cc wrote:

> What about the crystals to make alkaline water sold in pharmacy or in
> Chinese grocery store ?

Yes, that might work.

> I don't know what you're doing

A trick with red cabbage:
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Chop up the red cabbage and soak it overnight, or boil it for a few minutes.
Strain off the water, which should now have turned purplish red, and throw
away the cabbage.  Allow the water to cool; for best effect, put it in a
glass jug.

Prepare the three wineglasses as follows:  put 1 cm of vinegar in one, 1 cm
of alkali solution in the second, and leave the third empty.

You are now ready for the demonstration.  Top up each of the prepared
wineglasses with the cabbage water and observe the resultant colours.  If
all goes well, you should have reproduced the famous scene in Mary Poppins,
in which Ms Poppins successively pours out three different beverages from a
single bottle.
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> it's  probably less dangerous if it's pure.

Well, it's for demonstration purposes only - not for consumption!

--
John
http://rarebooksinjapan.com