_Ex._—Place in a glass a dilute solution of acetate of lead; suspend in it a strip of zinc. Some of the lead will be precipitated in crystals upon the zinc. This is caused by the zinc taking a portion of the acetic acid, and thus forming a new compound called zinc acetate, thereby liberating some of the lead.] Besides, that awful, fiery sea within is subject to tides, currents and convulsions that constantly threaten to disrupt and destroy this crust. It is supposed that masses of water percolate through cracks and fissures until they reach the internal fires and are suddenly converted into steam at an enormously high temperature, which gives it such tremendous expansive force as to shake the globe itself. This action, combined with the violent explosion of gases, creates the sublime and dreadful phenomena of EARTHQUAKES AND VOLCANOES. The destruction of Lisbon and many other cities is matter of history. But last year a charming city in the Mediterranean was destroyed in a few seconds, and the stricken inhabitants of Spain are still trembling with horror at the recent shocks that have desolated their fair country. Man looks in vain elsewhere for such exhibitions of the power of chemical forces as are here displayed. Lord Lytton[12] gives a most impressive description of an eruption of Mount Vesuvius, in “The Last Days of Pompeii:” “In proportion as the blackness gathered, did the lightnings around Vesuvius increase in their vivid and scorching glare. Nor was their horrible beauty confined to the usual hues of fire; no rainbow ever rivaled their varying and prodigal dyes. Now brightly blue as the most azure depth of a southern sky, now of a livid and snake-like green, darting restlessly to and fro as the folds of an enormous serpent; now of a lurid and intolerable crimson, gushing forth through the columns of smoke, far and wide, and lighting up the whole city from arch to arch; then suddenly dying into sickly paleness, like the ghosts of their own life! “In the pauses of the showers you heard the rumblings of the earth beneath, and the groaning waves of the tortured sea; or, lower still, and audible but to the watch of intensest fear, the grinding, hissing murmur of the escaping gases through the chasms of the distant mountain. “Sometimes the cloud seemed to break from its solid mass, and, by the lightning to assume quaint and vast mimicries of human or of monster shapes, striding across the gloom, hurtling one upon the other, and vanishing swiftly into the turbulent abyss of shade; so that, to the eyes and fancies of the affrighted wanderers, the unsubstantial vapors were as the bodily forms of gigantic foes—the agents of terror and death.” [Illustration: TESTING FOR GOLD WITH PURPLE OF CASSIUS. _Ex._—When gold is placed in a solution of Stannon’s chloride and ferric chloride, a precipitate called Purple Cassius appears. Sometimes the color varies to brown or blue.]