Reaction of calcium hydroxide solution and carbon dioxide gas.
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Saturated calcium hydroxide solution is diluted to about 1/3 saturated and
equally divided into two separate one liter beakers, one test sample and
one control sample, each about 600 ml.

Carbon dioxide is bubbled vigorously though each solution until a
precipitate of calcium carbonate forms.  Bubbling is discontinued in the
control sample.

In the test sample, as the bubbling continues,  the solution begins to
clear and remains clear with continued bubbling of carbon dioxide.

In the control sample, the solution clears upon the addition of a few
milliliters of 1M HCl (addition of H2SO4 has the same effect).

Conclusion: The redissolution is primarily due to the decrease in pH,
rather than ... [ in progress ... TBD ]

Discussion: ... [ in progress ... TBD ]

see also: B.Z. Shakhashiri, "Chemical Demonstrations, a Handbook for
Teachers of Chemistry," v.1, p. 329.