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Dilatation of sand
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rounded shape; the sand has now settled down to the bottom, and the excess of water appears above the sand, the surface of which is free. The bag may now be squeezed and its shape altered, apparently without resistance; but this is only as long as the surface is free.
Fig. 16.
Putting the bag between two vertical plates and slightly shaking and squeezing, so as to keep the sand at its densest, it still has a free surface and it can, in this way, be spread out until
