[Illustration: Detail of Paddle Boat]
** Peculiar Properties of Ice [100]
Of all the boys who make snowballs probably few know what occurs
during the process. Under ordinary conditions water turns to ice
when the temperature falls to 32 degrees, but when in motion, or
under pressure, much lower temperatures are required to make it a
solid. In the same way, ice which is somewhat below the freezing
point can be made liquid by applying pressure, and will remain
liquid until the pressure is removed, when it will again return to
its original state. Snow, being simply finely divided ice, becomes
liquid in places when compressed by the hands, and when the
pressure is removed the liquid portions solidify and unite all the
particles in one mass. In extremely cold weather it is almost
impossible to make a snowball, because a greater amount of
pressure is then required to make the snow liquid.
This process of melting and freezing under different pressures and
a constant temperature is well illustrated by the experiment shown
in Figs. 1, 2 and 3. A block of ice, A, Fig. 1, is
[Illustration: Experiment with a Block of Ice]
supported at each end by boxes BB, and a weight, W, is hung on a
wire loop which passes around the ice as shown.
Pages:
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250