, but 20m later the cups were indistinguishable in both ice and temp.

I graphed out the temperature change and it turns out the hot water cooled at a rate faster then the cold, especially in the beginning. Of course, water will only go to a little below 32F. But I think I have to call it a tie.

Once I find a test that can be reproduced consistently, I'd love to try ruling out some of the suspected causes. Evaporation, convection, frost, supercooling, solutes, thermal conductivity or the effect of dissolved gasses.

It's kind of intriguing. Especially the rediscovery and the ridicule the student received.
Quote:


Mpemba asked a visiting physics professor, Dr. Osborne, the same question. This professor replied that he did not know, but he would test the experiment. Dr. Osborne had a lab tech perform Mpemba's test. The lab tech reported that he had duplicated Mpemba's result, "But we'll keep on repeating the experiment until we get the right result."




Edited by Footbag (12/20/13 03:19 PM)


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The Mighty Mo
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Re: Mpemba effect? Home experiments... new [Re: Footbag]
      #6264112 - 12/20/13 04:47 PM

I've tried this experiment many years ago, except that I boiled the one sample first and let cool just enough so it didn't break the container when I poured it in. Sample sizes were 16oz. My findings, the cold water froze first, and both had about the same rate of cooling. My conclusion, the whole thing was just an old fable.

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Footbag
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Re: Mpemba effect? Home experiments... new [Re: The Mighty Mo]
      #6264136 - 12/20/13 05:00 PM

Quote:

I've tried this experiment many years ago, except that I boiled the one sample first and let cool just enough so it didn't break the container when I poured it in. Sample sizes were 16oz. My findings, the cold water froze first, and both had about the same rate of cooling. My conclusion, the whole thing was just an old fable.




I tried it twice. The first time, I used 170F and 42F; the cold water froze first. Then I found an article that suggested using 95F and 41F water to make the effect more obvious. The cold water had ice form on the surface first, but the hot seemed to catch up quickly.

I am not convinced that it is actually happening, but I was surprised that the water temps equalized before both cups fully froze. It's the only thing that gave me reason to believe there might be some veracity.

When I started the experiment, I though it was a tale. I didn't think I would be able to reproduce it. Even now, I don't know if I did.

How did you measure the rate of cooling? For me, the hot water cooled dramatically quicker then the cold. I suspect this is because the cold was approaching it's lower limit. But in the first hour, the hot cooled at close to 1F per minute while the cold cooled at .16F per minute. The cooling of the hot, was much more dramatic in the first 20 minutes.

Edited by Footbag (12/20/13 05:14 PM)


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GlennLeDrew
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Re: Mpemba effect? Home experiments... new [Re: Footbag]
      #6264419 - 12/20/13 08:29 PM

I should think that materials cool to equilibrium with the environment at an asymptotic rate. When considering the freezing of water, we have the very considerable energy to lose in changing from liquid to solid while remaining at 0C.

I recall first hearing of the hot water freezing faster than cold back in '73 (at age 11), but never did hear the name ascribed to the purported effect. It always did strike me as odd that the more energetic substance could equilibriate more quickly; this would imply some magical 'super rate' of cooling which just seems to fly against common sense.


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dan777
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Re: Mpemba effect? Home experiments... new [Re: GlennLeDrew]
      #6264613 - 12/20/13 10:59 PM

Quote:

I should think that materials cool to equilibrium with the environment at an asymptotic rate



Indeed, in these experiments, the primary heat transfer mechanism is convection. The rate of heat transfer via convection is a function of delta T. The greater the delta T the higher the rate of heat transfer. The hotter liquid will cool at a quicker rate but the heat transfer rates will decrease as the liquids get closer to ambient temp.


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Footbag
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Re: Mpemba effect? Home experiments... new [Re: dan777]
      #6264953 - 12/21/13 09:11 AM

Asymptotic - Thanks for giving me a word to describe the graph.

I was going to try the test again last night, but I'm having difficulty coming up with a determination of when the ice is frozen. It's actually very hard to tell and introduces too much error to keep me happy.

I may have top buy some glass beakers.


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llanitedave
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Re: Mpemba effect? Home experiments... new [Re: Footbag]
      #6265308 - 12/21/13 01:32 PM

I've heard of it from the standpoint of someone claiming that their hot water pipes had frozen in severe cold while the cold water pipes remained clear. There are a lot of hidden variables that could be in play, but some of the stories are are nevertheless interesting.

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Footbag
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Re: Mpemba effect? Home experiments... new [Re: llanitedave]
      #6265328 - 12/21/13 01:45 PM

Quote:

I've heard of it from the standpoint of someone claiming that their hot water pipes had frozen in severe cold while the cold water pipes remained clear. There are a lot of hidden variables that could be in play, but some of the stories are are nevertheless interesting.




That's actually common. My friend does plumbing and it's frequently the hot pipes that burst as opposed to the cold. When I brought up the effect, he brought up the pipe issue.


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ColoHank
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Re: Mpemba effect? Home experiments... new [Re: Footbag]
      #6265469 - 12/21/13 03:07 PM

Friends and I conducted a number of trials of this one day to settle an argument, and the water that started out at the lower temperature always froze first (I won the argument!). This was during the depths of winter in North Dakota, on the back patio of the visitor center at Theodore Roosevelt National Park. It stands to reason that the warmer water at some point on its way down toward freezing had to cool off enough to equal the starting temperature of the cooler water, which in the meantime had gotten even colder, and that it was never going to catch up until both samples were frozen solid for a protracted period. No?

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Jay_Bird
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Re: Mpemba effect? Home experiments... new [Re: ColoHank]
      #6265496 - 12/21/13 03:23 PM

I think Hank just nailed the reason, not quite Xeno's paradox but akin. Both cool asymptotically, the rate of cooling is higher for the hot water at first, but the cold water is always further along the curve of T vs. time as it flattens out to reach freezing.

Hot water pipes have hot corrosion reaction rates between hard freezes, a factor for hot vs. cold pipe burst. Others mentioned dissolved gas as a variable, less gases in hot water. Or the role that evaporation plays for initial cooling of the hot water.


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Footbag
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Re: Mpemba effect? Home experiments... new [Re: ColoHank]
      #6265520 - 12/21/13 03:42 PM

I found two videos...

The first is Mpemba himself with the professor who listened to his question and promised to test it. Then the scientists who led the tests. I've seen a lot of hoaxes, and this doesn't seem to have that feel.
http://youtu.be/dOAUdJR0SIo


The second is a visual representation of the two vessels cooling and demonstrating the effect. It is probably easier to create the video then demonstrate the effect, so take it FWIW.
http://youtu.be/3u5tvdOXc70

The biggest problem I have with it is that the warmer cup has to cross the temp of the cooler cup. At some point they should be indistinguishable. But from my experiment, the hot cup seemed to freeze in a completely different way. The cold froze from the top down. The hot seemed to just start freezing near the edges of the cup.


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GlennLeDrew
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Re: Mpemba effect? Home experiments... new [Re: Footbag]
      #6266221 - 12/22/13 12:15 AM

Unless there is something extraordinary going on, or the cooling is severe and localized, water undusturbed will always freeze first on the surface. Water is densest at 4C, which is a wonderful property rejoiced to no end by many fish in northern climes, I'm sure. Convective overturning as heat escapes always ensures that as the freezing point is approached, *colder, less dense water is always at the surface*.

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Footbag
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Re: Mpemba effect? Home experiments... new [Re: GlennLeDrew]
      #6266773 - 12/22/13 11:57 AM

So I ran the experiment again last night. The cold froze first...

The cold sample developed ice first on the top first at approx 15m, then the hot sample developed it at approx 45m. At this point, both samples were the same temperature. Or they were so close that my thermometer couldn't tell between them.

The next 2 hours were spent developing ice. The cold sample finished first, but the warmer sample never seemed so far behind.

I have a few ideas about what is going on and why some may see the effect. First, as Glenn pointed out earlier, much more energy goes into converting the water from liquid to solid then in the actual cooling. Since such a significant portion of the process occurs after the temps had stabilized, the significance of other factors could potentially be increased.

Evaporation, for example, may remove enough of the water that the lower volume actually freezes faster. This has been controlled for in other experiments, but may be the reason many people claim to have reproduced it. I would see an ice cube tray, commonly used for this experiment, as allowing for more evaporation and reducing the control over that factor.

Depending on what has been done to certain samples of water, some will freeze at different temperatures. IE boiling first.

Maybe, since so much energy goes into freezing, and that the crystallization requires the bonds to find each other (a somewhat random process); it becomes a bit of a *BLEEP*-shoot which one cools first. Maybe rapid cooling aids in the bond creation. This is obviously not a scientific hypotheses, it's pretty hard to study something that isn't easily reproduced or even confirmed as real.

I had thought xeno's paradox. But as I've done the experiments a few times, I am realizing the numerical data isn't as important as the observational. And it is very difficult to determine when the ice is frozen.

Or maybe I'm trying to turn lead into gold.


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Re: Mpemba effect? Home experiments... new [Re: Footbag]
      #6266838 - 12/22/13 12:43 PM

Just a side note on the hot water pipes freezing first. Unless the hot water has been running recently the water inside is very likely the same temp as the water in the cold pipe.

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Footbag
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Re: Mpemba effect? Home experiments... new [Re: mich_al]
      #6266876 - 12/22/13 01:11 PM

Quote:

Just a side note on the hot water pipes freezing first. Unless the hot water has been running recently the water inside is very likely the same temp as the water in the cold pipe.




But that wouldn't explain why they freeze more frequently then cold. I read someone suggest that the hot water actually supercools and the ice develops crystals faster. This causes more stress and the makes the hot pipe more likely to burst.


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GregLee1
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Re: Mpemba effect? Home experiments... new [Re: Footbag]
      #6267048 - 12/22/13 02:56 PM

There is a Wikipedia entry on the Mpemba effect, which is inconclusive.

Here is my guess (which is rather vague). (1) There are difficult to control circumstances which produce a large uncertainty in the outcomes of the freezing experiments, (2) People tend to keep experimenting after any failures, because a failure isn't interesting, until they observe the effect. (1) and (2) result in an unusually high number of positive reports.

Edited by GregLee1 (12/22/13 02:58 PM)


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Footbag
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Re: Mpemba effect? Home experiments... new [Re: GregLee1]
      #6267318 - 12/22/13 05:44 PM

Quote:

There is a Wikipedia entry on the Mpemba effect, which is inconclusive.

Here is my guess (which is rather vague). (1) There are difficult to control circumstances which produce a large uncertainty in the outcomes of the freezing experiments, (2) People tend to keep experimenting after any failures, because a failure isn't interesting, until they observe the effect. (1) and (2) result in an unusually high number of positive reports.




The definition of the effect itself is very vague perhaps so much that it is not falsifiable. I think your guess is accurate, but does that mean it doesn't exist? Are all positives a result of observational error? Given the difficulty of making the observation, that could be likely.

Here is one issue that is growing on me. From the original story, they repeated the experiment 16 times with 16 positives. Why haven't they specified the procedures?


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gavinm
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Re: Mpemba effect? Home experiments... new [Re: Footbag]
      #6267828 - 12/23/13 01:36 AM

We have an experiment, which no-one seems to be able to reproduce reliably, there is no theory to explain it and we can't even agree on the starting conditions...

If this was called the E-Cat effect, would this thread be different? Would the members posting be as consistent? or supportive? or..

I wonder...

Have a great Christmas everyone (yes.. I'm on the other side of the date-line so this may be premature...)


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Mister T
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Re: Mpemba effect? Home experiments... new [Re: gavinm]
      #6268021 - 12/23/13 06:56 AM

heating water does drive out dissolved gases which slightly lowers the BP.

but this is not enough to over come the initial ∆t

but in the case of HW pipes that have not been used this could be a factor


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groz
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Re: Mpemba effect? Home experiments... new [Re: Mister T]
      #6268323 - 12/23/13 10:42 AM

I've done this experiment, but it was worded completely different. Does a tray of ice cubes freeze faster if you use hot water, than if you use cold. LOTS of folks will tell you it does.

We did a semi-controlled experiment. Water just boiled in one tray, and tap water in the tray beside it. Sure enough, the hot tray froze faster. BUT, then we continued, we let both trays thaw, and measured how much water came out of each after the freeze / thaw cycle. About 2/3 of the amount of water came from the hot tray.

Final conclusion, hot tray lost a lot of water to evaporation during the process, ended up with more surface area per unit volume because of it, and heat transfer out of the water is a function of surface area per unit volume. We got ice cubes faster, but, they were smaller. Shape of the ice cube tray plays a big role in this experiment, hunt around and you can find trays that work both ways.

FYI, back when we did this, experiment was accelerated slightly by using a freezer set to -42 degrees C, conditions that were available 'on the front porch' at the time. We had an argument during the experiment about 'is it cold outside', and came up with a simple way to answer that question, formally. Take a normal drinking glass, fill it half full of tap water. Put the glass out on the porch, wait 15 minutes. Tip over the glass. If no water runs out of the glass, it's cold. If water runs out of the glass, it's not cold out. Simple definition, with a proof that can be re-created using no fancy equipment.


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llanitedave
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Re: Mpemba effect? Home experiments... new [Re: gavinm]
      #6268380 - 12/23/13 11:19 AM

Quote:

We have an experiment, which no-one seems to be able to reproduce reliably, there is no theory to explain it and we can't even agree on the starting conditions...

If this was called the E-Cat effect, would this thread be different? Would the members posting be as consistent? or supportive? or..

I wonder...

Have a great Christmas everyone (yes.. I'm on the other side of the date-line so this may be premature...)




If somebody was trying to package and sell it, I'd definitely be a bit more critical.


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Mxplx2
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Re: Mpemba effect? Home experiments... new [Re: groz]
      #6268421 - 12/23/13 11:57 AM

http://amrita.vlab.co.in/?sub=1&brch=194&sim=354&cnt=1

See the above link about Newton's Law of Cooling.

The curve shows a starting temperature and an ending temperature depending on the ambient. Imagine a second curve depicting another temperature on the same graph. It would curve down to the ambient in it's own path and never equal the other curve until it reached ambient. So if they are never equal any where but ambient, they could never be 32 degrees at the same time.

To look at it by way of the formula, the temperature at time "t" is proportional to the difference between the original temperature T(H) and ambient T(A). In the formula it's shown as (T(H)-T(A)).

At least that's the way I see it.

I should add in summary, that the cooler cup of water will reach 32 degrees before the warmer cup, but both cups will reach 0 degrees at the same time.

Edited by Mxplx2 (12/23/13 01:15 PM)


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Footbag
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Re: Mpemba effect? Home experiments... new [Re: groz]
      #6268524 - 12/23/13 01:00 PM

Quote:

I've done this experiment, but it was worded completely different. Does a tray of ice cubes freeze faster if you use hot water, than if you use cold. LOTS of folks will tell you it does.

We did a semi-controlled experiment. Water just boiled in one tray, and tap water in the tray beside it. Sure enough, the hot tray froze faster. BUT, then we continued, we let both trays thaw, and measured how much water came out of each after the freeze / thaw cycle. About 2/3 of the amount of water came from the hot tray.

Final conclusion, hot tray lost a lot of water to evaporation during the process, ended up with more surface area per unit volume because of it, and heat transfer out of the water is a function of surface area per unit volume. We got ice cubes faster, but, they were smaller. Shape of the ice cube tray plays a big role in this experiment, hunt around and you can find trays that work both ways.

FYI, back when we did this, experiment was accelerated slightly by using a freezer set to -42 degrees C, conditions that were available 'on the front porch' at the time. We had an argument during the experiment about 'is it cold outside', and came up with a simple way to answer that question, formally. Take a normal drinking glass, fill it half full of tap water. Put the glass out on the porch, wait 15 minutes. Tip over the glass. If no water runs out of the glass, it's cold. If water runs out of the glass, it's not cold out. Simple definition, with a proof that can be re-created using no fancy equipment.




Some friends came over last night. We discussed the effect. My friend pointed out that he fills his ice cube trays with cold water and his wife hot. He says her cubes are too small and very brittle. His cubes are much harder and last longer. They didn't notice which froze first.

Evaporation would play a factor in any experiment it's not controlled for. That said, if evaporation, convection, dissolved gassed or any combination of the suggested mechanisms are responsible and the hot sample freezes first, that means it doesn't violate Newton's laws, but does exist.

Edited by Footbag (12/23/13 01:04 PM)


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FirstSightModerator
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Re: Mpemba effect? Home experiments... new [Re: Footbag]
      #6270583 - 12/24/13 12:27 PM

Quote:

Quote:

I've heard of it from the standpoint of someone claiming that their hot water pipes had frozen in severe cold while the cold water pipes remained clear. There are a lot of hidden variables that could be in play, but some of the stories are are nevertheless interesting.




That's actually common. My friend does plumbing and it's frequently the hot pipes that burst as opposed to the cold. When I brought up the effect, he brought up the pipe issue.




Couldn't this phoenomena be due to the fact that hot water pipes in general experience vastly greater, faster, and more frequent fluctuations in temperature than cold water piples, thus being subjected to greater stress from repeated thermal expansion and contraction, eventually causing stress fractures that finally break open enough to cause a leak under the additional stress of a severe cold spell? In short, hot water pipes are subjected to far greater and more frequent mechanical stress than are cold water pipes, and hence are more likely to reach an earlier failure point.


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mich_al
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Re: Mpemba effect? Home experiments... new [Re: FirstSight]
      #6271800 - 12/25/13 07:56 AM

Quote:

Some friends came over last night. We discussed the effect. My friend pointed out that he fills his ice cube trays with cold water and his wife hot. He says her cubes are too small and very brittle. His cubes are much harder and last longer. They didn't notice which froze first.



Sounds like time to flush out that hot water tank!


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Footbag
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Re: Mpemba effect? Home experiments... new [Re: mich_al]
      #6327965 - 01/22/14 10:06 AM

Well... I woke up this morning and went to get in the shower. Sure enough, my pipe was frozen.

Guess which one... Yup, the hot.

I got it thawed out with a hairdryer and there doesn't seem to be any leaking. Good thing!


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ColoHank
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Re: Mpemba effect? Home experiments... new [Re: Footbag]
      #6328201 - 01/22/14 12:05 PM

Minerals such as lime which are dissolved in water have a greater tendency to precipitate and accumulate in water heaters than in cold water pipes. Perhaps bits of those precipitates which are subsequently carried through the hot water pipes act as seeds for the crystallization of water ice. No?

I once had an old electric water heater whose tank was so full of precipitated "rocks" that it had little residual capacity for water. One had to shower quickly before the hot water gave way to cold.


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Footbag
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Re: Mpemba effect? Home experiments... new [Re: ColoHank]
      #6328262 - 01/22/14 12:26 PM

Quote:

Minerals such as lime which are dissolved in water have a greater tendency to precipitate and accumulate in water heaters than in cold water pipes. Perhaps bits of those precipitates which are subsequently carried through the hot water pipes act as seeds for the crystallization of water ice. No?

I once had an old electric water heater whose tank was so full of precipitated "rocks" that it had little residual capacity for water. One had to shower quickly before the hot water gave way to cold.




Yes. That was most likely the cause. Just irony that it actually happened to me weeks after thinking about it.

I was just thinking about something. Every time I did the test, I used reverse osmosis water. Had I used tap water, I may have gotten different results.


Edited by Footbag (01/22/14 12:47 PM)


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