In article <[log in to unmask]>, Sharyn
Horowitz <[log in to unmask]> writes
>We're trying to create a mechanical interactive for our exhibit about blood.
We
>want visitors to see an oversized vial of separated blood. Then they shake it
>up, and then the vial appears to be filled with whole blood. Then it resets
for
>the next visitor.
>
>Has anyone seen anything remotely similar to this? We've been imagining beads,
>glycerin, colored light, paint shakers, snow globes, etc. but we can't make it
>work. Any tips will be much appreciated.
>

Is this exhibit intended to teach visitors that, if you shake up a vial
of separated blood, it is instantly and magically restored to "whole
blood"?

Be careful!

If instead you really want to demonstrate that "whole blood" can be
separated, then you might consider the following . . .

Many plastics have a similar density to that of water, and so sink
fairly slowly.  Plastics can be obtained in pellet form (several
millimeters diameter), cheaply, for use in injection-moulding processes.
I happen to have been experimenting recently with some bright red
acrylic pellets that would be ideal for this.  You'll easily find a
local supplier (I'm in the UK!).

Keep the pellets nicely suspended by rotating & swirling the water in
the giant vial by means of a submerged jet of water from a hidden pipe.
An easy plumbing job, with an electric pump (and simple filter to keep
the pellets out of it).

The pump runs continuously and the "blood" swirls and glitters under
your tastefully-arraged spotlamps.

Offer a nice, robust, maintenance-free push-button with an appropriate
label.  Press it and the water flow stops and the blood separates
gracefully within a few seconds.

Better to use a solenoid-valve rather than switch the pump on and off
constantly.  Add a simple timer to start off the water jet again after a
few more seconds.

If you think this sounds complicated, believe me it isn't.  This kind of
approach could give you a trouble-free exhibit that doesn't become a
maintenance headache.

Let me know how you get on.

--
Ian Russell
[log in to unmask]
:-)nteractive Science Ltd
http://ourworld.compuserve.com/homepages/intsci/