Glass consists of sand, carbonate of soda, and red lead, heated
together. If water be poured into a glass vessel, neither of the
ingredients will be affected by it; but, if the glass be reduced to
a fine powder, and water be poured on it, the soda will instantly be
dissolved.
Or, moisten, with water a piece of tumeric, or test-paper, drop on it a
little powdered glass, and the soda in it will change the yellow paper
to brown.