Chapter IV: Part 4

BOIL, in medicine, a progressive local inflammation of the skin, taking the form of a hard suppurating tumour, with a core of dead tissue, resulting from infection by a microbe, _Staphylococcus pyogenes_, and commonly occurring in young persons whose blood is disordered, or as a complication in certain diseases. Treatment proceeds on the lines of bringing the mischief out, assisting the evacuation of the boil by the lancet, and clearing the system. In the English Bible, and also in popular medical terminology, "boil" is used of various forms of ulcerous affection. The boils which were one of the plagues in Egypt were apparently the bubonic plague. The terms Aleppo boil (or button), Delhi boil, Oriental boil, Biskra button, &c., have been given to a tropical epidemic, characterized by ulcers on the face, due to a diplococcus parasite.

BOILEAU-DESPREAUX, NICOLAS (1636-1711), French poet and critic, was born on the 1st of November 1636 in the rue de Jerusalem, Paris. The same Despreaux was derived from a small property at Crosne near Villeneuve Saint-Georges. He was the fifteenth child of Gilles Boileau, a clerk in the parlement. Two of his brothers attained some distinction: Gilles Boileau (1631-1669), the author of a translation of Epictetus; and Jacques Boileau, who became a canon of the Sainte-Chapelle, and made valuable contributions to church history. His mother died when he was two years old; and Nicolas Boileau, who had a delicate constitution, seems to have suffered something from want of care. Sainte-Beuve puts down his somewhat hard and unsympathetic outlook quite as much to the uninspiring circumstances of these days as to the general character of his time. He cannot be said to have been early disenchanted, for he never seems to have had any illusions; he grew up with a single passion, "the hatred of stupid books." He was educated at the College de Beauvais, and was then sent to study theology at the Sorbonne. He exchanged theology for law, however, and was called to the bar on the 4th of December 1656. From the profession of law, after a short trial, he recoiled in disgust, complaining bitterly of the amount of chicanery which passed under the name of law and justice. His father died in 1657, leaving him a small fortune, and thenceforward he devoted himself to letters.

Such of his early poems as have been preserved hardly contain the promise of what he ultimately became. The first piece in which his peculiar powers were displayed was the first satire (1660), in imitation of the third satire of Juvenal; it embodied the farewell of a poet to the city of Paris. This was quickly followed by eight others, and the number was at a later period increased to twelve. A twofold interest attaches to the satires. In the first place the author skilfully parodies and attacks writers who at the time were placed in the very first rank, such as Jean Chapelain, the abbe Charles Cotin, Philippe Quinault and Georges de Scudery; he openly raised the standard of revolt against the older poets. But in the second place he showed both by precept and practice what were the poetical capabilities of the French language. Prose in the hands of such writers as Descartes and Pascal had proved itself a flexible and powerful instrument of expression, with a distinct mechanism and form. But except with Malherbe, there had been no attempt to fashion French versification according to rule or method. In Boileau for the first time appeared terseness and vigour of expression, with perfect regularity of verse structure. His admiration for Moliere found expression in the stanzas addressed to him (1663), and in the second satire (1664). In 1664 he composed his prose _Dialogue des heros de roman_, a satire on the elaborate romances of the time, which may be said to have once for all abolished the lucubrations of La Calprenede, Mlle de Scudery and their fellows. Though fairly widely read in manuscript, the book was not published till 1713, out of regard, it is said, for Mlle de Scudery. To these early days belong the reunions at the _Moulon Blanc_ and the _Pomme du Pin_, where Boileau, Moliere, Racine, Chapelle and Antoine Furetiere met to discuss literary questions. To Moliere and Racine he proved a constant friend, and supported their interests on many occasions.

In 1666, prompted by the publication of two unauthorized editions, he published _Satires du Sieur D...._, containing seven satires and the _Discours au roi_. From 1669 onwards appeared his epistles, graver in tone than the satires, maturer in thought, more exquisite and polished in style. The _Epitres_ gained for him the favour of Louis XIV., who desired his presence at court. The king asked him which he thought his best verses. Whereupon Boileau diplomatically selected as his "least bad" some still unprinted lines in honour of the grand monarch and proceeded to recite them. He received forthwith a pension of 2000 livres. In 1674 his two masterpieces, _L'Art poetique_ and _Le Lutrin_, were published with some earlier works as the _Oeuvres diverses du sieur D_.... The first, in imitation of the _Ars Poetica_ of Horace, lays down the code for all future French verse, and may be said to fill in French literature a parallel place to that held by its prototype in Latin. On English literature the maxims of Boileau, through the translation revised by Dryden, and through the magnificent imitation of them in Pope's _Essay on Criticism_, have exercised no slight influence. Boileau does not merely lay down rules for the language of poetry, but analyses carefully the various kinds of verse composition, and enunciates the principles peculiar to each. Of the four books of _L'Art poetique_, the first and last consist of general precepts, inculcating mainly the great rule of _bon sens_; the second treats of the pastoral, the elegy, the ode, the epigram and satire; and the third of tragic and epic poetry. Though the rules laid down are of value, their tendency is rather to hamper and render too mechanical the efforts of poetry. Boileau himself, a great, though by no means infallible critic in verse, cannot be considered a great poet. He rendered the utmost service in destroying the exaggerated reputations of the mediocrities of his time, but his judgment was sometimes at fault. The _Lutrin_, a mock heroic poem, of which four cantos appeared in 1674, furnished Alexander Pope with a model for the _Rape of the Lock_, but the English poem is superior in richness of imagination and subtlety of invention. The fifth and sixth cantos, afterwards added by Boileau, rather detract from the beauty of the poem; the last canto in particular is quite unworthy of his genius. In 1674 appeared also his translation of Longinus _On the Sublime_, to which were added in 1693 certain critical reflections, chiefly directed against the theory of the superiority of the moderns over the ancients as advanced by Charles Perrault.

Boileau was made historiographer to the king in 1677. From this time the amount of his production diminished. To this period of his life belong the satire, _Sur les femmes_, the ode, _Sur la prise de Namur_, the epistles, _A mes vers_ and _Sur l'amour de Dieu_, and the satire _Sur l'homme_. The satires had raised up a crowd of enemies against Boileau. The 10th satire, on women, provoked an _Apologie des femmes_ from Charles Perrault. Antoine Arnauld in the year of his death wrote a letter in defence of Boileau, but when at the desire of his friends he submitted his reply to Bossuet, the bishop pronounced all satire to be incompatible with the spirit of Christianity, and the 10th satire to be subversive of morality. The friends of Arnauld had declared that it was inconsistent with the dignity of a churchman to write on any subject so trivial as poetry. The epistle, _Sur l'amour de Dieu_, was a triumphant vindication on the part of Boileau of the dignity of his art. It was not until the 15th of April 1684 that he was admitted to the Academy, and then only by the king's wish. In 1687 he retired to a country-house he had bought at Auteuil, which Racine, because of the numerous guests, calls his _hotellerie d'Auteuil_. In 1705 he sold his house and returned to Paris, where he lived with his confessor in the cloisters of Notre Dame. In the 12th satire, _Sur l'equivoque_, he attacked the Jesuits in verses which Sainte-Beuve called a recapitulation of the _Lettres provinciales_ of Pascal. This was written about 1705. He then gave his attention to the arrangement of a complete and definitive edition of his works. But the Jesuit fathers obtained from Louis XIV. the withdrawal of the privilege already granted for the publication, and demanded the suppression of the 12th satire. These annoyances are said to have hastened his death, which took place on the 13th of March 1711.

Boileau was a man of warm and kindly feelings, honest, outspoken and benevolent. Many anecdotes are told of his frankness of speech at court, and of his generous actions. He holds a well-defined place in French literature, as the first who reduced its versification to rule, and taught the value of workmanship for its own sake. His influence on English literature, through Pope and his contemporaries, was not less strong, though less durable. After much undue depreciation Boileau's critical work has been rehabilitated by recent writers, perhaps to the extent of some exaggeration in the other direction. It has been shown that in spite of undue harshness in individual cases most of his criticisms have been substantially adopted by his successors.

Numerous editions of Boileau's works were published during his
lifetime. The last of these, _Oeuvres diverses_ (1701), known as the
"favourite" edition of the poet, was reprinted with variants and notes
by Alphonse Pauly (2 vols., 1894). The critical text of his works was
established by Berriat Saint-Prix, _Oeuvres de Boileau_ (4 vols.,
1830-1837), who made use of some 350 editions. This text, edited with
notes by Paul Cheron, with the _Boloeana_ of 1740, and an essay by
Sainte-Beuve, was reprinted by Garnier _freres_ (1860).

See also Sainte-Beuve, _Causeries du lundi_, vol. vi.; F. Brunetiere,
"L'Esthetique de Boileau" (_Revue des Deux Mondes_, June 1889), and an
exhaustive article by the same critic in _La Grande encyclopedie_; G.
Lanson, _Boileau_ (1892), in the series of _Grands ecrivains
francais_.

BOILER, a vessel in which water or other liquid is heated to the boiling point; specifically, the apparatus by which steam is produced from water, as one step in the process whereby the potential energy of coal or other fuel is converted into mechanical work by means of the steam-engine. Boilers of the latter kind must all possess certain essential features, whilst of other qualities that are desirable some may not be altogether compatible with the special conditions under which the boilers are to be worked. Amongst the essentials are a receptacle capable of containing the water and the steam produced by its evaporation, and strong enough continuously to withstand with safety the highest pressure of steam for which the boiler is intended. Another essential is a furnace for burning the fuel, and a further one is the provision of a sufficiency of heating surface for the transmission of the heat produced by the combustion of the fuel to the water which is required to be evaporated. Desirable qualities are that the arrangements of the furnaces should be such that a reasonably perfect combustion of the fuel should be possible, and that the heating surfaces should be capable of transmitting a large proportion of the heat produced to the water so as to obtain a high evaporative efficiency. Further, the design generally should be compact, not too heavy or costly, and such that the cleaning necessary to maintain the evaporative efficiency can be easily effected. It should also be such that the cost of upkeep will be small, and that only an average amount of skill and attention will be required under working conditions. It is for providing these qualities in different degrees according to the special requirements of various circumstances that the very different designs of the various types of boilers have been evolved.

_Classes of Boilers._--Boilers generally may be divided into two distinct classes, one comprising those which are generally called "tank" boilers, containing relatively large quantities of water, and the other those which are generally called "water-tube" boilers, in which the water is mainly contained in numerous comparatively small tubes. There are, however, some types of boiler which combine to some extent the properties of both these classes. Each class has its representatives amongst both land and marine boilers. In "tank" boilers the outer shell is wholly or partially cylindrical, this form being one in which the necessary strength can be obtained without the use of a large number of stays. The boilers are generally internally fired, the furnace plates being surrounded with water and forming the most efficient portion of the heating surfaces. On leaving the furnace the products of combustion are led into a chamber and thence through flues or through numerous small tubes which serve to transmit some of the heat of combustion to the water contained in the boiler. In "water-tube" boilers the fire is usually placed under a collection of tubes containing water and forming the major portion of the heating surface of the boiler. Both the fire and the tubes are enclosed in an outer casing of brickwork or other fire-resisting substance. In some forms of water-tube boiler the fire is entirely surrounded by water-tubes and the casing is in no part exposed to the direct action of the fire. In "tank" boilers generally no difficulty is experienced in keeping all the heating surfaces in close contact with water, but in "water-tube" boilers special provision has to be made in the design for maintaining the circulation of water through the tubes. (For "flash" boilers see MOTOR VEHICLES, and for domestic hot-water boilers HEATING.)

Lancashire.

_Tank Boilers._--Of large stationary boilers the forms most commonly
used are those known as the "Lancashire" boiler, and its modification
the "Galloway" boiler. These boilers are made from 26 to 30 ft. long,
with diameters from 6-1/2 to 8 ft., and have two cylindrical furnace
flues which in the "Lancashire" boiler extend for its whole length
(see fig. 3). The working pressure is about 60 lb. per sq. in. in the
older boilers, from 100 lb. to 120 lb. per sq. in. in those supplying
steam to compound engines, and from 150 to 170 lb. where triple
expansion engines are used. In some cases they have been constructed
for a pressure of 200 lb. per sq. in. The furnace flues are usually
made in sections from 3 to 3-1/2 ft. long. Each section consists of
one plate bent into a cylindrical form, the longitudinal joint being
welded, and is flanged at both ends, the various pieces being joined
together by an "Adamson" joint (fig. 1.). It will be seen that these
joints do not expose either rivets or double thickness of plate to the
action of the fire; they further serve as stiffening rings to prevent
collapse of the flue. In most of these boilers the heating surface is
increased by fitting in the furnace flues a number of "Galloway"
tubes. These are conical tubes, made with a flange at each end, by
means of which they are connected to the furnace plate. They are so
proportioned that the diameter of the large end of the tube is
slightly greater than that of the flange of the small end; this
enables them to be readily removed and replaced if necessary. These
tubes not only add to the heating surface, but they stiffen the flue,
promote circulation of the water in the boiler, and by mixing up the
flue gases improve the evaporative efficiency.

In the "Galloway" boiler the two furnaces extend only for about 9 or
10 ft. into the boiler, and lead into a large chamber or flue in which
a number of "Galloway" tubes are fitted, and which extends from the
furnace end to the end of the boiler. A cross section of this flue
showing the distribution of the Galloway tubes is shown in fig. 2.
When boilers less than about 6-1/2 ft. in diameter are needed, a
somewhat similar type to the Lancashire boiler is used containing only
one furnace. This is called a "Cornish" boiler.

In all three types of boiler the brickwork is constructed to form one
central flue passing along the bottom of the boiler and two side flues
extending up the side nearly to the water-level. A cross section of
the brickwork is shown in fig. 2. The usual arrangement is for the
flue gases to be divided as they leave the internal flue; one-half
returns along each side flue to the front of the boiler, and the whole
then passes downwards into the central flue, travelling under the
bottom of the boiler until the gases again reach the back end, where
they pass into the chimney. In a few cases the arrangement is
reversed, the gases first passing along the bottom flue and returning
along the side flues. This latter arrangement, whilst promoting a more
rapid circulation of water, has the disadvantage of requiring two
dampers, and it is not suitable for those cases in which heavy
deposits form on the bottoms of the boilers.

Vertical.

Where floor space is limited and also for small installations, other
forms of cylindrical boilers are used, most of them being of the
vertical type. That most commonly used is the simple vertical boiler,
with a plain vertical fire-box, and an internal smoke stack traversing
the steam space. The fire-box is made slightly tapering in diameter,
the space between it and the shell being filled with water. In all but
the small sizes cross tubes are generally fitted. These are made about
9 in. in diameter of 3/8-in. plate flanged at each end to enable them
to be riveted to the fire-box plates. They are usually fitted with a
slight inclination to facilitate water circulation. and a hand-hole
closed by a suitable door is provided in the outer shell opposite to
each tube for cleaning purposes. A boiler of this kind is illustrated
in fig. 4. This form is often used on board ship for auxiliary
purposes. Where more heating surface is required than can be obtained
in the cross-tube boiler other types of vertical boiler are employed.
For instance, in the "Tyne" boiler (fig. 5) the furnace is
hemispherical, and the products of combustion are led into an upper
combustion chamber traversed by four or more inclined water-tubes of
about 9 in. diameter and by several vertical water-tubes of less
diameter. In the "Victoria" boiler made by Messrs Clarke, Chapman &
Co., and illustrated in fig. 6, the furnace is hemispherical; the
furnace gases are led to an internal combustion chamber, and thence
through numerous horizontal smoke-tubes to a smoke-box placed on the
side of the boiler. In the somewhat similar boiler known as the
"Cochran," the combustion chamber is made with a "dry" back. Instead
of a water space at the back of the chamber, doors lined with
firebrick are fitted. These give easy access to the tube ends.

Marine.

The cylindrical multitubular return tube boiler is in almost universal
use in merchant steamers. It is made in various sizes ranging up to 17
ft. in diameter, the usual working pressure being from 160 to 200 lb
per sq. in., although in some few cases pressures of 265 lb. per sq.
in. are in use. These boilers are of two types, double- and
single-ended. In single-ended boilers, which are those most generally
used, the furnaces are fitted at one end only and vary in number from
one in the smallest boiler to four in the largest. Three furnaces are
the most usual practice. Each furnace generally has its own separate
combustion chamber. In four furnace boilers, however, one chamber is
sometimes made common to the two middle furnaces, and sometimes one
chamber is fitted to each pair of side furnaces. In double-ended
boilers furnaces are fitted at each end. In some cases each furnace
has a separate combustion chamber, but more usually one chamber is
made to serve for two furnaces, one at each end of the boiler. The two
types of boilers are shown in figs. 7 and 8, which illustrate boilers
made by Messrs D. Rowan & Co. of Glasgow, and which may be taken as
representing good modern practice. The furnaces used in the smaller
sizes are often of the plain cylindrical type, the thickness of plate
varying from 3/8 in. up to 3/4 in. according to the diameter of the
furnace and the working pressure. Occasionally furnaces with "Adamson"
joints similar to those used in Lancashire boilers are employed, but
for large furnaces and for high pressures corrugated or ribbed
furnaces are usually adopted. Sketches of the sections of these are
shown in fig. 9. The sections of the Morison, Fox and Deighton types
are made from plates originally rolled of a uniform thickness, made
into a cylindrical form with a welded longitudinal joint and then
corrugated, the only difference between them being in the shapes of
the corrugations. In the other three types the plates from which the
furnaces are made are rolled with ribs or thickened portions at
distances of 9 in. These furnaces are stronger to resist collapse than
plain furnaces of the same thickness, and accommodate themselves more
readily to changes of temperature.

There are two distinct types of connexion between the furnaces and the
combustion chambers. In one, shown in fig. 8, the furnace is flanged
at the crown portion for riveting to the tube plate, and the lower
part of the furnace is riveted to the "wrapper" or side plate of the
combustion chamber. In the other type, shown in fig. 7, and known
generally as the "Gourlay back end," the end of the furnace is
contracted into an oval conical form, and is then flanged outwards
round the whole of its circumference. The tube plate is made to extend
to the bottom of the combustion chamber, and the furnace is riveted to
the tube plate. The advantage of the Gourlay back end is that in case
of accident to the furnace it can be removed from the boiler and be
replaced by one of the same design without disturbing the end plates,
which is not possible with the other design. The Gourlay back end,
however, is not so stiff as the other, and more longitudinal stays are
required in the boiler.

The flat sides and backs of the combustion chambers are stayed either
to one another or to the shell of the boiler by numerous screw stays
which are screwed through the two plates they connect, and which are
nearly always fitted with nuts inside the combustion chambers. The
tops of the chambers are usually stayed by strong girders resting upon
the tube plates and chamber back plates. In a few cases, however, they
are stayed by vertical stays attached to T bars riveted to the boiler
shell. A few boilers are made in which the chamber tops are
strengthened by heavy transverse girder plates. The end plates of the
boiler in the steam space and below the combustion chambers are stayed
by longitudinal stays passing through the whole length of the boiler
and secured by double nuts at each end. The tube plates are
strengthened by stay tubes screwed into them.

Where natural or chimney draught is used the tubes are generally made
3 or 3-1/4 in. outside diameter and are rarely more than 7 ft. long,
but where "forced" draught is employed they are usually made 2-1/2 in.
diameter and 8 to 8-1/2 ft. long. A clear space of 1-1/4 in. between
the tubes is almost always arranged for, irrespective of size of
tubes.

Stay tubes are screwed at both ends, the threads of the two ends being
continuous so that they can be screwed into both tube plates;
occasionally nuts are fitted to the front ends. The stay tubes are
expanded into the plates and then beaded over.

Locomotive.

The locomotive boiler consists of a cylindrical barrel attached to a
portion containing the fire-box, which is nearly rectangular both in
horizontal and vertical section. The fire-box sides are stayed to the
fire-box shell by numerous stays about 1 in. in diameter, usually
pitched 4 in. apart both vertically and horizontally. The top of the
fire-box in small boilers is stayed by means of girder stays running
longitudinally and supported at the ends upon the tube plate and the
opposite fire-box plate. In some boilers the girders are partly
supported by slings from the crown of the boiler. In larger boilers
the crown of the boiler above the fire-box is made flat and the
fire-box crown is supported by vertical stays connecting it with the
shell crown. Provision is generally made for the expansion of the tube
plate, which is of copper, by allowing the two or three cross rows of
stays nearest the tube plate to have freedom of motion upwards but not
downwards. The ordinary tubes are usually 1-3/4 in. diameter. The
fire-bars are generally, though not always, made to slope downwards
away from the fire door, and just below the lowest tubes a fire-bridge
or baffle is fitted, extending about half-way from the tube plate to
the fire-door side of the fire-box. In some cases water-tubes are
fitted, extending right across the fire-box. In a boiler for the
London & South-Western Railway Co., having a grate area of 31.5 sq.
ft. and a total heating surface of 2727 sq. ft., there are 112
water-tubes each 2-3/4 in. diameter. These are arranged in two
clusters, each containing 56, one set being placed above the
fire-bridge, and the other set nearer the fire-door end of the boiler.
The water-tubes are of seamless steel, and are expanded into the
fire-box side plates. In way of these tubes the outer shell side
plates are supported by stay bars passing right through the
water-tubes. The usual pressure of locomotive boilers is about 175
lb. to 200 lb. per sq. in.

A good example of an express locomotive boiler is shown in fig. 10. In
this case the grate area is 30.9 sq. ft. and the heating surface 2500
sq. ft. The barrel is 5 ft. 6 in. diameter, 16 ft. long between tube
plates. The fire-box crown is stayed by vertical stays extending to
the shell crown, except for the three rows of stays nearest the tube
plates. These are supported by cross girders resting upon brackets
secured to the outer shell.

Babcock and Wilcox stationary.

_Water-Tube Boilers._--The "Babcock & Wilcox" boiler, as fitted for
land purposes, and illustrated in fig. 11, consists of a horizontal
cylinder forming a steam chest, having dished ends and two specially
constructed cross-boxes riveted to the bottom. Under the cylinder is
placed a sloping nest of tubes, under the upper end of which is the
fire. The sides and back of the boiler are enclosed in brickwork up to
the height of the centre of the horizontal cylinder and the front is
fitted with an iron casing lined with brick at the lower part.
Suitable brickwork baffles are arranged between the tubes themselves,
and between the nests of tubes and the cylinder, to ensure a proper
circulation of the products of combustion, which are made to pass
between the tubes three times. The nest of tubes consists of several
separate elements, each formed by a front and back header made of
wrought steel of sinuous form connected by a number of tubes. The
upper ends of the front headers are connected by short tubes to the
front cross-box of the horizontal cylinder, the lower ends being
closed. The upper ends of the back headers are connected by longer
pipes to the back cross-box, and their lower ends by short pipes to a
horizontal mud drum to which a blow-off cock and pipe are attached.
The headers are furnished with holes on two opposite sides; those on
one side form the means of connexion between the headers and tubes,
and the others allow access for fixing the tubes in position and
cleaning. The outer holes are oval, and closed by special fittings
shown in fig. 18, the watertightness of the joints being secured by
the outer cover plates. The holes being oval, the inside fitting can
be placed in position from outside, and it is so made as to cover the
opening and prevent any great outrush of steam or water should the
bolt break. Any desired working pressure can be provided for in these
boilers; in some special cases it rises as high as 500 lb. per sq.
in., but a more usual pressure is 180 lb. Like all water-tube
boilers, they require to be frequently cleaned if impure feed-water is
used, but the straightness of their tubes enables their condition to
be ascertained at any time when the boiler is out of use, and any
accumulation of scale to be removed. The superheaters, which are
frequently fitted, consist of two cross-boxes or headers placed
transversely under the cylindrical drum and connected by numerous
C-shaped tubes. They are situated between the tubes and the
steam-chest, and are exposed to the heat of the furnace gases after
their first passage across the tubes. The steam is taken by an
internal pipe passing through the bottom of the drum into the upper
cross-box, then through the C tubes into the lower box, and thence to
the steam pipe. When steam is being raised, the superheater is flooded
with water, which is drained out through a blow-off pipe before
communication is opened with the steam-pipe. In large boilers of this
type, two steam-chests are placed side by side connected together by
two cross steam pipes and by the mud drum. Each, however, has its own
separate feed supply. The largest boiler made has two steam chests
4-1/2 ft. diameter by 25-1/2 ft. long, a grate surface of 85 sq. ft.,
and a total heating surface of 6182 sq. ft.

Stirling.

Another type of water-tube boiler in use for stationary purposes is
the "Stirling" (fig. 12). This boiler consists of four or five
horizontal drums, of which the three upper form the steam-space, and
the one or two lower contain water. The lower drums, where two are
fitted, are connected to each other at about the middle of their
height by horizontal tubes, and to the upper drums by numerous nearly
vertical tubes which form the major portion of the heating surfaces.
The central upper drum is at a slightly higher level than the others,
and communicates with that nearest the back of the boiler by a set of
curved tubes entirely above the water-level, and with the front drum
by two sets--the upper one being above and the lower below the
water-level. The whole boiler is enclosed in brickwork, into which the
supporting columns and girders are built. Brickwork baffles compel the
furnace gases to take specified courses among the tubes. It will be
seen that the space between the boiler front and the tubes form a
large combustion chamber into which all the furnace gases must pass
before they enter the spaces between the tubes; in this chamber a
baffle-bridge is sometimes built. Another chamber is formed between
the first and second sets of tubes. The feed-water enters the back
upper drum, and must pass down the third set of tubes into the lower
drum before it reaches the other parts of the boiler. Thus the coldest
water is always where the temperature of the furnace gases is lowest;
and as the current through the lower drum is slight, the solid matters
separated from the feed-water while its temperature is being raised
have an opportunity of settling to the bottom of this drum, where the
heating is not great and where therefore their presence will not be
injurious. When superheaters are required, they are made of two drums
connected by numerous small tubes, and are somewhat similar in
construction to the boiler proper. The superheater is placed between
the first and second sets of tubes, where it is exposed to the furnace
gases before too much heat has been taken from them. Arrangements are
provided for flooding the superheater while steam is being raised, and
for draining it before the steam is passed through it.

Woodeson.

A somewhat similar boiler is made by Messrs. Clarke, Chapman & Co.,
and is known as the "Woodeson" boiler (fig. 13). It consists of three
upper drums placed side by side connected together by numerous short
tubes, some above and some below the water-level, and of three smaller
lower drums also connected by short cross tubes. The upper and lower
drums are connected by numerous nearly vertical straight tubes. The
whole is enclosed in firebrick casing. The design permits of the
insides of all the tubes being readily inspected, and also of any tube
being taken out and renewed without displacing any other part of the
boiler.

Belleville.

The earliest form of water-tube boiler which came into general use in
the British navy is the Belleville. Two views of this boiler are shown
in fig. 14. It is composed of two parts, the boiler proper and the
"economizer." Each of these consists of several sets of elements
placed side by side; those of the boiler proper are situated
immediately over the fire, and those of the economizer in the uptake
above the boiler, the intervening space being designed to act as a
combustion chamber. Each element is constructed of a number of
straight tubes connected at their ends by means of screwed joints to
junction-boxes which are made of malleable cast iron. These are
arranged vertically over one another, and except in the case of the
upper and lower ones at the front of the boiler, each connects the
upper end of one tube with the lower end of the next tube of the
element. The boxes at the back of the boiler are all close-ended, but
those at the front are provided with a small oval hole, opposite to
each tube end, closed by an internal door with bolt and cross-bar; the
purpose of these openings is to permit the inside of the tubes to be
examined and cleaned. The lower front box of each element of the
boiler proper is connected to a horizontal cross-tube of square
section, called a "feed-collector," which extends the whole width of
the boiler. When the boiler is not in use, any element can be readily
disconnected and a spare one inserted. The lower part of the
steam-chest is connected to the feed-collector by vertical pipes at
each end of the boiler, and prolongations of these pipes below the
level of the feed-collector form closed pockets for the collection of
sediment. The tubes are made of seamless steel. They are generally
about 4-1/2 in. in external diameter: the two lower rows are 3/8 in.
thick, the next two rows 5/16 and the remainder about 1/5 in. The
construction of the economizer is similar to that of the boiler
proper, but the tubes are shorter and smaller, being generally about
2-3/4 in. in diameter. The lower boxes of the economizer elements are
connected to a horizontal feed pipe which is kept supplied with water
by a feed-pumping engine, and the upper boxes are connected to another
horizontal pipe from which the heated feed-water is taken into the
steam-chest. Both the boiler proper and the economizer are enclosed in
a casing which is formed of two thicknesses of thin iron separated by
non-conducting material and lined with firebrick at the part between
the fire-bar level and the lower rows of tubes. Along the front of the
boiler, above the level of the firing-doors, there is a small tube
having several nozzles directed across the fire-grate, and supplied
with compressed air at a pressure of about 10 lb. per sq. in. In this
way not only is additional air supplied, but the gases issuing from
the fire are stirred up and mixed, their combustion being thereby
facilitated before they pass into the spaces between the tubes. A
similar air-tube is provided for the space between the boiler proper
and the economizer. Any water suspended in the steam is separated in a
special separator fitted in the main steam-pipe, and the steam is
further dried by passing through a reducing-valve, which ensures a
steady pressure on the engine side of the valve, notwithstanding
fluctuations of pressure in the boiler. The boiler pressure is usually
maintained at about 50 lb. per sq. in. in excess of that at which the
engines are working, the excess forming a reservoir of energy to
provide for irregular firing or feeding.

Niclausse.

Another type of large-tube boiler which has been used in the British
and in other navies is the "Niclausse," shown in fig. 15. It is also
in use on land in several electric-light installations. It consists of
a horizontal steam-chest under which is placed a number of elements
arranged side by side over the fire, the whole being enclosed in an
iron casing lined with firebrick where it is exposed to the direct
action of the fire. Each element consists of a header of rectangular
cross-section, fitted with two rows of inclined close-ended tubes,
which slope downwards towards the back of the boiler with an
inclination of 6 deg. to the horizontal. The headers are usually of
malleable cast iron with diaphragms cast in them, but sometimes steel
has been employed, the bottoms being closed by a riveted steel plate,
and the diaphragms being made of the same material. The headers are
bolted to socket-pieces which are riveted to the bottom of the
steam-chest, so that any element may be easily removed. The tube-holes
are accurately bored, at an angle to suit the inclination of the
tubes, through both the front and back of the headers and through the
diaphragm, those in the header walls being slightly conical. The tubes
themselves, which are made of seamless steel, are of peculiar
construction. The lower or back ends are reduced in diameter and
screwed and fitted with cap-nuts which entirely close them. The front
ends are thickened by being upset, and the parts where they fit into
the header walls and in the diaphragm are carefully turned to gauge.
The upper and lower parts of the tubes between these fitting portions
are then cut away, the side portions only being retained, and the end
is termed a "lanterne." A small water-circulating tube of thin sheet
steel, fitted inside each generating tube, is open at the lower end,
and at the other is secured to a smaller "lanterne," which, however,
only extends from the front of the header to the diaphragm. This
smaller "lanterne" closes the front end of the generating tube. The
whole arrangement is such that when the tubes are in place only the
small inner circulating tubes communicate with the space between the
front of the header and the diaphragm, while the annular spaces in the
generating tubes around the water-circulating tubes communicate only
with the space between the diaphragm and the back of the header. The
steam formed in the tubes escapes from them into this back space,
through which it rises into the steam-chest, whilst the space in the
front of the header always contains a down-current of water supplying
the inner circulating tubes. The tubes are maintained in position by
cross-bars, each secured by one stud-bolt screwed into the header
front wall, and each serving to fix two tubes. The products of
combustion ascend directly from the fire amongst the tubes, and the
combustion is rendered more complete by the introduction of jets of
high-pressure air immediately over the fire, as in the "Belleville"
boiler.

Durr.

The "Durr" boiler, in use in several vessels in the German navy, and
in a few vessels of the British navy, in some respects resembles the
"Niclausse." The separate headers of the latter, however, are replaced
by one large water-chamber formed of steel plates with welded joints,
and instead of the tubes being secured by "lanternes" to two plates
they are secured to the inner plate only by conical joints, the holes
in the outer plate being closed by small round doors fitted from the
inside. In fixing the tubes each is separately forced into its
position by means of a small portable hydraulic jack. The lower ends
of the caps are closed by cap-nuts made of a special heat-resisting
alloy of copper and manganese. Circulation is provided for by a
diaphragm in the water-chamber and by inner tubes as in the Niclausse
boiler. Baffle plates are fitted amongst the tubes to ensure a
circulation of the furnace gases amongst them. Above the main set of
tubes is a smaller set arranged horizontally, and connected directly
to the steam receiver. These are fitted with internal tubes, and an
internal diaphragm is provided so that steam from the chest circulates
through these tubes on its way to the stop-valves. This supplementary
set of tubes is intended to serve as a superheater, but the amount of
surface is not sufficient to obtain more than a very small amount of
superheat.

Yarrow.

The Yarrow boiler (fig. 16) is largely in use in the British and also
in several other navies. It consists of a large cylindrical steam
chest and two lower water-chambers, connected by numerous straight
tubes. In the boilers for large vessels all the tubes are of 1-3/4 in.
external diameter, but in the large express boilers the two rows
nearest to the fire on each side are of 1-1/4 in. and the remainder of
1 in. diameter. They are arranged with their centres forming
equilateral triangles, and are spaced so that they can be cleaned
externally both from the front of the boiler and also cross-ways in
two directions. In some boilers the lower part of the steam-chest is
connected with the water-chambers by large pipes outside the casings
with the view of improving the circulation.

The largest size of single-ended large tube boiler in use has a steam
drum 4 ft. 2 in. diameter, a grate area of 73.5 sq. ft. and 3750 sq.
ft. of heating surface, but much larger double-ended boilers have been
made, these being fired from both ends.

In most of the boilers made, access to the inside is obtained by
manholes in the steam-chest and water-chamber ends, but in the smaller
sizes fitted in torpedo boats the water-chambers are too small for
this, and they are each arranged in two parts connected by a bolted
joint, which makes all the tube ends accessible.

The Babcock & Wilcox marine boiler (fig. 17) is much used in the
American and British navies, and it has also been used in several
yachts and merchant steamers. It consists of a horizontal cylindrical
steam-chest placed transversely over a group of elements, beneath
which is the fire, the whole being enclosed in an iron casing lined
with firebrick. Each element consists of a front and back header
connected by numerous water-tubes which have a considerable
inclination to facilitate the circulation. The upper ends of the front
headers are situated immediately under the steam-chest and are
connected to it by short nipples; by a similar means they are
connected at the bottom to a pipe of square section which extends
across the width of the boiler. Additional connexions are made by
nearly vertical tubes between this cross-pipe and the bottom of the
steam-chest. The back headers are each connected at their upper ends
by means of two long horizontal tubes with the steam-chest, the bottom
ends of the headers being closed. The headers are made of wrought
steel, and except the outer pairs, which are flat on the outer
portions, they are sinuous on both sides, the sinuosities fitting into
one another. The tubes are of two sizes, the two lower rows and the
return tubes between the back headers and steam-chest being 3-15/16
in. outside diameter, and the remaining tubes 1-13/16 in. The small
tubes are arranged in groups of two or four to nearly all of the
sinuosities of the headers, the purpose of this arrangement being to
give opportunities for the furnace gases to become well mixed
together, and to ensure their contact with the heating surfaces.
Access for securing the tubes in the headers is provided by a hole
formed on the other side of the header opposite each of the tubes,
where they are grouped in fours, and by one larger hole opposite each
group of two tubes. The larger holes are oval, and are closed by
fittings similar to those used in the land boiler (fig. 18). The
smaller holes are conical, with the larger diameter on the inside,
and are closed by special conical fittings: the conical portion and
bolt are one forging, and the nut is close-ended. In case of the
breakage of the bolt, the fitting would be retained in place by the
steam-pressure. A set of firebrick baffles is placed so as to cover
rather more than half of the spaces between the upper of the two
bottom rows of large tubes, and another set of baffles covers about
two-thirds of the spaces between the upper small tubes. Vertical
baffles are also built between the smaller tubes, as shown in the
longitudinal section. These baffles compel the products of combustion
to circulate among the tubes in the direction shown by the arrows.
Experience has shown that this arrangement gives a better evaporative
efficiency than where the furnace gases are allowed to pass unbaffled
straight up between the tubes. The boilers are usually fitted in pairs
placed back to back, and one side of each is always made accessible.
On this side the casing is provided with numerous small doors, through
any of which a steam jet can be inserted for the purpose of sweeping
the tubes.

Express boilers.

A class of water-tube boilers largely in use in torpedo-boat
destroyers and cruisers, where the maximum of power is required in
proportion to the total weight of the installation, is generally known
as express boilers. In these the tubes are made of smaller diameter
than those used in the boilers already described, and the boilers are
designed to admit of a high rate of combustion of fuel obtained by a
high degree of "forced draught." Of these express boilers the Yarrow
is of similar construction to the large tube Yarrow boiler already
described with the exception that the tubes are smaller in diameter
and much more closely arranged.

Normand.

In the Normand boiler (fig. 19) there are three chambers as in the
Yarrow, connected together by a large number of bent tubes which form
the heating surface, and also connected at each end by large outside
circulating tubes. The two outer rows of heating tubes on each side
are arranged to touch one another to nearly their whole length so as
to form a "water-wall" for the protection of the outer casing. They
enter the steam-chest at about the water-level. The two inner rows of
tubes, which are bent to the form shown in the figure, also form a
water-wall for the larger portion of the length of the boiler, and
thus compel the products of combustion to pass in a definite course
amongst all the tubes. In the Blechynden and White-Foster boilers
there are also three chambers connected by bent tubes, the curvature
being so arranged that in the former boiler any of the tubes can be
taken out of the boiler through small doors provided in the upper part
of the steam-chest, and in the White-Foster boiler they can be taken
out through the manhole in the end of the steam-chest.

Reed.

In the Reed boiler the tubes are longer and more curved than in the
Normand boiler, and there are no "water-walls," the products of
combustion passing from the fire-grate amongst all the tubes direct to
the chimney. The special feature of the boiler is that each tube,
instead of being expanded into the tube plate, is fitted at each end
with specially designed screw and nut connexions to enable them to be
quickly taken out and replaced if necessary. At their lower ends the
tubes are reduced in diameter to enable smaller chambers to be used
than would otherwise be necessary. Provision is made for access to the
lower tube ends by means of numerous doors in the water-chambers.
Access to the top ends is obtained in the steam-chest.

Thornycroft.

Messrs John I. Thornycroft & Co. make two forms of express boiler. One
called the Thornycroft boiler consists of three chambers connected by
tubes which are straight for the major portion of their length but
bent at each end to enable them to enter the steam- and water-chambers
normally. The outer rows of tubes form "water-walls" at their lower
parts, but permit the passage of the gases between them at their upper
ends. Similarly the inner rows form "water-walls" at their upper
parts, but are open at the lower ends. The products of combustion are
thus compelled to pass over the whole of the heating surfaces. The
fire-rows of tubes in this boiler are made 1-3/8 in. outside diameter
and the remainder are made 1-3/8 in. diameter. Large outside
circulating pipes are provided at the front end of the boiler.

Thornycroft-Schulz.

In the other type of boiler, known as the Thornycroft-Schulz boiler
(fig. 20), there are four chambers, and the fire-grate is arranged in
two separate portions. The two outermost rows of tubes on each side
are arranged to form water-walls at their lower part, and permit the
gases to pass between them at the upper part. The rows nearest the
fires are arranged similarly to those in the Thornycroft boiler.
Circulation in the outer sets of tubes is arranged for by outer
circulating pipes of large diameter connecting the steam- and
water-chambers. For the middle water-chamber several nearly vertical
down-comers are provided in the centre of the boiler. Boilers of this
type are extensively used in the British and German navies.

_Material of Boilers._--In ordinary land boilers and in marine boilers of all types the plates and stays are almost invariably made of mild steel. For the shell plates and for long stays, a quality having a tensile strength ranging from 28 to 32 tons per sq. in. is usually employed, and for furnaces and flues, for plates which have to be flanged, and for short-screwed stays, a somewhat softer steel with a strength ranging from 26 to 30 tons per sq. in. is used. The tubes of ordinary land and marine boilers are usually made of lap-welded wrought iron. In water-tube boilers for naval purposes seamless steel tubes are invariably used. In locomotive boilers the shells are generally of mild steel, the fire-box plates of copper (in America of steel), the fire-box side stays of copper or special bronze, and other stays of steel. The tubes are usually of brass with a composition either of two parts by weight of copper to one of zinc or 70% copper, 30% zinc; sometimes, however, copper tubes and occasionally steel tubes are used. Where water tubes are used they are made of seamless steel.

_Boiler Accessories._--All boilers must be provided with certain mountings and accessories. The water-level in them must be kept above the highest part of the heating surfaces. In some land boilers, and in some of the water-tube boilers used on shipboard, the feeding is automatically regulated by mechanism actuated by a float, but in these cases means of regulating the feed-supply by hand are also provided. In most boilers hand regulation only is relied upon. The actual level of water in the boiler is ascertained by a glass water-gauge, which consists of a glass tube and three cocks, two communicating directly with the boiler, one above and one below the desired water-level, and the third acting as a blow-out for cleaning the gauge and for testing its working. Three small try-cocks are also fitted, one just at, one above, and one below the proper water-level. The feeding of the boiler is sometimes performed by a pump driven from the main engine, sometimes by an independent steam-pump, and sometimes by means of an injector. The feed-water is admitted by a "check-valve," the lift of which is regulated by a screw and hand-wheel, and which when the feed-pump is not working is kept on its seating by the boiler pressure.

Every boiler is in addition supplied with a steam-gauge to indicate the steam-pressure, with a stop-valve for regulating the admission of steam to the steam-pipes, and with one or two safety-valves. These last in stationary boilers usually consist of valves kept in their seats against the steam-pressure in the boiler by levers carrying weights, but in marine and locomotive boilers the valves are kept closed by means of steel springs. One at least of the safety-valves is fitted with easing gear by which it can be lifted at any time for blowing off the steam. Blow-out cocks are fitted for emptying the boiler.