In the manufacture of oil gas it is only ne cessary to project a small stream of oil into a red-hot retort, in which pieces of brick or coke are inclosed ; the gas immediately passes off through another pipe, and may be at once re ceived into the gasometer.
The gasometer employed in gas-works is a very large cylindrical vessel, closed at the top and open at bottom ; it is suspended by a rope or chain, and weight, in a tank filled with water, in which it rises and falls freely, being kept in its place by guide-wheels. Two tubes pass under and through the water, reaching above its surface into the hollow of the gaso meter ; one of them comes from the purifiers to admit the gas into the gasometer, the other carries it off when wanted for use. The action of this part of the apparatus is simple; when the gasometer is near the top of the water, it is full of gas, wbich has no communication with the air, because the edge of the gaso meter is under water. If now it be pressed downwards, which is effected by lessening the counterbalancing weight, the gas will be forced through the pipe which is to convey the gas out, and which must be left open for the pur pose. When the gasometer reaches the bot tom, it will be full of water, and ready to re ceive gas again, which is admitted through the other tube ; the gasometer then rises to the top as the gas goes in, and may be pressed down again. In this way it is alternately filled and emptied. In most establishments there are many gasometers, some filling and others emptying. Some gasometers are now made so large of them have the telescope construction ; that is, there are two gas holders, one within another, and both within the tank ; the inner gas-holder is filled first, and then, by an ingenious contrivance, it elevates the outer one as the gas continues to enter.
Many other contrivances are used before the gas is carried to its destination : a meter, to measure it; a governor, to equalise the flow ; a pressure-gauge, to indicate the resistance offered to its passage ; and a tell-tale, to c.v4 ; show the quantity manufactured during every hour.
The tubes which convey the gas to the streets are of course larger or smaller, accord ing to the number of burners which they supply. The largest in use are about 18 inches in diameter, the smallest about a quar ter of an inch. The street gas-pipes are laid in slightly inclined planes, and a vessel is placed at the bottom of each descent to re ceive and carry off any deposition which would otherwise clog the pipes.
The burners are of many different forms, and each has its technical name ; such as the argand, the fan, the cock-spur, and the bat's wing. The arrangement and management of the burners in practical use are exceedingly varied.
It was estimated in 1848 that at that time there were 6,000,000 tons of coal consumed in England for gas-making ; that one-twelfth of this, or 500,000 tons were used in London alone ; that the production in London was 500,000 cwts. of coke, and 4,500,000 cubic feet of gas ; and that the length of the gas-mains in London was upwards of 1500 miles. The length of gas mains must now be much greater, owing to the operations of rival companies.
The Western Gas Light Company has re cently erected extensive works near Mensal Green. The gas is here made from Cannel coal, on a principle patented by Mr. Palmer. The retort-house is a remarkable building. It is a polygon of twelve sides; 166 feet in diameter, and contains 360 retorts. The pro cesses, after the making of the gas in the retorts, differ in many respects from those usually adopted; principally in the mode of purifying the gas. The largest gas-holder or gasometer is of great magnitude ; it is 135 feet in diameter by 25 feet deep, and will con tain more than 350,000 cubic feet of gas.
The recent agitation of the gas question in London has led to the formation of a new company, by whom mains have been laid down through the principal streets, and a much lower rate of charge introduced than was before known. The mode of charge per cubic feet, as estimated by one among the many varieties of meter, is gradually super seding the old mode of charge per burner.