Returning to our glass, let us suppose that the bottom has been so perforated that two little strips of platinum wire can be inserted side by side, at the distance of half an inch from each other, and so as to leave the tumbler water-tight. Now attach the lower ends of these wires to wires connected with the poles of an ordinary galvanic battery. Small bubbles will be seen to rise immediately around the wires in the water. Fill two glass tubes (closed at one end) with water, and having placed a little piece of paper over the top, hold the finger on the paper, and quickly invert the tubes over the wires. The escaping gases will thus be secured. The electric current is counteracting the affinity of the two elements that form water, and they are collecting in the tubes. You will soon find that the H gathers more rapidly than the O, and upon measuring them there will be twice as much of the former as of the latter. Weigh them, and the O outweighs the former eight times. If, then, one atom of O weighs eight times as much as two atoms of H (H₂O is the symbol for water, remember,) then one atom of O weighs sixteen times as much as one atom of H; or, in other words, H is sixteen times lighter than O, and is the lightest substance known. Place the O and H in a eudiometer over mercury, and send an electric spark through them; the gases will disappear, with a loud explosion, and there, resting on the quicksilver, will be seen the original drops of water which we decomposed. We have now shown the composition of water, both by analysis and synthesis. HYDROGEN. An atom of H is the chemist’s unit. This is a colorless, odorless, tasteless gas, fourteen times lighter than air. When burned it produces a more intense heat than any other substance. Iron burns in its flame like paper. When united with O, and a piece of lime is inserted in the flame, the latter becomes exceedingly brilliant, forming the Drummond light, which has been seen at the distance of one hundred miles in the daytime. So diffusive is H that if a sheet of paper or gold-leaf be placed over an escaping jet of the gas, it will pass directly through the paper, and may be lighted on the upper side. H is easily prepared, and many interesting experiments may be performed with it, some of which it may be well to mention. Take up on a pointed wire or needle or with tweezers, a piece of the metal sodium, quickly insert it under a tube filled with water and invert in a glass of water; the sodium will at once take the O and leave the H to displace the water in the tube. Remove the tube, still holding it with opening downward; apply lighted match and a slight explosion will follow. What two properties of H have you shown by your experiment? [Illustration: COLLECTING HYDROGEN EVOLVED FROM WATER BY SODIUM.]