The
flower-room and root-cellar were therefore so much warmer during the
night than if the water had not been there. The plants that were nipped
probably suffered after the ice became so thick as to check in a great
measure the freezing process."
"How can ice stop water from freezing?" Alf asked, in much astonishment.
"By keeping it warm, on the same principle that your bed-clothes kept you
warm last night. Heat passes very slowly through ice-that is, it is a
poor conductor. With the snow it is the winter wrap of nature, which
protects all life beneath it. When our ponds and rivers are once frozen
over, the latent heat in the water beneath can escape through the ice but
very gradually, and every particle of ice that forms gives out into the
water next to it one hundred and forty degrees of heat. Were it not for
these facts our ponds would soon become solid. But to return to the tub
of water in the flower-room. The water, when placed there, was probably
warmer than the air, and so would give out or radiate its heat until a
thermometer, placed either in the room or in the water, would mark
thirty-two degrees above zero. At this point the water would begin to
freeze, but plants or vegetables would not. They would require slightly
severer cold to affect them. But as soon as the water begins to freeze it
also gradually gives out its latent heat, and before a particle of ice
can form it must give out one hundred and forty degrees of heat to the
air and water around it.
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