Purple Air.
Obtain an olive-oil flask, the glass of which must be colorless. In default of an oil-flask, a large test-tube may be employed. Put into it a small quantity of solid iodine (procurable at the chemist's and very cheap), then lightly stop the mouth of the flask or test-tube with some cotton-wool, but not hermetically, and hold it slantwise over the flame of a spirit-lamp. The heat will soon dissolve the iodine, which will next turn into a most beautiful violet-colored vapor, completely filling the glass, and disappearing again as the glass gets cold.