Neither common air, nor oxygen, has any action on alcohol at moderate temperatures, whether in a liquid or aeriform state. On hydrogen, carbon, and charcoal, it has little or no action, but on phosphorus it acts, a portion of which it dissolves. With sulphur, it may be made to unite, as also with the alkalies, but not with the earths, except strontian and barytes. It is decomposed by sulphuric and nitric acids, with both of which it forms ether. It dissolves some salts, and has scarcely any effect upon others. Lastly, it dissolves resins and essential oils; but it neither acts upon gums, properly so called, nor on fixed oils. It is a compound of hydrogen, carbon, and a small proportion of oxygen, and may be decomposed, by passing its vapour through an ignited porcelain tube. Alcohol, by its combustion, as it is used in spirit-lamps for chemical and other purposes, produces no smoke, in consequence of the carbon it contains being totally converted, during that process, into carbonic acid; and its hydrogen, uniting with another portion of the oxygen of the atmospheric air, passes off in the form of aqueous vapour. Alcohol, used in this way, is preferable to oil; for the latter produces a large quantity of smoke, unless it is burnt in the Argand lamp. Alcohol is inflamed, when it is brought in contact with an ignited body. The combustion is rapid without any residue, and the flame white. As to the strength of alcohol, the best means of determining it, is with the hydrometer; but usually its _proof_ is ascertained by means of gunpowder. A portion of powder, put into a cup, and alcohol poured on it and inflamed, will, if the latter be strong, be set on fire; if, however, the powder should not take fire, but the flame of the alcohol be extinguished, we infer the existence of water, and that the alcohol is not of the proper strength. This experiment is founded on this circumstance, that, if the alcohol contains water, after the alcoholic portion is all consumed, the water will not only extinguish the flame, but also prevent the inflammation of the powder. The hydrometer, however, is the best experiment, as it determines at once the fact of the _strength_ of the liquor. Alcohol is used in the preparation of certain fulminating substances, as fulminating mercury and silver in particular; the preparation of which, we will give in the two next sections.