ILLUMINATING GAS.

Thus far our various methods of artificial lighting have been very simple. At first men burned the pitch from the pine, and it produced a flame; then they burned olive oil through a wick, and it gave forth a flame. The tallow in the candle was burned through a wick, and it made a light; the whale oil in the lamp was burned by means of a wick, and a light was the result. In the same way refined petroleum, which we call kerosene, was burned by means of a wick, and that gave a strong light. These methods of lighting were all very similar.

We come now to a real invention. What would a boy of the year 1800, could he return to the earth, say to see you strike a match, turn a stopcock, and light the gas as you do to-day? He has never seen a match. He is just as ignorant of a stopcock, and surely it would be difficult for him to understand the burning of the gas. Many things would need to be explained to this boy of a hundred years ago. He must be told all about the production of illuminating gas, the storing of that gas under pressure, the transportation of it to the place where the light is wanted, and the proper apparatus for turning it on, setting it on fire, and regulating its pressure so as to produce a steady, uniform light.

Before the year 1700 Dr. John Clayton, an Englishman, prepared gas from bituminous coal, collected it, and burned it for the amusement of his friends. An English bishop in 1767 showed how gas could be produced from coal and how it might be conveyed in tubes. These were the first two steps toward our present almost universal illumination by gas: making gas and conveying it in tubes.

The real inventor of practical gas-lighting was William Murdoch, of Cornwall, England, who sometime before the year 1800 carried pipes through his house and office, and lighted the various rooms with gas which he had made from coal. Indeed, Murdoch did more than this: he lighted with his new gas a small steam carriage in which he rode to and from his mines. In 1802 he first publicly exhibited this gas-lighting in Ayrshire, Scotland, and showed two immense flames from coal gas. Nor did he stop here, for in 1805 he succeeded in lighting some cotton mills by the same method.

In our country various experiments were made, but without any practical result until 1821, when illuminating gas was successfully manufactured and used in Baltimore. In 1827 the New York Gaslight Company introduced this new method into many houses and sold the gas to the people for lighting purposes.

That was over seventy years ago. What a change has been made within these seventy years! In cities and large towns almost every new house is piped for gas. Gas companies are formed for supplying this illuminating product to the inhabitants. Gas meters have been perfected which measure the quantity of gas, so that one pays for no more than he uses. Moreover, the towns and cities put up street lights which burn this same gas in the night, making it easy, convenient, and safe to traverse the streets at any hour.

Bituminous or soft coal is used in the manufacture of illuminating gas, as anthracite contains less of the needed materials. Gases are easily driven off from bituminous coal whenever it is heated, if air is kept from it. At the works, therefore, the coal is placed in large closed ovens, called retorts. These are directly over furnace fires, which are kept vigorously burning. The gases pass out of the coal and, rising, enter a series of long pipes. The coal which is left in the retorts is called coke. This process is called distillation.

Many substances pass off with the gas, from which it must be cleaned. Tar and ammonia become liquids when cooled, and are left behind as the gas passes through cold water. The series of iron pipes in which this process is carried on is called the condenser. Then the gas is carried through the purifier, in which all other impurities are removed.

When thoroughly purified the gas passes into the gasometer. This usually consists of two round iron cylinders of nearly the same size, one inside of the other. The outside cylinder has no roof; the inside has no floor. The sides of the inner one go down into a trench filled with water. Its top is held up by the gas, which comes into it from the purifier.

The roof of the inner cylinder presses down heavily upon the gas, pushing it into the large main pipes, which run from the gasometer through the principal streets. Smaller mains connect with these and the gas is pushed into the service pipes, which enter the houses. When a stopcock is opened in any house the pressure of the gasometer pushes the gas through, it may be, miles of pipes, and out through the burner, where it may be lighted.

Many houses have a simple electric-lighting attachment, so that by merely turning a stopcock the gas is turned on and by pulling a chain an electric spark sets the gas on fire, flooding the room with light.

Within a few years illuminating gas has greatly diminished in price. It costs a little more than kerosene, but it is more convenient in many ways. The danger of carrying lamps from room to room is avoided, as well as the disagreeable task of filling them. Still the gas flame is less steady than that of the kerosene lamp, and is therefore less serviceable for reading. For the poor man the kerosene light is a great blessing, while for all who can afford the extra cost the gaslight is a greater convenience.