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I recently saw a demonstration of a water filtration and purification system. In one of the demos two glasses were filled with tap water and then someone put three fingers into one of the glasses and made a scissor kick motion for about a minute or so.

Afterward, the chlorine content of both glasses was measured using standard pool maintenance equipment, and the glass that had not been touched had a noticeably higher reading.

chlorine measurement kit

Supposedly this demonstrates how rapidly chlorine is absorbed into the skin (which ostensibly makes a system that removes chlorine beneficial from a public health as well as a water taste standpoint).

Is this the only plausible explanation for the test? For example, is it possible that the agitation increases chlorine evaporation or that oils on the hand react with and neutralize the chlorine? Is chlorine absorbed that quickly through the skin?

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Stirring the water will make the chlorine evaporate faster... It's as dishonest as the AK test they do for those bracelets... –  Brightblades Oct 11 '11 at 18:42
Next time the guy comes by to do the demo, get him to stir it with something other than a finger. –  DJClayworth Oct 12 '11 at 19:25
can you verify that the water wasn't tampered with prior to the "test"... –  jwenting Jun 12 '13 at 5:42

2 Answers 2

up vote 21 down vote accepted

The reaction of chlorine gas and water is reversible. That means that stirring chlorinated water will release the chlorine gas into the atmosphere, somehting you'd easily smell.

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Some of the information contained in this post requires additional references. Please edit to add citations to reliable sources that support the assertions made here. Unsourced material may be disputed or deleted.

The link doesn't indicate the reaction is reversible, and I couldn't draw the same conclusion from it (that stirring would release the gas). Furthermore, this site indicates only the secondary Hypochlorous Acid reaction is reversible, not the initial reaction of chlorine gas or hypochlorite with the water. Further, it indicates that chlorine is more stable if introduced as a gas than as a hypochlorite, as energy (e.g. light, heat) breaks down hypochlorites. This makes it seem like how the water is chlorinated is a factor. –  Adam Wuerl Oct 11 '11 at 21:00
The key words are 'equilibrium mixture'. Non-reversible reactions don't have an equilibrium. –  MSalters Oct 12 '11 at 22:28
@Danny Yeah, duh. I think I just missed the reversible part when first reading the article and probably put too much stock in the reaction formulas that didn't use the two-headed arrows I would have when describing an equilibrium. –  Adam Wuerl Oct 14 '11 at 0:40

According to this paper from the government of Michigan:

The skin does not absorb chlorine well, but small amounts can pass through the skin when people are exposed to chlorine gas, bleach, or come into contact with water or soil containing high levels of chlorine. Although small amounts of chlorine can pass through the skin, it is eliminated from the body rapidly. Chlorine may irritate or burn the skin, especially moist areas.

Note that the paper is discussing Chlorine gas and bleach-strength solutions, as well as drinking water, which explains the reference to burning the skin.

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protected by ChrisW Apr 26 at 13:33

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