Page:On the various forces of nature and their relations to each other.djvu/59

Rh have the opportunity as it cools (for that is the condition which favours their coalescence) of uniting together again and forming one mass.

Now, having brought the alum into solution, I will pour it into this glass basin, and you will, to-morrow, find that those particles of alum which I have put into the water, and so separated that they are no longer solid, will, as the water cools, come together and cohere, and by to-morrow morning we shall have a great deal of the alum crystallised out—that is to say, come back to the solid form. [The Lecturer here poured a little of the hot solution of alum into the glass dish, and when the latter had thus been made warm, the remainder of the solution was added.] I am now doing that which I ad- vise you to do if you use a glass vessel, namely, warming it slowly and gradually; and in repeating this experiment, do as I do—pour the liquid out gently, leaving all the dirt behind in the basin: and remember that the more carefully and quietly you make this experiment at home, the better the crystals. To-morrow you will see the particles of alum drawn together; and