Here we can see a section of the engine fire-box and boiler. It is very interesting and very ingenious. But probably a novice would ask, "Where is the boiler? I see little else but tubes."
That is the explanation. The tubes chiefly form the boiler; for they are full of water, and they communicate with a narrow space, or "jacket," also full of water, and which reaches all round the fire-box.
This fire-box is held in a hollow below the tubes, which are placed in rows, one row across the other, just at the bottom of the funnel and above the fire-box. When, therefore, the flaming steam-match is dropped down the funnel, it finds its way straight down between the crossed mass of tubes to the shavings beneath; and the tubes full of the hot water are at once wrapped in heat from the newly-kindled and rapidly-burning fire. Every particle of heat and smoke and flame that rises must pass upward between the tubes. Furthermore, the hot water rises and the colder falls, so that there is a constant circulation maintained. The colder water is continually descending to the hottest tubes; and when bubbles of steam are formed, they rise with the hot water to the top. A space is reserved above the tubes, and around the funnel, called the "steam-space" or "steam-chest," where the steam can be stored; the steam pressure at which the engine frequently works being a hundred and twenty pounds to the square inch.
The result of all these ingenious arrangements is that, starting with very hot water, a hundred pounds of steam can be raised in five minutes.
"But," it may be asked, "why is a fire not always kept burning, and steam constantly at high pressure?"
The answer is that a constant fire, whether of coal or of oil, would cause soot or smoke to accumulate; while the Bunsen gas-burner affords as clear a heat as any, and maintains the water at a great heat, or even at boiling-point.
Near the funnel, but not so high, rises a large, gleaming metal cylinder, closed and dome-shaped. This is the indispensable air-chamber, without which even the powerful force-pumps could not yield so steady and persistent a stream.
A small air-chamber is now added to the suction-pipe by which the water is drawn to the engine. The use of the air-chamber in connection with this pipe greatly steadies the engine, the vibration caused by the throbbing of the powerful machinery as it draws and forces along such a quantity of water being very great. The nozzle of the hose belonging to one of the largest steam fire-engines measures 1¼ inch in diameter, some nozzles being as small as ¾ inch; and a large column of water is being constantly driven along the hose at a pressure of a hundred and ten pounds to the square inch, and forced through the narrow nozzle; here it spurts out, in a large and powerful stream, to a distance of over a hundred feet. It is obvious, therefore, that the power exerted by the steam-driven force-pumps and air-chamber is very high; and although such an engine may be in some folks' opinion only a force-pump, it is a force-pump of a very elaborate character; and not inexpensive, the average price being about £1,000.
Every steam fire-engine carries with it five hundred feet of hose. The hose is made in lengths of a hundred feet, costing about £7 a piece, without the connections. If you examine a length, you will find it made of stout canvas, and lined with india-rubber, the result being that, while it is very strong, it is yet very light.
Miles of it are used in the service; and upstairs in the hose-room you will find a large stock kept in reserve. Every piece is tested before being accepted.