Date: Mon Apr 23 12:07:01 2007

Author: Michael Timmins

Subject: Re: Big, loud, impressive demos

I'll reply to several messages at once:

I got my cornstarch from It was about $15/25lb bag
plus shipping (3 bag minimum). You will need at least 100 lbs for a 3ft
diameter by 6" deep pool. Sam's idea of checking with the campus kitchen is
a good one.

As far as mixing goes, add the water first. We used a couple of 6' 2x4's to
stir it. If I do it again I may consider getting a paint mixer drill
attachment. It took two people about 45 min to mix a little over 100 lbs of
cornstarch. Also, the stuff settles so if you do it before the show, you
will have to remix before using. This is where I would try the paint mixer,
the stuff at the bottom is real thick.

I'm not sure what other powders would work as well as cornstarch but I suspect
that clay might work pretty well.


On Monday 23 April 2007, Sam Sampere wrote:
> Mike,
> How did you mix a baby pool full of the stuff?? I'm doing that exact thing
> tomorrow and am wondering if you have better ideas?
> After they took their baggies, how did you dispose of the stuff??
> Thanks!
> Sam
> ________________________________
> From: on behalf of Michael Timmins
> Sent: Mon 4/23/2007 11:00 AM
> To:
> Subject: Re: [tap-l] Big, loud, impressive demos
> For our show this year, I filled a kiddie pool with cornstarch and water
> and let one kid come down and walk on it. It went over really well. It
> was the last demo so I announced that people could come down and take some
> home in a zip lock bag. What a mess! The kids had a great time shoving
> their hands in and playing with large globs of the stuff.
> Mike Timmins
> On Monday 23 April 2007, Scott Shelley wrote:
> > Hi all,
> >
> > Our Chemistry department put on an impromptu outdoor demo show last
> > year that included a host of impressive demos: The thermite
> > reaction, igniting a hydrogen balloon, natural gas soap bubbles,
> > sodium in water, among others.
> > This year, I'd like to counter their demos with a series of my
> > own. I have questions about a specific one I saw a few years ago,
> > but please feel free to add suggestions to this thread.
> >
> > At a Summer AAPT meeting in years past (Sacramento, I'm thinking), I
> > witnessed the following demonstration.
> >
> > A weighted 2-liter bottle was partially filled with liquid nitrogen
> > and then sunk to the bottom of a barrel full of water. A few seconds
> > went by and BOOM - a large volume of water was displaced in
> > approximately three nanoseconds. There was an audible gasp from the
> > audience. I've been talking about this demo ever since I saw it, but
> > since we don't typically do large demos shows at Haverford, I've
> > never tried it myself. I have a few questions about the safety of
> > this demo, before I blindly test it out.
> >
> > 1. By what mechanism was the bottle sunk in the barrel? I want to
> > ensure I design something that doesn't become a projectile.
> > 2. Is it safe to do this demo in an industrial sized plastic barrel
> > (i.e. a large cylindrical trash bin) or should I use a metal
> > drum. If it's the latter, does anyone know where I can acquire one?
> > 3. How much LN2 should I use?
> > 4. Is this demo as surprising as I remember?
> >
> > Other ideas for spectacular outdoor demos would also be appreciated!
> >
> > Thanks very much,
> > Scott Shelley.
> --
> Mike Timmins
> University of Virginia
> email:
> phone: (434) 924-6800
> mail address:
> 382 McCormick Rd
> Charlottesville, VA 22904

Mike Timmins

University of Virginia
phone: (434) 924-6800
mail address:
382 McCormick Rd
Charlottesville, VA 22904