Is it not remarkable that four of the brightest “red letter days” in the history of this science should be embraced within two decades, from 1754 to 1774? In 1754 Joseph Black discovered carbonic acid gas; in 1766 Dr. Cavendish found hydrogen; in 1772 Dr. Rutherford discovered nitrogen, and in 1774 Dr. Priestly found the King of the Elements, oxygen. Until then mankind were ignorant of the existence of a substance which composes in the aggregate one half the earth.
ANALYSIS OF WATER.
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?
COLLECTING HYDROGEN EVOLVED FROM WATER BY SODIUM.
Take a bottle holding one or two pints, fit a cork to it, through which pass a glass or metallic tube, the end of which is drawn out so as to leave a small aperture at the top. Place in the bottle a few pieces of zinc, and some sulphuric acid, diluted with water, in the proportions of one part of acid to six of water, then insert the cork. You will immediately see bubbles of H rising. The explanation of this is as follows: The zinc takes O from the water, thus liberating H; the O forms an oxide on the surface of the metal, which would prevent further action, did not the acid dissolve the oxide, thus leaving a fresh surface to take the O, and continue liberating H until the metal disappears. After the H has been forming for two or three minutes, hold over the tube an inverted tumbler for a moment, remove the tumbler and then apply a match to the contents of tumbler. When the bottle has become filled with H you can light the gas at the top of the tube, and thus have a steady flame. Be careful not to attempt to ignite the gas until all of the air has been forced out of the bottle, as air mixed with H produces an explosive mixture. In the intense heat of the faint flame you can melt metals or glass. By placing a larger glass tube, open at both ends, over the flame, you may be able to produce the celebrated acoustic tones, varying in pitch and intensity with the size and length of the tube used. A hydrogen gun can easily be made by taking a tin tube five or six inches long (closed at one end), from one half inch to an inch in diameter; make a small aperture near the closed end; then invert the tube for a moment over the escaping H, keeping the small hole closed with the finger, place a cork in the open end, and apply a match to the hole. The cork will be forced out with a loud explosion. What compound is always produced when H is burned? Let us see. Invert a cold, dry tumbler over a burning jet, and you will always observe moisture gathering on its surface. Another pretty experiment may be performed with H by inserting the stem of a common clay pipe in a piece of rubber tubing, slip the other end of the tubing over the gas jet, prepare some strong soap suds, and with a little care you can blow beautiful soap bubbles with your pipe, which, by a skillful movement may be detached, and they will rise in the air like miniature balloons; by placing a burning match under them they will explode. Strike a bell in a large jar filled with H, and it has a squeaky sound. Our whole art and science of music would be changed if H should be mixed with the air to any great extent.
Nicely balance a flask or jar containing air; fill the same flask with H, and the beam will at once be seen to rise.