Boileau
NICOLAS (bwä-lō'), a French poet, born at Paris, Nov. 1, 1636.
He was educated at Beauvais, and received both a legal and a theological training. In his 21st year, however, he inherited a competence, and decided to ter spherical boilers, cylindrical ones came into use, at first set on end, and afterward laid on their sides, and, later on, these were furnished with internal cylindrical tubes for furnaces.
Boilers may be classified in several ways-as horizontal and vertical; internally and externally fired; and plain, multitubular and tubulous. Large boil- BOILER ers are almost invariably horizontal, but small vertical boilers are often used.
They are employed in steam cranes and other situations where great length would be an inconvenience, and otherwise very frequently when small powers are required, especially for temporary purposes. As the size of a furnace limits the fuel which it can burn, this frequently involves having a much larger grate than could be conveniently arranged inside the boiler, and on this and other accounts boilers are usually externally fired. Under the head of plain boilers come all ordinary cylindrical boilers, with or without internal furnaces, horizontal or vertical. They are the cheapest and simplest which can be made, and, if properly proportioned, possess a considerable evaporative efficiency. When it is necessary, however, to economize fuel, or space, or both, multitubular boilers are frequently used. These derive their name from the fact that in them the flame and gases of combustion are made to pass through a great number of small tubes (surrounded by the water) on their way to the chimney.
The steam generating power of a boiler depends greatly on the extent of surface which it presents to the flame, and it is obvious that a great number of small tubes present a much larger surface than one large tube occupying the space of them all. Thus, with the same heating surface, a multitubular boiler will occupy much less space than a plain one, and, at the same time, the efficiency of its surface is found to be greater. It is, however, necessarily more expensive and more liable to get out of order. Tubulous boilers differ from multitubular boilers in not only containing tubes, but consisting of them, and having no large cylinders whatever. Their chief advantages are their great strength, for it is easy to make a metal tube strong enough to withstand pressures far higher than any at present in use; and the peculiarity, that if any accident happens or explosion occurs, it will only be to one tube at a time, and not to an immense boiler shell, an and its evil consequences will thus be greatly reduced. For this reason tubulous boilers are often called safety boilers.
Locomotive boilers are always multitubular, for much the same reason as marine boilers. The boiler of a single locomotive often contains 1,500 or 1,800 square feet of heating surface, and occasionally as much as 2,000 square feet. The principal test of the efficiency of a boiler is the quantity of water (generally expressed either in pounds or gallons), which it will evaporate from and 87:
BOILER at a temperature of 212° F., with the consumption of one pound of coal. Of course, this varies very much with the quality of the fuel, but with good pit coal (not dross), a Cornish boiler often evaporates 6 to 8 pounds of water per pound of coal, and a multitubular boiler about 10 or 11 pounds per pound of coal. Good Cornish or Lancashire boilers, however, often attain as great economy as those of any other type. The best rate of combustion on the grate varies with the construction of the boiler, from 10 to 18 or 20 pounds per square foot of grate surface per hour, and much more with forced draft, as in a locomotive.
For all first class work, and work where high pressures are to be used, the common material for boiler construction is mild steel, made by the open hearth process, and having a tenacity of about 28 tons per square inch. Copper is often used in the fire boxes of locomotives, but seldom in any other description of boiler.
Brass boiler tubes are sometimes seen, and on account of its better conducting qualities, brass is to be preferred to iron, but its costliness prevents it superseding iron in the great majority of cases. ng's or Every boiler has, to render it complete and workable, a number of fittings mountings, of which the following are the principal: A glass gauge to show the level of the water inside the boiler, and gauge cocks for the same purpose; a gauge to show the pressure of the steam; a valve for admitting water; a cock at the bottom for emptying or blowing off; a valve for the discharge of the steam; one or two safety valves, weighted so that when the pressure of steam in the boiler reaches a certain height, they open and allow the steam to rush into the air; a door by which a man can get in to clean the boiler, etc.
The Cornish boiler has often two internal flues or tubes, which is a much more advantageous construction. In the Galloway boiler, there are two furnaces, but these join together in one chamber just behind the bridges, and the gases are made to pass through a space considerably narrowed by side pockets projecting inward in order that they may be well mixed. From this point to the back of the boiler there is just one flue, made oval in section, and crossed by a considerable number of vertical taper tubes, which form a direct communication between the water beneath and that above the flue. These tubes both promote circulation and strengthen the flue. water tube boiler, which is extensively A later development of the boiler is the used. In this type one or more drums of water legs connected by tubes of com- BOILING paratively small diameter are used.
These are filled with water and the gases from the furnace pass around and between the tubes, heating the water contained in them. An advantage of the water tube boiler is the possibility of making it light, powerful, and compact.
It is especially well adapted for forced draught, and steam can be raised quickly.
These boilers are the safest against explosions. For these and other reasons they are largely used on war vessels and especially torpedo boats.
The most frequent cause of boiler explosions is the inability of the boiler to resist the regular working pressure. A boiler may be weak through various reasons, and old boilers are likely to be weakened by rust and general decay. See STEAM.