Hydrogen gas may be prepared more easily by other processes, which do not show, however, so clearly the fact of its being derived from the decomposition of the water. The property which iron acquires at a bright red heat may be given to it without any heat, by means of some oil of vitriol (called in the language of chemists, sulphuric acid). Iron quite cold will decompose water, if the water be previously mixed with some sulphuric acid. The oxygen goes to the iron, which dissolves, and the liquor contains green copperas. The metal zinc, which is now so very much used in the arts, may also be employed with sulphuric acid and water to decompose water, and it gives a purer hydrogen gas than iron, the latter metal containing always a little charcoal, which mixes with the hydrogen and contaminates it. In all of these processes, although the water is decomposed, yet we obtain only one of its elements; the other, the oxygen, remaining combined with the iron, the charcoal, or the zinc. We may, however, produce the separation of water into its elements, so as to exhibit both. This is done by passing a current of electricity from the apparatus termed the galvanic battery, through the water. One of the grandest and most fruitful discoveries ever made in chemistry was that by Sir Humphry Davy, who proved that electricity possesses the power of separating compound substances into their elements; and by that means he succeeded in decomposing numerous bodies which had resisted all processes known before that time, and obtained new substances of a simple nature, and of most curious and important properties. To decompose water by means of electricity, the wires from the galvanic battery are made to dip into a little cup of water, and over each wire there is hung a bell-shaped vessel, inverted, full of water. When the current passes, pure oxygen gas is disengaged from one wire, and pure hydrogen gas is liberated at the other, and being received as the bubbles rise in the bell-glasses, the gases are collected for use. So much for the separation of water into its elements; the production of water by the union of its elements is still easier. The simplest way to show this is to take a little bottle, and put into it the zinc, water, and sulphuric acid, by which the hydrogen is to be obtained, to fit to the mouth of the bottle a cork, through which passes a little glass or metal tube, ending in a fine jet. The gas may be set on fire as it issues from the jet, and by holding a cold plate or a tumbler over the flame, and at a little distance, a copious dew of water will be deposited upon it, which after a few moments will increase so much as to run into large drops. This water is formed by the hydrogen gas combining as it burns with the oxygen of the air.