Dilute a saturated solution of chloride of gold with five times its bulk of water; place a thin strip of fresh burned charcoal into it, and apply heat, gradually increasing it until the solution gently boils. The heat will make the charcoal precipitate the metal on the charcoal, in the form of brilliant spangles. To Give a Piece of Charcoal a Rich Coat of Silver. Lay a crystal of nitrate of silver upon a piece of burning charcoal; the metallic salt will catch fire, and throw out the most beautiful scintillations that can be imagined. The silver is reduced, and, in the end, produces upon the charcoal a very brilliant appearance. Many animal and vegetable substances, consist, for the most part, of carbon, or charcoal, united with oxygen and hydrogen, which remember, together combined, form water. Now oil of vitriol or strong sulphuric acid, has so powerful an affinity or so great a thirst for water, that it will abstract it from almost any body in which it exists. If you pour some of this acid on a lump of sugar, or place a chip of wood in a small quantity of it, the sugar or wood will become speedily blackened, that is charred, in consequence of the oxygen and hydrogen being removed by the sulphuric acid, and only the carbon or charcoal left. When Cleopatra dissolved pearls of wondrous value in vinegar, she was unwittingly giving an example of chemical affinity. The pearl is simply carbonate of lime stored up by the oyster in layers. Consequently the precious jewels were decomposed by the greater affinity or fondness of lime for the acetic acid in the vinegar, than for the carbonic acid with which it had been before united. This was an example of inconstancy in strong contrast with the conduct of their owner, who chose death rather than become the wife of her lover’s conqueror. Combustion. It is necessary to distinguish between burning and the mere appearance of it. A gas flame is gas in a state of combustion, whereas the electric light is no example of it, although the wire within the glassen cylinder is red hot, and to all appearance burning. Combustion generally takes place through the strong affinity of some element, such as carbon in a substance for the oxygen in the atmosphere. In coal gas, for instance, the carbon contained in it unites with the oxygen in the air to form a colorless substance called carbonic acid gas. The latter is unable to support life, and may be called, therefore, poisonous. It is the presence of this gas which makes it unhealthy to burn many jets without proper ventilation.