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General Science by Bertha M. Clark
page 23 of 391 (05%)
The invention of the "Fireless Cooker" depended in part upon the
principle of non-conduction. Two vessels, one inside the other, are
separated by sawdust, asbestos, or other poor conducting material
(Fig. 18). Foods are heated in the usual way to the boiling point or
to a high temperature, and are then placed in the inner vessel. The
heat of the food cannot escape through the non-conducting material
which surrounds it, and hence remains in the food and slowly cooks it.

[Illustration: FIG. 18.--A fireless cooker.]

A very interesting experiment for the testing of the efficacy of
non-conductors may be easily performed. Place hot water in a metal
vessel, and note by means of a thermometer the _rapidity_ with which
the water cools; then place water of the same temperature in a second
metal vessel similar to the first, but surrounded by asbestos or other
non-conducting material, and note the _slowness_ with which the
temperature falls.

Chemical Change, an Effect of Heat. This effect of heat has a vital
influence on our lives, because the changes which take place when food
is cooked are due to it. The doughy mass which goes into the oven,
comes out a light spongy loaf; the small indigestible rice grain comes
out the swollen, fluffy, digestible grain. Were it not for the
chemical changes brought about by heat, many of our present foods
would be useless to man. Hundreds of common materials like glass,
rubber, iron, aluminum, etc., are manufactured by processes which
involve chemical action caused by heat.



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