Agar is a rather unusual material, in that its melting point is much higher
than the temperature at which it solidifies.  The engineers call it
hysteresis.  I don't remember the melting temperature, but it could be as
high as 90+ degrees.

The reason for this strange behavior is supposedly that it is composed of
long carbohydrate chains, and a lot of energy (= heat) has to be supplied to
get them to untangle, and so melt the bulk material.  Conversely, a lot of
energy has to be taken out (= cooling) to stop then thrashing around enough
to settle down and solidify.

Hope that helps,

Adrian Leek

		-----Original Message-----
		From:	Donna Sitrin [mailto:dsitrin@unipathllc.com]
		Sent:	Wednesday, April 12, 2000 7:21 PM
		To:	histonet@pathology.swmed.edu
		Subject:	Agar and heat


		I was asked by a curious tech today, the following:

		How come the agar used in the cell blocks does not become
liquid again in
		the heated chemicals in the processor.  Why does it keep
it's shape?

		We melt agar down in order to use it in making a cell block,
and when it
		cools, it solidifies.  Why doesn't it melt and cause the
loss of cells
		when it is heated in the processors?  Why does it stay
solid?

		Any who would like to, please reply.