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LECTURE III.
COHESION.—CHEMICAL AFFINITY.
We will first return for a few minutes to one of the experiments made yesterday. You remember what we put together on that occasion—powdered alum and warm water; here is one of the basins then used. Nothing has been done to it since; but you will find on examining it that it no longer contains any powder, but a multitude of beautiful crystals. Here also are the pieces of coke which I put into the other basin, they have a fine mass of crystals about them. That other basin I will leave as it is. I will not pour the water from it, because it will show you that the particles of alum have done something more than merely crystallise together. They have pushed the dirty matter from them, laying it around the outside or outer edge of the lower crystals—squeezed out as it were by the strong
