The particular chore which you boys must perform is to see that the voltage of these batteries is maintained at about 1.2. It should be charged up to 1.8 volt at least once a week and never allowed to discharge to a lower pressure than one volt. The level of the electrolyte must be maintained one half inch above the plate by adding distilled water occasionally.
A few years ago every student of chemistry was more or less agitated by the thought that more than half of every clay bank was composed of metal nearly as valuable, or at least as costly, as gold. This is aluminum. By all the methods then known it was a very difficult and expensive process to extract the metal from the clay. At length, by the perfecting of the dynamo, the chemist had under his control great and powerful electric currents which enabled him to unlock any chemical compound however refractory and isolate its elements. As a result aluminum became common enough and cheap enough for even kitchen utensils.
The metal calcium which a short time ago was an exceedingly rare substance worth $40 an ounce is now fairly abundant and cheap for chemical experiments, although it has no qualities which will give it an extended use.
Powerful electric currents, such as are obtained at Niagara, enable us to combine elements into hitherto unknown chemical compounds. Carbon and silicon are made to unite to form carborundum, which vies with the diamond for hardness. Carbon and calcium unite to form calcium carbide, used with water to form acetylene gas.
In such processes the intense heat of the electric arc—perhaps 6000 degrees—is employed, together with the electrolytic action of the current, to separate and combine substances. Enormous currents are used in the electric furnaces for producing chemical reactions—from 1000 to 30,000 amperes at a time.
Electric currents passing through the human body expend their energy partly in heat and partly in electrolysis. So simple and harmless a thing as common salt would become a virulent poison if it could be electrolized in the body into its elements sodium and chlorine.
Let us make use of an electric current to decompose water into its elements, hydrogen and oxygen. I have a three-ounce wide-mouthed bottle ([Fig. 153]) and through its cork I pass two short pieces of No. 24 platinum wire by pushing a stout needle through first. I fill this bottle with pure water and cut a slight furrow in the side of the cork, where water may drip out when the gas is produced in the bottle. We crowd the cork firmly into the mouth of the bottle and invert it. No water drops out. We bend the ends of the platinum wires into hooks and hang upon them the wires bringing the dynamo direct current. There is no evidence of chemical action. Pure water is an exceedingly poor conductor of electricity. Let us now put about fifty-five ohms of resistance into the dynamo circuit, so that it will pass about two amperes, and put a very small pinch of salt into the water, which makes it so good a conductor that its resistance may be ignored. When now we close the circuit, as before, a brisk effervescence takes place. Bubbles of gas rapidly form on the platinum wires and break away, rising through the liquid. Twice as many form on the negative wire as on the positive one. As these gases rise to the top of the bottle an equal volume of the water drips out through the small hole in the cork.
