Modern brickmaking

MODERN BRICKMAKING

Plain brick.

Pressed brick
showing "frog

Hollow brick.

o o o o o

o © o o
o o o o o

Perforated brick.

Jamb.

Arch brick or
Wedge.

Diamond stretcher.

X

Plinth brick.

Dog-tooth stretcher.

Fancy squints, or stop bricks, for corners, etc.

Half-moon stretcher.

Stable brick.

Channel brick.

String course brick. Coping brick. String course brick.

n

Ventilator or air brick.

MODERN

BRICKMAKING

ALFRED B. SEARLE.

CONSULTING EXPERT ON CLAYS AND CLAY-PRODUCTS,
LECTURER ON BRICKMAKING UNDER THE CANTOR BEQUEST, ETC. ETC.

WITH TWO HUNDRED AND SIXTY ILLUSTRATIONS

LONDON
SCOTT, GREENWOOD & SON

"THE POTTERY GAZETTE" OFFICES

8 BROADWAY, LUDGATE HILL, B.C.
ign

[All rights reserved}

D. VAN NOSTRAND COMPANY

NKW YORK

PREFACE

THE brickmaking industry is one of the oldest known, but
most of the modern methods of manufacture are of such recent
growth that no single volume contains a description of the most
important ones used in this country. The result is that many
brickmakers are using machinery and kilns of which they have
but little knowledge, and they are labouring under the disad-
vantage of not knowing what progress has been made.

In the present volume, the Author has endeavoured to con-
dense the results of a wide practical experience of all the better-
known processes, machines, and kilns now in use — both in this
country and on the Continent — into convenient limits, and to
express this information in terms which shall be readily under-
stood by all interested in the subject. In other words, he has
aimed at clearing up ideas regarding the various processes and
appliances used in modern brickmaking and to remove various
obscurities at present prevailing in many minds.

In this work the Author has had the hearty co-operation
of all the chief firms who supply machines, kilns, and other
requirements of the brickmaker, together with the assistance of
numerous authors of papers, booklets, and larger treatises (both
British and Foreign). Their names will usually be found
attached to the illustrations, though the publication of anony-
mous articles in the trade journals prevents acknowledgment in
some cases.

Whilst it is not possible to give a complete list, the Author
hereby acknowledges, with thanks, his indebtedness to all who
have been of assistance to him in the manner indicated, as well
as to various members of his staff, without whose aid this
volume could not so readily have been written.

VI PREFACE

From so large a mass of material, it has often been neces-
sary to descrjbe only one machine, or kiln, of each type, indi-
cating, more or less fully, the points of difference between the
one chosen and others equally well known. In deciding which
machine, or kiln, to select for such fuller description, the Author
has been guided chiefly by his personal knowledge and experi-
ence, prominence being given, whenever possible, to those
designers or firms to whom the credit of introducing the pro-
cess under consideration is primarily due.

The experienced brickmaker who wishes to develop a new
bed of clay, or shale, as well as the capitalist unacquainted with
the details of the various appliances, is often placed at a dis-
advantage when endeavouring to choose between the claims of
various firms. After studying such details as are given in the
present volume, such prospective purchasers should be able to
select a given appliance or process without so serious a risk of
loss as if they were ignorant of the different materials to which
each process is best adapted. It is not to be supposed that the
study of any book will place the reader in the position of an
expert, -but a careful perusal of the present work will, it is-
hoped, enable any intelligent person acquainted with the rudi-
ments of the subject, to see the reasonableness or otherwise of
suggestions made to him by various persons and to enable hinx
to make use of such new methods as are mentioned in it.

To students, builders, civil^ engineers, andjo those interested
in the development of estates, as well as to brick manufacturersr
the present volume will, it is anticipated, prove to contain a
useful summary of the chief matters of importance in connexion
with the various branches of brickmaking. Those who wish
for further information on the testing, analysis and scientific
control of the materials and processes involved should consult
special works (by the author and others), in which these matters-
are more fully described.

ALFRED B. SEABLE.

/ THE WHITE BUILDING,
SHEFFIELD.

CONTENTS

PAGE

Preface . . . . , ... . ... . . . v

CHAPTER I.

The Nature and Selection of Clays — Their Special Suitability for Certain
Purposes — The Colour and Characteristics of Various Bricks — Sand,
Breeze, and other Materials used ........ 1

CHAPTER II.

The General Manufacture of Bricks . . 20

CHAPTER III.
Hand- Brickmaking Processes . . . '. 4 . .'.... . 39

CHAPTER IV.

Plastic Moulding by Machinery — Wire-cut Bricks — Mixers and Feeders —
Expression Rolls — Pug-Mills, Mouthpiece Presses and Auger Machines
— Cutting Tables — Represses — Dryers 68

CHAPTER V.
The Stiff-Plastic Process . 177

CHAPTER VI.
The Semi-Dry or Semi-Plastic Process 219

CHAPTER VII.

The Dry or Dust Process . . . < 240

vii

Vlll CONTENTS

CHAPTER VIII.

PAGE

Kilns— Setting and Burning . . . . '. . \ . ,. .243

CHAPTER IX.
Vitrified Bricks for Special Work . . . . 36S

CHAPTER X.

Fire-Bricks and Blocks . . . . ; * < V . . . . . 373

CHAPTER XI.
Glazed Bricks . . . . , . ... 397

CHAPTER XII.
Perforated, Radial, and Hollow Bricks and Blocks— Fireproof Flooring . 412

CHAPTER XIII.
Moulded and Ornamental Bricks . . . .... . . 418

CHAPTER XIV.
Drying Raw Clay . . . . . . ..'... . 420

CHAPTER XV.
Sources of Difficulty and Loss '. ' .- , 424

Index

429

CHAPTER I.

THE NATURE AND SELECTION OF CLAYS— THEIR SPECIAL
SUITABILITY FOR CERTAIN PURPOSES— SAND, BREEZE,
AND OTHER MATERIALS USED.

BRICKS and tiles may be made from a large number of different
kinds of material but they must usually possess a certain amount
of plasticity.

The plasticity of clay is a property which distinguishes it
from nearly all other mineral substances, and may be denned
as the property of a body which enables it to absorb water in
such a manner that the properly moistened body yields to
mechanical pressure, but, when the pressure has been removed,
the shape of the body remains as though the pressure were still
acting upon it.

The cause of plasticity i is practically unknown, but it appears
to be closely related to the ability of each clay particle to sur-
round itself with a coating of water sufficiently large to produce
plasticity, but insufficient to cause the body to lose its shape when
the external pressure is removed.

Clay or brick earth is almost the only substance of a mineral
nature which possesses this plasticity, and then only when it is
what geologists term " secondary clay," that is to say, clay which
has been carried a considerable distance from the place where
it was originally formed.

No satisfactory definition of " clay " is possible owing to its
peculiar nature, though the development of plasticity when wet
is its main characteristic. The term " brick earth" is much
more suitable for general use, as meaning those clays, or mixtures
of clay with other materials, which can be employed in the
manufacture of bricks and tiles.

Strictly speaking, the term " clay " should be reserved for a
certain hydrated silicate of alumina, or at any rate for earths
chiefly composed of this material, unless the word is prefixed by
another as "boulder-clay," "sandy-clay," etc.

1

2 MODERN BRICKMAKING

The term " clay substance " is usually employed to denote
the essential material in all clays, but the composition of this
varies so greatly when different clays are treated by different
processes for removing the other ingredients that the term has
acquired a variety of meanings according to the person employing
it. Thus Seger (who originated the term) employed it to represent
a theoretical material, the nearest practical approach to which
was obtained by carefully washing china clay and then treating
this purified product with sulphuric acid, soda, etc. In this way
he obtained a series of analytical results which were fairly
constant for most varieties of clay, though the pure uclay
substance " could only be won from certain clays ; its proportion
in the others was deduced from the analysis of the partially
purified material.

The use of the term "clay substance " for the finest particles
obtained by washing a commercial clay is unsatisfactory and
should not be used. Much reform is necessary in the nomen-
clature of clays, as at present there is no agreement as to the
precise meaning of " clay," "clay substance," and other terms.

"Primary clays " (i.e. those found near to the place of forma-
tion by rock decomposition) are usually lean or deficient in
plasticity. " China clays " (Kaolins) are of this kind.

Under the action of water and other geological agencies,
these slightly plastic primary clays may be ground, carried
about from one place to another, undergoing purification or
contamination in the process, until they are finally deposited in
a more plastic condition in beds or seams, when they form
secondary deposits as surface-clay, bed-clay, shale, fire-clay,
boulder-clay, etc.

The degree of purity of a clay deposit must depend on the
nature of the treatment it has received since its first formation
by the breaking down of the felspar rocks which are, as far as
is known, the original sources of all clays.

Red clays are those which have been formed from felspar
rocks rich in iron oxides, or which have taken up this substance
during their conversion into plastic clays.

When no more than a very small proportion of iron oxide, lime,
magnesia, and alkalies is present a fire-clay or kaolin is produced
and burns to a white or cream colour according to the proportion
of colouring oxide present.

The exact processes which occur in the formation and de-
position of clays is only of secondary interest to the brick and

THE NATUBE AND SELECTION OF CLAYS 8

tile maker ; he has to deal with the clay deposits at his disposal,
and has no control of their formation. It is very important,
however, that he should know a little of the origin of any
deposit he is called upon to work, or about which his opinion is
being asked, as clay deposited by rivers must usually be worked
differently from that deposited in a lake, the water from which
has afterwards disappeared.

As the primary clays (kaolins) are often very pure, they are
not usually employed for brickmaking and need not be considered
at present, though some makers have found considerable profit
in utilizing the waste material produced by the washing of these
clays.

The secondary clays may be divided into three groups: (a)
river deposits (fluviatile) ; (b) lake deposits (lacustrine) ; (c) sea
deposits (marine).

River Deposited Clays. — River deposited clays are in^beds jof
small sizes and of very irregular thickness ; they are formed by
the particles of decomposed rock carried along by the river
settling out when the speed of the river is reduced, as at the
bend of the river. They are usually rich in fossils, and it is not
unusual for them to change in character very frequently. Thus
the necessity of working a relatively large area of only a small
depth is a great disadvantage in the production of the best
qualities of bricks and tiles from this kind of clay.

In spite of this, the clay deposited by the Thames has been
very largely used for brickmaking in the neighbourhood of
London, and the lower deposits of clay made by this river reach
as far as Leighton Buzzard and Seven Oaks respectively, and
even beyond.

The difficulties of working river clays are particularly well
shown in the case of the London clay, of which it has been said
with much truth that " London clay inevitably spells ruin to the
brickmaker not thoroughly familiar with its nature, for it is too
strong to be used alone and no non-plastic material suitable for
mixing with it (grog) is found in its neighbourhood. Yet when
properly worked, no bricks can withstand the trying conditions
of the London atmosphere as well as ' stocks 'mile from London
clay." A study of fig. 1 will show that great care is needed to
ensure that the clay used is really London clay, as it is very easy
to confuse it with others which possess the same soapy shell-
shaped fracture as the dried London clay, though they are really
quite different and must be treated separately.

4 MODEEN BEICKMAKING

In addition to the shallowness of the deposits, the stones
found in clays of this kind often cause serious trouble, and alto-
gether the working of fluviatile clays is less certain, more com-
plicated, and far less profitable than the use of the lake deposits
or marine clays.

The rapidity with which rivers change their beds produces so
great a variety in the nature and composition of the clay deposits
that it is quite usual to find in neighbouring brickyards clays
which have been deposited by the same river, but which are
entirely different in their origin, nature, and properties. On
this account methods of treatment which may be successfully
employed in one yard may be quite unsuitable for another near
by. This is a matter which must never be overlooked by the
brickmaker.

Boulder -Clay has been produced in a similar manner to river

FIG. 1. — Diagrammatic section of London clay formation.

clays, but the river has been replaced by a glacier ; it is usually
seriously contaminated with sand and stones of a limy nature,
and is difficult to work satisfactorily into other than common
bricks.

Lake Deposited Clays. — Clays of lacustrine origin are in many
ways similar to those deposited by rivers, but when extensive
(as is usually the case) they are easier to work, because the
deposits of differing composition may be more accurately mixed
or separated.

Some of the most typical lacustrine clays are those of the
Isle of Wight ; unfortunately their situation and shallowness
greatly detract from their commercial value.

The Reading mottled clay, which also occurs in France, is the
product of another lake.

At Bovey Heathfield, near Newton Abbot, lacustrine clays of
perfectly regular character occur and are over 150 feet deep, but
this is exceptional in England.

THE NATURE AND SELECTION OF CLAYS 5

Sea Deposited Clays. — The extent of marine clay beds is almost
incredible, as they often stretch for hundreds of miles with a
depth of thirty feet or more throughout the entire area. Their
composition is remarkably uniform, and consequently they
possess innumerable advantages over other kinds of clay.

The impression that they contain salt in excessive quantities
is quite erroneous.

The fact that these marine deposits are almost free from fossils
and remains of the higher animals points to their great antiquity,
and the presence of sea-shells clearly indicates their origin.

Good marine clays, of which the famous Oxford clay is the
best known in this country, cannot be but highly appreciated,
but marine deposits of certain compositions can never be used
satisfactorily. Many such deposits are rendered entirely useless
by the excessive quantity of lime (" shell ") they contain, whilst
others are so excessively plastic as to be unusable without the
addition of some non-plastic material, though this latter is seldom
found near them, and the present prices of ordinary bricks will
not permit it to be made by calcining raw clay.

Rock Clays are those which have been compressed owing to
their situation, and are properly known as shales, slates, and fire-
clays. The great compression has resulted in the consolidation
of the clay, so that it has to be broken down either by the weather
or by mechanical means before it can be used. Such clays are
not found plastic, but become so on grinding and mixing with
water.

Shale is the general name given to clay rocks which are
laminated, and so split easily into thin layers. They vary in
hardness and in colour, and are usually moderately pure. Some
of them, being rich in iron, burn to a red or blue colour, whilst the
pure ones (fire clays) are buff coloured when burned.

Most shales contain a small proportion of carbonaceous matter
which is expelled on heating. In some cases, as at Peterborough,
so much of this matter is present as to render the use of coal or
other fuels in the kilns almost unnecessary. Many shales are
seriously affected by the presence of nodules of pyrites, marcasite,
and allied compounds of iron, which form spots of fair size in the
fired goods and so spoil their appearance.

Shales are commonly found near the coal deposits, particularly
in the North of England, and often extend to enormous depths.
The Accrington shale is particularly famous, the analysis given
of a shale from Whinney Hill, Accrington, being typical : —

6 MODERN BBICKMAKING

Silica ........ 61-46

Alumina 24-84

Protoxide of Iron ...... 5 '59

Sesquioxide of Iron T30

Lime . -60

Magnesia .... . . . 2-42

Combined Sulphuric Acid -i . . . -23

Alkalies. ...... . . "32

Organic Matter and Water . . . . 3-24

This shale produces fine red facing bricks.

Slate is really a compressed clay, but owing to impure com-
position cannot usually be made into bricks, though some slates
which are worthless to builders may produce good common
bricks.

Knotts Clay. — Near Peterborough (which is situated on the
Oxford clay already mentioned) Knotts clay is found. This
clay is highly valued ; it has all the characteristics of shale and
is. rich in combustible matter, whilst its enormous depth and
area, together with its regularity and composition, enable it to
be made into bricks and fired at less than the cost of the fuel
alone for bricks in some other parts of the country. The clays
on the east and south of Peterborough can be most cheaply
worked by the semi-plastic process, and everything is in favour
of their being used for the production of a common brick at a
remarkably low price.

Fire-clay is found throughout the coal measures. That in the
neighbourhood of Stourbridge is highly prized, but carefully
selected materials from North Wales, North Cumberland and
Durham, Teign Valley in Devonshire, South Yorkshire and
Derbyshire, Leicester, and the district around Glasgow, Kilmar-
nock, etc., in West Scotland, are equally satisfactory as refractory
materials. The Irish fire-clays are usually of inferior quality.

The composition and qualities of fire-clays vary very greatly,
and many varieties are known. The best type of fire-clay con-
tains almost as much alumina as silica, but in the North of
England the fire-clays used contain nearly twice as much silica
as alumina. The highest grades of fire-clay are difficult to work
on account of their low plasticity, but highly refractory clays
which are at the same time plastic are very valuable on account
of their scarcity. The fire-clays from the Midlands and Devon-
shire are specially noted for their suitability for the manufacture

THE NATUKE AND SELECTION OF CLAYS 7

of salt glazed sanitary goods. Those of Northumberland, York-
shire, and West Scotland, have an equal importance in the
manufacture of sanitary ware and glazed bricks. In the south
of Yorkshire a material, corresponding to silica, with about 10
per cent of plastic clay and known as " ganister," is found in large
quantities. Similar material is found in Dowlais (Wales), and
Gartcosh (Scotland). The best ganister contains from 87 to 96
per cent of silica, with 4 or 5 per cent of alumina.

A more highly siliceous material is found in various parts of
the country, and especially in the Vale of Neath in Wales. This
is used for the manufacture of Dinas or silica bricks. It is not
a clay, strictly speaking, but a powdered rock consisting almost
entirely of quartz, though the term " clay " is often applied to it
in the places where it is found.

The, value of a refractory clay consists in the^ possession of
particular characteristics.^ It may best be ascertained from a
consideration of its behaviour in the following directions repro-
duced here from " Modern Clay working " : —

(a) Its resistance to high temperatures.

(b) Its resistance to pressure at high temperatures.

(c) Its non -absorptive power at any temperature.

(d) Its uniformity in size and composition.

(e) Its expansion and contraction due to heating and cooling
while in use.

(/) Its resistance to the cutting action of the furnace flame,
to the abrasive action of molten metal, and to the searching
action of certain slags and metallic oxides.

(g) Its resistance to the reducing or oxidizing atmospheres in
the furnace.

(h) Its resistance to ordinary wear and tear and to accidental
blows.

It is, however, seldom that all these conditions can be
realized at once, and that clay should be chosen which combines
the most advantageous characteristics. Thus, a good second-
class clay made up into bricks of a uniform size, of sufficient
hardness, with low contraction and highly infusible, would be
far preferable in practice to one which might have a lower
percentage of alkalies and was, therefore, less fusible but lacked
some other qualities.

Most of the above characteristics must be ascertained by a
practical test, made for the purpose, but some of them can be
determined by observation and analysis. Usually, the actual

8 MODERN BEICKMAKING

value of a refractory clay can only be ascertained as the result
of an extensive series of tests, which must be of a chemical as
well as a physical nature.

Fire-clays burn to a white or cream colour, though some of the
less pure ones are reddish in tone.

THE COLOUR OF BRICKS.

When heated, clays change their colour and produce bricks
which may be white, cream, brimstone yellow, dark yellow,
buff, red (terra-cotta), brown, black, blue, grey, or any combina-
tion of these colours. The tint produced depends on the com-
position of the clay and the nature of the heating.

White Bricks. — A perfectly white brick is practically unknown,
as it requires the use of clays of such purity as to make them
too expensive for this purpose. When the effect of perfectly
white bricks is required it is usual to cover bricks of inferior
clay with a mixture of better quality which will produce the
required results. This process is known as " bodying " (see
" glazed bricks ").

Suffolk Bricks and others of whitish colour may be produced
by making mixtures of certain clays and chalk, or by using
such mixtures of chalk and clay as occur naturally in some
districts and are known as marls.

Gault beds are of this character and contain about one-third
of their weight of chalk. They are chiefly used in conjunction
with other clays for the production of the "white Suffolk " brick
already mentioned. Similar bricks may be made by the addition
of a sufficient quantity of chalk to almost any red-burning clay.

Marls or Malms are clays that have become mixed with chalk
or limestone during their formation, and form one of the most
important sedimentary deposits. In South Staffordshire arid in
some other districts the term " marl " is incorrectly used to
indicate clay or brick earth. True marls always contain chalk.

In Nottinghamshire and in some other districts, clays are
formed which contain so little chalk that they produce excellent
red bricks. In such cases it is preferable to consider these as
mild clays, though the local brickmakers invariably speak of
them as marls. The local name is correct so far as the general
clay deposits are concerned, as these turn to a creamy white,
or to a dirty straw colour, but should not be applied to the red-
burning clays in those districts.

THE NATURE AND SELECTION OF CLAYS 9

If the chalk and clay are in the correct proportions, the niarl
may be used at once for brickmaking. This is, however, seldom
the case. Marls which are deficient in clay must have some
clay added, and those which are deficient in chalk must have
this material added in a finely powdered condition. The mixing
of the ingredients is usually effected by treating each separ-
ately with water, reducing the whole material to a slip or slurry,
and mixing these liquids in the correct proportions. The mix-
ture is then allowed to settle until, either by running off the
water or by evaporation, a marl of the proper consistency is
obtained.

The chalk diminishes the contraction of the clay during the
drying and burning ; it also acts as a flux, producing a much
stronger brick than would otherwise be the case, and, in addition,
it forms a white or cream coloured compound with the iron
oxide in the clay, and so produces a brick which is nearly white
in colour. In some cases the proportion of chalk or similar
material in these clays is large and not in a very fine state of
division ; the bricks made from it will fall to pieces on exposure,
owing to the presence of uncombined lime in them which
" blows " and disintegrates the bricks containing it.

The amount of chalk which may be present in the marl or
mixture used for brickmaking should not exceed 25 per cent, and
if the original marl contains more than this (as is often the case)
sufficient clay must be added to reduce the chalk in the mixture
to this proportion. In many cases bricks should not be made
from marls containing more than 12 per cent of chalk, and for
red bricks not more than 5 per cent should be present. White
bricks (or the nearest to white commercially obtainable) are
chiefly made in Devonshire, Dorsetshire, Cambridgeshire, Norfolk,
Suffolk, and Essex.

Yellow Bricks are made in the neighbourhood of London and
in all other places where the clays found are suitable for brick -
making, yet do not contain sufficient iron to produce a red
brick, though in some cases the natural colouring effect of the
iron is obscured by the presence of chalk or lime compounds,
as in the marls just mentioned. The precise shade of yellow
produced depends on the proportion of impurities in the clay
and on the nature and extent of the firing.

Bed Bricks are produced in almost any part of the country.
Some of the finest reds are made in Leicestershire, Hampshire,
and Berkshire, Ruabon, and Accrington in Lancashire, but

10 MODEKN BKICKMAKING

sufficiently pleasing shades of reds are obtainable with care with
clays in many other districts. The chief substance to which the
red colour is due is the iron oxide in the clay, and to produce a
pleasing shade of red a clay must contain at least 4 per cent of
this material, and must be nearly free from lime compounds
which would detract from the colour. The addition of iron
oxide to clay to improve the colour is seldom satisfactory.

Bagshot clays are well known for the excellent red colour of
the bricks produced from them. The Oxford clay burns to a
lighter tint. With Midland and Western clays almost every
variety of shade can be obtained. Most surface clays can be
burned to a good red colour, though there are some notable ex-
ceptions.

Many shales also produce bricks of a fairly good red colour,
but the sources of red-burning bricks are so numerous as to make
a complete list impossible.

Red-burning clays are popularly divided into two classes,
" strong " and " mild " or " loamy ".

Strong clay is highly plastic and, in a certain sense, may be
regarded as pure clay. It is generally free from stones, sand,
chalk, or other non-plastic material, and is liable to crack and
become misshapen in the kilns and to shrink excessively. This
difficulty may be removed by mixing it with sand, crushed rock,
grog, ashes, or other non-plastic material in order to open it and
diminish the shrinkage.

On account of its plasticity and stickiness, strong clay is
very difficult to work, but with sufficient non-plastic material
available it usually forms an admirable brickmaking material.
Without this addition the attempt to work it is almost certain
to end in failure. Unfortunately the typical strong clay near
London is not found contiguous to suitable non-plastic material.
It must, therefore, be mixed with ashes (breeze) in order to
reduce its shrinkage, and to permit it to be more easily dried
and fired. Strong clays when free from stones are referred to as
" pure " by brickmakers, other strong clays are known as " foul " ;
the latter are to be abhorred unless the brickmaker is unusually
skilled or takes up the manufacture of bricks for other than com-
mercial purposes.

Loams or mild clays contain a considerable proportion of
gravel or sand, so that they are less liable to warp or shrink ex-
cessively than the strong clays.

When excessively sandy, the texture of the earth is so loose

THE NATUKE AND SELECTION OF CLAYS 11

that the addition of chalk or clay is necessary to bind the mass
together, but when of medium plasticity the mild clays are
among the best for brickmaking purposes. The majority of
clays used for brick and tile making are of a mild character ;
others must be made so by the addition of suitable non-plastic
materials. The term " loam " is commonly restricted to certain
light sandy clays, the term " mild " clay being much broader in
meaning. Highly sandy clays are particularly used in the
manufacture of " cutters " and " rubbers," though these bricks are
often made from more plastic clays to which a suitable proportion
of sand has been added.

Terra-cotta is made from any fine red-burning clay, but the
best varieties require material which has been many times de-
posited by natural causes in order that it may be sufficiently
fine in texture ; it must also produce a pleasant colour when
fired. For terra-cotta work, clay should be moderately porous
when burned, should contain sufficient flux to give it a slight
natural glaze when fired, and should be sufficiently fine to enable
the most delicate carving to be satisfactorily carried out.

The precise shade of colour produced by a red-burning clay
cannot be foretold, as it depends so much on the state of iron
oxide in the clay, the nature of the firing, and other conditions
of manufacturing. Clays which burn to an unsatisfactory colour
cannot, as a rule, be improved by the addition of iron oxide,
as this material when artificially prepared never gives the same
colour as when it occurs naturally in the clay. Attempts to
improve the colour of red-burning clays must therefore be con-
fined to the purification of the clay used, to the addition of other
clays, or to an alteration in the method of firing.

At Ruabon, terra-cotta is made from a rock clay to which
one-third of its weight of brick dust is added.

Where terra-cotta is required to be of a buff or cream colour
most fire-clays may be used in its production, but the most
suitable terra-cotta clays are those near Poole, Tamworth,
Ruabon, and in Devonshire ; smaller deposits being found in
many other parts of the country.

The term " terra-cotta " usually applies to objects of a certain
shade of red, but originally it was used for all kinds of baked
earth. At the present day any vases and similar objects made of
unglazed clay are classed as " terra-cotta " by dealers, quite
irrespective of their colour.

As the best terra-cotta clays occur in only a few localities,

12 MODEBN BEICKMAKING

many manufacturers prepare artificial mixtures which they
grind to the requisite fineness.

Brown Bricks. — Brown bricks are made of clays which have
a different composition and texture to red bricks, though in
many respects they are very similar. Many impure shales, for
example, contain so much fluxing material that they vitrify
before the temperature is reached at which the full red colour of
the iron oxide is produced, and consequently a brown brick of
more or less pleasing appearance is produced. Some red bricks
which are over -heated also produce a brown colour.

Blue or Black Bricks are chiefly made in Staffordshire from a
clay very rich in iron oxide. When under fired they are reddish
in colour, the blue being only developed at a high temperature.
In Germany and some other parts of the world where no clay
suitable for blue bricks is to be found, artificial means are
employed to produce the colour ; these are not so satisfactory as
bricks made from the Staffordshire clay. Staffordshire blue
bricks are partly vitrified, extremely hard, and with a glazed
surface. They are almost invariably used where great strength
is necessary, and are very highly thought of for engineering
purposes.

The material used in Staffordshire for the production of blue
and red bricks is a friable kind of clay which is heated to such
a temperature as to bring about a partial vitrification and reduc-
tion of the iron oxide. Marls and clays suitable for brickmaking
are very abundant in Staffordshire, and a most extensive bed of
red " marl " runs in an almost unbroken line from north to south
throughout the county.

Grey Bricks are of two kinds, this term being sometimes used
for a variety of blue bricks and sometimes for a kind of red-
burning brick, the colour of which has not been fully developed,
or which has been hidden by a kind of " scum," as in the grey
bricks of Lancashire.

GENERAL CHARACTERISTICS OF BRICKS,

A thoroughly good brick should be regular in shape, texture,
and colour, equally and perfectlyTmrnt throughout, and should
be free from all cracks and flaws— even though they be hair-
cracks — sharp in the arrises, and should give out a clear ringing
sound when struck either with a stone, another brick, or a piece
of metal. For many purposes, however, it is unnecessary to
insist upon all these qualities, any hard and well burned brick

THE NATUEE AND SELECTION OF CLAYS 13

will suffice for foundations and internal work which is to be
subsequently covered ; and for such purposes rougher and
cheaper bricks are frequently the more useful, affording a better
key for plastering than those with a smooth surface, and often
being better weight carriers than soft, well-finished, facing bricks.

Sandy and absorbent bricks should not be used in foundations,
nor in external walls likely to be exposed to water or driving
rain. Such bricks are generally soft and do not weather well,
being frequently under-burned ; and by retaining moisture they
encourage the growth of lichen and climbing plants, which all
gather and retain damp.

Soft, under-burned bricks are valueless. No brickmaker with a
reputation to lose will sell them, preferring to pass them through
the kiln a second time, or to crush them for sand or grog. On
the other hand, a remarkably non-absorbent brick, heavily
pressed and highly burned, may have too smooth a face to adhere
readily to mortar, especially in summer time, in spite of a good
wetting.

Over-burned bricks will melt and run together forming
" burrs," which are useless except to be broken up for road metal
or concrete.

Faulty bricks are more often met with amongst those which
are hand made, hack dried, and clamp burned, than amongst those
which are machine made, chamber dried, and kiln burned. To
give a complete list of all the different kinds of bricks now made
in this country is almost impossible. But the following are the
most important when bricks are classified by their (1) colour,
(2) place of origin, (3) method of manufacture, (4) use, (5)
quality. The various colours of bricks have been mentioned
on page 8. It must be remembered, however, that in different
localities the colour may be known by a different name, and
bricks of different colour are often classified as if they were all
of one shade, so that sorting them on a basis of colour alone is
not always satisfactory.

The place of origin of bricks and tiles is also misleading in
many cases, because the successful use of these goods from one
locality often leads to their imitation by firms in other districts,
and it is becoming customary with certain classes of goods to
name them after the place from which such bricks were origin-
ally produced, though the particular samples offered for sale
may never have been near to it. Goods which are classified
according to the place of origin are easily recognized, as most

14 MODERN BRICKMAKTNG

of them bear some title and imprint upon them. In many cases
they are specified under the name of the district from which
they are supposed to come, as Flettons, Accringtons, London
stocks, Bath bricks, etc.

Fletton Bricks, sometimes known as " Flettons," are made by
the semi-dry or semi-plastic process from clay found in the
neighbourhood of Peterborough. The quality and colour vary
greatly, but as the bricks are cheap, and generally used where
colour is unimportant, they command a good sale. The best are
of a good red colour, but most of them have a yellowish tinge ;
they are very smooth on the surface, and it is sometimes found
that plaster will not adhere to them satisfactorily.

Bath Bricks are made near Bridgwater, in the West of
England, from a very siliceous clay, they are only slightly heated
and are not used for constructional purposes.

Accrington Bricks have gained a high reputation for their red
colour and strength, and Leicester bricks, together with those from
many other districts, have a more local reputation for size,
colour, and strength.

London Stocks are made for many miles round London, but the
term " stock bricks " is used in many other parts of the country to
denote the particular kind of brick made for general use in any
district. The London stock brick is coarse, hard, and strong,
with a grey, yellow, or, occasionally, red colour. They are fre-
quently cracked superficially, and are very irregular in structure
and colour, but if well burned are excellent for general purposes,
being partly vitrified and stronger than their appearance would
indicate. London stock bricks are classified locally under a
number of different terms according to their quality.

Under methods of manufacture may be placed : —

Dry-Dust Bricks, made as the name indicates from powdered
clay without any addition of water. This method is not often
used for bricks, though very popular for tiles. The material
must contain sufficient flux to bind the particles together during
firing.

Semi-Dry or Semi Plastic Bricks are made from material which
is almost but not quite dry. This method of manufacture has
for some time been very popular on account of the cheapness
with which it enables bricks to be made, but it is now being
replaced by the stiff -plastic process. The most important centres
of semi-dry or semi-plastic bricks (the terms are identical in
meaning) are Accrington and Peterborough.

THE NATUBE AND SELECTION OF CLAYS 15

Stiff Plastic Bricks are made from a paste which is worked
through machines in as stiff a condition as possible, so as to save
time and expense in drying the bricks. This method of manu-
facture is rapidly increasing in popularity.

Plastic Bricks are those made from clay which has been con-
verted into a highly plastic paste, or in which the plasticity has
been developed as fully as possible. All hand-made bricks and
tiles are of this kind, but the term is also used in connexion with
machine-made goods, particularly with loamy clays. The main
difference between this and "the stiff-plastic process is the greater
quantity of water added to the clay, which necessitates thorough
treatment and more careful drying.

Sand-Faced Bricks are largely used in the South of England
for exterior work. They are characterized by a good red colour
which is very even in tone, but are soft and highly absorptive
on account of the clays from which they are made. The name
is derived from the mould being sprinkled with sand to prevent
the clay from adhering to it, instead of using water for this pur-
pose as in slop-moulded bricks. Incidentally the sand, if properly
chosen, produces an improvement in the colour of the bricks.
As a rule they are not very durable, and only those which " ring "
well should be used for best work. When really well made they
are in every way excellent for buildings in the country and
smaller towns.

Marl Facing Bricks are those made near London to be used
along with stocks, to which they are distinctly superior for out-
side work.

Rubbers and Cutters are soft bricks made from sandy loams,
and will bear cutting and rubbing to any required shape. They
are used for making bricks of special shapes for arches, carved
work, etc., being cut or rubbed down after the completion of firing
(usually on the building site). Consequently, they must be of
the same colour throughout and should be of such a nature that
the interior as well as the exterior of the brick can resist the
weather. White, red, and buff rubbers are made, though the red
ones are most popular.

Slop-Moulded Bricks are made, as the name indicates, from a
soft paste or " slop ". They are necessarily hand made, the
mould being wet with water to prevent the clay from sticking to
it, instead of being covered with sand as in the manufacture of
sand-faced bricks.

Pressed Bricks are those which have their final shape given to

16 MODERN BRICKMAKING

them by means of a press, but the term is also used for most
machine-made bricks. They are usually heavier and denser
than hand-made bricks or " wire-cuts " and are often perforated,
or provided with " frogs " to lessen their weight. Pressed bricks
should be perfectly uniform in size and shape and should have a
smooth surface and arrises. They usually require great care in
drying and in manufacture generally, but are certainly the most
accurately formed of all bricks and tiles.

Polished Bricks are not really polished, but are rubbed on an
iron plate so as to produce a moderately smooth surface. They
were originally made to compete with pressed bricks, but are
now seldom seen.

Clamp Bricks are those which have been fired in a temporary
kiln known as a " clamp " ; they are usually irregular in shape,
but are useful in many cases where a better grade of brick can-
not be obtained, as in new districts and in the Colonies.

Glazed Bricks are those having their surface covered with a
glaze so that they are more easily kept clean, or so as to produce
a definite artistic effect. By the use of an intermediate layer
of white or coloured clays between the brick and the glaze,
beautiful decorative effects may be obtained.

The uses made of bricks gives rise to the following names
amongst others : —

Fire-bricks are those made from clay with a great power of
resistance to heat. They vary greatly in quality, shape, and size,
and are chiefly used for furnace lining. Fire-bricks must be
almost free from metallic oxides, and are usually of a pale cream
colour. Low grade fire-clays are largely 'used for the production
of paving bricks, sanitary ware, and building bricks.

Paving Bricks are chiefly made of a clay which vitrifies in the
kiln, as it is found that such bricks have a greater resistance to
traffic than more porous ones. They are blue or yellow in colour
and are sometimes known as " clinkers ".

Clinkers are small, well-vitrified bricks used for paving. In
this country they are commonly yellow in colour, but the same
term is used for any vitrified brick.

Engineering Bricks are used in the construction of railways,
bridges, and other civil engineering work. They must be of great
strength and durability, and are usually vitrified and " ring "
well. The blue bricks from Staffordshire are used in enormous
quantities in this way.

Floating Bricks are of little practical use, though apparently

THE NATURE AND SELECTION OF CLAYS 17

popular among the ancients. These bricks were made of a
special fossil earth (found in Italy) and weighed only about one-
fourth as much as clay bricks of an equal size, whilst their
strength is the same as common hand-made bricks. In recent
years light-weight bricks have been made by the addition of
sawdust to the clay and by making the bricks hollow.

Channel Bricks, Air Bricks, Plinth and Coping Bricks, derive
their name from the uses to which they are put ; they must be
made in special moulds, and so resemble terra-cotta work rather
than ordinary brickmaking.

Squints, Jambs, Bullnoses and Other Terms are used to denote
special shapes.

The qualities of bricks are responsible for the following
terms : —

Malm Bricks, which are best quality hand-made bricks pro-
duced from marl ; they are of a yellow colour.

Seconds and Thirds are bricks sorted from contents of the kiln
after the best bricks have been removed. " Seconds " are much
used for work for which the best quality of bricks is not neces-
sary ; seconds bricks are not good enough in shape or colour to be
used as facings.

Stocks are the average quality of bricks made in any district,
but the term is mainly used for a certain quality of London
bricks.

Washed Stocks are a low quality of malm bricks.

Grey Stocks are good bricks but irregular in colour, so cannot
be used for facings.

Rough Stocks correspond to " thirds," and are not suited for
good work on account of their irregular shape and colour. For
foundation work they are very satisfactory, being usually hard
and sound.

Place Bricks are only a low grade of brick, used chiefly for
temporary purposes.

Grizzles are insufficiently durable for outside work, but find
a use in interiors and partitions.

Shuffs and Shakes are unsound bricks and should not be used.

Bats are rubbish, being the residue left when all the saleable
bricks have been removed from the kiln.

Crozzles are bricks which have been so over-heated in the
kiln that they have become vitrified and have adhered to each
other. They are badly shaped and of little value, being in-
cluded in the " bats " in the South of England.

2

18 MODERN BRICKMAKING

SAND, BREEZE, AND OTHER MATERIALS,

As already mentioned, it is necessary with many clays to use
non-plastic material in order to produce a satisfactory brick
earth. The following are the materials most frequently em-
ployed for this purpose : —

Sand, like clay, is a product of decomposition of rocks, but
when of good quality consists almost entirely of silica.

For mixing with clay, sand need not be pure so long as it is
free from undesirable matter.

When used for moulding bricks (in the hand-making pro-
cess) the colour of the sand when burned is important. The
finest Bagshot sand is considered to be the most suitable for
red-burning bricks, and great pains are taken by brickmakers of
good reputation to secure a satisfactory material.

A white-burning sand is used for buff and white bricks and
is of the Calais sand type. It must be fairly free from iron
oxide and in a very finely powdered condition.

Coarse, sharp sand is useless for moulding, though often
valuable for mixing with the clay.

Soil, as a brickmaking material, is only used in the neigh-
bourhood of London. The clay in that district is so strong that
it is necessary to reduce its plasticity, and " soil," being com-
bustible as well as non-plastic, has special advantages for this
purpose. " Soil " is the fine material obtained by sifting do-
mestic ashes or cinders, the coarser parts (known as " breeze ")
being used for fuel. The " soil," in addition to reducing the
contraction of the bricks, produces a special colouring, not
otherwise obtainable, and attributed to the impurities (sulphur
compounds) which it contains.

" Soil " — meaning surface-clay or loam — is quite a different
material, and is usually unsuitable for brickmaking, though in
some districts it is successfully employed. Most brickmakers
find it necessary to remove the top layer of earth (" soil ") and to
discard it. This operation is known in some districts as " en-
callowing ".

Grog is, strictly speaking, clay which has been heated suffi-
ciently to destroy its power of becoming plastic and has then
been reduced to a powder. The term is, however, conveniently
applied to ground bricks or other waste from a clay works, which
is mixed with raw clay in order to produce a mixture in which
the amount of contraction is within convenient limits. In

THE NATUKE AND SELECTION OF CLAYS 19

this country, grog is seldom prepared by calcining and grinding
clay, but on the Continent several firms make a speciality of
the manufacture of this material, which they supply under the
trade term " chamotte ". For most purposes fire-bricks, which
are of too poor a quality to be offered for sale, may be ground and
used as grog, but for the manufacture of the best fire-bricks it is
desirable that a special grog should be prepared. The use of this
material is described more fully in the Chapter on " Fire-bricks ".

Chalk is found in such enormous quantities that it is readily
procurable by those brickmakers who require to add it to their
clay in order to form an artificial marl (page 8). For this pur-
pose the chalk must be freed from stones and pebbles, and is
generally washed in a special mill similar to that used for wash-
ing clay. Chalk, being harder, requires a preliminary crushing,
though the inclusion of heavy wheels with spiked rims in place
of two of the hurdles of the wash-mill is usually found to be
efficient.

Water is a material of great importance to the brickmaker,
and if much difficulty is experienced in obtaining it cheaply the
yard cannot be a success. For most brickmaking purposes the
purity of the water is of small importance, but sea-water must
be avoided on account of the salts it contains. Other water
rich in salts must be avoided for the same reason, as it would
produce a scum on the surface of the goods during drying. For
use in boilers, water should be as pure as possible, and facilities
for collecting rain and other surface-water should be provided.
With a little provision in this way it is often easily possible to
procure ample supplies of pure water at little or no cost, and
the saving effected in the cleaning of the boilers is an item well
worth consideration at the present time.

Hard Water should be avoided in boilers unless it is softened
before use. There are many arrangements now on the market
whereby this softening may be effected. Most of them are un-
necessarily costly for the brickmaker's purposes. The best
water-softening agents are (in order of merit) : (1) baryta, (2)
lime in conjunction with soda, (3) caustic soda and tan liquor.
Hard water should be fed into a large tank, treated with the
softening material, and allowed to settle before it enters the boiler.
Rain-water and surface-water need no treatment as they are
practically pure, though occasionally a little soda is necessary
in order to prevent corrosion from slight traces of acids sometimes
contained in them.

CHAPTER II.
THE GENERAL MANUFACTURE OF BRICKS.

THE clay which is thought suitable for brickmaking having
been located, it is necessary to decide on the best method of
working it, if good quality bricks are to be produced. The com-
position of the clay varies so greatly in some districts that it is
impossible to decide which is the best method of brickmaking
unless the characteristics of the clay are well known.

Practically speaking, several methods of brickmaking are
possible, according as the clay requires a smaller or larger
quantity of water to be mixed with it ; if no water at all is used,
the semi-dry or dry process may be employed, although in many
cases a better quality of brick will be produced if the plasticity
of the clay is developed by the addition of water and subsequent
treatment in the mixer. When only a little water need be
added, the stiff plastic process may be used, and where more
water is necessary the clay must be made thoroughly plastic
and may then be shaped either by hand or by machinery.

Clay is obtained from the pit or quarry, as the case may be,
by digging or blasting, or by any of the improved methods of
mining. As in most clay deposits the composition of the bed
varies at different parts, it is necessary to exercise much care in
choosing portions of the bed from which the clay lias to be
taken. It is, therefore, usual to work horizontally in a series of
terraces or steps, each step being the height of the particular
strata worked, but conditions vary so in different deposits that
each brick manufacturer must, to a large extent, be left to use
his own judgment in the matter. Care and attention are re-
quired if the clay hole is to be worked economically, as other-
wise a large amount of useless material may be shifted. Water
in the clay hole is often a source of trouble, as its removal en-
tails considerable expense. For most purposes a " Pulsometer "
pump is the most suitable, as it can deal with very dirty water
and has no wearing parts. When steam can be carried to the

(20)

THE GENERAL MANUFACTURE OF BRICKS 21

<?lay hole this pump is particularly suitable, otherwise some
form of diaphragm pump should be substituted. The ordinary
types of pump, whilst excellent for clean water, are not desirable
for use in clay holes.

Special oversight is needed to prevent the wrong strata be-
coming mixed with those containing suitable material, par-
ticularly at certain stages in the quarrying, but with capable
men no special difficulty in this direction need be experienced.

In a few instances it is sufficient to work straight forward
without any attempt to separate the impurities occurring in the
clay. It is then wise to use a steam-navvy or other mechanical
means of obtaining the clay, as with such appliances the cost of
getting it is greatly reduced. Steam-navvies are useless where
much sorting of the clay has to be done, and cannot be used in
the coal mines from which certain shales and fire-clays are
obtained.

Digging should, when possible, be paid for " by the piece ".
This is very advisable because it enables the men to earn more
per hour than day wages if they should wish to do so ; yet,
whilst keeping the cost of digging at a figure agreeable to the
employer, it enables them to do something in very bad weather.
In the latter contingency an employer would stop his men
entirely if employed by the hour, whereas on piece-work the
men can earn something if they are so minded. The only
danger in " piece-work " is where careful sorting of the clay is
necessary and the men are tempted to send unsuitable material
to the mills. In paying " by the piece " the labour may be
classed in two sections : (1) digging and filling barrows or wagons,
(2) wheeling to the heap.

Easy, flat digging and filling is worth as a rule about 4d.
to 6d. a cubic yard, but this item varies according to the
hardness and accessibility of the clay. Wheeling away usually
costs about l^d. per run of 20 yds. There is also the expense of
untopping or encallowing a clay bank, putting in and shifting
" roads " on which to wheel, and frequently of sorting out and
getting rid of useless veins of earth. It is seldom thaf earth can
be got on to the heap for less than Is. per yard all told, or 2s. 9d.
per thousand bricks, and it is in this that th^ hand maker is at
a disadvantage compared with the makers of those Midland
clays which are uniform to a great depth. The standard price
for loading by hand into the hoist wagons is Is. per thousand,
but when a steam-navvy is used, less than half these figures will

22 MODEEN BRICKMAKING

suffice. In yards which only work for a portion of the year, the
clay is usually dug out in the autumn when the brickmaking
has ceased. It is then all heaped up and left to be mellowed by
the winter weather and especially by the frost, during which
operation the clay is completely broken up. Once or twice in
the winter the heap may be turned over with shovels, so as to
expose it more thoroughly, and to enable stones to be picked out
as far as possible. This exposure of the clay is known as
" weathering".

The thickness of the layers of clay on the heap should not be
too great, as the frost will seldom penetrate to a depth of more
than 8 in. On this account it is desirable to use a definite area
of ground for exposing the clay to be weathered, and to cover
this all over to a slight depth and repeat the covering as often
as possible, instead of tipping the clay into a heap in the ordinary
way. Sometimes the clay will be sufficiently broken up by very
slight exposure to the air, and in some instances summer heat
is quite as efficient as frost. The object of the weathering is the
separation of the particles from each other so that they may
more readily become plastic and produce a mixture of even
composition when worked up with water. It is not only the
powerful mechanical action of frost which is so beneficial in
weathering. The mechanical actions which take place are often
extremely valuable, and some clays which are almost unworkable
when freshly dug, will be found to produce first-class bricks after
the clay has been exposed for as little as forty-eight hours to
the air. This aspect of weathering deserves more attention than
it has received hitherto, and quite a number of brickmakers
would find it well worth their while to crush their clay and
spread it in the open air for a couple of days before proceeding
to use it.

The getting of fire-clay from underground mines forms a
special branch of mining, and must be studied from textbooks
devoted to that subject. It is beyond the province of the brick-
maker, who usually purchases such clay delivered at ground
level.

Whilst some clays are found in a state in which they can be
made into good bricks without any purification, there are many
others which must undergo a preliminary picking or cleaning
before they are fit to use. Many clays are so contaminated with
impurities that much difficulty is experienced in working them.
The Midland marls and shales are always troublesome on account

THE GENEKAL MANUFACTUKE OF BEICKS 23

of the veins of impure limestone (" skerry ") which they con-
tain, and which tends to make the bricks " blow " on exposure.
Other clays are contaminated with gravel or other material which
must generally be removed before they can be used.

It will readily be understood from the above that the treat-
ment a clay must undergo will depend upon its nature, the im-
purities it contains, and the purposes for which it is to be used.
Three chief methods of treatment are possible : (I) It may be
used direct ; (2) it may be mixed with some other material ; (3)
it may be picked, washed, or otherwise purified before use. The
first method is to be preferred when it is practicable, though it
can only be used for certain clays. The second method is fre-
quently employed (especially in the manufacture of fire-bricks
and other special work), and in the South of England in connexion
with " maiming " or adding chalk.

The material to be added may be almost any mineral of a
non-plastic nature which will not spoil the bricks and which is
sufficiently cheap. In the real "maiming," chalk is invariably
used, but in some districts the clay is reduced in strength, and
made easier to work by the addition of sand or some other
siliceous matter. In the neighbourhood of London, " soil " is
mixed with the clay for a similar purpose, and not only assists
the drying of the bricks but aids their burning. The third
method includes two entirely different modes of treatment (a)
removal of stones or other obvious impurities, and (b) washing.

To separate large stones, or unsuitable materials of a rocky
nature, the clay must be- examined carefully and the undesirable
constituents removed by hand. Thus, the larger pieces of rock
may readily be removed from boulder-clay and large nodules of
pyrites, etc., from fire-clay, by this means, though pebbles of less
than one inch diameter are usually too small to be thus separated.
From some clays the smaller stones may be separated by mixing
the material into a paste with water, and compressing it in a
drum with perforated ends on sides. The clay passes through
the perforations leaving the stones inside the cylinder. A number
of appliances for, this purpose (known as " clay purifiers ") have
been placed on the market and have met with considerable
success on the Continent. The most popular one in this country
is Whitehead's perforated pug-mill. It consists essentially of a
pug-mill which mixes the clay into a paste, and forces it through
the perforations in the cylinder, the stones being discharged
through an aperture in the base of the machine.

24 MODEKN BEICKMAKING

A simpler appliance for the same purpose consists of a long
drum of perforated steel open at both ends and fitted with a pair
of pistons which work in opposite directions alternately. One
piston is fixed at one end of the drum and the latter is filled
with clay paste. The second piston is then inserted and is used
to compress the material. The clay exudes from the perfora-
tions, and by the time the piston reaches the farther end of the
cylinder only stones remain behind. The first piston is now
withdrawn, and the second moved forward driving the stones in
front of it, so cleaning the drum. This appliance suffers from
the disadvantage of not working continuously, but for small
yards it is often useful, and is less costly to install than the more
efficient clay purifier previously described.

Another form of clay purifier, which has met with great suc-
cess in the working of Continental boulder-clay, is the invention
of M. Bohn. It consists of a pug-mill with a perforated barrel

FIG. 2. — Bohn's clay cleaner.

and a partially closed end (fig. 2). The clay is delivered into the
open trough of a mixer, and after being treated with sufficient
water to make it into a paste is forced forward by the blades of
the pug-mill. Under the great pressure exerted, the paste is forced
through the perforations in the barrel, all the stones being forced
out of an aperture in the end of the barrel along with some clay.
This aperture can be closed partially or completely by means of
the lever shown. In the most recent machines provision is
made for adding water under pressure to the " stones " from
which most of the clay has been separated, and in this way the
remaining clay adhering to them is removed. The special feature
of the machine is the construction of the barrel in small sections
so that renewal of the perforated portions, as these become
worn, is readily and cheaply effected. It is found in practice
that perforations less than y^ in. diameter are inadvisable in clay

THE GENERAL MANUFACTURE OF BRICKS 25

purifiers, and consequently gravel and sand cannot be removed
by their means. When it is necessary to remove these materials
the clay must be washed.

Washing, or mixing the clay with a large quantity of water, i&
a simple and frequently used method of separating it from stones
and other impurities. Chalk when used is also washed so as to-
clean it and reduce it to the necessary fineness to be properly
mixed with the bulk of the clay. Some mixtures of chalk and
clay in suitable proportions occur naturally, and are known as
"real malms," but more frequently a certain amount of chalk
is added to produce an artificial malm. The clay and chalk
are usually washed separately in large circular tanks known as
wash-mills. In the centre of this tank is a pillar with the lower
part of brickwork and the upper of metal. This latter acts as
the pivot on which is hung a horizontal frame containing a
number of suspended harrows, or washing gates. The frame is
rotated by horse or mechanical power (the latter for preference, as
it is much cheaper), the circular tank being filled to three-fourths
of its depth with water and the material to be washed, a thick slip
or slurry is soon formed by the tearing action of the tines on the
harrows on the clay. At suitable intervals the mill is stopped,
and the slurry allowed to run out into settling tanks or wash-
backs, stones and other undesirable matter remaining in the mill.
After being filled and emptied three or four times the mill must
be thoroughly cleaned out, though the frequency with which
this operation must be performed depends upon the proportion
of impurity in the clay. During the last twenty years several
important improvements have been made in the design and
construction of wash-mills, and it is now possible with some clays
to work them continuously.

A modern wash-mill may conveniently be about 14 ft. in
diameter, the framework revolving 9 to 10 times per minute.
It will require about 7 h.p. to turn it, and will treat from 20 to
40 cub. yds. of material per day, the higher figure being reached
with a fine clay or marl.

The wash-backs are usually constructed like shallow reservoirs
by building earthwork walls so as to form a series of large ponds
or tanks about 50 ft. sq. and 3 to 4 ft. deep. Each wash-back
should be provided with a wooden or brick flue, the height of
which can be altered to suit the level of the clay and water in
the back. This flue leads to a drain, and serves to carry off the
water when the clay has settled. The water should be returned

26 MODEEN BRICKMAKINCr

to the wash-mill and used again. A simple but effective flue
consists of a wooden trough, sloping steeply ni the wash-back,
the " top " of the trough being covered by a row of bricks which
converts it into a "square pipe". By removing the bricks one
at a time the water may be run off from the clay at convenient
intervals.

As it is not always possible to arrange the settling tanks or
wash-backs at a lower level than that of the wash-mills, the slip
or slurry is often pumped out of the mill (plunger pumps being
used for this purpose), and by fixing a comparatively fine screen
to the suction end of the pump the necessity of emptying the
wash-mill more than once every few weeks may be avoided, un-
less the clay is exceptionally impure. Even when no pumps
are used, the outlet from the mill is best covered with an iron
screen, so that all the larger particles may be kept out of the
slip going to the settling tanks. It is often customary to drive
the mill for a certain time and then to stop it whilst the liquid
is run off. This wastes time and should be avoided when possible,
a constant speed of output being generally preferable, and usually
attainable.

In the simplest form of power-idriven wash-mill the harrows
are hung at each end of a pair of T-irons, each about 14 ft. long,
by chains attached to the hooks, so that as the mill becomes
partially filled with stones the harrows do not touch the bottom
of the tank. To the centre of the T-irons is attached a hori-
zontal pulley, the hub of which fits loosely over the vertical
post in the centre of the mill. This pulley is driven from a chain
from the engine, or, in the case of a horse-driven mill, it is
replaced by a long wooden beam.

The harrows should be about 3 ft. sq. and each should have
a dozen teeth, or tines, made of iron rods an inch square. In
some yards instead of driving the mill direct from the engine
it is connected to a special pulley from the pug-mill.

The chalk may be washed in a similar mill, but it is more
usual to replace one or two of the harrows by a heavy spiked
roller which more readily breaks down the lumps and enables
the washing to be carried out more rapidly (fig. 4).

A sufficient quantity of slurry having been run into the settling
tank, or wash-back, to fill it to a reasonable depth, a second tank
must be brought into use, and the first left undisturbed until most
of the water has risen to the surface ; it must then be run off care-
fully by means of sluices at the side of the tank, until only a

THE GENERAL MANUFACTURE OF BEICKS

28 MODERN BRICKMAKING

thick mass of paste is left. This rnust then be left till suffi-
ciently stiff for a man to walk on it without sinking, after which
men are sent to dig out the material preparatory to its further
treatment. During the last period of stiffening it is desirable
to cover the mixture with a layer of sandy loam, so that it may
not become hard and leathery. In the south of England " soil :r
(cinder dust) is used instead of loam (page 18). The workmen
should dig vertically, starting at one corner and working down
one side of the tank, and should not dig out the clay in horizontal
layers.

' When a mixture of clay and chalk is used for brickmaking,
the washing process is precisely similar to that described above,
but the chalk should be mixed with an equal weight of clay
before being washed, as if washed alone and then mixed with
the clay it is difficult to avoid the formation of white specks in
the brick. Instead of feeding the clay-mill with water only,
slip from the chalk-mill may be added in proportionate quantity.
As the amount of water used will be about 100 gallons for every
cubic yard of clay, it is wise to return the water run off from the
settling tank to the wash-mills instead of wasting it. In some
cases, owing to the position of the tanks and the mills, a pump
will be necessary.

It is a curious fact that most clays suitable for brickmaking
by hand will pass through a sieve having 100 holes per running
inch, when the clay is mixed with twice its weight of water. So
fine a sieve can only be used for testing, but the moving water
in the wash-mill acts as though the clay were passed through a.
sieve, and by keeping the speed of the mill constant at the
proper rate a wonderfully fine separation of the clay from the
other materials may be made. When clay and sand are to be
mixed together, washing machinery is not resorted to, owing to
the density of the sand, but the mixture is made in a wet pan-
mill or in a pug-mill or similar paste-mixing machine.

It is customary when using malms (mixtures of clay and
chalk) to add a certain proportion of ashes ("• soil ") ; this is known
as soiling. The ashes used are ordinary cinders collected by
the dust-bin men and sifted so as to remove the larger pieces..
The sifted " soil " is then laid on the top of the clay mixture in
the settling tank and remains there throughout the winter. The
amount of " soil " required is usually 20 cub. ft., or one-third of
a chaldron, to every thousand bricks. At a later period it is
thoroughly mixed with the clay, this latter operation being,

THE GENERAL MANUFACTURE OF BRICKS 29

-called " tempering ". In many parts of the country " soiling " is
not employed, as the sulphur in the ashes has a strong effect
in colouring or discolouring the bricks.

Haulage. — The use of mechanical appliances in getting the clay
must depend upon the nature of the material and the depth of the
yard, but in any case the construction of a tramway or rails will
lessen the cost of moving the clay from one place to another ;
the employment of these appliances is far cheaper than that of
wheelbarrows. In fact, barrows should only be used where
wagons cannot be employed. It is not at all necessary for a
permanent track to be laid, though this is usually desirable on
account of the smoother running. The ordinary track is made
with 9 Ib. to 16 Ib. rails set 20 in. apart. If it is to be portable,
one end of each rail should be made with a sleeve into which
the other end can be fitted, but for a permanent track the rails
are nailed or bolted on to sleepers. The most useful form of a
track for moderate sized or small yards is a single track made
double in places so as to allow the wagons to pass each other,
but where endless haulage is employed it is usually better to
have two tracks, as this greatly lessens the risk of accidents.

Direct Haulage is cheapest when effected by means of the
rope or chain, but in small yards, or in special cases, horses or
locomotives may be necessary. For instance, it not infrequently
happens that the clay hole is on one side of the road and the works
are on the other, so that rope haulage (unless of the overhead
variety) cannot be used. Horses and locomotives are, however,
much more costly in relation to the work they do than other
systems of haulage, except in those cases where there is an
enormous output over a long distance, when it may be found that
& locomotive, with a train of wagons, is cheaper than an endless
rope or chain.

The simplest system of haulage by rope or chain is obtained
by attaching a drum to the engine or other shaft by means of a
friction clutch, so that the clutch being put into action the rope
or chain is made to coil round the drum and so haul up the
wagons. One wagon is hauled up at a time, but with a suffi-
ciently strong rope a number of wagons may be coupled together
so as to form a train. This arrangement does not work con-
tinuously as does the endless system of haulage, as the wagons
must be hauled up and returned to the pit on the game track ;
but the arrangement is simple in construction, and by choosing
wagons of a suitable size can be made to work very satisfactorily

30

MODEEN BBICKMAKING

in many yards. If the incline on which the returning wagons
travel is at all steep, a brake (usually of the band form) must be
employed on the winding drum. On level tracks, or on those
which are nearly level, some means must be provided for hauling
back the empty wagons, in such cases the ordinary main and
tail system, or an endless chain or rope may be used. The main
and tail system consists of two drums, one of which works the
rope which hauls out the full wagons, and the other, a lighter
rope, which pulls back the empty ones. A pulley-block placed
at the end of the track farthest from the drums keeps both ropes
fairly taut, and one drum unwinds whilst the other winds the
rope. The thinner rope or tail rope must usually be about twice
the length of the track, and is attached to the free end of the

FIG. 5. — Endless rope haulage.

thicker main rope. The wagons are always fastened to the main
rope as only one track is used.

In hauling by an endless rope or chain a horizontal pulley is
usually employed. This pulley is mounted on a vertical shaft
and is driven by gearing from the main shaft (fig. 5). The
rope or chain is supported at the farther end by a similar pulley
which runs " loose," and the wagons are usually attached by
means of simple vertical bars, fitted with a V-shaped opening
(fig. 6) at the top. This opening engages with the rope or
chain and is sufficient for most inclines. Where necessary, a
special clip (fig. 7) may be used to secure a more perfect at-
tachment to the rope. When the number of wagons required
is sufficient to support and balance the rope or chain, this system,
of haulage is the most satisfactory and convenient. It is often
necessary to push the wagons by hand for a short distance,,

THE GENERAL MANUFACTURE OF BRICKS 31

FIG. 6. — Wagon with V-shaped clip.

FIG. 7. — Cracldock's clip for rops haulage.

&A MODERN BRICKMAKING

especially near the working faces of the clay, but owing to the
€ost of human labour for this purpose, this part of the work
should be made as small as possible, and every advantage given
by means of iron plates, turn-tables, or portable rails. The main
essential in a tramway system is that a large part of the track
must be fixed permanently, though portable switches or joints, as
well as permanent ones, often facilitate working.

Turn-tables are essential in some cases. Usually they are
permanent structures, but for some purposes a climbing turn-
table is better. The climbing turn-table, which is in itself a

FIG. 8. — Climbing turn-table in use.

special form of large iron plate, can be laid over the rails, and is
provided with sloping sides so that the wagons travelling over
the traclj: get on to the turn-table (figs. 8 and 9). They may then be
turned round in any direction desired, and led on by similar
guides to another set of rails. Such a turn-table can be placed
at any portion of the track, and so can be used as a temporary
switch in places where permanent points are undesirable. It is
mainly used to take the wagons in a direction at right angles to
the main track when forming a heap for weathering, or in filling
and emptying kilns. It has several other uses, and its applica-
tion at the working face of the clay might usefully be extended
to more than is at present the case.

THE GENEKAL MANTJFACTUBE OF BEICKS 33

The wagons can be made to hold any quantity from a
barrowful to a ton of clay, according to the nature of the material
and the system of manufacturing. A number of excellent types
of wagons are now on the market. As a rule with endless chain
haulage small wagons are preferable, as the load is distributed
more evenly, but where horse haulage is used the wagons
should hold about a ton of clay. Iron wagons which tip side-
ways (fig. 10) or endways (fig. 11) are deservedly popular and
are made by several well-known firms. Steel wagons of the
two shapes illustrated are the best for conveying large quantities
of clay at a time. They should be strongly built, without
any joints at the corners of the body rim, and should have

FIG. 9. — Klemp, Schultze & Co.'s portable turn-table (in course of erection).

a strong angle steel framing at inside. The wheels should
be specially toughened and provided with ball bearings for
easier running. The body should be well balanced so as to tip
easily when required, but should be provided with a simple and
reliable fastener to keep it from tipping unexpectedly. Where
several cars are to be fastened together, swivelled couplings are
desirable.

When endless haulage up a steep incline is necessary, small
oblong wooden wagons, each holding about 8 cub. ft., are very
satisfactory. These are run into a tipping frame and so are
emptied. These tipping frames can only be used where the
material has to fall to a lower level than the track, whereas

3

34

MODERN BRICKMAKING

tftHur Koppel,
FIG. 10. — Side-tipping wagon.

FIG. 11. — End-tipping wagon.

THE GENEEAL MANUFACTUKE OF BEICKS 35

side-tipping wagons of the type illustrated (fig. 10) can tip on to
the level of the track.

The track should be made as straight as possible, as a straight
line is always shorter than a curve, and it will often pay to re-
move irregularities in the ground rather than take the line a
further distance round. The slope of the track should not ex-
ceed 35 degrees, and it is much better when the inclination is
less, as the cost of transporting and the risk of accidents are
both reduced on more level tracks. In many yards an artificial
staging, or gantry, is used, it being found that this, when made
of rough timber, is cheaper than the levelling of the ground for
the construction of an earth embankment. The rails used are
light and laid 16 to 22 in. apart. Unless used on the gantry they
must be laid on sleepers. It is usual to lay the sleepers at right
angles to the rails, but brickmakers in America claim that there
are advantages to be derived by laying the timbers in the same
direction as the rails themselves, and it is certainly far cheaper
so to lay them.

The most suitable means for haulage in most brickyards is
an endless chain or rope, or a combination of rope and chain.
This should not be heavier than is necessary, and a rope f in.
diameter is sufficiently large for most purposes. The rope or
chain should be supported at intervals by rollers or pulleys,
especially if it is near the ground, as nothing wears it out more
rapidly than dragging it over a rough surface. The speed with
which it travels should not exceed four miles an hour. The
wagons are attached to the rope by means of a special clip, but
when a chain is used a simple fork projecting above the wagon
and engaging one of the links is sufficient. In this case it is
usual to arrange the chain so that the wagon is automatically
released as soon as it reaches the place where it is desired to
stop it. This is done by taking the wagon to a rather greater
height than is required, and letting it run down a short incline
at the last, the chain being raised well out of the way. With an
endless chain the adaptability of wagons in turning sharp curves
is very noticeable, especially if at the point flanged rollers are
placed to receive the wagon and enable it to leave again in the
desired line, the road being inclined in such a way that the fork
of the wagon disengages from the chain until the wagon has
passed round the curve, when it again comes in contact with
the chain and is hauled forward. No special mechanism is
necessary, as all that is required is to fix the rollers at the right

36 MODEEN BEICKMAKING

height above the wagons, and to see that the slope of the track
at the curves is in the right direction. When clips are used they
should be provided with an automatic release.

It is often convenient to use two or more endless chains in-
stead of one, as changes in the direction of the track can then
be more easily arranged. In such cases a vertical shaft is
erected, and on it are fixed two or more rollers or pulleys, one
being used for the first endless chain and the others for the
second and, if need be, for a third chain.

With all systems of endless chain haulage it is desirable to
have some kind of brake to prevent the wagons from running
backward on a temporary stopping of the hauling engine, and
with several chains on the same axle some brake arrangement
is essential. For the former, the simplest form is a collar round
the shaft fitted with cogs above and below. A loosely hung bar
of steel fits into these, one at a time, and forms a ratchet which
compels the pulleys to travel in one direction only. Without
some arrangement of this kind the wagons may run back and
serious damage be done.

Quite recently aerial ropeways (fig. 12) have been used where
the ground is occupied, or where it is irregular or otherwise
unsuitable for a tramway. Several firms are now prepared to
supply these aerial systems of transport, but the one which has
been most successful in connexion with clayworking is that of
Adolf Bleichert & Co. In this the bucket is carried by two
pulley wheels connected together and running on one rope,
whilst a clip on these wheels grips another rope which hauls the
bucket to its destination. It is in the peculiar construction of
the clip or jaw that the apparatus shown has the advantage over
many other arrangements for aerial ropeways, as the Bleichert
grip (fig. 13) is formed of two jaws which grip the traction rope.
One of the jaws is firmly fixed to the carriage, while the other,
constructed as angle-lever, constitutes the counterpiece to the
fixed jaw. The weight of the hanger, car, and respective load
is borne by the longer arm of the angle-lever. The power of the
grip is therefore determined by the proportion of the angle -
lever's arms, and as this proportion can be adapted to the maxi-
mum gradient of any line, the safety of the apparatus is ensured.
The jaws can be made of a sufficient length to avoid damaging
the traction-rope. The pressure, with which the rope is gripped
by the gripping jaws is produced by the weight of the car and
its load, and is increased by means of levers.

THE GENERAL MANUFACTURE OF BRICKS 37

FIG. 12. — Overhead or aerial ropeway.

38

MODERN BRICKMAKING

When barrows are used for moving clay their shape and size-
is more important than
is often supposed, and
the distance of the
centre of gravity when
loaded from the line
joining the point of con-
tact with the ground,
must be carefully ad-
justed. If it is over 12
in. the workman will
find it difficult to bal-
ance the barrow and his
output will be dimin-
ished.

The spades used in
digging clay should be
of medium weight, not
too wide, and should
have a flat or slightly
curved blade, if the clay is pasty (fig. 14). For dry clay a wide
shovel with side flanges may be used. In this country the

FIG. 13. — Clip and runners for Bleichert
conveyer.

FIG. 14. — Spades, etc., used in clay-digging.

spades have almost straight blades, but in America a strongly
sloping blade is considered more satisfactory.

CHAPTER III.
HAND-BRICKMAKING PROCESSES.

MOST clays which can be worked up into a suitable plastic
paste can be made into bricks by the aid of hand-moulds, but
at the present time hand-making is chiefly practised in the
South of England for ordinary facing bricks, and in the Midlands
and North for the manufacture of fire-bricks, for specially moulded
bricks, and terra-cotta. As almost any clay with sufficient
plasticity can be moulded into bricks formed by hand, the
number of clays of widely differing characteristics described as
" brick earth " is very large, and the prospective brickmaker must
be careful in his choice of material, for some clays are impossible
to use commercially, even when, apart from the cost of manu-
facture, it is quite p'ossible to make good bricks from them.
It by no means follows that because good bricks can be made
from a certain clay that they can be produced at a cost which
would be commercially satisfactory, and the prospective brick-
maker should exercise the greatest caution before embarking on a
new enterprise, even when he has seen excellent specimens of
articles made from the clay it is proposed to use. Thus, true
London clay is very troublesome to those unacquainted with its
special nature, as it appears to be highly plastic though in reality
it is not so, though it is very sticky. It is very doubtful whether
first-class bricks can ever be made from strong London clay,
though a commoner brick is made in large quantities. A strong
clay, in the absence of an ample supply of mild loam or sand, can-
not be made into good bricks, though those of an inferior quality
may be produced in some cases. The reason for this is that clay
which is very strong shrinks excessively on drying and burning,
and so it is almost impossible to prevent cracking to such an
extent as to make the bricks composed of it practically useless.
Nodules of all kinds should be avoided in clay to be moulded
by hand. They can be removed by washing the clay, but it
seldom pays to do this.

(39)

40 MODEEN BRICKMAKING

Stones, when occurring in a strong clay, are a blessing to the
brickmaker, provided that the stony matter is of a siliceous
nature (not limestone), but in a very mild clay the presence of
stones will reduce the plasticity too much, so that they must be
removed before such clay can be used.

Siliceous or sandy stones, when found in strong clay, may be
ground up with it, and so produce a mild mixture which will have
the proportion of stones and clay which produce a good quality
of brick, the colour of which will depend upon the composition
of the mixture. When stone-bearing beds occur with clean, mild
or sandy clays the stones may be picked out by hand or by some
form of mechanical clay-cleaner (page 22), and are frequently
valuable as a by-product.

Sand and Gravel can only be removed by washing.
The most popular clays for hand-brickmaking are the Oxford,
Reading, Bagshot, and Gault beds in the South and the East
and the Midland beds, but many surf ace- clays in different
parts of the country are locally considered to be of great value
for this purpose.

The Preparation of the Paste for hand-brickmaking is effected
as follows : The clay, after any necessary purifications and
the addition of any non-plastic material, must be made up into
a paste of sufficient softness and plasticity to turn out easily
from the mould and to dry and burn without cracking or warp-
ing. It is necessary to effect a thorough mixing of the various
materials, to ensure their reduction -to a sufficiently fine state,
and to incorporate the precise amount of water to produce the
desired plasticity. The clay may be sufficiently pure to be used
direct, with or without the addition of non-plastic materials,
such as sand or chalk, or it may have been purified by washing
or some other treatment. Turf, top-soil, gravel, or an excessive
amount of stone or sand must be removed in the getting of the
clay, so far as this is possible, but in certain clays washing
cannot be avoided.

Washing is carried out in wash-mills similar to the one de-
scribed on page 25, the clay being churned up with a sufficient
quantity of water to produce a thin slip, or slurry, out of which
the stones settle whilst the clay is carried round in the slurry.
This is run off to a wash-back, and the clay having settled, the
water is run off leaving a stiff paste.

Another useful method of cleaning clay from stones is a
mechanical clay-cleaner which consists of a sieve or perforated

HAND-BBICKMAKING PROCESSES 41

screen through which the clay (previously made into a paste)
is forced, the stones being left behind (page 24). The disad-
vantage of these clay-cleaners is that, they only separate the
larger stones, yet the very small ones, in the case of limestone,
may be as detrimental as any ; hence, whilst clay-cleaners may
be satisfactory when only stones over J in. diameter are present,
clays containing limestone must be washed if the removal of the
small stones or gravel is really necessary.

Clay sufficiently free from objectionable ingredients having
been obtained, it is next necessary to reduce it to a state in
which it will readily mix with the water required to make it
into a uniform plastic paste. If it has been washed it will
already be in a pasty condition as it comes from the settling-
tanks or wash-backs (page 25), otherwise it must be crushed,
unless it is so fine and mild that treading or repeated turning-
over with a spade will convert it into a state in which it may be
taken to the pug-mill.

The crushing or grinding may be effected by a pair of crush-
ing rolls or in a pan-mill with edge runners, the former being
generally employed for strong sticky clays and the latter for
hard ones. In some cases it is necessary to use several pairs of
rolls or a combination of rolls and edge-runners (page 86). Much
unnecessary grinding or crushing may be avoided by weathering
the clay thoroughly. Indeed, weathering (page 22) should never
be omitted when it is likely to benefit the clay, as it effects a
disintegration far more complete than is possible with any kind
of crushing machine. The oxidizing and other actions which
take place in weathering are also important to the brickmaker,
and many clays which cannot be used when freshly dug will
make excellent bricks and tiles if the clay is exposed to the
action of the weather for a short time previous to its being sent
to the mills.

Most makers of hand-made bricks declare that hand-mould-
ing cannot be effectively carried out with clays which require
much preliminary crushing, and when crushing rolls have to be
employed, it is customary to manufacture only machine-made
bricks. A notable exception to this is found in the case of fire-
brick manufacture in which the hard, rocky clay is first crushed
by rollers or pan-mills before being mixed with water and pugged.
With most other hand-made bricks the clay is taken direct from
the bed or weathering heap and pugged, or it is washed, and the
purified clay from the wash-backs is sent to the pug-mill.

42 MODERN BEICKMAKING

For some purposes edge-runner mills give better results than
crushing rolls, though they require the clay to be dry and not
too sticky if large outputs are desired. The use of edge-runner
or pan-mills is described in the chapter on " Stiff- Plastic Brick-
making ". These mills are seldom used for bricks made by
hand-moulding, though in the manufacture of fire-bricks their
manufacture is common and desirable owing to the peculiar
nature of fire-clay, which is essentially a rock needing to be
ground to a powder before being mixed with water. Clays of a
rocky character are usually most conveniently treated by the
stiff-plastic system, but when very low in plasticity it may be
preferable to use more water (as with fire-clays) and to mould
them by hand. They are then best crushed in an edge -runner
mill and, after sifting, are mixed with water in a pug-mill until
a uniform paste is obtained and a consistency suitable for hand-
moulding. Such instances are comparatively rare, so far as
ordinary hand-made building bricks are concerned.

After the material has been treated so that no hard lumps
remain in it, water must be added so as to convert it into paste.
This operation is known as tempering, and is best performed a
couple of days before the clay is to be pugged. The reason for
this is the souring, or putrefaction, which most clays undergo
when kept in a moist state, whereby the water is more fully
distributed and a more homogeneous paste is the result. The
preliminary tempering should be made by mixing some of the
clay with water and turning it over with a spade, this operation
of watering and turning over being repeated until sufficient
water has been added. It is not wise to shirk this part of the
process of manufacture, as some makers do who put their clay
direct from the crushing plant into the pug-mill.

It is generally wise to allow the clay to soak for some little
time before it is turned over by the spade, though in some cases
this turning over is unnecessary if the soaking is sufficient.
Rocky clays, on the other hand, are scarcely effected by soaking.
The use of hot water instead of cold is valuable in the tempering
of some clays.

When the clay is taken from wash-backs, the men should be
instructed to dig downwards and not take off layers of clay from
the top of the deposit. If the various earths of which the bricks are
to be made have been previously spread over the surface of the
tempering shed, or ground in layers of the required thickness,

HAND-BKICKMAKING PEG CESSES 43

cutting the material vertically will -ensure the portions taken
having the desired composition.

In former times it was customary to continue the spade work,
or tempering, of the clay until a plastic paste was produced, this
process being aided by the treading of the clay under horses ', or
men's feet ; but this method has, to a large extent, died out in
this country (though it is still practised in the manufacture of
crucibles for steel making, for retort clay, and for a few other
special branches of clay working) as it is found that pugging is
more effective and far cheaper for ordinary bricks. In the
neighbourhood of London, where ashes are added to the clay,
they are mixed in during the process of tempering it by spade
labour, previous to the mixture being taken to the pug-mill.

In the manufacture of tiles (where a better price is obtainable
in proportion to the amount of clay used) foul clays (i.e. those
containing stones) may be soaked for some time, and the paste
thus formed is " slung " or cut into thin slices with a wire before
being pugged; but this operation does not pay in the case of
bricks. When slinging is resorted to, the clay should be passed
once through the pug-mill and then cut up into thin slices with
a wire, as the time taken in the preparation of the paste is
thereby greatly reduced. The object of slinging is to enable the
stones in the clay to be readily picked out. A similar purpose
is served by the mechanical cleaners already described.

Pugging. — After being mixed with water in the operation of
tempering, the clay is in the form of a paste of fairly regular
composition. It must be made homogeneous by \a further pro-
cess of mixing ; the usual plan being to treat it in a pug-mill, or
in a grinding-pan with edge runners and a solid revolving pan.
The pug-mill is more commonly used, though in the manufacture
of fire-bricks and fire-clay goods the clay paste may be kept in
a pan for about twenty minutes with most satisfactory results.

For hand-brickmaking the pug-mill is usually of the vertical
type, the tempered clay being thrown in at the top and gradually
becoming more uniform in character as it passes through, and is
finally discharged at the bottom. The mill with an upright
shaft, to which are attached knives passing through its centre,
is usually made of wood and resembles a large barrel, but during
recent years various alterations in the construction of pug-mills
have been made, and many iron cylinders and wooden conical
bodies are now in use. The horse-driven mill is slowly, but

44 MODEEN BRICKMAKING

surely, giving way to the mechanically driven one, as a horse is
unable to give more than a very slight pugging. This is un-
satisfactory in the case of unwashed clays, and the use of washed
earth is rapidly diminishing on account of the expense of wash-
ing and the space occupied by the settling tanks. With washed
earth, pugging is scarcely necessary, though it should never be
omitted.

The value and efficiency of a pug-mill depends upon its size
and upon the arrangement of the knives. If too small, and
especially if too short, the mill will not mix the clay sufficiently,
and if the knives are incorrect in shape, or are badly arranged,
the clay will emerge without being homogeneous. The older
forms of pug-mills are singularly inefficient, as the blades are too
small to be of much service and the amount of kneading and
mixing which occurs is comparatively small. Broader knives,
which would act better, require more power than can usually be
given by a horse.

A better type of mill is shown in fig. 15, but this is power
driven. When constructed according to the suggestions of A. E.
Brown, it consists of a conical wooden vessel A mounted 011 6 in.
square oak cross sills B and between two equally stout uprights
CC tied near their upper ends by the cross beams DD and by
other strong struts (not shown) which take the thrust of the
driving belt or chain. The 2-^ in. countershaft F, supported by
two plummer blocks//, carries a 5 ft. pulley H (driven direct from
a 12 to 18 in. pulley on the engine) and the bevelled pinion K2
The 2-J- in. vertical shaft EE is carried by two plummer blocks
ee and a foot-step g. This shaft is made in two pieces, connected
with a sliding coupling G, in order that the upper portion may be
turned apart from the lower one when desired, as when a second
pug-mill or wash-mill is driven from the chain wheel L, on the
same countershaft, the present pug-mill not being required.

Five knives a, and a scraper b, to force the clay out through
the opening C, are provided, the shape of the former being of an
American type not well known in this country, but very satis-
factory wherever they have been used. The essential feature of
these knives is the possession of one unsymmetrical and one flat
side, as shown in fig. 16, the shape of the scraper b is better
shown by fig. 17.

When run at four or five revolutions per minute, a mill of
this type, 3 ft. 6 in. diameter at the top tapering to 3 ft. 2 in. at the
bottom and 4 ft. 6 in. to the top of the barrel A, will pug sufficient

HAND-BEICKMAKING PKOCESSES

45

FIG. 15. — Home-made pug-mill.

46

MODEEN BEICKMAKING

clay for 6000 bricks per day, although a larger quantity can be
turned out if it needs only a light pugging.

Fig. 18 shows a pug-mill of the old horse- driven type, but of

FIG. 16. — Blades of pug-mill (A. E. Brown).

superior construction and capable of preparing sufficient clay
for about 5000 bricks per day. The knife is the Archimedean
type, preferred by the makers. The knives in this mill do

cc

YIG. 17.— Bottom scraper of vertical pug-mill (A. E. Brown).

not merely cut the clay but turn it over in each revolution, so
that every part of the clay is submitted to their action, and being
furnished with scrapers or cleansing knives, clogging and exces-
sive adhesion to the sides of the mill are prevented, and the whole
mass of clay is more thoroughly amalgamated than in the earlier

HAND-BBICKMAKING PKOCESSES

47

forms of mill. Like many. other mills of this type constructed
of iron, this one is deficient both in height and diameter where
difficult clays are worked. Unless the circumstances are excep-
tional, the barrel of a vertical pug-mill for clay for hand-brick-
making should never be less than 3 ft. diameter in any part, nor
less then 4 ft. 6 in. high, and only one outlet should be used at
a time.

Feeding is facilitated by making the mouth of the barrel
somewhat bell-shaped, and the ejectment hole should be fitted
with a sliding door in order to regulate the speed at which the
clay travels through the mill and to secure its being sufficiently
pugged.

FIG. 18. — Horse-driven pug-mill.'

A typical power-driven mill of the all-metal type is shown in
fig. 19, but it would be more efficient if made both higher and
larger than those usually kept in stock. Mills of this type are
supplied by all makers of clay-working machinery and require
2 to 6 h.p. to drive them.

The illustration of the machine in fig. 20 represents a power-
driven pug-mill in which the upper part is expanded so as to
secure greater mixing power. The machine has two sets of
knives, one in the large pan and another in the barrel, and the
former are so arranged that at each revolution the clay is taken
one step nearer to the centre of the mill. The delivery opening,
which is placed tangentially to allow of free delivery, is fitted

48

MODERN BRICKMAKING

with a sliding door actuated with screw and hand wheel, so as to
adjust the opening to suit the condition of the clay required,
but a simple slide is sufficient for most purposes. Such machines
are specially suitable for hard clays which do not mix readily
with water, such as shales and fire-clays.

The " Vulcan " mill (fig. 21), made by the Horsham Engineer-

FIG. 19. — Pug-mill for small yards.

ing Co., has an elevating arrangement by which it delivers clay
on to the brickmoulder's table and is a useful labour-saving
device.

Some brickmakers maintain that horizontal pug-mills are
unsatisfactory for hand-made bricks, and that they require more
power to drive them. The contention is not well founded, though
the effect of gravity in a vertical pug-mill should, theoretically,
reduce the amount of power to pass the clay through it. In

HAND-BRICKMAKING PROCESSES 49

some tests made by the author this difference was so small as to
be negligible, and it may therefore be left to the brickmaker to
suit his own convenience in handling the clay as to whether a
vertical or horizontal pug-mill is used. Horizontal pug-mills
are described in Chapter IV.

FIG. 20. — Vertical pug-mill for fire-clay, etc.

The best speed for running a pug-mill will vary with its con-
struction and with the clay used. The makers should be con-
sulted on this matter. An ordinary vertical pug-mill should be
worked at a speed of five revolutions of the shaft per minute,
but the speed which is really most suitable for a particular clay

4

50

MODEEN BRICKMAKING

can only be ascertained by actual trial. The men engaged in
feeding the pug-mill must see that it is kept full of clay, or the
latter will be imperfectly mixed.

Moulding. — Two distinct methods of moulding bricks by hand
are in use at the present time. In the first, the mould is dipped
in water before being filled to prevent the clay adhering to it.
This is known as " slop-moulding ". In the second method the
internal surfaces of the mould are covered with sand, whence the
term " sand-moulding " for bricks made by this method.

Considerable differences in dealing with the clay when once
the brick has been formed in the mould are also common.
'Thus in ordinary slop- moulding a boy takes the filled mould

FIG. 21. — Elevating pug-mill.

from the maker's bench to the drying floor and turns out the
brick on to the floor, returning to the bench with the empty
mould. Meanwhile the maker fills a second mould. In sand-
moulding, on the contrary, but one mould is used, and the
maker, after filling it, turns out the brick on to a pallet or carry-
ing-board. This distinction does not hold good in all cases,
however, as with some clays (notably fire-clays) the bricks are
slop-moulded, and then turned on to pallets by the maker.
These differences in treatment really depend on the stiffness of
the brick in the mould, and the extent to which it can be
handled after leaving the latter.

Bricks which have been moulded and turned out on to a pallet
are placed on barrows, and a considerable number of them taken

HAND-BKICKMAKING PEOCESSES 51

to the hack or drying floor, which may be at a considerable
distance from the maker's table, but in some instances drying
floors on which the makers move their benches to and fro are
employed.

It is convenient, for the sake of clearness, to describe the
sand and slop-moulding processes and the subsequent hand-
ling of the bricks quite separately, though from the foregoing it
will be understood that in some works portions of one process
are made to follow those of the other, when the nature of the
clay enables this to be done, and time or labour to be saved
without detriment to the bricks.

The moulder's table or " stool " is very strongly made, about
6ft. by 3ft. and about 3ft. high, it is provided with various boxes,
etc., according to the method of brickmaking adopted, and whilst
the shape and size of the table and the fittings differ in various
localities the principal arrangements are the same in all.

In Slop-Moulding the table is furnished with a box for sand
and another for water, these being so placed that when the
moulder is at work the sand-box is at his left hand, the water-
tank is in front of him, and the clay ready for use at his right
hand, ample room being left for the working of the clay. A
larger tank for water stands at the left side of the table.

In making a slop-moulded brick the workman sprinkles some
sand on the vacant part of the table immediately in front of
himself, takes a lump of clay sufficiently large for his purpose,
and kneads it on the sanded table to the shape of a brick. He
then takes a mould and dips it into the water-trough so as to
wet it thoroughly, at the same time cleaning it from any adhering
material, and places it on the table. He next raises the rough
shaped clot of clay and dashes it with considerable force into the
mould. The next operation consists in compressing the clay so
that it may fill the mould completely, and this is done by the
workman using his hands, or a small flat board with a vertical
handle called a " plane ". The superfluous clay is then removed
by the workman's thumbs, an even surface being given by finally
drawing a straight edged strip of wood (termed a " strike ") across
the mould. The strike is then thrown back into the smaller
water-box. A boy picks up the mould with its contents, and
carries it to the dryer floor, where he lays it down, and with a
skilful twist of the hand turns out the ready-made brick on to the
floor. Meanwhile, the man fills a second mould, and has another
brick ready by the time the boy returns to the bench.

52 MODEEN BEICKMAKING

Numerous variations of this process are known. Thus, the
man may make the boy wash his moulds so that they are wet
and ready for use when required. Sand is not used in some
cases, the mould being then placed on a moulding-board covered
with fustian kept continually wet. Instead of a strike to smooth
the face of the brick, a flat polishing tool or plane is sometimes
used, both sides of the brick being smoothed in turn. In some
yards, as already mentioned, the bricks are sufficiently stiff to
bear more handling, and are therefore turned out on to pallets
as described in hand-moulding. It will be seen that the distance
the carrying-off boy has to travel must not be greater than will
allow him time to return to the table by the time the moulder
has a fresh brick ready. On this account, the men who work by
the slop-method are compelled to be close to the drying-shed,
and usually work in it. The boy starts setting down the bricks
in a series of straight lines extending from the wall of the shed
to the table, and as soon as a considerable portion of the floor is
filled with bricks the table is moved to a fresh position. The
object of this is to reduce the distance travelled by the boy as
much as possible, without unduly hindering the moulder by too
frequent movings of the table.

The bricks on the drying floor are often covered with a thin
sprinkling of sand to prevent them cracking, and may afterwards
be taken to the kiln or to a hack-ground where they are stacked
up for further drying.

The output of a man working by the slop -method with the
necessary attendance is seldom more than 10,000 bricks per
week, and 1500 bricks per table is reckoned a good day's work.
This is much less than the output where sand-moulded bricks
are made. Under specially good conditions, and with a clay
which can be worked fairly stiffly, a daily output of 2000 slop-
moulded bricks can be reached, but is only maintained with
difficulty. In Central Ireland the author has seen two men and
two boys producing 1000 bricks per hour for five hours at a
stretch. They were extremely rough, and the clots prepared by
one man were simply thrown into the mould and roughly
"thumbed off" by another, the mould being kept in a tub of
water when not being filled.

In making sand-moulded bricks a different mode of procedure
is employed. In this case the moulder's table is provided with
a deep rim at each end and partly along one side to keep the
sand in place, a small box containing water for holding the

HAND-BRICKMAKING PROCESSES 53

strike, and a " stock-board " or " bed " on to which the mould
fits close to the table, and often fastened to it is a projecting
beam, 3ft. to 6ft. long, on which are two thin iron rods fastened
parallel to each other, and which serve as rails along which the
pallet boards may slide. This appliance is termed a " page ".
The moulder stands facing the table with the " page " at his left
hand, and on his right is an attendant (often a woman) known
as the " clot-moulder," the sand for the use of these two workers
being placed at the opposite ends of the table.

In order to make bricks by this process, the clot-moulder
sprinkles part of the table with sand, and, on the portion thus
prepared, kneads up a lump of clay of the correct size into a
rough brick and places it ready for the moulder. This man,
having sprinkled the stock-board or bed with sand, plunges the
mould into the sand-heap and covers its inside surfaces with a
thin coating of sand and places the mould on the bed. He then
takes the clot prepared for him, dashes it forcibly into the
mould, and presses the clay with his fingers so as to completely
fill the mould. This operation is known as " walk-flatting " and
requires considerable skill. If the clot is too small sand-folds
will appear on the face of the brick, and if too large it will not
enter the mould properly.

When the mould is filled, a sufficient thickness of clay should
project from the top of it to provide a clean, raw base for the
next brick, and care must be taken that the moulder takes this
off with his thumbs or with a wire and lays it on the freshly
sanded table with the cut face downwards. Otherwise, sand-
folds are inevitable when the clot-moulder puts a fresh piece of
clay on to this and proceeds to shape one clot from both.

The excess of clay having been removed by " thumbing " or
with a wire, the surface of the brick in the mould is smoothed
by drawing a straight edged strip of wood (termed a " strike ")
across it in such a manner that the arris of the strike removes
any excess of clay. The flat side of the strike must not be used,
and to obtain a good finish the strike must be kept very wet.
The mould is next lifted from the stock-board, placed against an
empty pallet, and, by a dexterous twist, the brick is turned
out on to the latter and left on it on the page. The mould is
freed from any adhering material, again sanded, and is ready
for use. If the sand will not adhere properly to the mould the
latter is wetted occasionally.

The brick with its pallet is taken from the page by a boy and

54 MODERN BRICKMAKING

placed on an off-bearing barrow, and when the latter is full, sand
is sprinkled over the bricks and they are carefully wheeled away
to the hack-ground or dryer, where they are set on edge, in
hacks eight or nine bricks high with the aid of a second pallet
placed on top of the brick, so as to enable it to be carried and
turned sideways. Very thick bricks should only be set five or
six bricks high.

The construction of the off-bearing barrow is a matter re-
quiring some attention. Too many of those in use are badly
balanced (making the labour of wheeling unnecessarily great),
or they are built too low for the most convenient work. A well-
designed off-bearing barrow must be capable of travelling over
rough ground without the bricks on it being damaged, and yet
the arrangement of the springs must be simple and not likely
to get out of order. Spiral springs and those of the bow type
are not usually satisfactory, and a much better pattern is that
supplied by W. Bracknell. In this the spring is a plain strip of
steel with a double curve, and is so placed that the axle of the
wheel is at the strongest and most rigid part of the barrow,
whilst the bricks are supported by a spring of ample size and
power. In most barrows the springs are placed in such a
manner that strength is lost, and the " life " of such barrows is
consequently short.

With three barrows — one of which is always being loaded —
two men to wheel and hack, a boy and a clot-moulder, a brick-
maker can turn out 4000 to 5000 bricks per day if he is kept
well supplied with clay, and a weekly output of 30,000 bricks is
not infrequent. Where best quality facing bricks are required,
a lesser output must be expected on account of the greater care
required.

Although the work looks easy, moulding bricks by hand
really needs highly skilled labour, and it has with some truth
been said that " a good moulder is born and not made ". Much
may be done, however, by patient insistence and careful watch-
ing on the part of the owner of the works.

Until lately, the moulds used for hand-made bricks were
made of wood, but these have been largely superseded by brass,
or as they are technically called " copper " moulds, or by those
lined with or made of iron or steel. Wooden moulds are only
suitable for sandy clays and it is almost essential that they be
wetted during use (as in slop-moulding). Iron and steel lined
moulds can be used with sand and without water, and brass

HAND-BRICKMAKING PROCESSES

55

moulds need neither sand nor water, but are too costly and
insufficiently durable for ordinary use. Zinc-lined moulds are
much used for bricks of special shape.

Brick moulds must be sufficiently rigid to preserve their
shape perfectly in use, in spite of the force applied in filling the
moulds, and yet they must not be so stoutly made as to be in-
conveniently heavy. On this account wood is always used for
the major portion of the mould, a metal lining being inserted to
facilitate the turning out of the brick. Teak and oak are the
best woods for this purpose ; others swell and shrink too much
to be satisfactory.

A typical mould has a lining overlapping the woodwork on
each side, and as this wears away the moulds must be relined or
replaced with new ones. This mould has no bottom, the lower
face of the brick being formed by the table on which the mould
is laid.

Another mould is of the type chiefly used in the London
district. It has a separate bottom or " stock-board " which is
fastened to the table by a peg at each corner. This stock-board
is made of wood with an iron plate, a special centre-piece (termed
the " kik ") being used to make a frog or hollow centre-piece in
the brick. The mould itself is a rectangular frame of iron, or
wood faced with steel, which fits on to the stock-board and rests
on the four corner pins when in use.

The use of four set-screws in place of these corner pins, as
suggested in Barton
& Co.'s mould, fig.
22, is a great im-
provement. In this
case the plate B
and the stock-bed
A are fastened
firmly to the table
E by means of the
bolt C, and the
thickness of the
brick can be regu-
lated to the greatest
nicety by altering

FIG. 22. — Improved hand-brick mould.

the set screws A until a sufficient space exists between the top
of the plate B and of the mould D.

Box-moulds which have a fixed bottom piece attached to the

56 MODERN BRICKMAKING

sides, should only be used for fancy bricks. When plain bricks
are being made they are little or no better than when the
ordinary mould is used.

Dryitig. — By whichever method of hand-moulding bricks are
inadeTthey must be dried before they can be placed in the kiln.
The amount of water in the bricks will determine, to some
extent, the best method for removing it, for if the bricks are
very soft they must usually be laid out on a drying floor until
sufficiently stiff to bear stacking. If, on the other hand, sand-
faced bricks are made, they can usually be taken to the hacks
and stacked immediately.

In small yards where hand-made bricks are produced, arti-
ficial dryers are seldom worth installing, and a hack-ground will
meet most requirements. If bricks are to be made during the
winter, however, a drying-shed heated by steam or a series of
fires will be necessary.

The ordinary hack-ground consists of a large field. The usual
allowance is one acre of land for each million bricks produced
in the season, as level as possible, on which the bricks are laid
in narrow rows about 50 to 80 yds. in length, and 9 ft. to 12 ft.
from centre to centre of each hack or row.

The direction in which the hacks run is also important ; it
should be north to south or north-east to south-west, so that both
sides of the hacks should receive an equal amount of sun, and
yet neither side be exposed to the direct rays of the sun at mid-
day. Small trenches should be dug running in the same direc-
tion as the hacks, and 3 in. land drain-pipes laid under the hacks
at intervals of every ten yards to secure ample drainage. Though
not often done, it is a wise practice to use the earth dug out of
the trenches to form small embankments on which to place the
bricks. This simple arrangement will prevent a considerable
number of bricks from being spoiled by wet weather.

In very damp situations the bricks should not be set
direct on to the ground but on thin
planks, or preferably on hollow pipes
of rectangular section 12 x 4^ x 2^ in.
(fig. 23) placed side by side. These
" tiles " can be made quite cheaply in
an ordinary pipe machine. They last
FIG. 23.— Hack tile. several years, and the air passing through
them prevents the green bricks from drawing moisture from the
ground when such tiles are used.

HAKD-BBICKMAKING PEOCESSES 57

Each row, or hack, consists of two blades of bricks with a
space of about 8 in. between each. The bricks are set on edge
about 5 to 8 in. apart, the bricks in each row covering the
spaces between those in the row below it, and the whole hack
being about 36 in. high. In setting the bricks, each row must be
laid along the whole length of the hack before commencing
another, as, if set to the full height at once, the lower bricks
would collapse.

When hacking bricks, the men should always lay a setting
board (a kind of pallet board but sometimes a little thicker) on
the brick, and lift the latter between the two boards and so carry
and place it on the hack. Handling bricks with bare hands
invariably defaces them, and is no quicker than when pallet
boards are used.

To protect the bricks from rain, the hacks are covered with
small, roof-like structures made of light boards, though in some
cases straw is laid on the bricks. For many reasons straw is not
satisfactory, and wooden covers, either of the portable kind shown
or a permanent wood roofing over the hacks, should be used.
For a clay of unusual delicacy it may be necessary to cover the
bricks with straw to prevent too rapid evaporation of the moisture
in them. Loose wooden covers, such as that in fig. 26, cost about Is.
each. They should be made of 12 planks, 6 in. by f in., set at such
an angle as to measure 42 to 48 in. across the bottom of the gable.

For protecting the sides of the hacks from too rapid drying,
draughts, or rain, sacks, matting, or loose boards are used, the
last named being the best if properly constructed, though matt-
ing has the advantage of permitting a freer circulation of air. If
boards are used they should be fastened together to form " loos,"
6 ft. long by 2 ft. 6 in. wide, with the strengthening ribs lengthened
to act as legs as shown in fig. 24.

For better qualities of bricks, sheds containing racks must be
used, or an artificial dryer installed. A good type of plain shed
for this purpose is that shown in fig. 25. According to A. E.
Brown, such a shed 85 ft. x 30 ft. will dry 100,000 bricks per
season, and leave ample room for the moulder and engine, and
a clear 20 ft. x 30 ft. space for stacking dried bricks. The roof
is of galvanized iron, with J- in. match-board lining carried on
posts 10 ft. apart. The sides are fitted with a double row of
shutters, or they may be built of perforated bricks. The racks
are 15 ft. long and 2 ft. wide and about nine shelves high, with
gangways 3 ft. wide between them.

58

MODERN BRICKMAKING

In some parts of the country, the bricks as they lie on the

floor of the drying-
shed, or during the
process of hacking,
are tapped gently
with a clapper, which
is a piece of wood
rather larger than a
brick with a handle
in the centre. This
clapping is intended
to remove defects in
the shape of the brick
due to carelessness or
accidents in the set-
ting down. When
polished bricks are
required they must
be obtained with a
wedge - shaped tool
termed a dresser, this operation being carried out on a bench
or table about 4 ft. long by 2 ft. high, covered with a plate of
iron or steel so as to give them an even surface. This toughens
the bricks, corrects any accidental warping, and leaves edges on
the bricks very sharp ; but pressing has now replaced dressing
on acount of the lower cost.

FIG. 24. — Loo.

FIG. 25. — Drying shed.

An end view of a hack is shown in fig. 26, which is drawn
to scale. The height of the hack depends on the stiffness of
the bricks.

A different type of hack, which has been favourably received
in Germany, is shown in fig. 27. It is more expensive to con-

HAND-BRICKMAKING PROCESSES

59

struct than the temporary ones just described, and the wood
has be'en preserved with creosote before use. As the sketch is
drawn to scale, and the chief dimensions are shown, no further
description is necessary, especially as in this country a dryer
heated by steam or fuel is cheaper in the long run than is a per-
manently erected set of hacks of the type shown.

Skintling. — When the bricks in a hack are half dry and are
stiff enough to be handled, they are " skintled " or set farther
apart and diagonally to let air pass more freely through them.
As the skintled bricks occupy more space than those set apart

FIG. 26. — End view of hack.

in the ordinary manner, the hack must be built higher so as to
still accommodate the original number of bricks.

Pressing. — When hand-made bricks are to be pressed, it is
necessary to set them less than eight bricks high, and to take
them to the press before they have become too dry. To prevent
excessive drying of the ends, the bricks may be " skintled ".
Bricks which are to be pressed require very careful watching,
particularly in warm weather, and an ample supply of matting
is necessary to prevent them from becoming too hard. The
press most suitable for hand-made bricks is one which can be
wheeled alongside the bricks in the hacks, and must therefore

60

MODEKN BEICKMAKING

be of the portable, hand-power type. A number of such presses
are on the market and are very similar
to each other. Fig. 28 shows a press of
this type made by the Brightside Foundry
and Engineering Co., Ltd., which, in spite
of minor defects, can be recommended on
account of its portability and low cost.

A single motion of the lever closes the
box and presses the brick, and the reverse
motion of the lever opens the box and
raises the brick. The cover is thrown
back, leaving the top of the mould quite
free for the removal of the brick and the
insertion of a fresh one. The bottom piston
is fitted with a groove all round, in which
the makers suggest coarse wool may be
put for carrying the lubricating medium.
This wool may be soaked with paraffin
and a small quantity of engine oil, and
as the mould moves up and down this
lubricates the sides. If not lubricated,
the clay would stick to the sides of the
mould, and a clean brick would not be
turned out. If brick-press oil is used, the
bricks are liable to scum in drying. This
machine when operated by one man and
a boy will press '5000 bricks per day, or
one man working alone can press 2000
bricks and set them back again on the
hacks to complete the drying. The press
will need a considerable amount of clean-
ing when sand-faced bricks are pressed,
and care is needed to see that the mould
is kept really clean.

Fig. 29 shows a similar press made by John Whitehead &
Co., Ltd., in which the weight-lever is adjusted so that the pres-
sure given can be adapted to bricks of varying thickness.

The chief disadvantages of hack-drying are its extreme slow-
ness (three to six weeks being required), the loss through bricks
damaged by bad weather, and the very considerable expen
diture necessary for repairs. The wheeling to and fro from the
hacks, skintling, attending to matting, etc., are also expensive,

AN-

FIG. 27. — German hack.

HAND-BRICKMAKING PEOCESSES

61

and it may be taken as a general rule that from the moulds to
the kilns bricks cost at least 3s. 3d. per thousand for drying.

Kilns. — Hand-made bricks were at one time burned exclus-
ively in clamps, but in more recent years permanent kilns have
been used. Clamps are practically the only form of " kiln " used
for stock bricks in Kent, Essex, and parts of Sussex, as clamp-
burned bricks are preferred by architects and builders using
bricks from these countries.

The choice of a kiln is largely determined by the quality of
bricks it is desired to produce and by the financial status of the

FIG. 28. — Press for hand-made bricks.

brickmaker. If hand-made bricks are made in relatively small
quantities it is seldom desirable to burn them in continuous
kilns i notwithstanding the low fuel consumption of this type of
kiln, and clamps or single up- or down-draught kilns are, there-
fore, preferable.

Opinions differ greatly as to the best shape for a kiln for
hand-made bricks, but the author prefers a rectangular to a
circular shape, as he has found it both easier to build and set.

62

MODERN BBICKMAKING

For outputs of 1,000,000 and upward bricks a year a continuous
or semi-continuous kiln may be used with advantage.

Various types of permanent kilns — both single and continuous

— are described in Chapter
VIII, as they are appli-
cable to all kinds of build-
ing bricks. Clamp kilns
may, however, be more
conveniently considered
here as they have a special
connexion with hand-
made goods, being con-
sidered essential for the
manufacture of London
stock bricks in which fuel
is mixed with the clay
previous to its being made
into bricks. The great
popularity of the clamp
for temporary purposes is
fully justified where the
appearance of the bricks
is of less importance than
their strength, and it is
wise for a firm starting a
new yard to commence
with a clamp in order that
they may thereby obtain
bricks for erecting their buildings and permanent kilns.

A clamp is formed by setting bricks together in a special man-
ner, so that they may be efficiently baked without the necessity
of putting them in a permanent kiln. The term " clamp " is
used in two senses — one meaning merely a temporary kiln and
the other a special arrangement of bricks which it is necessary
to use when the clay is mixed with fuel before being shaped.
The latter meaning is the one used in the yards where London
stock bricks are made. The chief characteristic of this latter
kind of clamp is that the bricks become "fireballs " when the
fuel contained in them gets sufficiently hot to burn, and the
firing once properly started, no additional fuel is required.

Many differences in detail in the construction of clamps are
found in the various districts where they are employed, and as

FIG. 29. — Adjustable lever press.

HAND-BEICKMAKING PROCESSES 63

great skill is required both in the setting and burning of bricks
by this method, only men really used to the work should be em-
ployed. The following description by the late Edward Dobson
is typical of the best practice around London : —

A clamp consists of a number of walls or necks three bricks
thick, about sixty bricks long, and thirty -four to thirty -six bricks
high, in an inclined position on each side of an upright or double
battering wall in the centre of the clamp, the upright being of
the same length and height as the necks, but diminishing from
six bricks thick at bottom to three bricks thick at top. The
sides and top of the clamp are cased with burnt brick.

The ground is first carefully drained and levelled and made
perfectly firm and hard. The exact position of the clamp having
been fixed, the ground is formed with a flat invert, whose chord
is equal to the width of the intended clamp. The object of this
is to give a " lift " to each side of the clamp, which prevents the
bricks from falling outwards as the breeze becomes consumed.
The ground being prepared, the upright is commenced. But,
previous to building, the clamp barrow-roads, or tramways of
sheet iron, are laid down between the hacks and extended to the
clamp ground, to give an easy motion to the barrows used in
clamping ; the bricks being piled on each other several courses
high on these barrows, and the wheeling carried on with con-
siderable velocity, they are apt to upset.

The upright is commenced by building two 9 in. battering
walls, about 45 ft. apart, of burnt bricks laid on edge which are
termed close bolts, the length of each wall being equal to the
thickness of the upright which at the bottom is six bricks* thick,
or about 4 ft. 6 in. (their height is sixteen courses or about
6 ft.). Between these bolts a line is stretched, by which the
upright -is built true. The ground between the bolts is paved
with burnt bricks laid on edge, to exclude the moisture of the
ground. Upon this paving are laid two courses of burnt bricks
with spaces between them, termed skintles. In the bottom
course of skintles the bricks are laid diagonally about 2 in. apart.
The second course consists of burnt bricks on edge, laid across
the lower one, in lines parallel to the ends of the clamp and also
2 in. apart. In laying these two courses of skintles, a live hole
is left about 7 in. wide, the whole length of the upright ; and on
the completion of the second course the live hole is filled up
with faggots, and the whole surface covered over with breeze,
which is swept or scraped into the spaces left between the bricks.

64 MODERN BEICKMAKING

On this surface is placed the first course of raw bricks, laid on
edge and quite close> beginning over the live hole. Over this
first course of raw bricks is laid a stratum of breeze, 7 in. thick,
the depth being increased at the ends of the uprights to 9 or
10 in. by inserting three or four bricks on edge among the
breeze. The object of this is to give an extra lift to the ends.
The first course of bricks, it should be observed, is laid " all
headers ". Over the first layer of breeze is laid a second course
of raw bricks on edge, " all stretchers ", This is covered with
4 in. of breeze, and at each end are inserted two or three bricks
to increase the lift still more, but this time they are laid flat not
edgeways. Upon the 4 in. layer of breeze is laid a heading
course of raw bricks laid close, and on this 2 in. of breeze, with-
out any extra lift at the end. To this succeed stretching and
heading courses of raw bricks on edge, laid close up to the top of
the clamp, a layer of breeze not more than f in. thick being placed
on the top of each course, except on the top course which has
3 in. of breeze. The top of the upright is finished by a close
bolt of burnt bricks. The upright is built with an equal batter
on each side, its width diminishing from six bricks lengthways
at the base to three bricks lengthways at the top. In order that the
upright should be perfectly firm, it is necessary that the bricks
should be well tied in at the angles ; and, in order to obtain the
proper width, the bricks are placed in a variety of positions, so
that no very regular bond is preserved, as it is of more conse-
quence to keep the batter uniform.

The close bolts first commenced, and which form the outer
casing of the clamp, are not built close to the raw bricks, there
beings small space left between the clamp and the close bolting,
which is filled up with breeze. The close bolts, however, are
built with a greater batter than the ends of the upright, so that
they just touch the latter at the sixteenth course, above which
the clamp is built without any external casing. When, however,
the upright is " topped," and whilst the top close bolting is going
on, the casing is continued up to the top of the clamp. This upper
casing is called the "bestowing," and consists of five or six
courses of burnt brick laid flat, forming a casing 4^ in., or half a
brick thick ; and above the sixth course the bricks are laid on
edge, forming a still thinner casing only 3 in. thick. When the
weather is bad, and during the latter part of the brickmakiiig
season, a little extra bestowing is given beyond what is here
described. The great art in clamping consists in the proper

HAND-BEICKMAKING PEOCESSES 65

construction of the upright, as the stability of the clamp depends
entirely upon it.

The remainder of the clamp consists of a number of necks
or walls leaning against the upright. They are built in pre-
cisely the same way as the upright, as regards invert, close bolts,
paving, skintling, breeze, and end lifts. But there is this essen-
tial difference, viz. that they are parallel walls, built in alternate
courses, of headers and stretchers laid on edge, each heading
course in one neck being opposite to a stretching course in the
next neck, and vice versa. The thickness of each neck is made
up of three bricks lengthways in the heading courses. The
necks are closely bolted at the top, and " bestowed " in the
same manner as the upright. When the last necks have been
built, the ends of the clamp are close bolted, and " bestowed "
in the same way as the sides, and this operation completes the
clamp.

The number of necks on each side of the upright may be
extended to eight or nine, without an additional live hole ; but
if this limit be exceeded, additional live holes are required.
According to the judgment of the brickmaker or the demand
for bricks, the live holes are placed seven, eight, or nine necks
apart. It is not necessary that the additional live holes should
pass under the centres of the necks, and it is more convenient
to form each live hole so that the face of the last built neck
shall form one of its sides.

The erection of a good clamp is a difficult operation which
can only be learned by experience.

Firing a Clamp. — The fuel used in burning the laid bricks
consists of cinders (breeze, as before described) which are dis-
tributed in layers between the courses of bricks, the strata of
breeze being thickest at the bottom. To light the clamp, live
holes or flues 7 in. wide and 9 in. high are left in the centre of
the upright at every seventh or neck. These live holes extend
through the whole thickness of the clamp and are filled with
fraggots which, being lighted from the outside, soon ignite the
adjacent breeze.

The fire is kept up for about a day, until the faggots in the
live hole are thoroughly ignited, and as soon as this is found to
be the case, the fire is removed, and the mouth of the live hole
stopped with bricks, and plastered over with clay or mortar. In
firing a large clamp with many live holes, it should be begun at
one end only, the live holes being fired in succession one after

5

66 MODERN BRICKMAKING

another. The clamp burns until the whole of the breeze is con-
sumed, which takes from three to six weeks.

The bricks at the outside of the clamp are usually underburned;
they are called "burnovers," and are laid aside for reburning in
the next clamp that may be built. The bricks near the live
holes are generally partially melted and run together in masses
called " clinkers " or " burrs ". The bricks which are not fully
burned are called " place bricks " and are sold at a low price,
being unfit for outside work or situations where they will be
subjected to much pressure. The clinkers are sold by the cart-
load for rock-work in gardens and similar purposes.

The number of underburned bricks from the edges of the clamp
(" burnovers ") may be greatly reduced by feeding a little coal
into them during the burning of the clamp, or to a less extent by
partially covering the top of the clamp with asbestos sheets so
as to throw the draught more to the sides. The best way is to
place a row of screenings or small hard coal along each side of
the clamp, at the top, forming it into a ridge about 12 to 18 in.
high. The bricks at the outside are set a little more openly
than usual, and a row of skintled bricks forms the outer row.
When the bricks nearer the centre of the kiln are well under
fire, the burner goes on to the top of the kiln, and with a broad-
ended poker pushes the bricks under the coal ridge aside and
allows a little coal to fall among them. This operation is repeated
every forty or sixty minutes, care being taken not to drop suf-
ficient coal down to choke up the flues and not to add a fresh
portion until the previous one is nearly all burned away. This
method may also be used with great success in continuous kilns
of the archless type.

The quantity of breeze required varies much with the quantity
of earth. The usual proportions for every 100,000 bricks are
about 12 tons of the sifted ashes, mixed with the brick earth, and
about 4 tons of the cinders, or breeze, to light the clamp.

The quantity of fuel to the live holes it is difficult to calculate ;
about 2s. may be taken as the average cost of coals and wood
for every 100,000 bricks. If the proportion of breeze be too small,
the bricks will be underburned, and will be tender and of a pale
colour. If too much fuel be used, there is a danger of the bricks
fusing and running into a blackish slag.

Another system of clamping is to begin at one end and to
follow with the necks in one direction only. This is done when
the clamp ground is partly occupied by the hacks, so as to render

HAND-BRICKMAKING PROCESSES 67

it impossible to commence at the centre. When this system is
adopted, the clamping begins with the erection of an end wall,
termed the upright and outside, which is made to batter very
considerably on the outside, but of which the inside face is
vertical. As regards dimensions and modes of building, the out-
side and upright are built in the same way as the ordinary upright,
but it has, of course, no live hole under it, the first live hole be-
ing provided in the centre of the second or third neck. In this
style of clamping the necks are all upright. The live holes are
placed at every eighth or ninth neck, as in the usual system.

The practice with regard to the paving of burned bricks is very
variable. Some clampers omit it altogether, others pave only
when clamping for the first time on a new ground. When burned
bricks run short, as in building the first clamp on a new ground,
the second course is laid with raw bricks. This is, however, a
very objectionable practice.

The live holes are sometimes close bolted at the sides to pre-
vent the breeze from the skintles falling into them. This is not
often done, and its utility is questionable.

Some clampers put the 7 in. stratum of breeze on the top of
the skintles instead of placing it over the first course of raw
bricks ; very frequently the breeze is dispensed with after the 2
in. stratum, with the exception of the top layer. All clampers,
however, agree as to the necessity of having the 7 in., 4 in., and
2 in. layers. Where breeze (cinders or coke) cannot be obtained,
small coal or anthracite (culm) may be employed, and in Ire-
land peat or turf is used, though with indifferent success.

CHAPTER IV.
PLASTIC MOULDING BY MACHINERY.

IN order to overcome the difficulty of obtaining skilled moulders
— a difficulty which has greatly increased within the last fifteen
years — various machines have been placed on the market which,
it is claimed, do away with the skill ordinarily required in mould-
ing by hand. These machines must not be confused with others
in which no resemblance to hand-moulding is attempted, though
this latter class of machine has increased enormously in popu-
larity in recent years on account of the large outputs possible.

Machines which seek to replace the skilled labour of the
moulder are usually designed ' so as to force the clay into box
moulds, similar to those used in hand work, from a box or tank,
by means of either a pug-mill or special knives. Their great
drawback has been the ineffective filling of the moulds and the
inclusion of air within the bricks, but in the machines described
below, these difficulties have been sufficiently overcome to make
the manufacture of bricks by them satisfactory and far simpler
from the managerial point of view, at any rate as far as certain
mild clays are concerned.

In many districts the wire-cut process of brickmaking is dis-
placing the soft mud machines, though where a facing of sand on
the bricks is demanded, the latter machines, or hand labour,
must be used. •

It is essential that all machines used for making sand-faced
bricks must be provided with some safety release which comes
into operation when stones or other causes of excessive pressure
occur. Otherwise the machine will be damaged, and however
desirable a machine may appear to be in other respects, the
absence of some form of effective relief escapement should be
regarded as sufficient to condemn it.

When clay is found, and it is necessary to decide in which
way it shall be worked, some regard must be paid to the probable
output and to the nature of the goods required. Where sand-

(68)

PLASTIC MOULDING BY MACHINEEY 69

faced bricks are in great demand it will probably be necessary to
use a machine of the " Monarch " or " Bawden " type, in which
the production of hand-made and sand-faced bricks is skilfully
imitated. Where a dryer can be employed, and the sand-facing
of bricks is not considered necessary, a wire-cutting table attached
to a pug-mill press will be cheaper for a moderately large out-
put, especially as bricks with a wonderful accuracy of form and
size can be obtained by means of a re-press. Hand-made bricks
can also be re-pressed if desired, though in this case a portable
press is invariably used. The disadvantage of pressing sand-faced
bricks is that a large amount of cleaning of the press is necessary,
but a strong lad should be able to press, unaided, and re-place
on the hack for final drying, at least 1250 bricks per day and
1500 should be considered a reasonable output. It is better in
pressing sand-faced bricks to work in this way instead of wheel-
ing the bricks to a permanent press and back again to be dried.

Fig. 30 is an illustration of the " Monarch " sand-faced brick-
making machine made by Maxted & Knott, Ltd. The clay used
in this machine may be freshly dug, weathered, or washed and
dug out of the wash-back, according to the circumstances and
to the impurities (if any) in the clay. The machine will allow
the clay to be in a very soft state, softer even than can be used
in a hand mould, or it will also work with fairly stiff clay ; but
if too stiff the material is liable to stick in the moulds and so
cause trouble, or it may break the knives. Sand, similar in
every way to that employed in hand-brickmaking, is used for the
moulds filled by the machine.

The upper part of the machine consists of a double pug-mill,
from which the clay is passed down to the presses and delivered
to the moulds immediately beneath it. The action of the presses
is somewhat similar to that of the man's fingers and thumbs in
hand-moulding and is reciprocating, not rotary. A lad takes the
moulds out of a sanding-tank, places them at the back of the
machine, and after the clay has been mechanically pressed into
the moulds in the front of the machine, the mechanism at the
back brings another set into position under the die. A man
standing in front of the machine takes the mould and scrapes off
the surplus material with a " strike " (p. 53) and hands it to an-
other man, who inverts the mould on to the turn-table and lifts
it from the bricks which are thus deposited on pallet boards
which have been previously placed upon the turn-table by a lad.
The man then turns round, puts the mould in the sander, and

70

MODERN BEICKMAKING

gives the turn-table a push, placing a vacant leaf of the turn-
table before him, and placing the loaded leaf opposite another
man who takes off the bricks and puts them on to an off-bearing

barrow or a dryer car as the case may be, five or six bricks being
made at a time. The whole operation is very simple and requires
no skilled labour.

PLASTIC MOULDING BY MACHINERY

71

The amount of pressure exerted on the clay in the moulds
can be instantly regulated by moving a small lever in the front
of the machine. This lever engages one of several teeth on the
cam of the front shaft, carrying the clay presses or "wipers,"
and therefore determining to what extent the clay in the mould

FIG. 31. — Norris Krick machine.

shall be pressed. This capability of regulation is essential in
order to prevent difficulties due to variations in the stiffness of
the clay. When stones and other hard materials are -present,
they pass out through safety doors controlled by springs at the
front of the machine.

The Norris patent mechanical brick-moulder (fig. 31) (made
by the Brightside Foundry and Engineering Co., Ltd.) is similar

72 MODERN BRICKMAKING

in many respects to the foregoing,' but is of an older type, though
a great improvement on many of so-called " soft mud " machines
which have been used more in America than here. The clay is
mixed in a pug-mill in the upper part of the machine and forced
below a plunger. The latter then descends, filling a mould at
a stroke and compressing the clay. On the plunger .rising, the
mould is pushed to the front of the machine, struck, bumped (to
loosen the bricks), and their contents turned out on to pallet
boards. Each mould makes three bricks at a time, the patentee
claiming that this is better, with his machine, than producing a
larger number simultaneously. Ample time is allowed for the
operation of cleaning, sanding, and replacing the moulds, and
effectual means are adopted for preventing the clay displacing
the sand as the former enters the mould. The Norris machine
requires about 3 h.p. to drive it, and can make 8000 bricks per
day under normal conditions.

The " Norris " machine appears to be suitable for making
fire-bricks, and can be worked by horse power or by an engine.

In this respect it resembles a larger and more powerful
machine (fig. 32) with an output of 20,000 bricks per day, made by
T. C. Fawcett, Ltd. The feature of this last named machine is
its open construction and large size, whereby repairs and break-
downs are reduced to a minimum. It is best worked in con-
nexion with a pair of granulating rolls (which separate small
stones) and an automatic sand-moulder, such as the one shown in
fig. 33, supplied by the same firm. The addition of a simple belt-
conveyer (fig. 34) is often necessary in order to get the clay easily
into the machine.

The use of a disintegrator in conjunction with a machine of
this kind enables many clays which would be regarded as useless
for hand-brickmaking to be satisfactorily worked in a soft-mould
machine of the various types described. Even when it is not
absolutely necessary a disintegrator is often used, as it absorbs
less power in breaking up the clots than would be needed if they
were allowed to enter the pug-mill of the machine.

Another moulding machine for sand-faced bricks, suitable for
small yards and for places where skilled moulders are difficult to
get, is Eddington's Moulding machine (fig. 35), made by James
Buchanan & Son. Like the machine just described, it forces a
column of clay into two sanded moulds, each of which is filled
alternately. The clay is cut off by a wire drawn across the
mould, which is then moved forward. The surface of the brick

PLASTIC MOULDING BY MACHINEKY

73

is smoothed with a strike, the mould opened, and the brick
placed on the pallet ready to go to the dryer or hack. The
special feature of the Eddington machine is the mould, which is
specially designed to overcome the difficulty usually experienced

in emptying box moulds. On this account, the sides of the
mould are made in two pieces connected in such a manner that,
on moving two small arms or triggers, the mould expands and
leaves a clear space all round the brick (fig. 36).

74

MODEEN BEICKMAKING

PLASTIC MOULDING BY MACHINEEY

75

FIG. 35. — Eddington's moulding machine.

FIG. 36. — Eddington brick mould.

76 MODEEN BEICKMAKING

This machine produces a good square brick, free from sand
folds, though not of quite so good a colour as a hand-made sand-
faced brick. It is made in two sizes, the No. 2 machine having
an output (according to the makers) of 3000 to 4000 bricks per day,

WIRE-CUT BRICKS.

• An entirely different method of manufacturing bricks is that
in which the wire-cut system is employed, the clay being thrust
out of a pug-mill in the form of a .belt or band of clay, 9 ins. wide
by 4^in. high, which is cut into bricks by means of wires or
rotating knives. Bricks made by this process are equal in shape
to those made by hand, and the rapidity and ease with which
they can be produced by unskilled workmen, is such as to make
this method exceedingly popular. It is particularly suitable for
clays worked up into a plastic paste of moderate stiffness, but
can, on occasion, be used in connexion with what is ordinarily
known as the " stiff-plastic process ". It is especially intended
for earths which do not require washing or other preliminary
treatment in order to purify them.

The underlying principle involved in making wire-cut bricks
is the conversion of the clay into a paste and passing it through
a pug-mill, or closed mixer, to the discharge end of which a die
is fitted. The successful manufacture of wire-cut bricks depends
upon the durability and accuracy in shape and size of the die,
the ease with which the clay passes through it, and the extent
to which consolidation is produced without lamination. Whilst
apparently simple, the wire-cut method of brickmaking offers
many difficulties to the inexperienced brickmaker, and it is
therefore described fully in the following pages.

Almost any clay which can be made into a plastic paste of
sufficient stiffness can be made into wire-cut bricks, providing
that it is sufficiently finely ground. The custom of permitting
pieces of stone and other hard material of more than one-six-
teenth inch diameter to get into the machine used for this pur-
pose is unsatisfactory, as the wires are unable to cut this material,
and the cut faces of the bricks are thereby rendered unsightly.

There is a great temptation for brickmakers to employ rolls
to crush everything taken from the clay-bed without regard to
its nature, but this practice is detrimental to the production of
good bricks ; so that whilst rolls are invaluable for enabling
materials to be used which cannot, otherwise, be employed in
brickmaking, they do not by any means abolish the necessity
for care in the selection of materials.

PLASTIC MOULDING BY MACHINEEY

77

Opinions differ greatly as to how far grinding is necessary,
but the author is convinced, as the result of extensive observa-
tion and wide experience, that clay for making wire-cut bricks
should always be sufficiently fine to pass through a sieve having
twelve to twenty holes per running inch. Coarser ground ma-
terials are never, in his experience, really satisfactory. The clay,

which should preferably have been weathered (page 22), may be
treated in a variety of ways according to its nature and the impuri-
ties in it, and nothing less than a good knowledge of the material
itself will enable a man to state the exact treatment necessary.

The following are the most important arrangements of plants for
the manufacture of bricks by the wire-cut process for plastic clay : — •

(a) A Pug-mill with Mouthpiece or Die, and Cutting Table (figs. 37,

78

MODERN BEICKMAKING

38). This is very suitable for clean clays which are not too strong
or sticky, and is specially good for loams of good quality. 'It is the
final portion of all the plant used for wire-cut brickmaking, and
simply effects a mixture of the clay and water so as to form a

FIG. 38. — Horizontal brick machine. Type a.

homogeneous paste, and shapes this by forcing it through the
mouthpiece on to the table where it is cut into bricks. It can,
if properly arranged, be enlarged by the addition of rolls and
mixers.

(b) Pug-mill, Expression Rolls and Cutting Table (fig. 39). This

FIG. 39. — Brick machine. Type 6.

arrangement is specially used for clays which tend to produce a
core or lamination when the die is attached direct to the pug-
mill.

It is only suitable for clay free from hard and stony matter,
and is most adapted for use with strong plastic clays. Either a
horizontal or vertical pug-mill may be used.

PLASTIC MOULDING BY MACHINEEY

79

(c) Crushing Bolls, Pug-mill, Die, and Cutting Table (fig. 40).
This arrangement is used where the brick earth is strong (plastic),
and contains hard lumps of clay or stones. It is suitable for

materials which cannot be made into bricks by simple pugging,
on account of the hard portions just mentioned, as these would
catch the wires of the cutter and would produce an unsightly

80

MODERN BRICKMAKING

brick. About 10 h.p. is required for a daily output of 20,000
bricks under good conditions.

(d) Two sets of Eolls, Pug-mill, Die, and Cutting Table (fig. 41).
This plant is used for similar earths to that described in (b) but
the additional rolls enable rougher and more difficult materials

PLASTIC MOULDING BY MACHINERY

81

to be treated. Usually the upper pair of rolls is provided with
grooves — see figs. 46, 53 and 54 — which prevents the clay from
adhering and so being carried round the rolls (see "Kibbler Rolls ").

The second rolls are smooth and set much closer together than the

first ones. 15 to 30 h.p. is needed for a daily output of 20,000 bricks.

(e) Three sets of Rolls, Pug-mill, Die, and Cutting Table (fig. 42).

6

82

MODERN BRICKMAKING-

This plant is used where hard stones or lumps of hard clay are
present in such quantities that a smaller number of rolls is in-
sufficient to crush them. The first (uppermost) pair of rolls is
usuallyggrooved or spiked, the second pair being set to

in. apart and the third pair as close as possible. About 30 h.p.
is required to drive this plant effectively.

(/) A Feeder or Mixer, two or three sets of Rolls, Pug-mill, Die, and
Cutting Table (fig. 43). This is similar to arrangements (c) and

PLASTIC MOULDING BY MACHINEEY

83

(d) but is preferable where several clays are mixed together, or
where the clay is of a very varied character. The feeder, or
mixer, effects a preliminary mixture of the material and, by
supplying it in a regular quantity to the rolls, makes it easier to
keep the machine working under the best conditions. The
power required to drive this machine is about 50 h.p.

(g) Grinding Mill, Rolls, Pug-mill, Die, and Cutting Table (fig. 44).
In place of a mixer as in (e) it is sometimes better to use a
grinding pan, particularly if the earth contains much material
of a rocky or gravelly nature. The employment of a grinding
mill in connexion with the plant is also advantageous when the
earth is somewhat deficient in plasticity, and would otherwise
require much tempering. In this arrangement the clay is de-
livered as regularly as possible into the mill where it is mixed

FIG. 44. — Brick plant. Type g.

with the necessary quantity of water. After being ground and
mixed by the action of the mill runners, it passes through a
grid in the bottom of the pan to the rolls and thence to the pug,
die, and table. Such a plant will require 60 h.p. to yield an out-
put of 20,000 bricks per day.

(h) Feeder, Grinding Mitt, Rolls, Pug-mill, Die, and Cutting Table.
(fig. 45). This is the same arrangement as (/), but fitted with a
preliminary mixer or feeder. This addition greatly improves
the quality of the bricks when several clays are mixed, or when
a complex earth is used. Such a plant will often work satis-
factorily with unwashed London clay when others have failed,
and it is specially adapted for use with very strong and sticky
clays. The power required to drive varies with the clay or earth
used, but is about 55 h.p. for a daily output of 20,000 bricks of
strong clay ; with milder earths it is less, as one pair of rolls may
be omitted.

84

MODERN BKICKMAKING

(i) Rolls, Mixer, Two more, sets of Rolls, Pug-mill, Die, and Cutting
Table (fig. 46). This arrangement of plant is suitable for some
strong clays, marls, or shales, where repeated crushing and mixing-
is needed, or where the use of a grinding pan is impracticable on
account of the excessive hardness of the material and the im-
purities it contains.

When two sets of rolls are set before the mixer, or when the
material is passed through two sets of rolls before entering the pug-
mill, the usual arrangement for Staffordshire is obtained (fig. 47).
This gives the material an exceedingly thorough treatment,
and owing to the amount of power required should only be used
when absolutely necessary.

FIG. 45.— Brick plant. Type h.

When the full set of plant just mentioned is used, the hardest
materials can be fully ground and tempered. Somewhat softer
earth can be more conveniently treated by the plant referred to
in (/), (g), or (i).

(j) Feeder, Grinding Mill, Rolls, Mixer, Rolls, Pug-mill, Die, and
Cutting Table (fig. 48). This forms a suitable plant for hard
materials which require much tempering, but for which it is not
necessary to use the arrangement (h), though that described
under (/) is not sufficiently strong in tempering or mixing power.

(k) Grinding Pan Mixer, Pug-mill, Die, and Cutting Table. This
is a simplified arrangement of (i) and can be used for materials
of considerable, but not excessive, hardness. It is capable of

PLASTIC MOULDING BY MACHINERY

85

developing the plasticity of lean materials to a remarkable extent
and is specially recommended for fire-clay and shale, these
materials being screened before they enter the mixer.

Selection of Plant. — The selection of the plant to be used for
a given material must depend largely on the nature of the latter,
and particularly on its hardness and plasticity. It is wise to so

86

MODEEN BEICKMAKING

\

arrange the plant that additional rolls or mixers can be easily
applied, if necessary, but these should not be purchased until
they have been found to be really necessary. Many brickmakers
use too much machinery for their work, and a study of the
requirements of certain earths often enables a brickmaker to
effect a considerable saving in the amount of driving power
required. Whatever arrangement of plant is used it is essential
that it shall be strong, well made, and of good design and ma-
terials. In this connexion the following information about the

Fro. 47. — Plant (Type i) for Staffordshire "marls".

various portions of machinery required in the foregoing arrange-
ments of plant may be useful.

Crushing Bolls (fig. 49) are employed for reducing clays which
are too moist or plastic to be ground by other means. Dry or
hard clays are preferably treated in an edge-runner mill,
particularly if a stone breaker is used as a preliminary crusher.
These rolls consist of a pair of strong cylinders, or rollers, usually
smooth and placed side by side, so that when the clay is fed on
to them the rotation of the rolls forces the clay downwards and
reduces it to a size comparable to the distance between them.
They are driven by a simple gearing through a belt or clutch.

Both rolls in a pair may be driven at the same speed or one

PLASTIC MOULDING BY MACHINEKY

87

may rotate faster than the other, this latter having the advantage
of giving additional crushing power with sticky clays, owing to
the increased rubbing action.

Crushing rolls require a considerable amount of power to
drive them, and they are subject to violent strains. Lumps

88

MODERN BBICKMAKING

ends with bevelled edges.

larger than a man's
head occasionally
have to be dealt with,
but it is safer to break
these by hand. It is,
therefore', necessary
to have the roller
machinery built very
rigidly with no
skimping of metal for
the sake of cheapness.
The strong thrusts of
the machine must be
properly taken up by
suitable ties, springs,
and bearings, and
each part must be
readily accessible for
repairs and renewals.
Rolls vary con-
siderably in size,
being from 18 in. to
24 in. in diameter
and 2 ft. to 3 ft. long
and are made of
specially hardened
iron, soft iron cores
cast in iron chills, or
of iron cores with
steel rims. A par-
ticularly ingenious
method is that em-
ployed by John
Whitetiead&Co.,Ltd.
This construction en-
ables a shell of any
desired hardness to
be used, and this is
fixed truly in position
on the shaft by means
of the two cast iron
These ends are drawn together (after

O

PLASTIC MOULDING BY MACHINEEY 89

the shell has been placed over them) by means of two iron bolts.
A boss on the inside of the shell locks into a projection on the
left end and prevents the shell turning independently of the
shaft.

Instead of the rolls being true cylinders and of the same
diameter throughout they may be conical in shape. This enables
them to automatically throw out a portion of the stones in the
clay which, with cylindrical rolls, would be ground up. Only
large stones can be separated in this manner. It is oflten con-
venient to make rolls in three or more portions, so that as one of
these wears away only a portion of the roll needs renewal, and

FIG. 50. — Eolls with interchangeable sections.

by interchanging the centre and other rolls the need for new ones
may be indefinitely delayed.

Rolls of this type are a feature of the " Lancashire " machine
made by SutclhTe, Speakman & Co., Ltd. (fig. 50). In this, the
sections are all made interchangeable, so that as the centre
sections wear they can be placed at the outer ends of the rollers
and the end sections placed in the centre. Brickmakers who
have any stony materials to deal with much appreciate this
arrangement, as on the old system the rollers always wear away
in the centre and do not permit of them being closed up unless
the rollers are taken out and turned up in the lathe. The
sections should be rearranged frequently, even if little wear is
shown, so that the rollers will wear parallel. To enable this to

90 MODERN BRICKMAKING

be readily done all the gearing is so placed that one frame only
requires unbolting, when it can be drawn away, as shown, to-
permit of the sections being placed as desired.

The rollers in this machine are made large in diameter and
narrower than is the usual practice, and as they run at a high
speed the clay is very well ground. One roller is made to go at
a greater speed than its fellow, this giving a differential shredding
action.

All rolls should be provided with a relief escape, or a safety
slipping clutch to prevent the risk of breakage should a piece of
ironstone or other hard metal get into the machine by accident,
or should the resistance to crushing be so great as to endanger the
machine. Instead of two sets of rolls arranged one below the
other, some firms employ three rolls so placed that the clay
receives two distinct crushings. Machines of this type are shown
in figs. 51 and 52.

A hopper is often desirable to secure the material being fed
into the machine properly ; end plates will serve to prevent its
escaping. Scrapers are sometimes necessary when sticky clays
are being crushed.

Lubrication is of great importance, and if neglected will cause
a great waste of driving power.

For good work it is essential that the rolls should run truly,
with no variation in the space between them, and some simple
method of adjustment should be provided to enable them to be
set closer together when slightly worn.

The distance of the rolls from each other in each pair is
important. If only one pair of rolls is used they cannot well be
set closer than half an inch, but if two or more pairs are em-
ployed the first should be moderately wide apart — up to 2 in. —
the second should be closer, and the final pair should be set as
closely as possible. Some brickmakers work with all the rolls
too wide apart ; this is foolish, as it permits stones to be mixed
with the clay and to be made into bricks, and it is then impossible
to make goods of best quality. To obtain satisfactory results,
the clay should come from the crushing rolls in the form of a
thin sheet, like coarse brown paper. It is almost impossible for
a single pair of rolls to produce this.

The rolls should be made of chilled iron or steel, or covered
with a steel hoop truly turned with a lathe, but for the coarser
rolls this accuracy is unnecessary, as they are not intended to

PLASTIC MOULDING BY MACHINERY

:iV, '

91

92 MODERN BRICKMAKING

crush the clay so thoroughly. Steel-rimmed rolls are always
more desirable than those of chilled iron.

Close-set rolls must be kept true in shape, and when they
are used it is necessary to have an extra pair of rolls which may
be used whilst the worn ones are being turned true. Rolls which
are supposed to be run close, but which have a wider opening in
the centre than at the edges, are useless for good work. It is
desirable that rolls which are intended to work close together

FIG. 52. — Buchanan's triple-roll crusher.

should be provided with renewable rims so that these may be
replaced when necessary. More difficulties in working certain
clays arise from worn rolls than from any other single cause ;
the rolls should therefore be frequently examined.

Crushing rolls are usually smooth but, for preliminary crush-
ing, rollers with projections, bars, teeth, flutes, grooves, corruga-
tions and other uneven faces are employed. Sticky clays require
these irregular surfaces, as smooth rollers do not possess enough
adhesive power to crush the material. The nature of the pro-
jection is largely a matter of individual taste, though the

PLASTIC MOULDING BY MACHINERY

93

greater the projection the greater the power of the rolls. Hence
teeth and bars are better than grooves for sticky clays, but
corrugated or grooved rolls are best for stony clays.

FIG. 53. — Toothed crushing rolls (Whittaker).

Many designs of projections and grooves are in use, some of
them being comparatively valueless. Amongst the best are
hedgehog (toothed) rolls (fig. 53) kibbling rolls, (fig. 54) and
corrugated rolls.

FIG. 54.— Kibbling rolls.

The projections on one roller engage with those on another,
and the combined action of the two on the clay is much more
powerful than when smooth rolls are used. The material is

94 MODEKN BEICKMAKING

caught between the projections, and being unable to escape is
crushed sufficiently to enable a succeeding pair of smooth rolls
to deal with it effectively.

Broad spiral corrugations running right and left hand re-
spectively, throughout the entire length of the rolls, often increase
the rapidity with which a sticky material may be crushed, and
the larger portions are conveyed to one end of the rolls and drop
into a special receiver. According to their nature these portions
may be discarded, as stones, or may be reduced by hand or other
means. The use of corrugated rolls is, in fact, one of the simplest
methods of separating stones from clay. The corrugations should
be so arranged that the projections in one roll should fit into the
depressions of the other, so that wear may be compensated and
the rolls kept set close together.

For stony clays of a sticky and tough nature the rolls should
be both corrugated and conical ; this is far superior to the use of
smooth conical rolls, as the corrugations convey the material to
the large ends of the cones where the clay is crushed in conse-
quence of the greater peripheral speed. High speed rolls with
projections are popular in America, and are very efficient for
clays which are not too hard. The rolls should be made in
sections for easy renewal, as the wear on them is much greater
than in a slower machine. This is fully balanced by the in-
creased output and the condition of the product. The projections
or lugs should not go the whole length of the roll, but should
have intervals between each. By rearranging the worn sections
on the same roll the wear is more evenly distributed.

The use of crushing rolls is simple enough, provided that the
works possess the means of having- them trued and properly set ;
otherwise they may cause much trouble through their not crush-
ing the clay sufficiently, and in such cases it may happen that
an edge-runner mill will give better results. This is not always
the fault of the rolls, but often of the clay or the man in charge.
It is of the greatest importance in making wire-cut bricks that
the material should be finely ground and entirely free from lumps.
The size of the particles should not, on the other hand, be exces-
sively small.

Grinding Mills or Edge-Runners are of two main classes : (1)
Those used for crushing dry materials to a powder and known
as " grinding mills," and (2) those employed for crushing moist or
wet materials, and at the same time mixing them so as to obtain
a more uniform composition, and known as " wet pans " or (less

PLASTIC MOULDING BY MACHINEEY 95

correctly) " pan mills ". Both classes of mill are used in the
manufacture of wire-cut bricks made by the plastic process, but
for convenience mills for grinding dry material are described
in Chapter V in the section on " stiff-plastic process ". Their
sole purpose is to reduce the material to a fine powder, and in
certain cases, which are difficult to classify, they work more
economically than do crushing rolls, as the full weight of the
roller or runner is available for crushing. Broadly speaking, a
hard material, fairly free from sticky matter, is most econom-
ically ground with an edge-runner mill, but if much moist plastic
clay is present it is usually better, and often essential, to use
crushing rolls and a wet pan.

Wet Pans are chiefly used to secure an equal distribution
of the moisture throughout the clay mass and to secure the
latter being of the same composition throughout. For this
purpose it is passed many times underneath the rollers before it
leaves the machine, whereby any lumps are simultaneously re-
duced to powder.

In many cases the material is fed into the pan of the mill, a
suitable quantity of water added, and the pan kept in motion
from fifteen to twenty minutes. The speed is then reduced, and
the material removed by means of a special shovel working in
a rowlock.

Continuous wet-pans are well known, but are considered to
yield a less satisfactory product. They have a bed, or pan,
perforated near the centre, and the material is forced to travel
several times under the runners before it can escape through the
holes. The most important features of a wet-pan are the
weight and size of the runners, the construction and speed of
the pan, and the transmission arrangement for driving the
machine. It is essential that the runners should be heavy ; those
supplied by many firms are much too light to do their work
effectively. For a 9 ft. pan the runners should seldom weigh
less than 40 cwt. each, and for some clays they should weigh
about 4 tons if a satisfactory product is required in a reason-
ably short time.

The construction of wet-pans in this country is quite
different from that considered best in some others, and several
British makers of machinery recommend the stationary wet-pan
for certain clays, in spite of very conclusive evidence of its
inferiority to the rotary one for this purpose.

A typical stationary pan is shown in (fig. 55). It consists

96

MODERN BBICKMAKING

of two heavy runners and two scrapers mounted on a single
shaft and driven by means of an overhead crown wheel and

2
H

u

.+3
O

1

pinion. A grid is fixed in the pan, and the material passes
through this as soon as it has become sufficiently softened to-
do so.

PLASTIC MOULDING BY MACHINEEY 97

The mixing power of such a mill is relatively small, its chief
use being to reduce the material to a form in which it can be
more readily dealt with by succeeding plant than if the clay
were fed direct to the latter. Its efficiency depends largely upon
the smallness of the grid and, therefore, the extent to which the
material is treated before reaching it.

For some materials such a pan may be improved by inserting
a solid bottom and removing the material (after the mill has
been stopped) either by means of a spade or by opening a sliding
door in the bottom of the mill.

Sutcliffe, Speakman & Co., Ltd. have designed a special mill
for material which is free from large lumps, but requires an
unusual amount of mixing. The material is fed into an attach-
ment on the side frame just below the crown wheel. From this
it passes to a small pan, fixed to the upright shaft, which
ensures the material passing under the rollers where it is kneaded
and rubbed together, thus giving a very intimate mixing. The
material in the stationary pan on which the runners revolve is
turned over by multiple scrapers which gradually push it to the
discharge opening

According to the nature of the material supplied this will
mix two to five tons per hour using 8 h.p. for driving.

A wet-pan of more modern design is shown in fig. 56. The
pan (9 ft. diameter) is mounted on an upright shaft working in a
footstep bearing, and kept in position by a bridge-bearing above.
It is not perforated, has no .grid, and is driven by means of an
ordinary crown wheel and pinion and belt, these being placed
above (fig. 56) or below (figs. 57 and 124) according as it is
more convenient to have the pan over-driven or under-driven.
The bottom and sides of the pan are renewable.

The runners for a pan of this size are 4 ft. 8 in. in diameter
with 15 in. width of face and weight 43 cwt. each ; they are
preferably made with flush sides so as not to carry up any
ground material, and may be fitted with renewable rims. The
ends of the shaft connecting the runners to the centre block
work in guides which permit the runners to rise and fall with
varying thicknesses of materials on the pan but prevent them
rotating above the vertical shaft. If two shafts are used — one
for each runner — they can rise or fall independently of each
other, thereby saving power and keeping the machine in better
balance. The runners revolve by the action of the material on

7

98

MODERN BEICKMAKING

the pan and are not driven directly. They should not touch
the pan when it is empty but should be just clear.

The scrapers should be attached to cross stays bolted on to
the framework of the machine, and must be so fastened that
they can be turned to any desired angle and adjusted to any
height above the pan.

:::!:;::::;:-

Jfio. 56. — Whittaker's revolving wet pan.

When sticky clay is being ground it is useful to have scrapers
attached so as to keep the runners fairly clean (fig. 58), as no
purpose is served by runners thickly coated with clay. These
11 cleaners " should not actually touch the rims of the runners,
or too much iron' may get into the clay.

The footstep is an important factor in successful grinding.
It should be readily accessible, easily lubricated, and of such
construction that the bearing metal can be easily renewed

PLASTIC MOULDING BY MACHINERY

99

FIG. 57. — Light pan mill (Boultoa).

FIG. 58. — Edge-runners with scrapers (Horn).

100 MODEEN BEICKMAKING

when worn. It should be cased to keep out dust, but should
be examined frequently, as a worn footstep causes much loss of
power and may easily damage the pan. Anti-friction rollers
should be placed underneath very large revolving pans in order
to support them. The pan should be light but strong, and pro-
vided with a loose bearing ring, or false bottom, preferably of
manganese steel. There are advantages in having this bottom
ribbed for soft .clays, but with very hard ones it is undesirable.
A mechanical shovel is used for removing the material except
in self-delivery mills.

A measured quantity of the material to be treated is placed
in the pan, a definite volume of water added through a sprinkler,
and the pan set in motion at a speed of sixteen to forty revolu-
tions per minute according to the nature of the clay. After
fifteen or twenty minutes the speed is reduced and the mechani-
cal shovel used to withdraw the material, after which a fresh
batch is treated. Unless the clay and water are both measured,
the paste will vary in stiffness and plasticity. To avoid loss of
time, it is wise to have two mills and to run them consecutively.
By the insertion of a slotted grid in the roller path the
material may be delivered to a receiving plate, whence a fixed
scraper removes it continuously to the next stage of manufacture.

Runners with a conical instead of a flat face (fig. 59) may
be used for wet grinding. It is understood that they have a
somewhat larger output, but this has not, so far as the author is
aware, been definitely proved.

For clays containing a large proportion of small stones, es-
pecially if the latter are of a limey character, J. Buchanan & Son,
Ltd., recommend the use of a wet grinding pan of the stationary
type. In this pan (fig. 60) the runner path consists of six or
more manganese steel grids, the space between each being fitted
with steel plates — either smooth or corrugated — the mesh of the
grids being adjusted to the requirements of each clay.

The runners are made of hard cast iron and run upon hard
cast iron renewable bushes ; they are carried upon a square
steel shaft provided with slide blocks to rise and fall in the slotted
cross-head of the vertical shaft.

Steel scrapers are attached to the cross-heads, and revolve
with it, for throwing the material from the outside and centre
of the pan on to the runner path. The mill is driven with strong
bevel gearing by a steel driving shaft working in gun-metal
bearings, and fast and loose pulleys.

PLASTIC MOULDING BY .MACHINERY

101

FIG. 59. — Mill with conical runners

FIG. 60.— Mill for limey clays.

102

MODEEN BRICKMAKING

Where strong plastic clays containing large quantities of lime
and other stones (as boulder clays) are to be found, the use of a
stationary wet-pan of this type as a preliminary grinder and
mixer is desirable, as revolving pans are too lightly constructed
for this class of work. The material should afterwards be passed

FIG. 61. — Continuous self-delivery wet mill.

through two sets of rollers before entering the pug-mill. The
grids require frequent inspection, and should be made of man-
ganese steel as this possesses the greatest resistance to wear and
tear. They should be easily renewable.

The mill shown in fig. 61 is one made by Thomas C.
Fawcett, Ltd., who state that it is distinct from other plastic
pans in that both the rolls and pan revolve, and the material,

PLASTIC MOULDING BY MACHINERY 103

after being ground and mixed, is delivered on to a receiving plate
which is keyed on to the vertical shaft, and, revolving with the
pan, delivers the material by means of a fixed scraper direct to
the brick machine. The pan is 9 ft. in diameter and the power
required to drive it is 20 b.h.p. It is claimed that this machine
will give an output equal to other machines but through smaller
grids, thereby ensuring finer grinding and tempering of the
material without increasing the cost of treatment. Pan-mills
mix the water and clay more thoroughly than do pug-mills using
the same driving power, but the texture of different batches of
paste is more irregular.

MIXERS AND FEEDERS,

After the material has passed through crushing rolls or some
other form of preliminary grinding plant it must enter a mixing
machine. For some clays a mixer forms the first part of the
plant and it is then known as a feeder, though, mechanically, it
is really a mixing machine. The object of using mixers and
feeders is to produce a material of even composition from a
number of different materials which may occur together in nature
— as is the case of clay with stones or sand in it — or which may
occur separately, but which it is desirable to mix, as when cer-
tain properties are to be conferred on a clay which can only be
given by adding other materials to it.

Broadly speaking, the greater the amount -of mixing the better
will be the product, and as, by their construction, mixing
machines cannot easily be overloaded, they form admirable
appliances for securing a regular supply of material to grind-
ing pans, which are troublesome if supplied irregularly. It is
when used for this purpose that they are termed " feeders ". In
the United States the term " granulator " is identical with the
British " mixer". A special class of feeding machines which
do not mix the material will be described later (p. 182).

Mixers are distinguished from pug-mills for convenience ; in
reality pug-mills are only a form of "mixer," though this latter
term is commonly understood to refer to machines of the open
trough type. They are generally made of iron or steel with one
or more long shafts running through the centre, to which are
attached knives which thoroughly mix the clay before it enters
the pug-mill. In some cases the knives of the pug-mill and of
the mixer are both on one shaft, but it is more usual to have

104 MODERN BEICKMAKING

separate mixers which mix the clay and water together and then
discharge the paste into the pug-mill.

Mixers are generally placed just below the crushing rolls, and
sometimes other pairs of rolls are placed underneath them for a
final crushing before the clay enters the pug-mill. The value
and efficiency of a mixer must be judged by the extent to which
it converts the materials supplied to it into an even paste, but
no accurate conclusion can be reached unless it is first clearly
shown that the material is in a suitable condition to be mixed.
No mixer can be really effective unless the material supplied to
it is free from large pieces of hard material, though several
strong knives in a long mixer will often effect a remarkable
degree of homogenization.

The best test of a mixer is to take small samples from differ-
ent portions of the paste which issues from the machine, and to
examine them carefully by the eye and also by a simple sifting
test after stirring them up with water. When clay of a tough,
stony nature is used it will frequently be found advisable to
employ a powerful mixer to " granulate " it before passing it
to the crushing rollers. This custom is very common abroad
when highly plastic clays are being treated, the argument in
favour of this arrangement being that it is said to require less
power than the use of spiked or kibbler rolls.

The supply of material in a constant regular stream to the
various machines is so important that it should receive far more
consideration than it has, hitherto, done from many brickmakers ;
the employment of a simple mixer or feeder will often go far
towards solving the problem of " wasted engine power ".

The essential parts of a clay mixer are a case or shell of
ample strength, the shaft or shafts carrying the mixing knives,
a supply of water capable of being accurately regulated so as
to produce a paste of the required consistency, and the gearing
necessary for the transmission of power to the machine. These
parts should all be exceedingly strong and well fitted.

Clay mixers may have a single shaft to which the knives are
attached, or two or more such shafts may be used. For most
purposes two shafts placed parallel to each other form the most
efficient mixer.

Single shaft mixers form efficient conveyers for short distances.
The blades should be very strong, preferably of steel, and should
be fitted so that they work at a suitable angle to the shaft and
to each other. This angle can only be found by experimenting

PLASTIC MOULDING- BY MACHINERY 105

with the clay to be used, and it is not uncommon to find that a
mixer can be greatly improved in efficiency if the shape, size,
spacing, and angle of the blades are altered. These changes
should not be made, however, without expert advice of an Jim-
partial character.

In double shafted mixers the blades or knives should revolve
in opposite directions and at somewhat different speeds (preferably
in the ratio 1 : 2), as this enables them to break up and reduce
the material more readily and to mix it better with the water.
The materials, and as much water as is thought necessary, are
fed in at one end of the mixer, and leave in the form of a more
or less plastic paste at the other.

FIG. 62. — Single shaft mixer.

It is a curious fact that, although mixers are sold by all
makers of general brickmaking machinery, there are very few
really good machines for this purpose on the market. In most
of them the blades are too narrow or too fragile, and are made
of unsuitable metal, so that they are weakest in the most impor-
tant part. This is especially true of the single shaft mixers,
though the ones shown in figs. 62 and 63 are notable exceptions.

The bearings in most mixers are of good design, but in many
cases are too small to take effectually the sudden strains often
placed on the machine. In all clay -working plants it is essential
that the bearings shall be large, of good design, and of suitable
metal. They should, preferably, be able to work efficiently in
dusty places.

106

MODERN BBICKMAKING

Mixers with double shafts are much more efficient, as they
only require>oiie or two additional horse power to the single shaft
machines, and the material is more than twice as thoroughly
worked. They are, therefore, more popular and are correspond-
ingly better in design, so that little or no difficulty should be
experienced in selecting a suitable machine of the double shaft
type (figs. 64 and 65).

The blades on one shaft of a mixer of this pattern should
work close to those on the other shaft but should not actually
touch. They should be strong, well shaped, so as to turn over a
considerable amount of clay at a time, and should be set at an
angle so as to carry the clay slowly forward. The blades should
also be readily replaceable in case of wear or breakage, and should

FIG. 63. — German single-shaft mixer.

be secured in position by the use of square or hexagonal shafts
and of similarly shaped openings in the farther ends of the blades.
This is far more satisfactory than the older plan of fastening the
blades with a bolt or nut. Large bosses on the blades make a
convenient means of fitting them to the shaft and also occupy
space which would, otherwise, be injuriously taken up by clay.
The blades may have an elliptical rectangular or triangular cross
section, the first-named being, usually, the best. Cast-steel
blades are the most serviceable, but no blades should be used
when much worn. When in position the blades usually form
parts of a screw-thread or worm so as to exert a propelling-
action on the clay and carry it forward. It is seldom advisable
that the blades should exactly correspond to this " worm " shape,
as slight variations from it often produce a better mixture, but
these variations must not be too great.

PLASTIC MOULDING BY MACHINERY

107

The number of blades must vary with the clay to be treated ,
but if four blades con-
stitute one "turn,"
good results can usu-
ally be obtained. The
distance of the blades
from each other should
not be too great, and
should seldom exceed
14 in. between two
blades on the corre-
sponding positions on
the shaft.

In the United
States considerable
success has attended
the use of shafts one
above the other in-
stead of side by side
as is the custom here.
Fig. 66 shows one of
these machines which
has combined the fea-
tures of the double
shaft mill for mixing
different material with
the long enclosed case
containing a single
shaft only for pugging
clays. Immediately
over the main pug-
shaft and extending
for about one half of
the length of the pug-
chamber is an inde-
pendent mixing shaft
containing four rows of
steel bars, so located
that they just clear the
tempering knives in
the main shaft. The
distance between the two shafts only slightly exceeds the length

108

MODERN BEICKMAKING

of the knives. The operation of these two knives on the
material, with the close passage of the knives to each other,
secures a thorough mixture of different ingredients before reach-
ing that part of the chamber in which the pugging is completed.
Some other mixers are illustrated later (p. 227).

FIG. 65.— Plan of mixer (Bennett & Sayer).

PUG-MILLS, MOUTHPIECE-PRESSES, AND AUGER
MACHINES,

The final machine employed for the preparation of the paste
for the manufacture of wire-cut bricks by the plastic process is a
pug-mill, to the exit end of which is attached a mouthpiece 01*
die which gives the brick its shape. In a few cases this is all the
machinery that is required, but with most clays some crushing
or other preliminary treatment is necessary.

Pug-mills are also used without mouthpieces, in order to>
secure a plastic paste of regular composition and of suitable stiff-
ness for further work. In all these cases the same principle
is used, though the mill must be more strongly built if a very stiff
paste is to be worked than if a soft paste is desired.

At most works making plastic, wire-cut bricks the clay passes
through crushing rolls, sometimes through a pan-mill or a mixer
or both, and finally goes into a pug-mill where it is thoroughly
pugged and mixed under pressure, and eventually shoved out of
a die in the exact shape of a column of bricks, and from thence
on to a cutting table where it is cut up into bricks.

PLASTIC MOULDING BY MACHINERY

109

110 MODERN BEICKMAKING

A pug-mill is essentially a closed mixer and is constructed on
the same general principles as the mixers already described,
except that instead of being trough shaped, it is usually cylin-
drical and slightly smaller at the exit end than at the other.
Owing to its shape the clay paste in a pug-mill becomes much
compressed and this sets up a resistance, or back-thrust, neces-
sitating powerful construction and great care in design.

In an open mixer the clay falls through an opening in the
bottom of the trough at the exit end, but in a pug-mill the clay
passes out at the- end of the machine. For this reason special
arrangements have to be made for supporting the knife -carry ing
shaft at this end of the mill, and not a few failures in clay-work-
ing are traceable to faulty construction in this part of the
machine.

Pug-mills may be made with the barrel vertical or horizontal.
The former are used when preparing paste for hand-made bricks
(Chapter III) and for fire-clay, the latter for nearly all cases
where wire-cut goods are to be produced. As it is closed it is
impossible to see what is going on inside a pug-mill, and much
attention mus.t therefore be paid to the clay which issues from
it.

As in open mixers, the blades in a pug-mill are arranged in
the form of a screw-thread or worm, fixed projections or blades
being sometimes cast on to the inside of the barrel in order to
prevent the rotation of the clay. The mill will deliver a more
satisfactory column if the end of the shaft carrying the knives
is made of corkscrew pattern so as to act as a propeller (fig. 67). It
clears a way for the clay behind it and causes a solid column of
clay to exude from the die without creating unnecessary back-
pressure on the blades of the pug-mill. This is equally true
of both vertical and horizontal mills. . Valuable as is this
arrangement, but few pug-mills contain it, and many are so con-
structed that it cannot be fitted to them.

In selecting a pug-mill it is essential to have clearly in mind
the purposes for which it is to be used. If it is only re-
quired for mixing clay with water into a homogeneous paste the
blades should be set fairly flat, i.e. almost at right angles to the
shaft, and should be broad and numerous. In short, a pug-mill
for this purpose should have all the characteristics of a mixing
machine. If, on the contrary, the main purpose of the pug-mill
is to convert a plastic paste into a band of clay of definite width
and depth by forcing the paste through a die or mouthpiece, the

PLASTIC MOULDING BY MACHINERY

111

blades should be at a distinct angle to the shaft and should form
a screw conveyer of which the thread is broken by the spaces
between the blades. These latter should be very broad. Such
a mill will press the clay into shape satisfactorily, provided that
it be supplied with a
properly prepared paste,
but will do little or no
mixing work.

Intermediate between
these types of pug-mill
is the one which is most
frequently used, and is
intended to act as a
combined mixing and
pressing machine, the
clay in it being made
by it into a homogeneous
paste and afterwards
pressed through the
mouthpiece to the de-
sired shape. In such a
machine the majority
of the blades should be
arranged for mixing,
but those nearer the
exit end should be set
at a smaller angle so as
to be propulsive, and a
couple of turns of a com-
plete screw should be provided at the end of the shaft. These
precautions are often overlooked, with the result that many
troubles arise, particularly if a stiff paste is required.

A pug-mill should work with the least amount of water the
required consistency of the mass will allow, and that mill is,
broadly speaking, the better which can produce an equally good
mixture with less water than another, providing it does not re-
quire more driving power. The various parts of the mill must
be of ample strength owing to the great compressive forces
exerted, and on this account the shaft and blades must be of
ample proportions and the thrust bearings well made and kept
properly lubricated and covered so as to be free from dust. The
blades should not be used when unduly worn.

112

MODEEN BEICKMAKING

The speed at which pug-mills are driven is often ridiculously
slow ; thirty to forty revolutions per minute is good practice, but
many English clay -workers drive at half this speed, and thus waste
power and produce an inferior result. Much, however, depends
on the nature of the clay, and the brickmaker can only ascertain
the best driving speed by actual trial.

Many pug-mills are too short, and so fail to mix the clay
supplied to them ; 6 ft. is seldom too long, and many clays re-
quire a preliminary mixing to have taken place before they can
be dealt with satisfactorily in a pug-mill of this length. In such
cases the mixer is attached to the pug-mill and driven from the
same pulley, the mixer being fixed at such a height as will enable
the clay from it to fall into the pug-mill.

The construction of the thrust bearing is highly important,

FIG. 68. — Griessmann's pug-mill.

and most of the firms making pug-mills and brick machines have
paid special attention to the design of their bearings.

Friction discs are much used, as are also projecting rings on
the shaft working in grooves in the bearing (as in marine work).

An ingenious device by F. Lane consists in attaching a
hemisphere of hard steel to the end of the shaft, and a similar
one in the thrust block. As the shaft rotates its hard rounded
end works on the corresponding convex face of the thrust block,
and the arc of contact is reduced to a minimum. Whatever
type of thrust or journal bearings are used they must be kept
clean and well lubricated.

A German patent (fig. 68) by Griessmann, consists essentially
of a series of conoids with screws through their sides to prevent
the clay rotating, and a series of helicoidal blades to propel
it forward. This arrangement has increased the output of some
mills not provided with a clearance screw at the end of the
shaft by 30 to 40 per cent.

PLASTIC MOULDING BY MACHINERY

113

The best shape of the exit end of a pug-mill depends greatly
on the mouthpiece. If the latter has a small opening there
should be a long conical piece between the end of the mill and
the mouthpiece proper. If large articles are being made, this
conical piece may be shorter. The most suitable length must be
found by experiment.

Mouthpieces. — As a rule only one mouthpiece is used on each
machine, but where the clay will permit it there are advantages
in using two mouthpieces set at an angle to each other, as in
fig. 69.

The designing of a mouthpiece to work with a given machine
is one of the most delicate engineering operations connected
with brickmaking. Variations of apparently trifling magnitude

FIG. 69. — Brick machine with double mouthpiece.

cause serious defects, and the alteration of a mouthpiece is a
matter requiring careful thought and much experience and skill
before it can be done satisfactorily. With plain bricks made
from plastic-clay the difficulties are fewer and less troublesome
than when hollow goods are produced by the wire-cut process,
but in all cases some skill is required, and often much patient
experimenting must be carried out before success is gained.

In principle, the mouthpiece is extremely simple, it being
merely an opening at the end of a pug-mill. This opening is of
such a shape (usually about 9| in. x 4f in.) as to produce a column
of clay paste the width and length of a " green " brick ; and it
might be assumed that a plate attached to the exit end of the
pug-mill with an opening of the correct size is all that would be
required. If a very soft paste is used, and no attempt is made to

8

114 MODEEN BEICKMAKING

keep the clay to a special shape, such an assumption is correct ;
but as soon as the paste is made stiff enough to retain its shape
on leaving the machine, a back-pressure is produced on the
machine and troubles begin forthwith. A few tests will soon
show that some means for effecting a gradual change in the
shape of the clay column is necessary. Inside the mill this
column will be a cylinder of 12 to 18 in. diameter ; after passing
through the mouthpiece it will be a rectangular one of 9| in. x 4f
in. This reduction of cross-section must be effected so gradually
as not to cause avoidable friction in the pug-mill, and for this pur-
pose a conical collar must be placed between the mouthpiece
opening and the barrel of the mill, or the latter must be made
conical throughout its length. There are reasons, which need
not be detailed here, why the latter plan is less desirable than
the former, the most important being the end support of the shaft
carrying the knives.

As this conical reducing piece is in some ways of greater
importance than the opening in the mouthpiece, the two com-
bined may be considered as forming the mouthpiece. The
most suitable length for the reducing piece will depend upon (a)
the relative sizes of the mill-barrel and the mouthpiece opening,
and (b) the rapidity with which the cross -section of the clay
paste can be changed without detriment. Some clays can be
worked with a very short mouthpiece, as they can be rapidly
changed from one shape to another, but others need very gradual
reduction. No general rule can be given, as the length must be
found by trial with the clay mixture for which the mouthpiece
is to be used. Even then, variations in the stiffness of the paste
may prevent well-shaped articles being made. It is seldom that
the distance between the end of the cylindrical part of the barrel
of the mill and the opening of the mouthpiece can be less than
12 in., and a much greater distance is often required.

With certain clays, a very accurately constructed die, and a
suitably sized mill, the reducing piece is unnecessary, and as the
output of a mill in which it is not used is increased 19 to 40
per cent, most makers of mills prefer to keep the reducing piece
as short as possible. This is quite right providing that it is not
overdone, as an unnecessarily lengthy reducing piece or nozzle
may yield bricks with weak corners and edges. Too short a
nozzle will, on the other hand, give badly shaped bricks with
torn edges and will waste power.

As the clay paste on leaving the barrel proper is circular in

PLASTIC MOULDING BY MACHINERY 115

section and the final shape of it is rectangular, the internal shape
of the reducing piece is often peculiar and difficult to describe.
The reduction in cross-section puts a large amount of pressure on
the clay — in some cases it is sufficiently great to stop the machine
— and even when assisted by a powerful auger the amount of
power required is often serious if the reduction takes place in
too short a distance.

If a short collar is sufficient, one similar to that shown in
fig. 70 may be used, but if a longer one is needed it will be
better to introduce a conical casting, similar to that shown in
fig. 71.

Between an ordinary mouthpiece and the barrel of the mill,
or instead of a perfectly conical casting, a specially shaped
reducing piece may be used. If the mouthpiece is sufficiently
large no collar is necessary, as the mouthpiece produces the whole
of the change from a circular to a rectangular shape.

A third alternative may sometimes be employed, though this
is seldom the case, i.e. the barrel of the pug-mill may be of so
small a diameter as to need no reducing piece. This has the
disadvantage, however, of not mixing the clay so thoroughly as
when a larger mill is used.

Instead of the mouthpiece being at the end of the pug-mill
it may be at the side (fig. 72), though this, in the author's experi-
ence, is less satisfactory with many clays, as the thrust on the
solid end is great and the direction of movement of the clay is
changed suddenly just before it leaves the mill. At the same
time it must be admitted that machines of this pattern are
giving satisfactory results in some districts.

The mouthpiece must be made of, or at any rate lined with,
hard metal, as the internal wear is very great. It must also be
kept accurate or the bricks will vary in size. Ordinarily, fresh
liners must be inserted and the old ones " trued up " or discarded ;
but an ingenious device patented in France by T. Herve deserves
consideration in- this country. As will be seen from the illustra-
tion (fig. 73) the sides of the box are joined at two opposite
corners, and when the box has become too large it is only
necessary to remove the bolts (cc,) and to pull the two halves of
the box asunder along the lines 1 to 2, and 3 to 4. By
grinding these angles the four parallel sides of the box can
again be brought to their normal size, and the whole, bolted
together, is then ready for use. This invention attempts to do
away with most of the trouble ordinarily experienced in relining

116

MODERN BRICKMAKING

PLASTIC MOULDING BY MACHINERY

117

ordinary dies, as, provided reasonable care is taken, the sides of
the die cannot become untrue during the grinding of the angles.
It is especially important that the mouthpiece should be
capable of easy removal from the machine, so that another, with
a differently shaped opening, may be substituted or so that the
die may be cleaned or repaired. Many machine-makers have
paid too little attention to this matter, with the result that the
changing of a mouthpiece often requires a couple of hours'
hard work by two or three men. Instead of bolting it on with
long screws of slow pitch, shorter threads may be used or, pre-

FIG. 71. — Brick machine with long collar (Whittaker).

ferably, instead of being bolted all round, the mouthpiece may
be provided with a hinge at one side and a bolt at the other,
so that all that is necessary for its removal is the unfastening
of the bolt and the drawing out of the hinge-pin (fig. 776). For
cleaning the die it is sufficient to unfasten the bolt and turn
the mouthpiece on its hinge. If the hinge is made sufficiently
strong it will not be bent by the pressure of the clay in the press.
Much trouble is experienced if the clay cannot easily pass
through the mouthpiece, and to facilitate its passage the die is
usually lubricated with water, steam, or oil. If the clay is fine
in texture the die may be lined with copper or brass and water
used for lubrication, but with clays containing much hard

118

MODERN BRICKMAKING

PLASTIC MOULDING BY MACHINERY

119

material steel-lined dies are better, and oil may be the only
suitable lubricant, though
water or steam may some-
times be used.

One of the earliest
mouthpieces placed on the
market was that designed
by the late H. Clayton in
which two cylinders (fig.
74) formed the sides of the
opening. These cylinders
were slowly rotated by ap-
propriate gearing mechan-
ism and served to help
forward the clay column.
It has not been generally adopted.

During recent years it has been found that " lubricated dies "
are the most satisfactory, and many patterns of these are now
obtainable. They vary in complexity from a straight- edged die
lined with copper or fustian to very elaborate arrangements.

A die of modern type, made by James Buchanan & Son, is

FIG. 73. — Herve's mouthpiece.

B.CLAYTON fe CO£

P~AT ENT
BOIARY DIE.

FIG. 74. — Mouthpiece designed by H. Clayton.

shown in fig. 75. This has a double supply of lubricant, so that
the corners may be treated separately from the sides of the clay
column — an important convenience with some clays.

It is very necessary in constructing a die, to see that the clay
column issues at the same speed over the whole cross-section.
Unless special care is taken, the centre will travel faster than
the sides and far faster than the corners. Should this be the

120

MODERN BEICKMAKING

case, the die must be widened where the clay travels slowest,
and so adjusted until an even flow is obtained. Otherwise, the
bricks will be defective at the edges and will not be of average

FIG. 75.— Lubricated mouthpiece.

strength ; in bad cases, the edges will resemble " crocodiles' teeth "
owing to the clay being torn as it comes through the die.

To avoid the time, trouble, and expense connected with work-
ing-in metal, the author invariably uses wood for experimental
dies, and as soon as a reasonably satisfactory result is obtained
he has a casting made. When this casting has been altered

PLASTIC MOULDING BY MACHINEEY

121

until satisfactory, he has a proper die made to the exact shape
of the adjusted casting. No other method has been found so con-
venient as this with really difficult clays. Fortunately, it is
seldom necessary to carry out so full a set of tests, as one of the
numerous mouthpieces on the market will usually work admir-
ably with all except the most difficult clays.

Whenever possible, water or steam is preferable to oil, not
only on account of its cheapness (though the mouthpiece
requires more oil than is used to lubricate all the rest of the
machinery in the plant), for oil of a cheap grade is used, but
because oil enters the surface indenta-
tions and corner-cracks and prevents
them from healing under later pressure.
Steam has the advantage of warming the
clay as well as reducing the friction pro-
duced in its passage. But little pressure
is required on the oil, but with water a
pressure corresponding to that of most
towns' supply is needed. When all the
water used in the works » has to be
pumped, it may be necessary to use a
pressure cylinder. Fig. 76 shows a
simple and suitable design in which the
upper tank is filled with water and steam
is blown in at the top, so as to produce
the pressure desired at the mouthpiece.

By sliding the weight to and fro along
the regulator- arm, any desired pressure
between zero and that of the steam in
the boiler may be obtained. This is
necessary, as turning a tap on the supply-
pipe is often an ineffective means of
reducing the pressure, as it cuts off too
much of the lubricant. A pressure-
gauge, placed as shown in fig. 76, enables the pressure of the
water to be accurately regulated : an essential in the manufacture
of the best bricks from a difficult clay.

The water, or oil, enters the die and passing between the
lining and the clay facilitates the movement of the latter. In
many dies it also passes between the various sections or " scales "
of the die, so as to come into contact with the clay at several
points in the length of the die. In some dies the only outlet for the

IG. 76. — Stall's pressure
regulator for mouth-
piece lubrication.

122

MODEEN BKICKMAKING

FIG. 77. — Laminated mouthpiece.

lubricant is between the clay and the lining, but others are pro-
vided with a tapped drain pipe, which is useful in regulating
the pressure of the water or oil.

As the corners of the clay column require more lubrication

than the top, bottom, or sides,
special arrangements should be
made for an ample supply of oil
or water where it is most needed,
as by cutting the special channels
shown in Groke's patent mouth-
piece in fig. 77. It is also wise
to introduce sufficient oil, steam,
or water at the back of the
mouthpiece, so that directly the
clay enters it may be smeared
with the lubricant. If this is done properly little use will be
made of the lubricant introduced in the front or centre of the
die.

The supply of lubricant must be controlled by a tap,
arid an excess of either oil or water must not be used ; the
former causes cracks which *will not heal, and the latter
softens the clay unduly. There is a tendency with plastic
clay to allow the paste to become too soft. This is wrong,
as for wire-cut bricks the clay should be as stiff as can be ob-
tained without loss in evenness in composition. Indeed, the best
results* are obtained by working so stiff a paste that many dies
will tear it, yet -with a properly adjusted die almost perfect
bricks can be obtained.

For clays which are difficult to manipulate a mouthpiece
with a scale lining is usually the best. Such a lining, as shown
in fig. 77, consists of a series of plates, each jointed so as to form
a rectangular frame 3 to 4 in. deep. These frames are so
placed in the mouthpiece that they overlap considerably and the
lubricant, admitted between them and the casing of the mouth-
piece, oozes out at the overlapping portion. These laminated
plates are made of zinc, tin, or steel, the outer casing being made
of wood or cast iron and provided with channels to convey the
lubricant to the laminated plates. Some of the most successful
water-lubricated mouthpieces of this type used in Great Britain
are those patented by Halsband & Co., of Cassel. The laminated
linings are easily renewed, but if well made they will serve for
the production of half a million to a million bricks (fig. 77s ).

PLASTIC MOULDING BY MACHINEKY 123

R. T. Stull has investigated the structure of laminated and
other lined mouthpieces very fully, and has recommended the
use of a series of " scales " which touch but do not overlap each
other. These scales are in the form of rectangular frames which
fit inside the mouthpiece, and are held in position by bolts
passing from front to back of the latter. Various modifications
of this arrangement are in use by different brickmakers, the
object invariably being the production of a homogeneous column
of clay, quite free from lamination or other " structure," and

Water Water Water

FIG. lla. — Halsband conoid mouthpiece.

•devoid of internal stresses and strains which will later cause the
bricks to twist. A perfect clay column can only be obtained by
the use of a suitably constructed die, to which the clay is fed
by a properly arranged pug-mill or other feeding appliance, the
mouthpiece being properly lubricated so that the clay travels
at as uniform a speed as possible throughout its whole cross-
.section.

Sometimes the clay column will expand noticeably after it
leaves the mouthpiece or will crack on the face during firing.

124 MODERN BEICKMAKING

In each case the taper of the mouthpiece should then be re-
duced, either by reducing the size of the aperture next the pug-
mill or enlarging the exit of the mouthpiece until the defect is
removed.

Properly constructed scale-lined or laminated mouthpieces
greatly reduce the amount of power required to drive the
machine, as compared to that needed when a fustian-lined die
is used, and by adjusting the amount of overlap, the number of
plates, the position, size of the channels, and the pressure and
quantity of the water, it is not usually difficult to overcome all
the ordinary defects in the clay column, and several makers of
this type of die are willing to guarantee the production of a
perfect band from any kind of clay which can be made into a
plastic mass. The exit of the mouthpiece can only be enlarged
when the size of the brick is of minor importance.

Most of the defects in the shape of the bricks can be remedied
by slight changes in the mouthpiece. If they are hollow on top
or side a corresponding opposite curvature should be put in the
plate where the hollow occurs. If the bricks after firing are
longer on the back than on the face, giving a slightly wedge
shape, the liners should be closed in at the bottom, so as to
counterbalance this, unless the paste is used in too soft a state.
An excessively soft paste causes the clay to " squat " or spread
at the bottom and so produces bricks longer on the back
face.

It is important to keep the lining frequently renewed and
maintained of constant size, as bricks of different sizes are diffi-
cult to lay.

EXPRESSION ROLLER MACHINES.

In expression roller machines the die is not fastened on to
the end of a pug-mill, but the clay is pushed through the die by
a pair of rollers. It is essential that the clay shall be in a
perfectly homogeneous condition, as the rollers exert no mixing
or crushing action upon the particles.

Express rolls are valuable for making bricks from strong
clays in which, owing to great shrinkage, the bricks are liable
to twist or crack during the process of drying or burning. Such
clay, if of uniform consistence and free from stones, can often
be taken direct from the face, water applied to make it of the

PLASTIC MOULDING BY MACHINEEY 125

proper consistency for plastic bricks and the mixture thoroughly
pugged, carried along a copper- or zinc -covered table to the ex-
pression rollers, by means of which it is pressed through the die,
and will, if proper care be taken, produce a sound brick when
burned. With the edges and ends perfectly square, the bricks
can be used as " best fronts " with thin joints.

Expression rolls are also suitable for the treatment of clays
of a strong tough character, which, when made up with the
ordinary pug-mill, have a great tendency to show what is known
as " core cracks ". The use of a double shafted open pug-mill
or mixer in conjunction with expression rollers for feeding the
die has been found from long practical experience to be a very
effectual method of preventing " core cracks " in bricks, and
to produce an article of uniform character and free from
lamination.

The dies used with expression rolls are almost identical with
the mouthpieces used on pug-mills and described in the fore-
going section. Usually they are of rather simpler construc-
tion.

A complete machine comprising pug-mill, rolls, die, and
cutting table of a type at one time very popular is shown in fig.
78. It is known as the "Murray's patent," has a daily output of
15,000 bricks, and needs about 10 h.p. to drive under good con-
ditions. A similar machine using a horizontal pug-mill instead of
a vertical one and provided with hauling gear is made by Swinney
Bros., Ltd. (fig. 79). In this machine the rolls are 18 in. diameter
by 20 in. long and are grooved. Wootton Bros., Ltd.'s expression
rollers figs. 79a and 796 are 24 in. diameter by 14 in. long, and are
mounted on steel shafts carried in long cast-iron frames with
renewable side cheeks, which can be adjusted to compensate for
wear, the top roller being also adjustable. A rocking feeder is
fitted to the machine to compress the clay up to the rollers. This
is worked by an eccentric on one of the driving shafts.

This machine is powerfully geared, and driven by fast and
loose belt pulleys or friction clutch, as desired, and is practi-
cally self-contained on a massive bed plate. Such a machine
is extensively used for making quarries, hip and valley tiles,
ridge tiles, and a variety of solid, perforated, and tubular bricks
from clays liable to laminate when passed from a pug-mill
direct to a die, this defect being prevented if the clay is forced
through the die by the rollers instead of by a screw.

126

MODERN BRICKMAKING

PLASTIC MOULDING BY MACHINERY

127

Fig. 80 shows a front view of a similar machine made by
T. C. Fawcett, Ltd., which is simple in design, and of great
strength. It is self-contained on a strong bed plate requiring

little foundation and no skilled labour to fix. The same firm
also make another roller machine in which three pairs of ex-
pression rollers are used with correspondingly satisfactory results.
In this machine the clay is passed through one pair of expres-

128

MODERN BEICKMAKING

FIG. 79a. — Front view of Wootton Bros.' expression rolls.

FIG. 796. — Back view of Wootton Bros.' expression rolls.

PLASTIC MOULDING BY MACHINERY

129

sion rolls set wide apart, then through a second pair set some-
what closer, and finally through the third pair and the die.
Some strong clays which are notoriously difficult to work have
been very satisfactorily dealt with by this machine. It must
always be remembered that expression rollers are only formative
machines, and that to obtain good results with them the clay
must have been very thoroughly and carefully prepared. On this
account it must have been crushed (if necessary) as well as pugged.
With difficult clays it is often necessary to use extensive pre-

FIG. 80. — Expression rolls and die.

liminary plant, as may be seen from fig. 81, supplied by Wm.
Johnson & Sons (Leeds), Ltd., or other arrangements of plants
(pp. 77-87) may be used, the expression rolls being inserted be-
tween the exit end of the pug-mill and the mouthpiece.

Cutting Tables form the final machines used in the manufac-
ture of wire-cut bricks. They receive the clay in the form of
a long strip and cut it transversely into a number of bricks.
Usually a piece of clay at each end is not the full size of a brick,
this must be returned to the pug-mill.

The essential characteristics of a cutting table are that it

9

130

MODEKN BKICKMAKING

shall cut cleanly and rapidly, and that all the cut pieces shall
be of equal size. When these are secured the precise design of

the table is of minor importance, and the great variety of patterns
now on the 'market is due to minor variations rather than to
fundamental , differences in design. In the best cutting tables

PLASTIC MOULDING BY MACHINEET

131

the clay is either cut by wires or thin steel blades — the latter
giving a somewhat cleaner cut when in perfect condition, but the
former are more generally used because they are more easily
kept in order, and replaced when broken. Many brickmakers
use wires which are too thick to cut properly ; it is better to use
thinner ones even though they may break more frequently.

One of the simplest forms of cutting table consists of a zinc
or copper- covered table smeared with " brick oil," on to which a
sufficient length of clay, cut off from the column or clay band,
is pushed, .and cut into
bricks by depressing a
frame across which a
number of wires are
stretched (fig. 82). The
frame may then be
drawn back or it may
be of a rotary pattern
and move only in one
direction. The cut bricks
are then pushed on to a
board or pallet and taken
to be dried, the pushing
being direct by hand or
by means of a push board
operated by a lever.
The disadvantage of
drawing back the wires
is the production of a
rough edge or arris
which is avoided when the wire travels only in one direction
through the clay. Some brickmakers prefer to have the wires
in a fixed frame and to push the clay transversely across them.
This method is quite satisfactory where fine clay is used,
but for rougher material the downward cut is preferable, as the
cut is shorter and leaves the cut edges where they are of less
importance in the finished brick.

Such a table (fig. 83) is manufactured by C. Whittaker & Co.,
Ltd., in which the clay column issuing from the die of a plastic
brickmaking machine is received on the table, being supported
by the rollers shown at the left of the illustration. When a
sufficient length has passed on to the table the single cutting
wire (also at the left side) is drawn across, and the detached por-

FIG. 82. — Typical German cutting table
(Baupach).

132

MODEEN BEICKMAKING

FIG. 83.— Table with fixed wires.

tion pushed across by hand, in front of the pusher board. Then
by the action of the hand-lever the clay is pressed through the

cutting wires and cut
into bricks, but these
are not delivered on
to the pallet until the
next lot of bricks
pushes them forward,
thus preventing the
back edges from be-
coming broken. The
bricks thus cut are
perfectly true in shape
and serious waste is
avoided, for by this table the column of clay can be cut off to
one inch of the length required for each stroke. The front board
or pallet is removed when full of bricks and is replaced by an
empty one.

A similar table is manufactured by Woottoii Bros, of Coal-
ville, in which, in addition to the usual horizontal rollers,
two wooden vertical rollers are also provided to guide the clot
on to the table. A large heavy dressing roller is also fitted to
run over the bricks after they have passed through the wires.
This table (fig. 84) differs from the one just described, in that it
is fitted with a two face push-board arrangement and double pallet
boards. Sixty thousand bricks per day may be cut on this table.
The " Simplex " brick and tile cutting table made by William
Johnson & Sons, Ltd., is different from the two machines de-
scribed above. The chief feature of this machine (fig. 85) is
that the bricks are cut off without the attendant handling the
stream of clay in any way whatever. No cross-cut wire is used and
all waste ends are avoided, the whole operation being performed
by moving a single handle. The column of clay as it issues
from the die of the pug-mill is allowed to travel up to the end of
the table where a cross-board is fixed. The clay coming in con-
tact with this pushes the top part of the table forward (the table
is arranged to travel longitudinally and laterally). The attend-
ant then pulls over the handle (to cut the bricks), draws for-
ward the top of the carriage of the table (to clear the travelling
stream of clay), pulls back the handle (to deliver the bricks on
the moving board), then pushes the carriage back to receive the
column of clay and then repeats these operations.

PLASTIC MOULDING BY MACHINEEY

133

FIG. 84.— Cutting table with dressing roller.

FIG. 85. — " Simplex '' cutting table.

134

MODEKN BBICKMAKING

In the cutting table made by the Brightside Foundry and
Engineering Co., Ltd. (fig. 86), the motion is obtained by a simple
lever action, which entirely supersedes the use of racks and
pinions. It also has the handle, by which the cutting is per-
formed, placed close to the single cutting wire, so that one man
can, without moving his position, perform the various operations
of cutting and delivering the bricks on to the barrow, etc. This
arrangement renders the work easier and more rapid where the
clay is not too stiff.

Following the German custom, John Whitehead & Co., Ltd.,

FIG. 86. — Early type of cutting table.

mount the table on wheels which run on a short line of rails
(fig. 87), so that when the clay issues from the die of the brick-
making machine it eventually pushes against a vertical stop
placed at the front end of the table, thus pushing it along the
rails. The clay and table then move at the same speed, and the
stream of clay is divided squarely across by the single cutting
wire at the rear of the table into the length required to produce
a certain number of bricks, usually six or eight. This cut is
effected by moving a small -lever at the front of the table. The
attendant next pulls the table towards him and cuts the separ-
ated block of clay into bricks in the usual manner, a side
delivery action deposits them on boards, upon which they are

PLASTIC MOULDING BY MACHINEKY

135

transferred to the barrows, or to the repress, without being
handled. The table is then pushed back and the operations
repeated.

The table is easily worked by one lad, and can be applied to
any ordinary end-delivery machine which delivers its clay in a
horizontal stream ; the labour and time hitherto employed by
pushing the block of clay by hand in front of the fixed cutting
wires are abolished.

The machine shown in fig. 87 differs from the tables generally
used in Germany, as in the latter the frame moves, making a

FIG. 87. — Cutting table on wheels.

downward cut (fig. 82) instead of the bricks being pushed through
fixed wires. In the Batley cutting table (made by Oxley Bros.,
Ltd.) the clay band is cut by eight discs of steel instead of by
wires. A view of 'one of these cutting discs, with the band in
position ready to be cut, is shown in fig. 88. Each disc is pierced
with five circular holes, for the clay band to go through, and
when thrown into gear each disc makes a stroke of one fifth its
diameter, and cuts off the clay, the pug-mill being stopped
temporarily whilst this is being done.

Power-driven tables are slowly increasing in use, though their
advantages are not as great as is sometimes supposed.

136

MODERN BEICKMAKING

In Fawcett's patent power cutting table (fig. 89), as soon as

the end of the clay column
comes in contact with a

" stop," it moves it and starts
the machine, which auto-
matically stops as soon as the
bricks are cut and delivered
ready to be taken away.
The bricks are automatically
separated after cutting so
that they are the correct dis-
tance from each other (-J in.)
when placed on the cars. For
successful working, the clay
column must be sufficiently
stiff not to bend when press-
ing against the " stop " which starts the machine. The releasing
lever must also be kept in good order so that it will operate
directly there is a slight pressure on the stop.

FIG. 88.— Batley cutting disc.

FIG. 89. — Power-driven cutting table.

An automatic cutting table which is set in motion by an
electric contact-maker has been successfully used by the author
for clays which bend under the pressure needed to start an
ordinary releasing lever.

PLASTIC MOULDING BY MACHINEEY 137

Rotary cutters are much used in the United States but are
not employed in Great Britain, with the- exception of the Batley
cutter just mentioned.

It is a common practice in the United States to cut bricks
"endwise," but this practice has never become popular in this
country. It is claimed that the defects incidental to cutting are
minimized when the bricks are cut across the ends instead of
sideways, but this gain is trifling with British clays, and it is more
than counterbalanced by the loss due to diminished output.

In order to cut bricks by wires successfully, several details
require careful and constant attention ; the most important are
noted here : —

(a) The level top of the cutting table must not be higher than
the bottom of the inside of the mouthpiece, nor should it be
appreciably lower. In most cases the table is stationary and can
be packed up with wood, but where a neater job is required an
adjustable stand or table should be used, and is, indeed, essential
if large blocks are made by the same process as the bricks. Such
an adjustable stand is shown in fig. 90, the legs being lengthened
or shortened by rotating them. Another form of adjustment is
shown in fig. 91, where the upper portions of the table are
moved, the lower ones remaining stationary.

(b) The wires must be stretched tightly and must be kept
clean. They must also be sufficiently thin to give a good clean
brick. German piano-wire is the most suitable for the purpose,
and brickmakers should experiment to find which thickness gives
the best result. On the Continent, where the clay is ground finer
than in many works here, extremely thin wires are successfully
used, and the downward cut is invariably employed. In most
British yards the wires are too thick to give a perfectly clean
cut.

(c) The means used for attaching the wires must be simple,
strong, and adjustable. Usually a hook below the table receives
the lower end of the wire, and a butterfly-nut and bolt working
through the frame receives the upper end. Strong spiral springs
are frequently inserted between the nut and framework to absorb
vibration.

(d) In order to make a perfectly straight and uniform cut, it
is necessary to have the cutting table constructed with as much
care as a high-class lathe. It should be carefully machined
and put together, and should have bushings and liners for all
wearing parts so that the slightest play may be taken up at will.

138

MODEKN BBICKMAKING

This arrangement works fairly satisfactorily, particularly if
the lower end of the top bolt is made into a hook instead of being
bored, as is usual. It is then possible to keep wires in stock which

are cut to the correct length and have a small loop (fig. 92) at
each end. To replace a broken wire all that is necessary is to
slacken the butterfly-nut, unhook the broken wire, replace it by
a new one which has been previously prepared, and again tighten,

PLASTIC MOULDING BY MACHINERY

139

the nut. This is far better than the plan, often adopted, of
threading the wire through a hole and twisting it into a rough
loop, as such loops are seldom sufficiently rounded, and the strain
being unevenly distributed the wires break too frequently.

A series of keys similar to those used in pianos may also be
employed, but it is not easy to make such rapid renewals, and the
absence of a spiral spring is a disadvantage with rough clays.

FIG. 91. — Cutter with adjustable table.

Various special attachments and " wire-savers " have been placed
on the market from time to time, but the value of these the
brickmaker must judge for himself. The author has tried most
of them with indifferent results.

If bricks of different sizes are to be made, a cutting table in
which the wires can be moved closer together or farther apart
should be used, or preferably one to which an additional number

FIG. 92. — Cutting wire.

of wire holders can be attached. This latter arrangement avoids
the necessity of readjusting the holders each time the machine
is used. If the holders are properly constructed it is a simple
matter to remove those wires which are not required, but it is
often difficult to adjust the holders with sufficient accuracy when
once they have been moved from their place. Besides, the capital
tied up by the use of a few extra holders is too trifling to require
consideration.

Repressing. — The methods of brickmaking already described are

140 MODEEN BKICKMAKING

not often suitable for the production of bricks for facing purposes,
as the bricks are seldom sufficiently accurate in form ; it is, there-
fore, necessary to repress them when best facing bricks are re-
quired. Before this can be done to advantage it is necessary to
dry the bricks until they are black-hard, or leather-hard. They
must not be allowed to become too dry or the repressing will not
be effective, neither must they be pressed whilst too wet or they
will not leave the die properly. Some little skill is required to
know the precise moment when a brick is ready for repressing,
but it is not difficult to learn this with a little practice.

The presses used for giving bricks an accurate shape are of
the screw-press, toggle-lever, and hand-lever patterns, and are
driven by hand or steam power. The hand-driven patterns are
usually convenient where a portable press is an advantage, other-
wise a power-driven press is better. The hand-lever presses are
described on p. 60 in the section on Hand-made Bricks.

Screiv Presses are a special form of plunger press in which the
die-box is carried on a bed-plate or table, and the plunger or
male die is forced into contact with it by means of a quick-acting
screw, working in a bridge above. The bottom of the die is made
loose and rises with the plunger.

The plunger is raised to its full height and simultaneously
the bottom of the die is raised to near the top of the box. A
brick is then placed on the latter and the plunger lowered by
turning the wheel or arms at the top of the press. The speed of
descent increases rapidly, and after the plunger has come once
into contact with the brick and the force of rebound has started
it on an upward journey, the man in charge of the press pulls it
down again smartly so as to give a second pressure to the brick.
When a power-driven press is used this second pressure is not
given, but the single pressure is greater than in a hand-press.
There are reasons for believing that two lesser pressures are better
than a single more powerful one, and partly on this account
power-driven screw-presses have not, up to the present, displaced
many hand-driven ones.

Screw presses are made by most manufacturers of brickmak-
ing machinery, but resemble each other so closely that very few
examples suffice to show the essential details of their construc-
tion. Those of the older type are provided with a long arm (fig.
93) with a heavy ball at each end, but the more modern presses
have a heavy wheel (fig. 94) which is steadier and gives a better
pressure. The earlier and smaller screw presses were mounted

PLASTIC MOULDING BY MACHINERY

141

on wheels for portability, but the later ones are usually of heavier
construction and are necessarily fixtures.

The great desideratum in a screw press is the rapidity and

FIG. I' 3. — Screw press with ball weights.

steadiness of action. Both these are secured to an ample extent
in the press shown in fig. 94, as the double action steel screw
with right and left hand thread gives a traverse double that of
the ordinary^ screw, and the adjustable arms on each side of the
plunger make it impossible for it to shift sideways ^during its

142

MODEEN BEICKMAKING

descent. In this way the damage done by the plunger not exactly
entering the die- box is avoided. A man and a lad can press from
3000 to 4000 per day with this machine.

FIG. 94. — Portable screw press.

Power-driven presses of the screw, or Titley type, are largely
used on account of the greater output and more uniform pressure.
They are similar to the hand-driven ones, but two boys can re-

PLASTIC MOULDING BY MACHINEEY

143

place the man and lad, as the greater strength of the latter is
not needed. Fig. 95 shows a very good means of applying the

FIG. 95. — Power-driven screw press.

power, viz. by means of two discs which force the fly-wheel
round by friction, the one shown in fig. 96 with three pulleys

144

MODERN BRICKMAKING

and crown and pinion driving gear being quite as satisfactory.
The power gear starts and stops the press, the momentum of the
fly-wheel striking the blow as in a hand-driven press; and an
automatic reversing motion returns the wheel to its starting
point.

The Pullan & Mann machine (fig. 96) has an advantage in

that it can be fitted with the
maker's patent measuring ap-
pliance which ensures each
brick being the same size, any
inequalities being shown in
the varying depth of the frog.
In selecting a screw press,
care should also be taken to
ensure a simple yet effective
means being provided for
holding the die-box and for
setting it accurately in posi-
tion. Slotted flanges on the
box into which fit strong bolts
passing through the bed are,
probably, the best form of
fastening if the bolts are suffi-
ciently large.

With a machine subject to
such sudden strains as a screw
press, the bearings need to be
specially well made and to be examined occasionally to see that
they are in order. If a press of this type " runs hard " the bear-
ings should be examined immediately.

Eccentric Represses, working with a plunger driven by an
eccentric motion, are simple in action and have few parts to get
out of order. They are preferably made double, so that there is
less liability to shock when pressing is overcome, and the pressure
is maintained during a longer time. Such a machine is clearly
shown in fig. 97, worked by a single cylinder engine attached
to it. A front view of a similar press made by Bradley & Craven
(Wakefield) is shown in fig. 98, but in this the bricks are placed
in and taken off by hand instead of automatically, though a
push gear can be added if desired. The press should, as in this
case, stop automatically after each brick is pressed, so as to
prevent any risk of danger to the attendant.

FIG. 96. — Power-driven screw press.

PLASTIC MOULDING BY MACHINEEY

145

The essential parts of the machine should be very strong and
large'; the eccentric and shaft should be of steel and the die
lined with hard -metal or steel.

FIG. 97. — Brick press with eccentric action.

The output varies from 5000 to 6000 bricks per day accord-
ing to the size of the machine.

A good eccentric-motion press of somewhat different type is
made by T. C. Fawcett, Ltd. It has been specially designed for
repressing wire-cut bricks and has a daily output of 14,000, the
bricks being fed automatically or by hand (fig. 97 a).

10

146

MODEKN BEICKMAKING

Toggle-lever Presses work on an entirely different principle,
and give two entirely distinct pressures. Two arms or levers are
used, and the pressure is applied in such a manner that after the
brick has been pressed by the action of one lever, the motion of
the machine brings the second lever into action and a double
pressure is thus obtained. Fig. 99 shows a front view of a

FIG. 97a. — Eccentric double press for plastic bricks.

typical press of this type by Sutcliffe, Speakman & Co., Ltd., and
fig. 100 a back view of a similar press by the same firm, showing
an oil-engine attached for driving it, though a small steam-engine
is generally to be preferred. Another important feature of this
machine is that the pressure is retained on the brick whilst it is
being ejected from the mould, thus rendering it possible to pro-
duce bricks with a very good finish.

PLASTIC MOULDING BY MACHINEEY

147

The motions for feeding and delivering the brick to and- from
the mould and also for lifting them out of the mould are 'all
self-acting and simple. The bricks can be delivered to either

FIG. 98. — Bradley-Craven repress.

side and the press can be easily regulated to press bricks of, any
thickness.

In all toggle or knee-joint presses it is essential that the
pressure should be received where it is needed and not on the

148

MODEEN BEICKMAKING

framework, as this type of press is amongst the most powerful
used in repressing plastic bricks. The bearings must be of ample
size and kept in thorough order and adjustment.

Presses of the toggle-lever type are largely used for the " Semi-

FIG. 99. — Toggle lever press (front view),
dry " and " dry " brickmaking processes, and several other ma-
chines will be found described in those sections.

In the use of a press for repressing bricks, numerous little
points must be watched if lamination and other troubles are to be
avoided. The die itself must be kept true to shape and relined
as soon as it becomes appreciably worn, as with a worn die good

PLASTIC MOULDING BY MACHINERY

149

bricks cannot be produced. Many brickmakers are careless in
this respect and in the accuracy with which moving parts fit into
the die-box. Unless these are rightly arranged much power is
wasted and the best quality of bricks is never reached. Some

FIG. 100. — Toggle lever press (back view).

firms spoil their bricks with too much oil in the press ; others
are continually troubled by not using sufficient oil. It is a
mistake to suppose that whenever a brick sticks in the die more
oil is needed. Sticking is more frequently a sign that the bricks

150 MODERN BRICKMAKING

are pressed in too soft a state, and by leaving them to dry a
little more, much sticking may be prevented.

The use of colza or cod oil mixed with paraffin in the proportion
of one teaspoonful or more to a pint will often enable better bricks
to be produced than when a cheaper lubricant is used on the bricks.
Various methods for applying the oil have been suggested from
time to time, but none appear to be better than wiping the mould
repeatedly with a greasy rag, and occasionally leaving the die
full of oil for a night. Most of the trouble of bricks sticking is,
as already noted, due to pressing them when too wet.

One common defect is the plunger (or male) die not engaging
properly with the box (or female) die, but hitting the edge of the
latter and then slipping in. In time, the dies become so worn
that an arris, or false edge, is produced on the bricks, and their
value is seriously diminished. This can only be avoided by
keeping the guides for the plunger and the bearings through
which the moving portions work very steady, so as to prevent
slipping, and by placing the die-box very accurately in position
and clamping or bolting it down whilst the plunger is actually
engaged in it.

This matter of accurately fitted dies is more important than
appears at first sight, as defects in this part of the machinery
not only produce unsightly bricks, but cause so much waste of
pressure as, in many cases, to prevent the repressed bricks from
being any better for the treatment. This is one reason that
so many firms find that repressing adds little or nothing to the
strength of the bricks. Effectively performed, repressing is an
advantage, but if the process is badly managed it would be
better for the bricks had it been omitted.

A brick once formed has a definite " set " or structure, and if
it is repressed in a proper manner and at the proper time, the
particles will simply be compressed and a denser brick obtained.
If, on the contrary, the brick is placed in a die which is too large
for it, or into one of a different shape, the " set " of the brick will
be destroyed by the extensive movement of the particles under
compression, and a complex structure, due partly to the original
formation of the brick and partly to its deformation in the press,
will be produced. Such a brick cannot, by its nature, be so
strong as a brick of a more homogeneous structure. Hence, unless
the dies of the repress are kept in first-class order it is better
not to use a repress at all. For the same reason the production
of cylindrical clots to be later pressed into bricks, is undesirable.

PLASTIC MOULDING BY MACHINEEY

151

Die-Boxes in presses require to be made in such a manner
that corrections for wear and tear can readily be made. Many
ingenious devices for this purpose have been invented, amongst
the best being (a) renewable lining pieces (b) built up sides.

In dies or moulds with renewable liners the portions of metal
which come into direct contact with the clay are in the form of
thin strips of steel, which can readily be replaced when worn,
without much expense being involved.

With built-up dies the four sides of the die are made loose

FIG. 101. — Jones' patent brick dies.

and are held together by bolts, as in the patent dies made by
John Jones & Sons, Ltd. (fig. 101).

The " economic " moulds made by Sutcliffe, Speakman & Co.,
Ltd. are based on the principle of a mould made in two or four
parts held together by two massive bolts passing through the
body. Loose liners are arranged with notched edges and key-
pieces to fit perfectly to each other. On tightening the two bolts,
the whole mould, including the liners, is held rigidly together,
but on loosening the bolts it may be readily taken to pieces and
the liners turned or replaced. These moulds can be fitted to any
type of hand or power press and are very cheap in actual use ;
they deserve to be widely known. The saving of time they effect

152

MODERN BEICKMAKING

in relining is very great, and they are appreciated by all who
have used them, on account of this convenience.

The illustrations show an " economic " mould taken to pieces
(fig. 102) and put together ready for use (fig. 103). It is essential

that the dies should be kept accurate in size, as otherwise the
bricks will be faulty.

Any variations in preparing the paste, or in its composition,
will cause the size of the clot, or first-formed brick, to vary. To

PLASTIC MOULDING BY MACHINEEY

153

allow for this variation the clot or brick is made small enough
to drop easily into the die-box of the repress. Hence the brick
does not fill the press-box neatly, and when the pressure is
applied the clay is forced out until it meets the sides and ends
of the box, producing a different " set " and a rearrangement of
structure, which may seriously affect the final strength of the
brick.

This difficulty may be partly overcome by the use of a device
(such as that patented by Pullan & Mann) in which variations in

FIG. 103.— " Economic " mould ready for use.

the thickness of the original brick are automatically taken up
by varying the size of the frog in the repressed article.

Surface cracks in repressed bricks which have been fired are
sometimes existent before repressing, but instead of being healed,
oil enters the surface indentations and cracks and prevents the
surfaces from adhering. The removal of the brick from the
press partially smooths over these flaws, so that it is impossible
to detect them until they have been through the kiln.

The chief use of the repress is to put sharp corners and
square edges on an otherwise irregular block of clay, but by
exercising greater care and skill in forming the original brick,
much of the repressing now practised may be avoided.

154 MODEKN BKICKMAKING

DRYING,

Plastic -made bricks usually require to be perfectly dried
before being sent to the kilns as, if the moisture they contain is
removed too rapidly, good bricks cannot be produced.

Hacks (p. 56) are not usually employed except for drying
hand-made bricks, though in some instances they are quite
satisfactory for the machine-made article.

Artificial dryers are of various types, ranging from the simple
shed to the most complex of chamber- or tunnel-dryers using
waste kiln-gases, live or exhaust steam, or both, and fitted with
mechanical ventilators.

The main principles applied in the drying of bricks are con-
vection, conduction, and radiation, the heat necessary being
applied by placing the goods on heated floors or in a current of
air warmed to the desired temperature. When no artificial heat
is used, a large amount of air at the ordinary temperature will
be required, and if the clay is tender it will be necessary to dry
very slowly, as such clay is very sensitive to strong currents
of air.

The simplest form of dryer is a shed in which is a number of
racks or shelves on which the bricks are placed to dry (fig. 25).
The walls of this shed are made in sections of Venetian shutters
which are opened to admit fresh air, or of boards which can
be taken down and an open shed produced. The roof should
have shutters which can be opened to create a better circula-
tion of air when the bricks require it.

The racks, or shelves, should be arranged with aisles or gang-
ways between them if the shed is very large, and should not be
higher than a man can reach easily whilst standing on the ground ;
the use of trestles wastes much time and is far from satisfactory.
Ample space must be left between the top of the racks and the
roof of the shed, as if this space is too small there will not be
sufficient air in the shed to retain the moisture given off by the
bricks unless a very strong air-current is used. Such air-currents
are disastrous with many clays.

The cost of such a shed fitted with racks is by no means low
(it amounts to about £800 for an annual output of 1,000,000
bricks) and the cost of placing the bricks on and taking them off
the racks is also considerable. It is, therefore, advisable in many
cases to substitute some other form of dryer where the annual

PLASTIC MOULDING BY MACHINEKY 155

output exceeds 1,000,000 bricks. For small yards the use of such
a shed will effect a total saving of about 6d. per 1000 as com-
pared with hack-drying.

It is wise to erect such a shed the full width and to increase
its length when a larger capacity is required, as this arrangement
does not interfere so much with the working as when a series of
sheds is used. The output of such a shed may be increased by
laying three steam-pipes on the floor beneath each rack, or by
constructing the racks of 1 in. iron pipes through which steam
is passed. The use of steam is valuable when the bricks- have to
be made very soft, and the output of the works is too small to
warrant the installation of a tunnel-dryer.

Small vertical boilers quite suitable for this work can now
be obtained very cheaply, and the fuel being burnt under better
conditions than when " fires " are used for drying, much heat is
saved. The trouble of a limited water-supply need not be con-
sidered serious, because most of the steam can be condensed
and collected at the outlet of the dryer.

The main underlying principle of the best systems of drying
by artificial heat consists in the use of a small volume of air
at a higher temperature in place of a large volume of cooler
air. The advantages of this are so great as to make artificially
warmed dryers far cheaper for large outputs than is often
supposed by brickmakers who are unaccustomed to the use of
heat, and the volume of air being smaller the tendency of the
goods to crack is greatly reduced.

The best methods of applying heat are by no means easy to
ascertain ; the common idea — that of raising the temperature of
the drying-shed by supplying heat to the floor — being found, on
careful investigation, to require serious modification if the
best results are to be obtained. In the first place, bricks placed
in a heated, closed shed will not be dried completely unless their
temperature is so high that it would be difficult to deal with
them when dry without loss of heat (and therefore of fuel) by
allowing the shed to cool. In addition to this loss of heat, the
irregular distribution of heat which occurs in such a dryer is
liable to give unsatisfactory results, and better drying can, there-
fore, be obtained more economically by the more careful use of
the principles underlying the supply of heat and the evaporation
of water in bricks.

When a wet brick is heated, several reactions occur of which
the following are the most important : —

156 MODERN BEICKMAKING

(a) The dry or solid portion of the material absorbs heat
and its temperature increases.

(b) The moisture in the brick also absorbs heat, and if the air
surrounding it is capable of absorbing moisture some of the
water passes out of the brick into the air, this process of drying
being continued until either no moisture remains in the brick,
or until the air can absorb no more because it is saturated. In
this last case the temperature of the air must be still further in-
creased, or the air must be replaced by an unsaturated portion.

(c) As the moisture evaporates from the surface of the brick
it is replaced by other water -particles from the interior, and the
brick shrinks in size until a stage is reached where no further
contraction is possible, after which simple transference to the
surface and evaporation of the moisture alone take place. The
amount of air used, and the temperature attained by it and by
the finished bricks, will depend upon a number of circumstances.
Thus, as A. E. Brown has shown, " to raise a dry brick weighing
7 Ib. from 60° to 61° F. takes only 1-4 units of heat ; but to raise,
in the same way, the temperature of a wet brick weighing 7-J- Ib.,
and to evaporate at the same time the -J Ib. of water it contains,
will take 537 units of heat, « or nearly 400 times as much. The
latter figure represents the heat yielded by the consumption of
about f oz. of ordinary coal. Not only so, but the heat has ab-
solutely disappeared, and can only be recovered by condensing
the vapour of the water-bath into the water again. For this
reason the statements which are sometimes made that certain
drying systems use heat over and over again, and that the heat
is not allowed to escape, must not for one moment be credited,
although at first sight they seem to be borne out by the system
referred to." It will thus be seen that the supply of an ample
amount of air, at a suitable temperature, is the primary factor in
the drying of bricks, and the methods by which this is attained
must now be considered.

Three general methods are in use : —

1. The bricks are dried by convection, by placing them on a
hot floor which transmits its heat direct to the bricks, and these,,
in turn, warm the surrounding air and enable it to absorb the
moisture evaporated, providing that sufficient air is present. In
this case, the bricks are laid on the floor, or are stacked to a
height of about 3 ft. The disadvantage of this method of heat-
ing is that it is wasteful of heat, the air being warmed by the
bricks, and unless satisfactory means are supplied for its pro-

PLASTIC MOULDING BY MACHINEEY 157

•gressive renewal or removal, the drying is both irregular and
slow compared with the amount of heat used. Such floors are
not suitable for very tender clays. The floor may be heated by
steam flues, by flues from coke or coal fires, or by waste kiln
gases, or the dryer may be placed above or around a continuous
kiln — a custom very popular in Germany but seldom used by
British brickmakers.

In spite of the advantages which some other dryers un-
doubtedly possess, there are cases in which the drying room on
top of a continuous kiln is equally satisfactory and often cheaper
to work. This is especially the case where space is limited, and
there is>but little accommodation for a dryer on the ground level.
The saving in fuel is also quite noticeable when the bricks are
dried from the waste heat from the top of the kilns, even when
the goods are ordinarily dried without heat except in damp
weather. The cost of raising bricks to the top of a continuous
kiln is often greatly exaggerated, as a simple elevator with
balance weights will usually provide the elevating power, and
the number of men needed is no more (and sometimes even less)
than with the other forms of dryer. In short, the firm which
installs a simple drying room on top of their continuous kiln
need have no anxiety when they have once arranged it to suit
their clay, for an error can only be made when, without attempt-
ing to understand the conditions under which the clay must be
dried, a dryer is designed as a direct copy of one used by another
manufacturer.

Opinions differ greatly as to the relative value of steam and
fuel for heating dryer-floors ; the use of gases from kilns is only
employed to a very small extent, and many firms would profit
by more attention to this method of working.

The gases should be drawn from the kilns under the dryer
floor by means of an induction fan, placed at the farther end of
the dryer, as, by this means, the gases are cooled so that they
cannot injure the fan. The<floor is so constructed as to distribute
the heat evenly throughout, a design similar to that used for
steam but with flues 18 in. deep being satisfactory. Larger
flues may be used if a light floor is strong enough. The fan
should show a gauge reading of £ in. to 1 in. of water.

When steam is used, it is customary to employ exhaust steam
during the day and live steam at night, if necessary. The con-
struction of the floor is practically the same as when fuel or kiln
gases are used, except that the joints may require to be rather

158 MODERN BRICKMAKING

tighter to prevent condensation on the bricks, and the sub- floor
must be carefully concreted to prevent the ground being unduly
softened by the condensed steam. Some attention should also be
paid to the draining away of the water produced in the flues of
a steam-heated floor, and on this account the sub-floor should
slope in. the same direction as the steam travels, though E.
Thomas has found a depth of 2 in. of water on the sub-floor to
be an advantage in securing a more even distribution of the
heat. The steam being of a uniform temperature, the lines of
brickwork forming the flues may 'be broken by setting these
bricks about 1 in. apart ; incidentally this secures a better dis-
tribution of the steam. The floor should be divided into a num-
ber of separate sections, each about 10 ft. wide and each
capable of being worked independently. This serves to economize
steam and facilitates the regulation of the drying.

The steam from the boiler enters a transverse flue at one end
of each of these sections from a pipe controlled by a special
cock or valve, finally escaping through a similar transverse flue
at the other end of the section. It is important that a vent for
the escape of steam, as well as a drain outlet for the water,
should be provided at the end of each section. Some makers
prefer to let the steam enter a transverse flue in the centre of
the dryer instead of at one end ; this is desirable if the dryer
is more than 30 ft. in length, but otherwise it is more convenient
to have the steam-inlet pipes near to a wall and so out of the
way.

The use of drain pipes to form the flues of a drying floor
should be avoided, they are seldom, if ever, satisfactory, and if
the spaces between them are filled with solid ground the heating
power of different portions of the floor is very irregular.

A steam floor built in sections, 30 ft. long and 10 ft. to 15 ft.
wide, will dry ten bricks per week for every square foot of surface
if properly built and cared for. If the flues are covered with
iron plates instead of with cement a slightly larger output may
be obtained, but the use of iron presupposes that the bricks can
withstand somewhat rapid heating.

An excellent arrangement of flues for a steam-heated floor
consists in laying bricks end to end on their edge with their sides
6 in. apart (centre to centre) on a sub-floor made of concrete
2 in. in thickness, and covering these bricks with others laid flat as
" stretchers ". A finishing cover of cement, 2 in. thick, or iron
plates, 3 ft. square, completes the floor. The cement covering

PLASTIC MOULDING BY MACHINEEY 159

is preferable, as it does not transmit the heat so rapidly as do
iron plates.

The lowest bricks are set with their ends 1 in. apart until a
width of 10 to 15 ft. is obtained, when they are set close and
jointed with mortar or cement so as to form a series of indepen-
dent sections. In place of bricks, hollow blocks may be used
where the weight to be carried by the floor is not excessive. The
thickness of material between the steam and the bricks to be
dried is less than with a brickwork floor and the heat is transmitted
more readily. Such a floor is, however, more easily damaged by
carelessness in the use of the barrows employed for carrying off
the bricks.

Floors heated by coke, coal, or kiln-gases have the flues
arranged similarly to those employing steam (p. 157), the fires
being arranged at one end of the dryer and a chimney at the
other. The sections should not be more than 8 ft. wide for each
fire used, and the thickness of floor above the flues should be
greater nearer the fires than at the other end, so as to secure as
even a temperature as possible in the bricks. The whole of the
flues should slope slightly upwards towards the chimney-end and
the gases should be collected in a transverse flue before being
taken to the chimney. A floor heated in this way will dry 10
to 12 bricks per square foot per week if very carefully watched
and with a favourable clay, but with tender clays serious
difficulties may be experienced.

When kiln-gases are used they are delivered into a transverse
flue at one end of the floor through a flue connected directly to
the kiln. In order to prevent a back draught on the latter it is
usually necessary to employ a fan at the other end of the dryer
in order to draw the gases through the floor. A blowing fan can-
not well be used, as the gases are too hot, except when obtained
from continuous kilns. It is, however, a mistake to attempt to
use the gases from properly constructed continuous kilns for
this purpose, as their heat should have been used in the kiln
itself with the exception of a small amount necessary to carry
the gases up the chimney.

The use of waste gases from single intermittent kilns for
drying has not received the attention it deserves, yet when a
number of such kilns are connected to the same shaft it is not
usually difficult to connect them to the dryer and so use the
heat the gases contain. These gases must not, however, be
allowed to come into contact with the bricks or the latter will

160

MODEEN BEICKMAKING

be discoloured, though so long as gas-tight flues or pipes are used
for containing the gases no harm of this sort can occur. The
hot gases should be taken from the top of the kilns.

The hot floor is one of the oldest forms of artificial dryer
known, and for ordinary building bricks it has now been largely
replaced by tunnel dryers, though for fire-bricks, terra-cotta, and
in many somewhat small brickyards a hot floor is still used.

After the bricks have been partially dried on a hot floor they
are usually stacked, in order that they may take up less room
before they are taken to the kiln. This is a waste of labour
which should be avoided when possible, but is sometimes un-
avoidable. The bricks may be stacked in a variety of ways, and
suggestions in this connexion may -be gained from a study of the
illustrations in Chapter VIII on setting and burning.

Some clays permit the bricks to be stacked very openly, whilst
with others the bricks must be placed very close together so that

FIG. 104. — Bricks set in open chequer work.

they may dry very slowly. In the latter case, a simple chequer-
work arrangement of the bricks should
be used (fig. 104), but if an open setting
is required the arrangement shown on
this page (fig. 105) is to be preferred,
an " air flue " (a) running through each
set of bricks.

If the bricks are set in blades or
walls, these should be about 8 in. apart
so as to permit of easy handling and
ample air-space for drying. The height
of such blades or walls will depend upon
the stiffness of the bricks, but ought not
to exceed 4 ft.

FIG. 105. — Bricks drying on
hot floor.

PLASTIC MOULDING BY MACHINEEY 161

2. The goods are placed in special chambers — usually of a
tunnel form — and the air is drawn through these chambers,
lieing heated directly and communicating its heat to the bricks.

In tunnel-dryers the air is heated, and the goods are dried
chiefly by their contact with warm air, though they are, to a
limited extent, heated by radiation from the pipes, etc., in the
dryer. The basic idea in a tunnel dryer is the same as that in
a continuous kiln, with the difference that, instead of the goods
remaining stationary and the heat travelling (as in a kiln), the
goods usually, but not always, travel in the dryer.

In most cases the bricks are placed on cars and are moved
through the chambers, which are made sufficiently long to hold
a number of cars at a time, but dryers using warm air in which
the goods are stationary are also employed. These latter have
the disadvantage of wasting some heat and the goods must be
taken to the dryers, set, and again loaded on to cars or barrows
before being taken to the kiln, thus necessitating a loading, set-
ting, and reloading which are avoided when cars are used. On
the other hand, the cost of the cars is avoided.

The best results are obtained (providing the goods can with-
stand the slight shocks produced when a car is removed from a
dryer, the remaining ones moved forward, and a new one in-
serted) when the bricks remain on the cars during the whole
drying period, but with delicate articles, and where the cost of
cars would form a serious charge on the capital of the firm, it
may be necessary to place the goods in a tunnel until it is filled
and to remove them when dry, though a little consideration will
show that this method is more costly both in handling and in
heat than when the goods move forward through the dryer.

Tunnels in which no cars are used must be filled, the goods
dried, and the tunnels then emptied. Such tunnels are there-
fore intermittent in action. When cars are used the dryers are
generally made for continuous working. The chief use of car-
less dryers is for specially tender clays which will not stand the
shocks of the cars ; but if these vehicles are properly constructed
continuous dryers will be found preferable.

A simple form of continuous tunnel-dryer is shown in fig.
106 in section and in fig. 107 in plan. In this the cars (C) carry-
ing the bricks to be dried, enter at the cool end (B) and are
moved intermittently (i.e. each time a car is drawn out of the
dryer) towards the end (A). Hot air enters the dryer through
the flue (A) and is made to travel in the opposite direction to

11

162

MODEEN BEICKMAKING

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PLASTIC MOULDING BY MACHINEEY 163

the goods, the movement of air being indicated by the arrows.
When charged with moisture and cooled, the air passes out
through the flue (B). Only one track or tunnel is shown, but
any convenient number may be placed side by side. A conveni-
ent size of tunnel is 120 ft. long, holding sixteen cars, each carry-
ing 360 bricks. When properly constructed and worked, a tunnel-
dryer should dry even tender clays in twenty -four hours, or an
average of four bricks per minute.

It has been shown, by A. E. Brown, that a tunnel-dryer is
most efficient when the air enters it at 170° F., and leaves it at
82° F., but this latter temperature is too low in practice, because
the air is so charged with moisture as to make it difficult to
avoid its condensation on the goods just entering the dryer. In
some instances bricks are found to weigh several ounces more
after a short time in the dryer than they did before entering it ;
this is due to condensation of moisture on them. The result is
that, with a dryer of this type (i.e. one in which the air and
goods travel in opposite directions to each other), the air is
discharged at about 90° to 95° F., and a slight loss of heat thereby
is accepted as inevitable.

The movement of air is effected by means of a fan or a special
chimney stack. It is heated by passing over a special heater
using fuel or kiln-gases, or by mixing it with gases derived from
the combination of fuel, either directly or as the waste gases
from kilns. The latter method is not satisfactory when the
colour of the finished bricks is important on account of the im-
purities in the gases.

To prevent the bricks at the top from drying too rapidly,
some means of controlling the air currents and regulating their
velocity in different parts of the dryer must be provided. Other-
wise the topmost bricks will be dried more rapidly than the lower
ones. This is often overlooked by amateur dryer-builders.

The Blackman Ventilating Co draw air partly over grates
(G) (fig. 108) on which the fuel is burning, and partly through
other openings protected by gauze doors, so arranged that the air
is mixed with passing through the fire-brick flues (R) before it
passes the fan (V) and enters the dryer through the upcast (A)
as already described. Such an arrangement is known as a " slab-
heater ". It is very effective, as the flues (R) tend to heat the
air very uniformly when the heater is properly cared for, but the
warming of the air by its admixture with the products of com-
bustion of the fuel is a serious drawback except for common

164

MODERN BRICKMAKING

goods. On this account the tubular coke-heater (fig. 109) made
by the same firm, in which the air is kept pure and is heated by
passing through iron pipes, is to be preferred. In it the gases
produced by the burning of the coke pass around the iron pipes,
heating them, and then out through the chimney.

Slab-heaters lose a serious amount of heat when above
ground, hence the Sutcliffe Ventilating Co. place theirs below
the ground level, and employ a different arrangement for regulat-
ing the amount of air passing through and over the grates and
that used to dilute the products of combustion.

The " Aero " dryer used by H. Raynor at Witham, Essex, is
similar to those by Blackman & Sutcliffe, but an induced draught

FIG. 108. — Plan of Blackman heater.

fan is placed below the ground level at the opposite end of the
dryer to that at which the stove is fixed. The air, heated in a
slab-heater or in any other suitable manner, enters an expan-
sion chamber and then passes through a square hole (inlet-valve)
in the- floor of each tunnel. After traversing the tunnel it passes
out through another square hole (outlet-valve) in the floor to the
fan and the outside air. A chimney fitted above the exit (fan)
end of each tunnel enables the dryer to work at night without
the necessity for running the fan if the outlet-valve is closed.
Control of the heat is obtained by means of dampers. Thus,
heat is prevented from entering a tunnel by covering the inlet-
valve with a damper. The draught is also controlled in the
same way at the outlet-valve. An important feature in the

PLASTIC MOULDING BY MACHINERY

165

construction of this dryer is that each of the outside walls con-
sists of two separate walls of 4^ in. width, with a 1| in. space be-
tween them. The draught from the fan draws any warmth from
this cavity that may penetrate the inner 4^ in. wall back into the
tunnels, where it is again utilized for drying.

Steam-heaters are placed under the warm end of the tunnel
if of the tubular form, but when steam pipes are used they are
generally placed in the floor of the tunnel just below the rails on
which run the cars carrying the bricks. Tubular steam heaters
usually consist of a cylinder 10 to 20 ft. long fitted with about
200 tubes, each 3 in. diameter, through which air is blown by a
fan, and around which live or exhaust steam circulates at a
pressure not exceeding 60 Ib. Such a heater shown diagram-
matically in figs. 109 and 110 is supplied by several firms,

FIG. 109. — Heater and fan in position.

notably the Blackman and Sutcliffe companies just mentioned.
An excellent steam heater of American design is shown in fig. 111.

The Wolff dryer has steam pipes placed under the floor of
the tunnels to about three-quarters of its length, as shown in
fig. 112. The pipes are arranged in four or more sections, the
steam passing from one to the other in turn, and leaving any
condensed water in the 5 in. connecting or " service " pipes. The
amount of steam is so regulated that none escapes from the last
section. All the water produced by condensation is taken to the
boilers. The roof of this dryer is double and has several open-
ings at the cool end which may be used to increase the upward
movement of the air and to take it direct to the shaft. The
volume of air supplied in this dryer is comparatively small,
rarely exceeding 2500 cub. ft. per minute in each tunnel.

Drying is slower than in some other types of tunnel-dryers,

166

MODERN BEICKMAKING

being seldom completed in less than fifty hours and occasionally
requiring five days.

Condensation on the goods is often heavy, owing to the air
being highly charged with moisture at the entrance end of the
tunnel, and a preliminary " tempering chamber " about 40 ft. in
length is, therefore, used to prevent this deposition of water on
the bricks. In short, the Wolff dryer is economical in regard to
the amount of steam it requires, but it is capable of much im-
provement in several ways.

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FIG. 110. — Tubular heater for coke.

When kiln-gases are used in a tunnel-dryer, they should be
passed through somewhat wide metal pipes on account of their
corrosive powers, unless the smaller piping can be cheaply and
easily replaced. The flues or pipes should be some distance
below the goods so as to allow some circulation -of the air heated
by them, or the bricks will be irregularly dried.

It is, usually, best to employ waste steam as far as possible,
and only to finish the drying with air heated «by, passing around
flues containing kiln-gases.

The most efficient and effective drying of bricks is obtained
by the use of the tunnel-dryers in which both goods and air move
in the same direction. The air is cold as it enters the dryer, and

PLASTIC MOULDING BY MACHINERY

167

168 MODERN BBICKMAKING

it and the bricks are both warmed progressively, as they travel
forward, so that the air passes out of the dryer warm and leaves
the bricks hot and dry.

As the heat- carrying power of the air increases very rapidly
with an increase in its temperature by working in this " direct "
manner, there is no danger of condensation on the goods, and the
drying can be accelerated as soon as sufficient moisture has been
removed from the goods to enable this to be done.

As exhaust steam does not supply heat at a sufficiently high
temperature, the hot end of the dryer must be supplied with
gases from a furnace or kiln.

A typical dryer of this kind is one patented (fig. 1 13) by A. E.
Brown. A series of furnaces or slab-heaters (H) Is placed below
the hot end of the dryer, and the air from these passes through
a series of pipes (C) which are separated by broad transverse
chambers (G) covered with sheet iron (d) to facilitate sweeping
or obviate the defects of expansion. At the cool end of the dryer
these gases pass through a series of tubes (K), around which the
air for the dryer circulates, and are taken to the chimney by a
fan (not shown). Any additional heat that may be required is
supplied by steam pipes (e), and kiln gases carried in pipes or flues
may replace those from the slab-heaters (H) in whole or in part.

The air for drying the bricks enters below the floor level at
(/), passes around the heater (K) and into the tunnel at (h). It
then traverses the entire length of the tunnels in the same direc-
tion as the cars, becoming warmed by and taking up more and
more moisture from the bricks. It flows in a gentle stream, and
by reason of the overhead radiation , does not require diverting
by baffles or keeping in spiral movement by side fans. There is
consequently an entire absence of surface drying, and its attend-
ant warping and cracking of the goods. Below the roof (D) a
ceiling flue (F) is formed either by tubes or, as here shown, by
a sheet-iron ceiling (b). Into this flue the hot air now enters at
(&), travelling in the reverse direction, to the collecting flue (M)
by which it reaches the fan. The heat from the hot air radiates
downwards through the ceiling.

The air necessary for combustion of the fuel of the furnace
enters the cooling chamber at (I) and passes off the hot cooling
bricks from the openings (m), picking up the heat given up by
the dried bricks in cooling. The necessary suction of the air and
furnace circuits is created by a fan placed at the cool end. Some
amount of condensation of the moisture dried out of the bricks

PLASTIC MOULDING BY MACHINERY

169

170

MODEEN BRICKMAKING

occurs in the ceiling flue (F). The fan thus produces simultane-
ously the circuits of the furnace gases and the drying air.

When treated in a tunnel worked in this manner, most (even
tender) clays may be dried within thirty hours,as the amount of air
used is very small in volume. It is, during the greater part of
the drying, so charged with moisture as to be nearly saturated.
Excessive surface-drying and strong air-currents are thereby
avoided, and many clays which will inevitably crack when dried
in other ways can be readily and satisfactorily dried in a tunnel
of this description under careful management (see p. 175).

The Wolff dryer, when worked in the opposite manner to
that usually employed, is converted into a dryer of this type, and
so gives far better results for the reasons just mentioned.

The Moller and Pfeiffer dryer also works on this plan, and is
in extensive use on the Continent. This dryer has, however, a
number of fans at the side, so as to give a spiral or corkscrew

II

FIG. 114. — Single deck brick-car.

motion to the air in the dryer, this air being repeatedly passed
over the heaters and goods in its spiral journey. The makers
claim that they can dry any clay, no matter how tender, in
twenty-four hours, and many clays in a shorter time, and so far
as the author can learn they appear to have fulfilled this promise
in most instances. There is, in fact, no doubt that this type of
dryer is the most efficient on the market, but the cost of fans
makes it expensive to install, and, for most purposes, a similar
effect can be obtained without these fans by providing a false
ceiling, arranged as in fig. 113, to give an overhead radiation.

The power required to drive a fan suitable for a dryer need
not exceed 2 b.p.h. for four tunnels yielding together 15,000 bricks
per day. The fuel and steam consumption is distinctly less than
in any other form of dryer, amounting to about 1 J cwt. of fuel per
10,000 bricks dried at an average of four per minute.

The cars used for carrying the bricks may be of the single (fig,
114) or double deck (fig. 115) type. The method of loading them.

PLASTIC MOULDING BY MACHINERY

171

depends upon the softness of the bricks, pallets being used or
not, according to the height to which the bricks can be stacked
on each other.

FIG. 115. — Double deck brick-car.

On single deck cars the bricks may be set eight high, or seven
high if pallets (fig. 116) are used, but double deck cars are preferred
as being more stable. For very soft bricks, cars with' racks to
hold plain pallet boards (fig. 117) are preferable.

FIG. 116. — Stool-pallets for brick-cars.

All cars should have roller-bearings (fig. 118) and steel wheels
of 12 in. diameter. A suitable rail-gauge is 20 or 24 in., the
wheel base being 30 or 42 in. respectively. The narrower sizes
are preferable for ordinary work.

172

MODERN BRICKMAKING

As the dryer rails are usually at right angles to the presses it
is generally necessary to employ a transfer-car (fig. 119), which

FIG. 117. — Cars for soft bricks.

runs on a track placed in a trench transversely to the ends of the
dryer. The brick-car is run on to this transfer-car and the whole

FIG. 118. — Roller bearings for brick-cars.

is wheeled until it is in the right position for the brick-car to
enter the tunnel. A similar car and track receive the dry bricks

PLASTIC MOULDING BY MACHINERY 173

from the other end of the dryer. An ordinary brick-car costs £4
to £6, a transfer-car about £9.

The rails in the dryer should weigh at least 14 Ib. per yard
and should be securely bolted with fish plates. They should be
laid so as to slope 1 in 80 towards the exit end, though some
brickmakers prefer a level track.

The cars are usually propelled through the dryers by means
of a winch working on the car about to enter the dryer, A small
pulley on a horizontal axis is mounted below the rails about 6 ft.
inside the dryer, and over this is passed a steel rope with a hook
at one end, the other being wound round a hand winch. The
hook is attached to the back of the car, and on working the winch
the car is drawn forward into the dryer and the door closed.
When it is necessary to put another car in the dryer the hook is

1653;*"

FIG. 119.— Transfer-car.

taken off and placed at the back of the new car, which is then in
its turn made to enter the dryer by operating the winch.

Other appliances of a more or less automatic character may
be used, and in some yards the slope of the rails is sufficient to
enable a strong man to do all that is needed, without any winch
or other mechanism being necessary.

In general construction the outer walls of dryers are built of
9 in. brickwork, the inner ones being thinner. The roof may be
of galvanized iron or concrete; a wood, felt, or iron roof, well
pugged with sawdust or sand is preferable, as it does not con-
duct— and so waste — heat so readily. A sliding door, properly
counterbalanced so as to rise easily, should be provided at each
end of each tunnel. By constructing a dead air-space in the
roof and outside walls, much loss of radiated heat may be pre-
vented and fuel saved.

174 MODEEN BEICKMAKING

At the outlet-end (particularly if there is a sloping track) it
is wise to have some safety arrangement, so that in the event of
a car breaking loose it will not damage the door. For this reason
some dryers have the exit door hung with hinges at the top, a
chain hung over a pulley, and attached to the counterpoise,
being fastened near the bottom, but the simple rising door fixed
without guides is equally satisfactory if not made too heavy.

The cost of erecting tunnel-dryers varies greatly, but a fair
average for each thousand bricks' capacity is about £45 for the
" direct \ype " and £35 for the " inverse type ". The apparently
greater cos$ of the former is, however, saved in actual working
and upkeep ^Qsts and in the fewer worthless bricks produced.
Broadly speaking^ a tunnel-dryer costs the same as a continuous
kiln for the same annual output.

All continuous tunnel -dryers must work day and night, the
cars being withdrawn at regular intervals both day and night.
The kiln fireman can usually attend to this at night, as it
usually only means inserting" three cars and .withdrawing three
others.

The objection to running a fan at night urged by some brick-
makers has no real foundation, as wherever steam is employed
in a dryer it necessitates a night stoker, and he can attend to fan
and dryer at the same time as the boiler.

To get the best results from any dryer, means must be pro-
vided for testing the amount of moisture and the temperature of
the air in it as well as the volume of air used. For this purpose
wet-bulb thermometers should be employed, a recording ther-
mometer being also very desirable. Directions for using these
can be obtained with the instruments.

In comparing the relative cost of working with different
dryers all matters must be taken into consideration, as certain
firms' representatives are sometimes inclined to minimize the
importance of such subjects as " back-pressure " and "an odd
load or two of coal " each night. Yet these trifles may make all
the difference in obtaining an accurate comparison. In cal-
culating the cost of drying bricks by various methods, it is fairest
to take the number of good and perfect bricks as the basis, for
the others are practically useless. Most dryer builders do not
like this method* of calculation, for it tells against poor or un-
suitable dryers, but it is the correct way, nevertheless. Another
factor which is often omitted in comparing different kinds of
dryers is the depreciation and interest on capital ; in other words,

PLASTIC MOULDING BY MACHINERY 175

the special machinery, etc., needed, and their effect on the cost
of the dried bricks.

It is specially necessary to see which form of all those
suitable for a particular clay is cheapest in actual use ; depreci-
ation and interest charges must be included in this, as well as
the material used in construction (wood, brick, or iron, or all
three). The cost of working and of the labour required also need
•consideration.

The choice of a dryer is not so simple as most people suppose,
if the really best dryer for the particular clay is to be selected,
and in most cases impartial expert advice should be sought.
No matter how skilfully a dryer may be constructed, unless
it is properly managed it may prove a failure, particularly with
a tender clay. It is, therefore, necessary that the men in charge
pay full attention to instructions given to them.

In drying tender clays, the chief requirement is to use air fully
.saturated with moisture to raise the temperature of the bricks
to that at which drying may most suitably take place. So long
as the air used for this is sufficiently moist no drying or cracking
can occur. When the bricks are at the right temperature, the
moisture-content of the air used may be reduced in gradually
increasing amounts until the bricks are strong enough to allow
dry air to be used. In this manner, the tenderest clays may be
satisfactorily dried in a comparatively short time. One method
of keeping the air around the bricks sufficiently moist is to heat
them in a closed chamber, air only being admitted very cautiously
when the bricks are at 100° C. Instead of using a closed chamber
it is often sufficient to cover them with wet canvas and to cover
this with tarpaulin until they are fully heated. The tarpaulin
may then be gradually removed, and afterwards the canvas also.
This principle is simple of adoption in almost any brickyard,
even where the output is not sufficient to warrant the installa-
tion of a special tunnel-dryer.

In these ways the moisture is sweated out with a minimum
of air and consequently the liability to damage is at a minimum,
shrinkage is made regular, and warping and cracking are avoided.
Bleininger has found that clays which are difficult to dry
because of their high shrinkage, may be rendered normal by
heating the raw clay as it comes from the pit in a rotary furnace
at a temperature of 250° to 400° C. This destroys part of the
plasticity-forming power of the clay, and enables the material
to be dried in the same manner as less plastic clays. The cost is

176 MODERN BRICKMAKING

very slight. The addition of sand, burned clay, or other non-
plastic material will also convert many tender clays into those
of normal strength. It does this by separating the particles from
one another and so increasing the pore spaces. Mixing clays-
with boiling water instead of cold, during the pugging or temper-
ing, has a similar effect, and in addition causes the bricks to
harden slightly as they cool before entering the dryer.

Transport. — Plastic bricks are carried on barrows or cars,
or occasionally on belt or other conveyers. When continuous
tunnel-dryers are used, cars are invariably employed.

Kilns. — The kilns used in burning plastic bricks are of the
single, intermittent, and continuous types. These are described
in Chapter VIII, as the kiln used bears little or no relation ta
the method of manufacture employed.

General. — For the successful manufacture of wire-cut bricks
the clay should be thoroughly and carefully prepared ; all ma-
terial which is too coarse to pass a No. 10 screen being rejected.
A constant and uniform composition of clay and water must be
maintained so as to obtain a constant shrinkage, and for this,
thorough and careful tempering and mixing is necessary.
Sufficient water should be worked into the clay, but an excess
must be avoided. The machinery must all be maintained in
good order, and the drying, setting, and burning must be carried
out under constant skilled supervision, if the best results are to-
be obtained.

CHAPTER V.
THE STIFF-PLASTIC PROCESS OF BRICKMAKING.

WHILST almost any clay of sufficient purity can be made into
bricks by means of one of the processes described in the previous
chapter, these methods are far from being the most economical
so far as certain clays are concerned. The proportion of water
which it is necessary to mix with the clay in order to produce a
plastic clay may easily amount to more than 1 Ib. of water per
brick, and this involves the use of a large amount of time, or of
artificial heat, in its removal.

There has, therefore, within recent years, arisen a practice
amongst brickmakers whereby the clay is worked up into a much
stiifer and less plastic paste with a smaller quantity of water, or
in some cases with no water at all, so that the large amount of
water necessarily added in making bricks by the plastic process
is partially or completely avoided, and the bricks require but
little drying, and frequently can be set directly into the kiln.
These processes in which little or no water is used are known
respectively as the "stiff-plastic," "the semi-plastic" or "semi-
dry," and the "dry-dust" processes; the first of these will be
described in this chapter.

The advantage of the stiff-plastic process lies in the fact that,
when properly carried out the bricks need but little drying, are
stiff and easy to handle, and may be repressed, if desirable,
immediately after they are formed. At the same time, they
resemble in structure and characteristics those made by the
plastic process far more than when the drier processes are used.
In connexion with repressing it must be remembered that some
firms of brick-machine makers do not consider the " clot " as a
brick at all, but employ a press as an integral part of the machine,
and consequently understand by a repressed brick one which
has been passed through two distinct presses.

The disadvantages of the stiff-plastic system are that it
cannot be used for certain classes of clays of an excessively

177 12

178 MODERN BRICKMAKING

sticky character — though even with these much may be done
by the judicious admixture of sand or other non-plastic materials
—and there is a great temptation when it is used for brickmakers
to hurry the clay direct from the machines to the kiln and to
heat up too rapidly, with the result that the finished bricks are
badly discoloured and are often warped. Had they been dried
properly before being sent to the kiln, in many cases first-class
bricks would have been produced.

The advantages of the stiff-plastic system are, however, so
obvious and so important, that there is little doubt that this
will be the chief process of brickmaking in the near future. The
disadvantages are much more apparent than real, and with
reasonable care can be overcome with the majority of clays
suitable for brickmaking.

The process of making bricks by this system requires the
provision of a comparatively dry clay, or one in which a wet
clay can be mixed with a large amount of dry material so as to
make a relatively dry mixture. This is necessary, because in
this process the clay is ground and sifted in a relatively dry
state, and this sifting and grinding cannot be effected by the
same plant if the clay is very moist or damp. It is specially
suitable for certain shales, which are becoming increasingly
popular for the manufacture of hard burned, slightly vitrified
building bricks.

Briefly, in the stiff-plastic process, the clay or shale is brought
up from the pit in wagons and fed into a grinding mill, generally
of the edge-runner type, with revolving perforated pan, though a
preliminary breakage of the large lumps is desirable. The clay
is ground dry or in a slightly moist state, and is then taken by an
elevator to the screens, of which there is generally one to each
mill. The clay which passes through the screens goes down a
chute into a mixer, where a little water is added and the whole is
then thoroughly mixed. It next goes into the making-machines
and is pressed into rough blocks or " clots " about the size of a
brick. These are then repressed, this latter operation giving
the brick its proper shape, making the " well " or " frog " and
printing on the name of the firm. The bricks are then dried,
if necessary, and taken to the kilns. Drying is avoided when
possible, this being the great advantage claimed by the stiff-
plastic process, though even where it cannot be entirely avoided
its cost is greatly reduced. As the bricks when taken to the
kilns are, presumably, in the same state as those made by the

THE STIFF-PLASTIC PEOCESS OF BKICKMAKING 179

plastic process, similar kilns may be used. These are described
in Chapter VIII, but it may be noted here that for large outputs
some form of continuous kiln should be used for bricks made by
the stiff-plastic process.

The material must be sufficiently ground, and for the best
bricks must be able to pass through a sieve with twenty holes
per linear inch without leaving any residue, though for com-
mon bricks a coarser sieve may be used, one with eight holes
being popular. It must be mixed into a paste of even composi-
tion and of constant stiffness, and the machinery used must be
kept in first-class order. If these matters are attended to and
the material is suitable, no serious difficulties should occur in
the manufacture of stiff-plastic bricks.

The material used in the stiff-plastic process may be of
almost any kind that will make bricks, providing that it is not
too sticky. Shales and some loams are best for the purpose, but
some boulder-clays can be successfully used. As all these ma-
terials are somewhat variable in composition when first won,
it is necessary to mix them thoroughly, and for this purpose it is
better to use a grinding mill than crushing rolls, as the former
has a powerful mixing action. The material being practically
dry, the advantage of grinding mills with perforated revolving
pans is available, and this type of mill should be used except
under extraordinary circumstances.

A large mill is desirable so that there may be no trouble in
obtaining a sufficiency of ground material. With a small mill
the working of the plant is troublesome, but with a larger one
any excess of clay over that required can usually be stored until
it is needed. Moreover, the cost of running a large mill is less
per ton of material ground, and, consequently, if the plant is
well arranged a notable saving in power is effected. To gain
full advantage of this saving, the mill and the rest of the plant
must be capable of working independently of each other.

The output of all edge-runner mills for dry material is very
closely connected with the sizes of the pieces and the manner
in which they are fed. If too little material is supplied it is
obvious that they cannot work at their full capacity. But it is
seldom realized by those in charge of such mills that if overfed
the output is also reduced, even though the overfeeding is but
temporary. To secure the best results an edge-runner mill must
be supplied with small pieces and in as regular a manner as
possible, and the ordinary method of emptying a wagonful of

180 MODERN BRICKMAKING

material into the mill by means of a "tippler" or similar con-
trivance is not calculated to give the best results.

The best means for feeding the mills must be decided upon
by those in charge, as it is largely a matter of cost. Thus the
ideal way (regardless of expense) is to attach a preliminary
stone-crusher and a mechanical feeding appliance to the mill, so
that the supply of material to the latter is independent of the
amount brought from the clay pit. Such appliances require
power and cost a certain sum for installation, and it is sometimes
(though very seldom) found to be cheaper to run the mill below
its capacity, instead of using them to supply it with a regular
and suitable feed.

The method, sometimes used, of keeping a man at the mill
to break up large pieces and shovel in the material at frequent
intervals, is invariably more costly than the employment of a
breaker and feeding appliance, and is not so satisfactory. To
some extent feeding appliances may be avoided by the use of
very small wagons, so that only small quantities enter the mill
at a time. The wear and tear on these small wagons and the
cost of haulage must, however, be taken into consideration when
the question of a feeding apparatus is under discussion, and they
do not prevent lumps from entering the mill.

One great difficulty accompanying the introduction of auto-
matic breaking and feeding appliances into existing works, where
they would undoubtedly save money, is the lack of room in the
mill-house for such an apparatus to be inserted. In several
instances where the mills have not been capable of supplying
sufficient material under existing conditions, and where it was
necessary to work them at their maximum capacity, the author
has successfully employed the following arrangement :• — •

The material is brought from the pit in wagons of the usual
type, and the contents of these are tipped on to a sloping tray
covered with sheet iron and provided with sides about 18 ins.
high. This tray is perforated with holes about 3 in. diameter, or
it may be constructed of bars placed this distance apart. The
space between the clay and the ground is enclosed to prevent
the escape of dust and to keep the material dry, a similar grate,
but flat, is placed at the bottom of the slope, and receives the
material which has failed to pass through the perforations or
between the bars. These large pieces of material are either
broken up by hand, with a hammer, or are passed to a stone-
breaker before they are sent to the mill, this breaker being so

THE STIFF-PLASTIC PEOCESS OF BBICKMAKING

181

placed that it delivers the material below the tray just described.
All the pieces less than 3 in. diameter are taken to the mill by
some form of feeder, or where no such appliance is used they may
travel by gravity down a chute.

The saving thus effected in wear and tear of machinery and in
power, and the increased output obtained, has -more than repaid
the cost of installing this preliminary riddle in those cases where
it has been used. Its only disadvantage is the space it requires,

FIG. 120. — Blake-Marsden stone- breaker.

as the lesser attention needed at the mill enables the mill man
to attend to the riddle and breaker.

Stone-breakers are made in a variety of forms, but the one
most suitable for crushing clay lumps is that shown in fig. 120,
and made by several firms in this country. It requires relatively
little power and attention, and soon saves its cost when much
hard material has to be ground.

As the product need not be crushed very small there is
no need for the jaws to be set closely, and consequently they
can be arranged to give a large output if the makers are con-
sulted before such a machine is purchased. The jaws should be

182

MODERN BEICKMAKING

examined occasionally and any wear and tear made good, as the
machine will waste power if it is out of order.

A pair of old crushing rolls set 2 in. apart also makes a good
breaker for materials of medium hardness.

Mill Feeding Machines. — Various arrangements are in success-
ful use for> feeding mills with a dry material, the most advan-
tageous being (a) belt or trough conveyers fitted at the base of a
slope or hopper, and provided with some scoop or other appliance
which shall prevent their being overloaded (fig. 121). (b) Spiral

FIG. 121.— Haendle mill-feeder.

conveyers or worms which rotate and carry the clay forward in
definite quantities and at a definite speed. A number of worms
may be arranged side by side to deliver direct into the mill or
on to a conveyer belt ; this latter arrangement being used when
space within the mill-house is too limited to admit the insertion
of the feeding worms, (c) A pan (similar to that of the grinding
mill) provided with one or more scrapers, and rotated, or with
a rotating base (fig. 122), so that the material is withdrawn at a
constant rate which is independent of the manner in which the
feeder is supplied.

Each of these appliances has its advantages and disadvant-

THE STIFF-PLASTIC PEOCESS OF BRICKMAKING

183

ages, and a lengthy experience with each is necessary before a
satisfactory choice can be made. The author has had but little
opportunity of working with the last named (c), and of the ma-
chines in classes (a) and (b) has usually found worm-convey-
ers to be more accurate and reliable, 'though somewhat slower
and requiring rather more power. They have the further ad-
vantage that large lumps are not carried forward, though if these
are of very hard material they may stop the machine or break
it. If, however, a preliminary crusher is used no danger from
this source need be anticipated. Granted, however, that a

FIG. 122. — Eotary mill- feeder.

brickmaker realizes the advantages to be derived from supply-
ing his mills with a constant regular supply of material, he will
not long be at a loss as to the appliance which is most suitable
for his requirements.

Grinding Mills. — All grinding mills for use in the stiff-
plastic process of brickmaking should be provided with a loose
pulley, or friction clutch, arranged so that the machine can be
stopped instantly if necessary. They should also be made to
run independently of the rest of the plant, so that if there is a
shortage of clay they may be run at night, or if too much clay
is being ground they may be stopped and -the power saved.
Each evening the mill should be run almost empty, and should

184

MODEEN BBICEMAEING

be cleaned out to prevent iron bolts, etc., remaining in the
pan.

Usually mills of the over-driven type (fig. 123) are to be pre-
ferred, the machinery being more accessible and less liable to
be clogged with dust, though the under-driven type (fig. 124)
should be used in cases where unusually light runners may be
employed; this is seldom the case. Mills of the edge-runner

FIG. 123. — Over-driven grinding mill.

type, with revolving perforated pans, are most suitable for this
class of brickmaking, though those with a fixed bed are much
used. The perforations should not be too large or the screens
will be overworked and power lost in regrinding, nor should they
be too small or the output will be too low.

Generally speaking, the perforations' (figs. 125 and 133) should
not be less than J in. nor more than | in. diameter, the latter
being too large for most clays, | in. or J in. diameter being the

THE STIFF-PLASTIC PKOCESS OF BBICKMAKING

185

best size. Slots are somewhat less satisfactory than circular
perforations, as the product is coarser and more irregular.

The arrangement of the perforations on the pan is a matter
which has received very careful study, particularly on the Con-
tinent, where it is generally considered that the runners should

FIG. 124. — Under-driven grinding mill.

not pass over the perforations, but that these should be at either
side of the runner path. An excellent arrangement is for the
material to pass under one of the runners, then over a perforated
portion of the pan, under the second runner and over another
perforated portion, any uncrushed material being then passed
under the first runner again for further reduction.

FIG. 125. — Slotted perforations in grinding pan.

Where the perforated portions of the pan are made of
manganese steel they may occupy the runner path, and a larger
though coarser output obtained. For fine grinding the material
must be on a solid part of the pan whilst it is being crushed.

The pan generally used is 9 ft. or 11 ft. diameter, smaller sizes

186 MODEKN BEICKMAKING

being undesirable. It should revolve at least'ithirty times per min-
ute, but must not travel so fast as to throw up much dust, though
this may be retained by judicious damping. The pan is rotated
by means of a pinion and crown wheel operating on a vertical
shaft which carries the pan, the rollers being independently
carried on the side frames of the mill. The lower end of the
vertical shaft terminates in a footstep bearing, the construction
of which and its maintanance in good order are very important.

It should be of bronze metal and work as nearly frictionless
as possible. This is best effected by running it submerged in
an oil-reservoir, so that it does not heat or wear under the most
exacting conditions. The oil-reservoir should be fed through a
pipe connexion located at the outer edge of the pan. A large
base plate underneath the step should be provided to facilitate
adjustment in all directions. It should scarcely be necessary
to point out that the whole of the mill should be strongly con-
structed, as it is subject to sudden and severe shocks in use.
When of large diameter, several loose-running wheels (some-
times called anti-friction supports) may be placed underneath the
pan so as to restrain the vibrations when unusually large pieces
enter the mill. Care should, however, >be taken that these loose
wheels do not become clogged with dust, or they may increase
the amount of power required to drive the mill.

The edge runners or rollers may be all in one piece (fig. 126)
as shown, or they may be provided with renewable wearing-
hoops or rims, caulked on with cement or wedged on with
wooden slips (fig. 123). This latter method is preferable as it
enables a renewal of the rims to be readily effected.

When the pan is empty, the runners should not rest on the
grinding plate, but should be suspended by powerful springs in
such a manner that when the material is fed into the pan the
full weight of the runners comes on to it, because the springs are
prevented from following the runners. Should some hard metal
accidentally get into the pan the spring buffers will prevent the
runners from seriously damaging the pan in bumping over it.

The runners must be kept flat on the " tread " or they will
not grind properly. They should be very heavy (from 2 to 5 tons
each), the general tendency being to use those which are rather
light ; and the whole machine should not (for the 9 ft. size) weigh
under 13 tons. It will then need 25 to 30 b.h.p. to drive it under
normal conditions.

Each runner should be mounted on a separate shaft, the two-

THE STIFF-PLASTIC PROCESS OF BRICKMAKING

187

being bolted together at the centre in such a manner that they
are able to rise and fall, preferably independently of each other.

Most mills would be improved by greatly lengthening the
hubs of the runners. If these are too short the runners soon
lose their uprightness.

The scrapers used to direct the material under the runners
require occasional adjustment. They must have their lower
edges parallel to the pan but not quite touching it.

FIG, 126. — Mill with solid edge runners.

The material which has passed through the perforations in
the pan may be received on a base plate or in what is termed an
"open base," the latter being preferable when there is sufficient
space available.

In the ordinary pattern of mills (with a base plate) the under-
side of the revolving can is provided with one or more scrapers
(fig. 123) which collect the clay as it falls on the base plate (not
shown) and push it over or through an opening in the latter. It

188

MODERN BRICKMAKING-

then falls into a " well " from which it is raised by a bucket
elevator. These scrapers, of course, wear away in time, and so
require regular attention to keep them in proper adjustment.
In the " open base " pattern of mill (fig. 127) scrapers are not

FIG. 127. — Open base grinding mill.

necessary, and so the friction of the mill is reduced nearly 50 per
€ent. This means a very important saving in the power necessary
for driving it. In such a mill the material which has passed
through the perforations falls on the inclined face of the founda-
tions of the pit and so passes easily to the elevator.

THE STIFF-PLASTIC PROCESS OF BEICKMAKING

189

Mills of both types are supplied by the principal makers of
brick machinery, but James Buchanan & Sons, Liverpool, also
supply a pan with conical runners (fig. 128), which they claim

FIG. 128. — Grinding mill with conical runners.

gives a greater efficiency and larger output than the cylindrical
runners.

In America, it is not unusual to see two pans geared together
and working side by side, one receiving the " residue " or " tail-
ings " from the screen and the other the clay from the wagons ;
but both delivering into the same well. This arrangement is

190

MODERN BRICKMAKING

very useful when hard material is present in the clay, and is now
used in this country by several fire-clay and shale grinders.

Several Swiss and German firms favour the use of grinding

mills fitted one
above the other
(Buhler's patent, fig.
129), but in this
country their use is
restricted to a few
firms with unusual
facilities for de-
livering the clay at
a high level. Usu-
ally the pans in
Britain work quite
independently of
each other, a suffi-
cient number being
used to secure the
desired output.
This arrangement is
advantageous when
the output of the
works varies greatly,
but for a large and
steady output it is

FIG. 129.— Buhler's two-stage mill. more economical in

power to let a rough mill do the first crushing and, after the
material from this has been screened, to pass the coarse residue
to a second or even to a third mill.

The use of three rolls in one piece, with a pan arranged in
steps as shown in fig. 130, is sometimes found valuable. Machines
of this type have been much used on the Continent, and were in-
troduced into this country in 1907 by John Whitehead & Co., Ltd.
So far they have not become popular, though their advantages
are undoubted where a material needs a large amount of crush-
ing and mixing. In the machine shown, the material is fed in
at the centre, is crushed by the smallest pair of rolls, passes
down to the next step and is treated by the second pair of rolls,
and after falling to the lowest step it is treated by the third pair
of rolls, and finally discharged from the machine. Such an ap-
pliance is more compact than those of the type shown in fig. 129,

THE STIFF-PLASTIC PROCESS OF BRICKMAKING

191

but is intended for similar materials. For most brick-clays
they are not necessary.

Elevating. — For elevating the ground material from the
grinding mill to the screen, an elevator may be used, having
buckets or pockets fastened on to a belt (fig. 131), or to chains.
The belt elevator is the most used, and has the advantage over
the chain elevator that it can travel at nearly any angle, and
the contents cannot fall out ; but the chain elevator can only go
almost vertical, because there is nothing between the two chains

Arrangemrnt of Runners in Patent Multiple Edge Runner Mill.

i - -

FIG. 130. — Multiple runner mill.

to^stop the clay from falling out, though some chain elevators
are made to swing from the chain so that when going horizon-
tally or at an angle the buckets keep the right way up and do
not spill their contents. The elevator must be run at a speed
suitable to the screen used.

The buckets on elevators are generally iron oblong boxes and
are fastened to the belts by two or three rivets (fig. 132). These
buckets should be shallow, so as to spread the clay on the screen.
Deep ones are less efficient for this purpose.

Numerous small buckets are preferable to fewer large ones,
as they give a more regular feed.

192

MODERN BEICKMAKING

Screens, Sieves, or Riddles are
used for separating the coarse and
finer particles of material from
each other, the former being re-
turned to the mill for further
treatment.

Two chief forms of screens are
in use at present : (a) the station-
ary sloping screen ; (b) the revolv-
ing screen.

Stationary screens consist, usu-
ally, of a sloping tray 4 ft. to 6 ft,
in length, and 18 in. or more in
width, the tray itself being made
of wire gauze, perforated sheet
metal, or of a number of wires

FIG. 131.— Belt Elevator.

FIG. 132. — Bucket for raising
crushed clay.

arranged i side by side (piano -wire
screen).

The wire-gauze screen is the
oldest, but is seldom very efficient,
as many particles lodge 011 the
cross wires and soon clog up the
sieve. At the same time it is
used by many firms who do not
know the advantages of other
forms of screen.

The perforated steel plate (fig,
133), if arranged at an angle of about
45 degrees, is admirable for dry or
almost dry materials. The correct
angle can readily be found by at-
taching a rope carrying a weight
to the top of 4he screen and raising
or lowering the screen until the
distance from the bottom of the

THE STIFF-PLASTIC PROCESS OF BRICKMAKING- 193

screen (a) (fig. 134) is equal to the height of it (b). The perfora-
tions in it may be much larger than the size of the particles to
be separated, so that the wear and tear is very slight, and in
most cases no "rapping " or vibration is necessary.

The author has repeatedly found that with dry clay a screen
with perforations J in. diameter will act precisely the same as a
revolving screen having 20 holes per linear inch. The mathe-
matical reason for this curious behaviour need not be given
here ; it is interesting, however, and suggests why some brick-
makers have failed to appreciate this type of riddle — they have
used too fine a screen.

The screen should be fixed at the lower end but hung at the
upper one with chains so that its angle may be adjusted to suit
the clay. The sides of the screen should be about 9 in. in height,

*••••

FIG. 133.— Perforated <*-

steel plate. FIG. 134.

and a canvas or sheet-metal cover should be used to prevent
loss of dust. The upper part of the screen should have a plain
metal plate (called the " feed plate "), attached so that the material
may spread itself over this before travelling down the screen.
If necessary one or more "guides," or baffle plates, may be
placed above this plate to secure the proper distribution of the
material. If much dust is produced the screen should be en-
closed in a light wooden casing, or should deliver the clay into
a special chamber.

When more difficult material is being treated a modification
of this screen — " The Newaygo " — supplied by T. C. Fawcett, Ltd.,
may be employed (fig. 135).

This consists of a large sheet of perforated metal, the size of
the perforations depending on the fineness of the" required pro-
duct. This sheet or screen is mounted on a frame which is

13

194 MODERN BBICKMAKING

hung by chains at a suitable angle, and in such a way that the
screen may be kept vibrating by the blows of a series of hammers
acting on " anvils " on the framework and screen supports. The
clay is fed into a trough which runs along the top of the frame
and in which runs a spiral conveyer, so arranged that the clay is
discharged over a " weir " in a perfectly regular stream over the
whole width of the screen.

It will thus be seen that in this arrangement the advantages
of the perforated sheet are fully recognized, arid where baffle
plates cannot be arranged satisfactorily the use of a special
trough, spiral and "weir," will be found advantageous in the
securing of a regular and even feed of clay. Indeed, such an
appliance is usually superior to any arrangement of baffles,
and the amount of power needed to drive it is too small to be
worth consideration.

"/ 7
I

I

FIG. 135. — Fawcett's " Newaygo " screen.

As in other stationary screens, the fine material falls through
the sieve into a hopper or on to a receiving floor, and the coarse
material runs down the screen into a chute and is returned to-
the mill.

Piano-wire screens are made by arranging a number of wires
parallel to each other, and fastening them with a stretching key
in a manner identical with that used in pianos. This screen
was invented by Adam Adams, and the ones of his design,
supplied by Whittaker & Co., Ltd., consist of a strong frame
over which the wires are stretched and tensioned at one end
with screw pegs. The pitch of the wires, which determines
the mesh, can be varied by the insertion of fresh pitching-bars
which are detachable from the frame, and the adjustment of

THE STIFF-PLASTIC PROCESS OF BRICKMAKING 195

the wires is thus readily made. As ordinarily used, the wires
supplied for these screens are too thin, and consequently hard
pieces of shale are apt to cause them to open. By using thicker
wires this objection may to some extent be avoided, though
these screens are never really suitable for clays containing hard,
thin pieces of shale or rock-clay. For other clays, when not
overloaded, they are good.

The standard meshes for piano -wire screens vary from 8 to 20
wires per linear inch.

As with all other riddles, the piano -wire screen should be set
so that the elevators deliver the clay to a spreading-bpard at the
top of the screen and not directly on to the wires. By using the
spreading-board the clay is delivered on to the screen constantly,
and is spread evenly over the entire surface so that it screens
more rapidly.

Revolving Screens were formerly very popular, but have largely
been replaced by the piano-wire or perforated steel screens. In
the revolving screens the clay enters at one end, which is elevated,
and causes the clay to gravitate towards the lower end. As the
screen revolves, the fine material passes through the mesh of
the screen, whilst the coarser material passes out through the
lower end and is returned to the pan for further grinding.

The screen is usually 4 to 9 feet long>with an average of about
6 ft., and about 3 ft. in diameter. It is generally mounted on a
timber-frame in simple bearings, and should be provided with
ample oiling devices. The frame may be covered with perforated
steel plates or with wire-gauze, with any size of opening desired,
the usual sizes being J in. to ^ in. If the cylinder makes twelve
revolutions per minute this will usually be sufficient. Perforated
metal is seldom satisfactory in a revolving screen. The frame
may be cylindrical (fig. 136), or hexagonal, the latter being cheaper
to repair as it enables the gauze to be nailed to six frames, each
of which can be taken out when needing repair, and replaced far
more rapidly than when a cylindrical sieve requires patching.

Revolving screens must, usually, be fitted with a "rapper " to
shake the material through the holes. This produces a large
amount of dust, and necessitates the screen being boxed in if
effective results are to be obtained. Fixed screens, on the other
hand, can usually be left uncovered, a mechanical rapper being
seldom necessary.

When damp material has to be screened it is often useful to
have a battery of steam pipes below the screen. Fig. 136 shows a

196

MODEEN BEICKMAKING

cross-section of a revolving screen, supplied by C. Whittaker &
Co., Ltd., with this arrangement, and fig. 137 an adaptation of
it to stationary screens. In each case the steam circulating
through the iron pipes keeps the sieve warm, and reduces the
amount of clogging. It is, therefore, especially useful during
wet weather.

The screen, of whatever type, must always be fitted in such
a position that it can readily receive clay from the elevator and
jeturn any coarse material to the mills. The chief points re-
quiring attention are that the runs or chutes shall be as short and
as steep as possible, but never at a greater angle than 45 degrees,
i.e. the height should never be more than the distance along the
level (see p. 193). They should be closed to prevent loss of dust,

FIG. 136.— Bound revolving screen.

but made so as to be readily opened in case of stoppage and also
for facilitating cleaning or repairs.

STIFF-PLASTIC BRICKMAKING MACHINES,

The clay is mixed into a stiff-plastic paste by the addition of
a little water and treatment in a mixer or pug-mill (p. 103) or
both, and the clay is then made into a clot which is afterwards
repressed into a brick.

Several types of machines are used in the stiff-plastic system
of brickmaking, but nearly all of them first form a clot and then
repress it. In the most satisfactory ones, the clot is exactly the
shape of a brick, so that the repressing merely consolidates it
but does not in any way alter its shape. A cylindrical clot has
mechanical advantages in that it can be rolled from one machine
to another, but it can only be used for a limited number of clays

THE STIFF-PLASTIC PEOCESS OF BRICKMAKING

197

owing to the necessity of altering its shape so much in the re-
pressing.

Each of the machines described has special advantages for
certain clays ; some of these are obvious, others will be discovered
from the description, and others again can only be appreciated as

FIG. 137. — Steam-pipes for use below screen.

the result of experience. Clays vary so much in composition
and character that a machine may work splendidly in one district,
and yet give results inferior to another machine when working
in a different place. Under such conditions, complete compari-
sons of the different machines are practically impossible.

Three distinct classes of clot-making machines are in use : (a)

198 MODEKN BKICKMAKING

that in which the clot is made in dies contained in a round re-
volving table ; (b) that in which the die forms part of the circum-
ference of a drum, and (c) that in which sliding dies are used.
The pug-mill may be an integral part of the machine, or it may
be separate, though the former has the advantage of enabling
the mill to press the clay directly into the clot dies. The daily
output of each class of machine is 10,000 to 12,000 bricks.

The chief precautions to be observed in making stiff-plastic
bricks are to ensure that the dryness and fineness of the clay,
the amount of pressure in the pug-mill, the consolidation and
mixing of the clay paste, and in the distribution of the pressure
in the final press, are all sufficient yet not excessive.

Clay is such a peculiar material that, though it can be made
into articles of almost any desired shape, when once a definite
shape has been given to the plastic mass this shape must not be
altered if it is desirable that the article should retain its full
strength. On this account the clay, as delivered from the pug-
mill, must not be made into a clot materially different in shape
from that of the finished brick. Those brickmakirig machines
in which the clot is of a different shape to the finished brick are,
from this point of view, less satisfactory than others, though in
the case of machines constructed by the best known makers, a
slight difference in shape is found to be of little or no consequence.
Hence the argument as to the necessity of retaining the shape
of the finished clot must not be carried so far as to militate
against the use, for example, of the Fawcett duplex machine, or
Buchanan's and Johnson's machines, in which a clot with a
slightly rounded top is produced, though it is quite legitimate
for the makers of other machines to claim superiority in this
respect.

In judging the value of brick-machines a small point like this
is, however, only one out of many which have to be taken into
consideration.

It is important that the clay should be delivered with suf-
ficient rapidity from the pug-mill to the clot-mould to fill it com-
pletely and suddenly ; if it is filled in stages, as is always the
case when filled slowly, laminated portions or layers will be pro-
duced, and the bricks will be weaker than they should be. The
necessary speed of travel can always be given, when not other-
wise obtainable, by the addition of a short length of worm to the
end of the pug-mill shaft. This addition may necessitate the use
of an exceptionally long pug-mill or mixer. It is also important

THE STIFF-PLASTIC PROCESS OF BRICKMAKING 199

when using a vertical pug-mill, to slacken the speed of its rota-
tion when not delivering into the mould, as, otherwise, a large
amount of power is wasted by the pressure of the clay against
the plate in passing between the apertures forming the clot-
mould. The liners of the clot-mould, and particularly of the
final press-mould, must be kept in first-class order and require
frequent renewal. Any attempt to economize in this direction
is usually futile, as it results in the production of defective bricks.
It is usual for the liners of the clot-mould to be simply chilled,
but this is a mistake from the brickmaker's point of view. To
obtain the best results they should be planed so as to get a per-
fectly even and true surface.

Lubrication must be carefully watched or great loss of power,
as well as excessive wear and tear, will result ; on the other hand
too much oil or grease is a nuisance, and is more of a hindrance
than a help. In some presses, arrangements are made for the
insertion of automatic lubricators, and these, when properly made
and adjusted, are more economical than when oil is applied by
hand. The dropping of oil direct on to the brick or inside the
die should l>e avoided ; a piece of felt or some other absorbent
material of a similar nature will apply the lubricant in as even
a manner as possible.

When the clay sticks in the press-box, the common idea that
more oil is necessary should not be accepted until it is found
that the fault is not due to incorrect stiffness of the clay or to
the irregular working of the machine.

Most of the failures in the working of the stiff-plastic system
are due to the attempts to shorten the process of manufacture
by omitting weathering, tempering, or pugging and drying. Most
clays are of such a nature that unless they are treated in one or
more of these stages they cannot be made into good bricks or
tiles. It is difficult to say which of these stages is most impor-
tant, for they are all equally necessary in certain cases, and the
omission of, or part omission of, any one of them may prove vital
to success.

When a clay is' stored in a soft, plastic condition the distribu-
tion of the water throughout the mass will become even in course
of time, but in a stiff-plastic mass this distribution is less easily
effected ; and when, as in most cases, no storage of the mass is
attempted, there is a strong tendency for the faults due to ir-
regularities in mixing and composition to show themselves in
the finished articles. In consequence of all the widely different

200 MODERN BRICKMAKING

characteristics of various clays, it follows that no particular
brickmaking machine can be equally well used for all of them.

The selection of the best machine for a particular clay should,
therefore, be made with the aid of competent and disinterested
advice, based on experience with and knowledge of the clay, of
various machines, and of certain special tests which must be
carried out. In the purchasing of brickmaking machines, the
actual cost price is a matter of much smaller importance than
is generally supposed, as it will pay the brickmaker far better
to spend a few more pounds in obtaining a machine which is
suitable in every way to his needs rather than to purchase
another machine, on the recommendation of the makers or that
of a neighbouring brickmaker, without any tests being made ;
especially if he find later that the few pounds he saved in the
first cost have been spent many times over in lower output,
more frequent stoppages, or greater repairs than would have
been the case had the other machine been used. The following
example will illustrate this more clearly : —

In a certain part of the Midlands are three brickyards, A. B.
and C., within close proximity to each other. A. has a strong
and somewhat sticky, but otherwise good, clay overlying a con-
siderable bed of sand, and finds that the machinery best adapted
to his needs is that made by D. B. has a drift clay, different
from the clays used by his neighbours.

C., on the other hand, has a clay that cannot be used without
much admixture, being more of a loamy character, and finds the
machinery supplied by E. quite suitable. Some years ago B.
bought a plant similar to that used by A., but finding it not al-
together satisfactory, and having to extend his works, he installed
a plant similar to C. and discarded the older one. Having had
to extend his works still further, B. has now gone into the question
more carefully, and with the aid of skilled advice has considered
the whole question in a much more thoroughly technical manner
than was previously the case. A careful study of the outputs of
the machines supplied by D. and E. (similar to those used by A.
and C. respectively) convinced B. that as far as his works were
concerned he was not getting as much as he should do from the
power expended. Attempts from the makers of the machinery
to improve matters not proving satisfactory, B., following the
suggestions of his independent expert adviser, now employs the
brickmaking machine by E., in combination with the grinding
plant supplied some time previously by D. The result is that

THE STIFF-PLASTIC PEOCESS OF BKICKMAKING 201

with the altered machinery B.'s plant is now turning out 15
per cent more bricks 'per day than formerly, and these are stronger
and sounder, as well as of a better colour.

As all the machinery in the three cases quoted was of the
stiff-plastic type, and by first-class makers, the difference in
working can only be explained by differences in the clays worked,
and an examination of these showed that whilst A.'s clay is very
strong, C.'s clay is very mild, and that used by B. is a boulder-clay
and consequently requires treatment quite different from the
other two, although it will make bricks of a medium quality
when treated by the methods used by A. and C. Elated by his
success, B. soon informed his neighbours of the advantage he had
gained, and A., having sufficient capital, decided to put in an E.
machine. The makers warned him that it was not suitable, and
suggested the use of another type of machine of their make, but
A. was so convinced by the results produced by B. that, assuming
all the responsibility, he installed the machine. The result was
a failure, because A.'s clay required such vigorous treatment that
it could not be worked up properly in the E. machine. In due
course C. followed B.'s example, and, though not so satisfactory
as B., still made better goods than formerly, by a combination of
machinery from different firms. Yet, inspired by the success
of B., A. and C. cannot understand their own failures and do not
attribute them to the true cause, but to the machinery makers.
The lesson to be learned from these three cases is that owing to
the different character of the clays in the same district, it is not
wise to argue that a machine made by one firm is necessarily
suitable, because it is used by a neighbouring brickmaker.

A good machine of the revolving-table type is shown in fig. 138
and made by Bradley & Craven, Ltd., who claim to have originated
this process. It comprises a mixer, a short vertical pug-mill,
a circular rotary moulding-table, and an eccentric-motion press.
In operation, the clay is carried forward through the
mixer (which owing to its position behind the pug-mill is not
visible in the illustration) to the pug-mill, from whence, one at
a time, each of the sixteen moulds in the rotary table receives a
charge of clay. The table remains momentarily stationary while
a mould is directly under the operation of the pug-mill, a pugged
brick is, during that time, lifted out of another mould on the
table and delivered to the press by self-acting gear ; this delivery
motion to the press'pushing forward, for removal by the attendant,
a finished brick. The only manual labour required in the forma-

202

MODERN BRICKMAKING

tion of the bricks is for supplying the crude, freshly dug clay
either direct to the mixer (when its nature permits of this being;
done) or, where previous preparation is necessary, to either rollers
or to an edge-runner mill (its variety determining the alternative
method of treatment). The prepared material being fed into the
mixer by self-acting mechanism, one young lad is all that is

FIG. 138. — Stiff-plastic brick machine with clot-moulds on rotary table.

needed to attend to the mixer, and another to remove the
finished bricks from the press to the brick-trucks or barrows.

The machine is capable of producing 10,000 to 12,000 bricks
per day of ten hours, without the aid of any skilled labour, and
the bricks are usually hard enough to go direct to the kiln.

The value of the bricks made by machines of this type
depends upon the completeness with which the mould in the
rotary table is filled. If this filling is imperfect the brick will
be of little worth, as the edges or corners will be of a different

THE STIFF-PLASTIC PROCESS OF BRICKMAKING

203

density and hardness to the rest of the brick, and the clot will
often show a crack along its bottom edge (fig. 139 A).

Defective filling of the mould is usually due to the employ-
ment of too short a pug-mill, or to the absence of a sufficient
length of screw or worm on the pug-mill shaft. By increasing
the size of this worm any desired compression of the clay within
the mould may be reached, and a completely filled die assured.
With some clays the addition of an end piece of the shape shown
in fig. 140 (designed by Gilbert T. Smith) is sufficient to effect
the change shown in fig. 139.

Coring and cracking may often be prevented by the use of a
device shown in fig. 141 made by Wootton. Bros., Ltd.

A. B.

FIG. 139. — Clots made with (A) and without (B) end-piece shown in fig. 140.

Sutcliffe, Speakman, & Co., Ltd. (fig. 142), claim to have over-
come the principal cause of cracks and badly filled moulds, by
arranging the plunger in the clot-moulder to give a resistance
to the exit of the clay from the pug-mill into the mould, thus
keeping the clay column solid, and preventing it curling up or
breaking as it tends to* do when delivered into an empty mould.

Power is also saved by automatically driving the pug-mill
slower when no mould is being filled.

William Johnson & Sons (Leeds), Ltd., make a stiff-plastic
machine of the revolving drum-type which comprises a mixer,
pug-mill, and a six-mould cylinder, as preliminary moulder and
a press.

204

MODERN BRICKMAKING

The mixer and the pug-mill are situated on the same level,
and the functions of mixing and pugging are performed by an
arrangement -of ' knives fixed on one shaft. The material is de-
livered first to the mixer and carried forward by the knives to

FIG. 140. — End piece for mould filler.

the pug-mill, from whence it is fed into one of the moulds placed
at equal distances in a revolving cylinder, about 18 in. diameter.
This cylinder remains stationary while the mould is being filled.
The action of filling the mould automatically discharges a brick

FIG. 141. — Price's patent core preventer.

previously formed from the other end of the- drum. As the brick
issues from the cylinder it is fed by a self-acting arrangement
right into the mould of the press. The pressed brick is then
automatically raised out of the press, and is ready to be carried

THE STIFF-PLASTIC PROCESS OF BRICKMAKING 205

away. In the similar machine, made by Richard Scholefield

FIG. 142. — Stiff-plastic brick machine with variable speed of pug-mill.

FIG. 143. — Stiff-plastic brick machine with clot-moulds on cylinder.
(fig. 143i), the ground clay, or other material, is fed into the

206

MODEEN BEICKMAKING

hopper of the machine and is pugged and carried forward by
the pug-mill, from whence it is compressed into one of four
box-moulds, placed at right angles to one another in a revolving-
cylinder. This cylinder is stationary whilst being charged, and
the action of filling the mould automatically discharges the
brick previously formed. The brick, on issuing from the cylinder,
is passed forward by a self-acting arrangement into the mould of
the toggle press, and after being subjected to two powerful dis-

FIG. 144. — Stiff-plastic brick machine with open clot-moulds.

tinct presses, is automatically delivered on to a table ready to be
placed on the barrow or trough and taken direct to the dryer or
kiln.

A machine of similar type, but in which the drum is open —
the clots being moulded in what are practically spaces between
the cogs of a large wheel — is shown in fig. 144. The advantages
of this arrangement are the reduced number of wearing parts of
the mould and the simpler manner in which the moulding drum
can be constructed. In this machine, as made by T. C. Fawcett,
Ltd., the clay falls down a chute from the screens into a mixer,

THE STIFF-PLASTIC PROCESS OF BRICKMAKING 207

where a little water is added, and thence into a pug-mill.
After being well pugged it is thrust into a mould in the " cog
wheel ". At the same time as one mould is filled, the clot in
another is pushed out automatically, and sent under a press
where it receives its proper shape.

The press is fitted with a hydraulic balance which absolutely
prevents breakages. The amount of driving power required by
this machine is remarkably low (about 6 b.h.p.), and the bricks
produced under 'normal conditions are of excellent finish and
shape, with clean, sharp edges and of great hardness. This
machine has in fact been in use for some time for the manu-

FIG. 145. — " New Era " brick machine.

facture of the highest grades of bricks made by the stiff-plastic
process.

Brickmaking machines of the " sliding-die " type are well re-
presented by fig. 142, showing the machine made by Sutcliffe,
Speakman, & Co., Ltd., and by the " New Era " machine (fig. 145).

In the machine shown in fig. 142, the chief features are the
reduced speed of the pug-mill when not delivering clay into a
mould, and the rising of the bottom plunger of the mould in
order to create a resistance to the entering clay, and thereby
prevent the cracks which are so often noticed in machines
where no such resistance occurs. The special construction of the
moulds on the " economic " principle (p. 152) facilitates relining.

The " New Era " machine (fig. 145), made by C. Whittaker and

208

MODEEN BRICKMAKING

Co., Ltd., is the most recent of stiff-plastic machines. In it the
prepared material is fed into a hopper and is discharged into a
vertical pug-mill. This pugs the clay and forces it into a clot-
forming mould below. There are two of these moulds formed in
a sliding block, which brings each mould alternately under the pug.
As they are alternately filled, so are they alternately discharged.
There are two presses, and the bricks are fed into first one and
then the other, one press only being in operation at a time. The
makers state that the power used for the two presses is no more
than a machine having a single press, but the time of pressing is
greater than when a single press is used. The lubrication of the

FIG. 146. — Arrangement of plant in stiff-plastic process.

moulds and sliding parts is provided by a simple oil spray,
obtained by an air blast from a pressure blower.

The advantage of sliding-die machines is that the clot has
a .flat top instead of being slightly curved as in drum ma-
chines, and the power required to drive them is rather lower
than in machines having a rotary table.

A convenient arrangement of the plant for the stiff-plastic
process is shown in fig. 146, in which (1) represents the grinding
pan, (2) the elevators, and (3) the brickmaking machine ; in
this instance a Fawcett plant (fig. 144) being shown.

Repressing. — The ordinary product of a stiff-plastic machine
can by a little selection be divided into a small proportion of
facing bricks and a large proportion of common ones, but when

THE STIFF-PLASTIC PEOCESS OF BKICKMAKING-

209

large quantities of facing bricks are required these should be
made by repressing ordinary stiff-plastic bricks immediately they
come from the machine, and drying them more carefully than
the others so as to secure every possible advantage of form and
colour, as well-coloured bricks cannot be produced from undried
bricks without an excessive amount of trouble. Bricks may
be repressed in any of the machines described as represses on
pages 139-153, but the ones employing toggle-levers are in many
ways the ones most satisfactory for this purpose in connexion
with stiff-plastic bricks. Unlike plastic bricks, those made by

FIG. 147. — Conveyer belt for carrying bricks to repress or barrow.

the stiff-plastic system do not need to he dried previous to re-
pressing, but may be taken direct from the brickmaking machine
to the repress. It is, therefore, most convenient to arrange the
repress quite close to the brickmaking machine, so that when
repressed bricks are required they may be taken automatically
from one press to the other, a boy being all that is needed to
place them in the box of the repress. In most cases the repress
is supplied by the makers of the brick machine and is attached
to it. The bricks are then automatically fed into the mould
and delivered on to the table ready for removal to the drying
shed or kiln. A slide, or better still a conveyer-belt (fig. 147), of
sufficient length serves as an excellent bed for holding or con-

14

210 MODERN BEICKMAKING

veying the bricks from one machine to another when there is
much room between them, though usually the repress may be
placed close to the machine, and a boy standing between them
lifts the brick from the table of the latter and places it in the
box of the repress.

The precautions necessary to be observed in repressing bricks
are practically the same as those necessary in pressing a brick
made from a clot by the stiff-plastic process (p. 198).

Carrying Off. — Stiff-plastic bricks are usually carried to the
dryer or kiln on barrows of a pattern similar to the " crowding
barrows " used for hand-made bricks (figs. 148-149), or on cars
if tunnel-dryers are used.

FIG. 148.— " Crowding " barrow.

It is important, in selecting a barrow, to have one in which
the relative position of the handles, wheel, and load are correct,
as, otherwise, the work involved in their use is greatly increased.
To some extent the height of a man influences these factors, and
consequently when men do not adhere to their own barrows, no
great difference in the height of the wheelers should be per-
mitted. A few trials with a loaded barrow will soon show the
correct measurements for a particular man. To secure ease in
use, the load should be carried by the wheel of the barrow as far
as possible ; in a badly constructed barrow, or in one which does
not fit the wheeler, too much of the load is on the hands of the
man between the shafts. To aid the men and increase the speed

THE STIFF-PLASTIC PROCESS OF BRICKMAKING

211

at which they work, the track between the machine or dryer and
the kiln should have an iron strip laid for the barrow wheel to run
on, and the whole track should be kept in good condition for the
men to run on. If muddy and sticky the men cannot travel so
fast. The wheelers should be encouraged to run with the loaded
barrows ; it is easier for them, and more remunerative to their
employer. Care>should also be taken that each barrow is filled,

FIG. 149. — Barrow with reinforced frame.

as some men carry too few bricks at a time. A Fawcett " counter "
will prevent this. It consists of a recorder fixed to a convenient
wall or post and connected by a chain running in a pipe to a
balance box, containing a system of balanced levers and placed
with its lid level with the ground forming a wheeling plate, one
end of which is hinged and the opposite end connected to the
levers, which are balanced to the weight of a barrow or wagon
of bricks. The wagon or barrow containing the required num-

212

MODEEN BEICKMAKING

ber of bricks is wheeled over tbe lid of the balance box, causing
the chain to operate the recorder, and punch a hole in the
record disc. The lid then returns to its original position and
moves the record disc round a certain distance ready for the
next punching, when the operation is repeated. When a full
ring of holes has been punched, the punch automatically moves
a certain distance towards the centre ready for the next ring.
A full disc is sufficient for 29,000 bricks, counting fifty on a
.barrow. The number of bricks made may be seen at a glance

FIG. 150. — Counter made by Thos. C. Fawcett, Ltd.

at, any part of the day. It is impossible for any unauthorized
person to interfere with the working parts without the tamper-
ing being detected, and it thus forms a positive method of
counting the bricks.

Barrows are convenient, but the carrying off is facilitated,
where there is sufficient room, by employing a short belt running
horizontally (fig. 147), for taking bricks from the table of the
press or machine and delivering them several feet away to the
men with the barrows, or a long belt may sometimes be used to
•deliver i the bricks direct to the drying sheds or kiln.

THE STIFF-PLASTIC PKOCESS OF BEICKMAKING 218

Instead of a belt, two ropes may be driven parallel to each
other, and bricks on pallet boards laid across these will then be
carried forward to their destination. This arrangement is especi-
ally useful where the bricks are -taken direct from a cutting table.
The empty boards are placed on the lower part of the rope and
a permanent scraper throws them off directly they arrive at the
machine.

Where the relative position of the machine or dryer and the
kiln permits, a belt or conveyer may advantageously be used in
setting. One pulley or spool is taken inside the portion of the
kiln to be set and is slung up by means of a chain attached to
the roof or, through a pot-hole, to a bar above the kiln. The
other end is in the dryer or making shop. In this way the
bricks are delivered direct to the setters, just as they are required.
This method is increasing rapidly in popularity in the United
States, where it is worked under Scott's patents.

Another method, also largely used in America, consists in
setting the bricks out on a special carrier exactly as they are to
be placed in the kiln. This carrier is then taken by means of
an overhead ropeway to the kiln, and by a simple motion the
bricks are set and the empty carrier returned. For large outputs
with kilns of the " improved clamp " type, this arrangement is
good, as it saves handling, but the author has not found it so
satisfactory in continuous kilns of the Hoffman type.

Drying. — According to the amount of moisture in the bricks,
the size of the* solid particles, and the kiln in which firing takes
place, the bricks may be taken to a dryer or direct to the kiln.
In most instances where a continuous kiln of good type with at
least sixteen chambers is used, the bricks need not be dried
separately, but may be set in the kiln and the drying allowed to
take place therein. With single kilns, or where continuous
kilns with few chambers are employed, it is usually necessary to
dry the bricks before setting them in the kiln. Such drying is
also necessary where the bricks have a strong tendency to scum,
and where it is difficult to obtain a good colour.

Any of the dryers described in Chapter IV as suitable for
bricks made by the plastic process may be used, but as stiff-
plastic bricks contain less moisture they shrink less, and may,
therefore, be dried more rapidly. Being stronger on account of
their stiffness, they are specially adapted for treatment in tunnel-
dryers of the "direct type," in-which the bricks and air travel
in the same direction and are both heated progressively.

'214 MODERN BRICKMAKING

Failing a suitable tunnel-dryer, they -should be stacked about
eight bricks high in a shed with a heated floor (p. 156). If
such a shed has partitions or blinds, so as to separate it into a
number of tunnels and to enable the temperature in each section
to be regulated so as to suit the bricks in it, the drying will be
better and more economically carried out than where the usual
" open shed " is used. Ventilation must be provided, but draughts
on the bricks avoided.

A simple and cheap dryer of the intermittent form has been
patented by W. B. Hughes, and consists of skeleton timber
framing fixed upon a brick curb with adjustable sides, which,
when removed, give easy access for taking the bricks on the
ordinary off-bearing barrow. As the sections are filled, the
boards forming the sides are put into position and the dryer
started working. When the bricks are dry the side boards are
taken out, giving free access for the barrows.

The heat is obtained by means of 3 in. cast-iron pipes, to
which either live or exhaust steam is connected. A fan is used
for forcing hot air at any desired temperature up between
the already heated cast-iron pipes and through the goods to be
dried. Such a dryer is cheap to construct, requires little atten-
tion, and is easily built, but has the disadvantage that the bricks
must be stacked in it instead of being left in the cars as in other
tunnel-dryers.

The same principle is used extensively in the United States
in what is known as the Bechtel dryer. The floor of this dryer
is in the form of a number of trenches, the walls of which
are sufficiently wide to allow a special barrow (fig. 151) to travel
along them. After the barrow has been wheeled into position
the handles<are raised, and the pallet-boards containing the bricks
are deposited across the trench and the empty barrow can then
be wheeled away. The bricks are set in a series of blades the
whole length of the dryer, and when one trench is completely
covered with bricks from end to end they are covered with
special burlap coverings (fig. 152), so that as soon as the heated
air commences to extract the moisture from the drying bricks,
instead of it being immediately dissipated into the dryer, this
hot saturated air is largely retained on the outer surfaces of the
bricks by means of these coverings, and so long as this state of
humidity is maintained, the brick dries from the inside outwards,
the surrounding moisture preventing the hardening of the surfaces
of the brick and obviating " checking ". In other words the out-

THE STIFF-PLASTIC PKOCESS OF BRICKMAKING

215

side of the brick dries last. This is an important advantage,
especially where clays are of a tender nature. A fan is vised for
supplying the hot air to the flues.

One of the most novel forms of dryer at present in use is
that worked under A. Scott's patents, in connexion with a kiln of
the horizontal draught or archless continuous type. This system
is the most radical departure in drying methods yet introduced.
It boldly does away with not only cars, rails, pallets, and other
incidental apparatus, but with the dryer itself!

The system consists of two factors : First a belt conveyer to

FIG. 151.— Bechtel barrow.

take the bricks from the machine up to and into the kilns ;
second, the drying of the bricks in the kiln after they are set.
The system is, of course, specially adapted to the handling of
" stiff-plastic " and " semi-dry " bricks. For bricks made by the
plastic process it is not advantageous. The main conveyer takes
the place of the ordinary off-bearing belt of the brick machine. It
receives the bricks from the cutting table and carries them down
the yard under a shed built along in front of th,e line of kilns.
When the bricks arrive on this belt opposite the kiln into which
they are to be set, they>are transferred, by a man stationed at this
junction point, to another belt which extends through the kiln.

216

MODERN BEICKMAKING

S

THE STIFF-PLASTIC PROCESS OF BRICKMAKING- 217

This work of transferring is accomplished by one man, who can
handle from 60,000 to 70,000 bricks daily. The cross-conveyer,
as this second belt is called, carries the bricks into the kiln at
any height desired to ensure the efficiency of the setting. The
bricks are generally set from six to eight high. When the en-
tire kiln floor has been set to this height the cross-conveyer is
raised to the proper height for the next setting, and the setters
proceed to another kiln or chamber to continue the operation,
while these eight courses of brick are being dried. The object
being to dry these sufficiently for the next twelve hours to sup-
port the setting of the next eight courses. When these are dried
the next tier is set and that again dried, the operation being
repeated until the entire kiln is filled and ready for burning.
The burning is carried on in the usual manner. It is claimed
that when the top tier of bricks is dry, the bottom course is as
hot as the heated air will make it, and the kiln is in a perfect
condition to start firing without water-smoking.

The drying of the bricks in the kiln is accomplished chiefly
by the application of waste heat. It is maintained that the
saving on fuel and labour costs amounts to about 2s. 6d. per
1000, due to the fact that the bricks are drier than those turned
out from the ordinary dryer, and that the kiln is hot when the
fires are started, so that the water-smoking cost is reduced to a
minimum. The method requires considerable adaptation before
it can be used for most British yards. In the United States,
where it is chiefly used, large kilns with open tops (" scove kilns ")
are chiefly used for common bricks, and for these this system
is excellent.

Kilns. — Bricks made by the stiff-plastic process may be fired
in single or continuous kilns, the latter having the advantage of
using less fuel, and at the same time giving bricks of equally
good colour if properly constructed and managed.

Of the single kilns, the "down-draught" and " Newcastle "
types are usually best, but others are used to the satisfaction of
various brickmakers.

Where the output is large, a continuous kiln is undoubtedly
the most suitable, as if properly designed for the purpose it can
receive the bricks direct from the machine and dispense with a
dryer. Where only common bricks (with or without a small
proportion of facings) are to be made, a continuous or semi-con-
tinuous kiln should be used. These are described in Chapter
VIII.

218 MODERN BEICKMAKING

The preliminary heating of bricks made by the stiff-plastic
process should be effected with special care. If this precaution
is duly observed, the firing of bricks made in this manner pre-
sents no difficulties not met with in other methods of brick-
making.

CHAPTER VI.

THE SEMI-DRY OR SEMI-PLASTIC PROCESS OF BRICK-
MAKING.

IN the semi-dry or semi-plastic process the clay is used in its
natural condition, no weathering or other treatment being used
{except in special cases) to develop the plasticity. Both terms
" semi-dry " and " semi-plastic " are used for the same process,
though the former is better and clearer, as well as less likely
to be confused with the " stiff -plastic " process in which a small
amount of water is needed. The semi-dry process has the
advantage of remarkable cheapness in working, as the bricks
•can be sent direct to the kiln, but it is not so popular now as for-
merly, because of the introduction of the stiff-plastic system, and
of the greater ease with which the stiff-plastic bricks are sold
to builders.

Owing to the dryness of the material, the semi-dry process
oan be used in many instances where other processes are not so
suitable, but the bricks produced from this material are seldom
so satisfactory as those made from more plastic clays. The
greater cheapness of producing semi-dry bricks is very much in
their favour in certain districts (notably in the neighbourhoods
•of Peterborough and Accrington) and this process will, therefore,
hold its own in some localities for a considerable time to come ;
indeed, for the special clays found in certain parts of Lancashire
(Accrington), and near Fletton (Peterborough), it is difficult to
conceive a process by which bricks of saleable quality can be
produced more cheaply than when made by the semi-dry process.

The most suitable clays for the semi-dry process are those of
a lean or open character ; highly plastic -clays cannot be used,
and several attempts to employ them have only resulted in
failure, as they require more thorough treatment than is possible
when they are worked up in a semi-dry state. The ideal clay for
the semi-dry process is one which, when ground, balls together
when squeezed in the hand without losing its shape when the

219

220 MODEEN BEICKMAKING

pressure is removed and yet which does not feel sticky or plastic,
It must also contain sufficient flux to bind the particles together
into good bricks when fired at a reasonable temperature. The
clay must be free from gross impurities, and if not regular
in composition, some arrangement must be made for mixing it
thoroughly, as irregularities in this respect will cause failures
which it is often difficult to trace to their source. Many shales
are capable of being efficiently worked by this process.

The use of semi-dry process machines has been pushed
vigorously during recent years, but it would be unwise to install
them on new and untried clays unless precisely similar materi-
als had been successfully worked by this system, or unless the
brickmaker is willing to experiment on a very large scale, as
this is one of the most difficult of brickmaking processes to put
into satisfactory operation, and the most prominent users of it
have only attained their success as the result of incessant labour
of a highly skilled character.

In the semi-dry or semi-plastic process of brickmaking the
clay is dug from the pit, sent in wagons to a grinding mill of
the edge-runner type, and the ground material is subjected to
the action of powerful presses, which form it into bricks. Thesa
bricks are taken direct to the kiln.

The following is the arrangement of plant used by the London
Brick Co., Ltd., of Fletton, Peterborough, one of the largest
manufacturers of bricks by this process : —

Early investigations having proved the necessity of mixing
the different strata (including an oily shale) found in the Fletton
bed, steam navvies are used to take a scrape right up the whole
face of clay and ensure a good proportion of each stratum. As
in this district the topmost layer of earth (or " callow ") is not
suitable for treatment, it is removed by a preliminary steam
navvy and taken along a belt conveyer to a place where it may
conveniently be deposited.

The steam navvies used for obtaining clay in this manner
are of the type shown in fig. 153, and are so constructed
that when the bucket or grab is filled with clay it is swung
round, and after opening a door at the back of the bucket, its
contents are discharged into a wagon. The bucket is provided
with steel claws which break up the ground, and about 1 cub. yd.
of material is obtained at each stroke of the machine. With
such an appliance, and working under favourable conditions, it
is easily possible to cut up a face of clay and load it into wagons.

SEMI-DKY OB SEMI-PLASTIC PROCESS OF BRICKMAKING 221

at a cost of about twopence per cub. yd. As the wagons are filled
they are hauled by an endless chain to the mills.

For the most part the grinding is carried out in edge-runner
mills, though in a few cases disintegrators and stone-breakers
have been used, but these do not, on the whole, produce the de-
sired results. The most suitable mills are those of the revolv-
ing dry pan type (p. 183), as the material must be reduced to
-a fine powder.

FIG. 153. — Steam navvy (Euston-Proctor & Co.).

The crushed material is next taken to the screens by spiral
•conveyers (figs. 154 and 155) which assist in mixing it thoroughly,
though other forms of conveyers may be substituted, provided that
a special dry mixer is included at a later stage.

The screens used by the London Brick Co. are of the
"piano-wire" type (p. 194), this having been invented by
their manager, Mr. A. Adams ; but some other firms have found
perforated steel plates to be more efficient. This is clearly a
matter for each brickmaker to decide for himself, as so much
depends on the nature of the material used. The objection to
piano-wire screens as ordinarily supplied is that the larger por-

22*2 MODERN BRICKMAKING

tions of material are apt to lodge between the wires, parting
them and making' the screens ineffective. This may be over-
come by using two screens, providing the material is not too
lamellar in structure.

The material which passes through the screens is received in
a hopper or on to a floor, from whence it passes down a chute to
the machines ; but the material which is too large to pass the
screen is sent down another chute to the grinding mill for further
treatment.

The screened dust must possess sufficient dampness before it

FIG. 154. — Spiral conveyer.

is allowed to pass into the brickmaking machine. It should be-
able to be pressed by the hand into a ball ; if too dry it will not
hold together, and will necessitate the addition of water to the
clay in the grinding mill or mixer. In some cases enough water
may be present in the clay, though very unevenly distributed,
so that some parts are dry and will not hold together, the mate-
rial must then be passed through extra mixing machinery.

In the brickmaking machine, the material is pressed into a
block and, if desired, repressed and sent to the kiln. The
London Brick Co., Ltd., have found that four distinct pressures
are necessary to obtain the best results.

The presses employed by the London Brick Co. are made

SEMI-DEY OE SEMI-PLASTIC PROCESS OF BBICKMAKING 223

by C. Whittaker &
Co., Ltd., illustrated
in fig. 156. The
ground material
from the mill and
mixers is fed into
the hopper of this
machine, and thence
by means of a slid-
ing box into the first
mould. The amount
of material received
in the mould can be
regulated instantly,
so that as the damp-
ness of the material
varies from time to
time more or less
clay can be taken
into the mould. The
brick, after having
two pressures put on
to it, is automati-
cally fed into the
second mould and
there it is pressed
twice more ; thus it-
is subjected to four
distinct pressures,
each pressure being
about 80 tons. This
machine has an out-
put of 5000 to 6000
bricks per day, and,
according to the
makers, requires 5
h.p. to drive it. It
should be noted that
in this machine no
oil is used to lubri-
cate the moulds.

After leaving this machine the bricks are taken straight

to

224

MODEKN BEICKMAKING

the kiln, which, in the case of the London Brick Co., is a con-
tinuous one of exceptional size and designed in a special man-
ner rendered necessary by the proportion of oil and other
combustible matter in the clay used. This kiln (known as
the " English ") is described in Chapter VIII.

FIG. 156. — Semi-dry process brick machine.

The London Brick Co. lay much emphasis upon and attribute
much of their success to the use of (1) steam navvies which,
they claim, can secure an admixture of the material which is
far more thorough than is possible in hand digging ; (2) spiral or
other mixers to incorporate thoroughly the crushed material ;
(3) pressing each brick four times, and (4) efficient and economi-
cal burning.

SEMI-DBY OB SEMI-PLASTIC PBOCESS OF BBICKMAKING 225

It is undoubtedly true that the cracked faces, liability to
spall, and other defects of many bricks made by the semi-plastic
process is due to an insufficient recognition of the importance
of the material being thoroughly homogeneous and sufficiently
pressed.

Machines for making bricks by the semi-dry process are also
supplied by other firms. The arrangement of plant shown in
fig. 157 has been used successfully in several instances by Thos.
C. Fawcett, Ltd.

In this plant the material is ground in an open base revolving
pan mill (p. 188), and taken by a bucket elevator to a " Neway-
ago " (p. 194) or other suitable screen. The finer portions of
material are then passed through a double differential mixer
similar to that shown in fig. 158 where water is added (if neces-
sary) to bring the material to the proper consistency. The
mixture is then delivered to the press shown in fig. 159, which is
in many respects similar to the Fawcett duplex press used for
the stiff-plastic process. In this machine the damp powder is
rammed into a clot in open-ended moulds forming the cogs of
a special wheel, and each clot is in turn fed into the box of a
toggle-lever press where it receives two distinct pressures. This
produces a brick which is, in most cases, sufficiently dense and
ready to set directly into the kiln.

For best facing bricks, however, the use of a repress (fig. 160)
is desirable, particularly if this has an attachment for regulating
the thickness of each brick.

Such a plant as this has an output of 10,000 bricks per day
and requires 20 to 25 b.h.p. to drive it under normal conditions.

The machine made by Rd. Scholefield is identical in principle
with the Fawcett plant, but differs in several important details.
Thus, the moulds have closed instead of open ends, and instead
of an arm pushing the clot out of the press wheel, or drum,
in the Scholefield machine it is pushed out by the filling of
the opposite portion of the drum preparatory to making a new
clot. This " Sanspareil " machine is shown in fig. 161.

The efficiency of the machine has recently been enhanced by
the introduction of an adjustable feed, which, without stopping
the machine, can be regulated to feed a greater or lesser quantity
of clay into the moulding cylinder, thus preventing an excessive
escape of clay and consequent loss of ariving power and assur-
ing a full feed.

The centre and bottom joint of the toggles are of special

15

226

MODERN BRICKMAKING

SEMI-DRY OB SEMI-PLASTIC PROCESS OF BRICKMAKING- 227

228

MODEEN BEICKMAKING

design in the form of " knuckles " dispensing with the usual
joint (which is formed by a pin or shaft passing through
holes bored in the respective ends of the toggles. These
" knuckles," which are easily adjustable, have extra large wear-
ing surfaces, are machined to fit the steel cups or sockets,
bored out to receive them, and are also arranged in such a
manner that it is equally simple to subject the brick to two
exactly equal pressures, or to a heavy first pressure and a second

FIG. 159. — Semi-dry process brick machine.

light pressure, or to a light first pressure and a heavy second
pressure, with one revolution of the crank-shaft. After the first
pressure has been brought to bear upon the brick, it is released
for a short space, after which the second or final pressure is
applied, and the brick is automatically discharged from the press
mould on to the delivery table. The thickness of the repressed
brick can be regulated accurately by means of a " folding
wedge " adjustable pressure block, without stopping the machine.
Wm. Johnson & Sons, Ltd., Leeds, have for a number of years-

SEMI-DRY OE SEMI-PLASTIC PEOCESS OF BEICKMAKING 229

manufactured the semi-dry press shown in fig. 162. The
powdered material is fed into a hopper, which is part of the

FIG. 160. — Eepress for semi-dry bricks.

machine, underneath which passes a charger, and in doing so
becomes filled with ground clay. After this the charger passes
over the mould, drops the material into the latter, and then
returns to the hopper for a fresh charge of clay. During this

230 MODEBN BRICKMAKING

time the brick is pressed in the mould by a descending plunger
and also an ascending one underneath, these being operated by
a powerful cam and anti-friction roller so that the brick receives
the pressure simultaneously both from the top and bottom.
This insures a uniform pressure over the whole brick. The
pressure can be varied in a very simple manner by the attendant,
who also loads the bricks on to a barrow or cars ready for removal
to the kiln.

This machine has a daily output of 7000 bricks and, on the
maker's statement, needs about 6 h.p. for driving it.

FIG. 161. — " Sanspareil " brick machine.

The Stanley patent semi-dry dust machine is made by the
Nuneaton Engineering Co., Ltd., and shown in fig. 163. This
machine is altogether different from the types mentioned above.
The dust is fed from a reciprocating charger in the usual way,
but the pressure is applied by means of shaped cams working on
rollers fitted with cross heads, carrying on their lower sides
plungers which fit into dies. Pressure is gradually applied and
during the process is slightly relieved, allowing the escape of air
and the equal expansion of the clay dust in the die. At the
finish of the pressing stage the top plungers and dies are forced
dowmon to the stationary bottom plungers, regulated to a-greater
or lesser degree as required. This simple action gives the bottom,

SEMI-DEY OE SEMI-PLASTIC PROCESS OF BEICKMAKING 231

sides, and arrises as true and hard a finish as the upper parts of

FIG. 162.— Johnson's press for semi-dry process.

the brick. As the feed-boxes fill the dies 'they deliver the pressed

232

MODERN BRICKMAKING

bricks to the front, giving ample time for the attendant to remove

them.

The advantage of receiving such a second pressure on the

lower part of the brick is
very great. Machines
which only give a single
direct pressure usually
leave the centre of the
brick coarse and weak.
The extra movement of
the Stanley machine pre-
vents this weakness.

The clay is kept in
motion when under pres-
sure, and the contact with
the sides of the mould
causes the sides of the
brick to be thoroughly
smoothed and free from
signs of granulation,
though whether granula-

FIG. 163.-Stanley press for semi-dry bricks. tjon jg really removed or
only covered over is a moot point with some clays.

In its latest form the machine is fitted with two die boxes and
plungers so as to make two bricks at once, and with lifting fingers
which raise the brick and carry it forward to the delivery table,
where it is placed down gently and the fingers travel back to re-
ceive a second brick. This arrangement preserves the arrises
from the damage which is inevitable when the bricks are pushed
along to the delivery table.

The machine is also fitted with a special charging appliance
which takes the form of a false bottom in the feed box which
supplies the clay to the die. In the ordinary form of feed there
is an unavoidable tendency to produce bricks with one soft end,
owing to the manner in which the clay is fed into the die. In
the new arrangement the false bottom is closed until the box is
completely over the die, when it opens from the centre outwards,
fills the die with the dust, closes and carries the box out of the way
of the descending plunger.

Amongst other machines using cam rollers may be mentioned
the " Platt " machine (figs. 164 and 165), which has a falling cross
head carrying the piston and gives a hammer-like action to the

SEMI-DRY OR SEMI-PLASTIC PROCESS OF BRICKMAKING- 233

material under pressure, through the head dropping twice in each
revolution. The first drop displaces the air, which escapes when
the cross head is raised, and the second drop, followed by the
enormous pressure of both upper and lower cams, produces a very

REFERENCE

FIG. 164.— Platt Bros. & Co., Ltd., press (front view).

dense brick. An air-cylinder is placed at the upper part of the
press to regulate the speed of the falling plungers.

A press of an entirely different type is the " Emperor " made
by Sutcliffe, Speakman & Co., Ltd. (fig. 166). Though primarily
designed for materials devoid of plasticity, this press is well suited
for some clays worked in a dry or semi- dry .state.

234

MODERN BRICKMAKING

It consists of a horizontal, rotating table containing the moulds

arranged singly or in pairs, and,
depending on the size, there are
from six to', eight pairs of
moulds. The table is rotated
in such a manner that whilst
one pair is receiving the charge
of material to be pressed, an-
other is under pressure and a
third is over the discharge ram.
The feeding is quite automatic,
being effected by means of a
circular pan in which revolves
a series of stirrers which pre-
vent the material choking, and
ensure a regular and constant
feed. The quantity of material
fed into the moulds is regulated
by means of a hand wheel, and,
as this can be turned whilst the
machine is in motion, the pres-
sure can be regulated at will.
The pressing mechanism is of
the toggle and knee type, and
the distribution of the pressure

FIG. 165.— Platt Bros. & Co., Ltd.,
press (side view).

FIG. 166. — ".Emperor" press.

is so effected that massive steel bolts take all the greater strains

SEMI-DRY OE SEMI-PLASTIC PEOCESS OF BEICKMAKING 235

of the framework. Ample adjustments are made for taking up
wear and tear. The moulds are on the " economic " principle
(p. 152) and are easily relined, as in putting in new liners no fitting
or adjusting is required. Each set of liners can be reversed, giv-
ing two wearing faces.

FIG. 167. — Action of " Emperor " press.

This press can be made to give a top and bottom equal and
simultaneous pressure, or to give a bottom pressure only, or a
quadruple pressure, the final pressure being greater than the
first.

A patent expression attachment (fig. 167) operates by giving
each brick two pressings, the first squeezes and presses the
material from the centre into the corners and arrises, the final
pressure finishes the brick. By these means each brick is of even

236 MODERN BEICKMAKING

density throughout, with fine sharp corners and arrises. In fig
167 "A " shows the mould receiving the first preliminary pressure
and " B " the final pressure.

When used for brickmaking the goods are delivered on the
table for removal by the attendant, and are not pushed from the
moulds, as in presses of the vertical type, but an automatic
pusher-off can be attached to the machine to deliver the bricks
on to a travelling band if desired.

This machine has a maximum output from 1000 (single type)
to 2400 (duplex type) bricks per hour. The power required to
operate it is from 5 to 12 h.p. It works smoothly and easily,
and owing to powerful springs •shown in the illustration, it is
evenly balanced. These springs are not for relieving the pressure,
but merely to balance the heavy pressing mechanism and, if
desired, the machine can be run without them.

The " Emperor " press has deservedly made a great reputation
for itself for working all kinds and qualities of non-plastic or
slightly plastic material, including ores of all descriptions, arti-
ficial fuels and sands, iron and steel slags, destructor clinker,
coral rock, puzzolana, and cement mixtures as well as clay.

Eepressing. — As the solidity of the unfired bricks is chiefly due
to the pressure to which they have been subject, it is important
that this should be sufficient, and whilst some firms prefer to
press the bricks only once, a second pressing should not be
omitted where the best and strongest bricks are required. As
already stated, the best machines subject the bricks automatically
to two or more pressings, thereby avoiding the necessity of
repressing.

Transport. — In most instances pressed bricks are taken on
crowding barrows (fig. 148), and are wheeled along iron strips to
the kiln. In a few works they are loaded on to double deck cars
(p. 171) and taken along rails, turn-tables, and portable rails
inside the kiln.

Kilns. — Any good type of kiln may be used, but as the semi-
dry method is chiefly used for large outputs, some form of con-
tinuous kiln is to be preferred. Details of these will be found
in Chapter VIII.

Difficulties in Working. The difficulties met with in working
clays by the semi-dry method are similar to those met with in
working the stiff-plastic process, but the weakness caused by
lamination is much more frequent ; indeed, it is the great bug-
bear of the maker of this kind of brick.

SEMI-DKY OR SEMI-PLASTIC PROCESS OF BRICKMAKING 237

Lamination is recognized by the production of thin layers of
material, easily visible when a brick is broken, which cause the
brick to split off or spall in certain directions. It is not often
due to insufficient pressure, but may be caused by excessive
pressure if this is applied at the wrong time.

In many instances the cause of lamination is very obscure,
but insufficient treatment of the material is a prominent factor,
especially if the clay is obtained dry and is damped and im-
perfectly mixed later. This produces portions of material
in which the plasticity is strongly developed, whilst in others it
is scarcely developed at all, and lamination consequently re-
sults. One brickmaker of the author's acquaintance has com-
pared it to the use of flour in preparing puff-pastry. " The dough
is rolled out into thin pieces, and sprinkled with flour and then
rolled again. On placing in the oven, the dry flour causes the
plastic layers of dough to part from each other, and the laminated
character of puff-pastry is thereby obtained."

The manner in which the pressure is applied is very im-
portant for, as pointed out by Lovejoy, it is important to remember
that on any machine in which the plungers approach each other
and squeeze the clay toward the centre of the mould, the brick
will show a comparative granulation on this centre plane, due
to a lack of density, quite noticeable even at some distance. " If
the pressure is all from the top, the granulation will be at the
bottom, and its position will depend upon the relative degree of
motion of the two plungers. This granulation is often attributed
to included air, and all machine manufacturers provide for its
escape, either through air holes in the plunger plates or by re-
leasing the pressure before the final pressure is applied. But,
admitting the effect of the included air and the desirability of
allowing it to escape, it is not sufficient to account for the
granulated surfaces obtained in practice.

" Dry or semi-dry clay will not flow under pressure. If a tube
punctured with holes from top to bottom to allow the escape of
the included air be filled with dry clay, and pressure be applied
at the top, a column of clay is obtained decreasing in density
from top to bottom, due to the friction against the walls of the
tube and the immobility of the clay.

" In a press with roller cam motion the clay is most compressed
at the top, and least at bottom during the downward stroke,
with the reverse during the upward stroke. The loosely packed
clay in the bottom offers little resistance to being forced down-

238 MODERN BEICKMAKING

ward in the mould, whilst the densely packed top offers great
resistance to being forced upward during the upward stroke, to
the advantage of the bottom of -the brick in density. From a
scientific standpoint it would be absurd to assert that the total
pressure received by the top of the brick is equal to that re-
ceived by the bottom, and that each is equal to that at the
centre of the brick. In practice, however, one notices no dif-
ference, and the brick is, to all intents and^ purposes, uniform in
density from top to bottom.

" The later toggle machines recognize the probability of this
difference in the top and bottom and provide for it by an ar-
rangement which, in a measure, reverses the motion at any
point in the stroke. The claim has been made that the motion
of the brick under pressure in the mould does not remove the
granulated centres but simply glosses them over, and this claim
is reasonable, since the>centres are>only removed through friction
against the sides of the mould. In practice it is difficult to
recognize any difference in density throughout the brick, but
from a theoretical standpoint it is difficult to believe that the
effect of the friction against the sides of the mould will extend to
the centre of the brick with a material so irresponsive to 'pressure
as dry clay. It is most probable that the internal core of the
brick will have less density than the faces.

" If these differences exist they are too slight to be noticed in
practice, but they may account for some trouble in drying and
burning such a body as semi-dry clay, in which the bonding
element is not developed as in the plastic process."

Scum is particularly troublesome in some clays used in the
semi-dry process, and the use of barium carbonate is impractic-
able owing to the small amount of water used. Some advantage
may be gained by using barium chloride, but great care is
necessary to avoid an excess of this material, or the remedy may
prove worse than the disease.

Drying Troubles. — Although, by sending bricks made by the
semi-dry process direct to the kiln; the drying process with all
its troubles is apparently eliminated, it is found in practice
that " semi-dry " bricks need as careful drying as any others,
the only difference being that it is carried out in the kiln
instead of in separate dryers. The reason is that in "plastic"
bricks the plasticity of the clay is fully developed and the
granular particles are cemented together, but in the semi-dry
clay the bond is largely mechanical. The colloid properties are

SEMI-DEY OE SEMI-PLASTIC PEOCESS OF BEICKMAKING 239

not developed, and, if the particles are connected at all, it must
be with dust, and at best imperfectly. When the pressure is
applied the particles are forced together and into each other,
and held there by interlocking, assisted, of course, by whatever
colloid properties may have been developed. The dust fills
the interstices under various degrees of pressure according to its
amount, and the protection it has received in the interlocking
of the particles and the opportunity for the escape of the air
during the final pressure. The air, in its escape, may play the
further role of sweeping clean the points of contact of the inter-
locking particles.

Bricks held together by such a doubtful primary bond must
be very carefully dried in the kiln from three to twelve days,
and in some cases (as with large blocks) two and three weeks are
required. It is more a sweating process' than a drying one, so
slowly is the moisture taken off. Rapid drying would loosen
the particles, which would not reunite in burning, and the re-
sult would be a rotten brick.

It is seldom practical to vitrify dry -pressed bricks, as the
finer state of division of the material in bricks made by the
plastic process is sufficient to explain the more ready fusibility
of the matrix, but in the dry process the contact of the particles
alone forms the bond. The shrinkage is comparatively little, and
is not due in any marked degree to the fine material.

As Ellis Lovejoy states : " In the one case the matrix fuses
and contracts, carrying with it at all stages the larger particles,
and imperviousness is attained with its fusion. In the other,
the fine material may fuse and collect in the bottom of the cells
formed by the larger particles, running into and around the
points of contact, cementing them together into a permanent
bond but only partially filling the cells, and imperviousness can
only be effected by the softening of the cell-walls themselves, and
the closing in upon the fused fine material contained therein."

An impervious brick made by the plastic process has a stony
structure, while an impervious dry -press brick tends towards a
glassy one.

Moulds and Arrises. — Semi-dry clay has a strong grinding
action on the moulds or dies, and these must be kept in good
order or the bricks will have bad edges. With badly worn dies
there would be no pressure around the edges and at the corners,
and without pressure there would be no primary bond, and the
edges and corners would crumble off in handling, either before
or after burning.

CHAPTER VII.
THE DRY OR DUST PROCESS.

NOTWITHSTANDING the many complaints which have been pub-
lished by clayworkers who have been unsuccessful in producing
a really sound brick in the " dry " way, this method is in great
favour in different parts of the world, especially on the Continent,
where the presence of enormous deposits of secondary clays,
which are very difficult to work by more plastic methods, makes
the problems confronting the clayworker more acute than they
are here.

It must be obvious to all practical clayworkers that a highly
plastic clay is not suited for working in a dry state, and that
attempts to treat it in this way will most probably end in failure,
though a few cases are known where satisfactory goods are being
produced by mixing such clays with a large proportion of non-
plastic material of somewhat coarse grain. As a general rule,
therefore, the clays which are suitable for dry treatment are
those of the secondary and shale classes, but other substances
which are not of a truly argillaceous nature, such as steatite,
lime-sand, or even concrete, may be treated satisfactorily in this
way. The great essential appears to be that the material to be
pressed shall have sufficient binding power, and yet shall be free
from the stickiness inevitably associated with plastic materials
in which the plasticity has not been fully developed.

The composition of the materials used will be found to be of
minor importance as far as the actual production is concerned,
though it must be considered in a study of the uses of finished
goods. It is the physical, rather than the chemical, composition
and nature of the clay which determines whether it can be
satisfactorily worked in the dry way, or whether an admixture
of water previous to pressing is necessary.

There are two reasons why the dry process of brickniakiiig~
appeals to brickmakers : First, the lessened cost of making, owing
to the absence of all drying either in the kilns or in special yards

240

THE DEY OE DUST PEOCESS '241

or sheds, and, second, the reduction in the number of cracked
and split bricks as compared with the products of many yards
working a plastic or stiff-plastic method.

Very coarse materials do not lend themselves readily to this
method of manufacture, as a certain proportion of fine dust
must be present to give solidity and strength.

An important point in the manufacture of dry -pressed goods
is to have the material really dry, as otherwise its water content
is apt to be unevenly distributed and a mixture is used which
will crack in the kiln. On this account it is often necessary to
dry the material before or after grinding.

Lamination requires far more attention than has hitherto
been given to it if this really serious defect is to be removed. It
is due in many cases to defective design in the presses, and to
the inclusion of air between the particles. Almost all dry -presses
at present in use cause a certain amount of lamination, though
it is often too insignificant in extent to warrant any special
comment. Its cause is obscure, but apparently the absence of
lubrication, such as is supplied by the water in plastic clay,
tends to permit the dry particles to move to different extents
in different directions, instead of regularly, as in the more mo-
bile, plastic clay. Lamination is especially marked in slightly
moistened clays, in which some of the particles are dryer than
others (see p. 237).

Dry -pressed bricks with sharp anises, and which are perfectly
sound, are difficult to produce when the moulds are worn, and as
they leave the mould less rapidly and wear it more quickly than
a well-oiled plastic brick, this is a matter of some importance,
and one which must be fully considered when proposing to lay
down a new plant.

Some dry-pressed bricks on the market are defective through
being under-fired. As the binding influence of plastic clay is
absent from such bricks, a somewhat higher temperature is often
necessary in the kilns in order to bring about incipient vitrifica-
tion, and so obtain a strong article. This effect of plasticity on
the fired goods is by no means well understood, though it is
undoubted. Probably it is due to the effect of the greater pro-
portion of water in the plastic clay in splitting up the latter into
finer particles, which commence to vitrify at a lower temperature
than when they are in the coarser form of stiff bricks.

The methods and machinery used are precisely similar to
those employed in the semi-dry process, except that no water is

16

'242 MODEBN BEICKMAKING

added to the material, and some form of clay dryer may be
required. Greater pressures are, however, necessary and the
presses must be made exceptionally strong. The " Emperor "
press (p. 234) is particularly suitable for materials practically
devoid of plasticity.

The dry or " dust " process is chiefly used in this country for
tiles, the manufacture of bricks by it being difficult on account
of lamination, irregularity in hardness in different portions of the
brick, and defective binding power before burning, which makes
the bricks difficult to handle. With tiles the difficulties are much
less because of their thinness. The small amount of moisture
present in the bricks made by the semi-dry process overcomes
these difficulties to a limited extent, and it is on this account
generally preferable.

The advantages of the dry process over the others are many
and obvious, but the process is limited to certain types of clay
and classes of goods, and those clayworkers who rashly imagine
that any clay may be satisfactorily made into bricks or tiles by
it may find their mistake out when it is too late. In such cases,
as in'many others, an absolutely impartial opinion, given by one
thoroughly acquainted with the disadvantages and advantages
of each method, and with the composition and character of the
clay and the goods to be made from it, is the best thing to obtain
before the plant is laid out. Such advice cannot, naturally, be
had for nothing ; but its cost is far less than that of experiments
with expensive plant and machinery which prove abortive after
a few months' trial.

Provided that the clay is in a suitable physical condition, its
use in a dry press is accompanied by many advantages, but until
more is known of the exact physical characteristics required, all
work in this direction must be somewhat in the nature of an
experiment.

CHAPTER VIII.
KILNS.

THE selection of a kiln -for burning bricks is a matter requiring
great care and skill, particularly if it is to be used in works where
the annual output is very large. In a small works the problem
is less complicated, as the choice is usually limited to some form
of single or intermittent kiln.

Brick kilns may be classified into two main groups : (a) single
or intermittent kilns, consisting of a single chamber, and (b) semi-
continuous and continuous kilns, consisting of a number of
chambers connected in such a manner that the gases and pro-
ducts of combustion produced in one chamber may be utilized
in heating others.

Kilns used for brick-burning may also be divided into three
classes according to the direction in which the air, flue-gases,
and products of combustion travel, viz. (1) up-draught ; (2) down-
draught ; and (3) horizontal-draught kilns.

Up-Draught Kilns are the most costly in fuel, but are con-
venient in many small yards and can usually be constructed
cheaply.

An up-draught kiln for brick-burning usually consists of two
side walls placed parallel to each other and containing a number
of fire holes. An arched roof may be fitted over these walls, or
a flat roof may be formed by covering the bricks in the kiln with
a layer of bricks laid flat and making this tight with ashes. One
or more small chimneys may be built 011 the top of the kiln,
or a flue may be built and connected to a single large chimney
erected at a convenient distance from the kiln. The heated air
enters through the fire-holes and rises to the top of the kiln,
whence it passes to the chimney, the kiln deriving its name from
the upward motion of this air or draught.

The chief failing of the up-draught kiln is its irregular heating,
the consequent large proportion of under-burned and over-fired

243

244 MODEEN BEICKMAKING

bricks produced, and the large proportion of fuel (seldom less
than 12 cwt. per 1000 bricks) it requires.

Its advantages are the low cost of erection, simplicity of
setting and drawing, and the low cost of repairs.

Down-Draught Kilns are amongst the best single chamber kilns
known. They should really be termed "up and down-draught,"
as the air entering the fire-boxes rises towards the top of the kiln
and is then deflected downwards, distributing itself throughout
the kiln and passing through an opening in the floor to the
chimney, which should be about 40 ft. high and 4 ft. dia-
meter.

This type of kiln is used throughout the country for high-
class bricks of all kinds, and is valuable on account of the even
heating which can be obtained. Though usually built as a
single kiln, it has been found that the same principle can be
applied to continuous kilns, with the result that the economy of
the latter, combined with the excellent colour and even heating
of the former, produce an almost ideal kiln.

Down-draught kilns may be either circular or rectangular in
shape, the latter being best for bricks. They may be made
sufficiently large to hold 250,000 bricks, but most British brick-
makers find a chamber holding 30,000 to 40,000 most convenient
for single-chamber kilns.

. Horizontal-Draught Kilns are those in which the air entering
through the fire-holes travels largely in a horizontal direction
before entering the chimney. The best known kiln of this type
is the " Newcastle ".

They are used for fire-brick manufacture and in other cases
where a high finishing temperature is required. They are not
usually economical in fuel, but are, if properly designed, less
wasteful than either up or down-draught kilns, though usually
they are built too short in proportion to their width. They may
be made of various sizes, but a capacity of 25,000 to 30,000 bricks
is most convenient. If very high temperatures are required it
may be necessary to add fuel through the holes specially con-
structed in the roof, but for most building bricks this is un-
necessary.

If a horizontal-draught kiln is constructed of a number of
chambers so connected together that the flue gases pass from
one chamber to the others in a straight line a semi-continuous
kiln is formed. If two semi-continuous kilns are placed side by
side and connected at each end by other chambers, the

KILNS 245

chimney being placed in the centre or to one side, a ring kiln or
continuous kiln is obtained.

It must be remembered, however, that, whilst any continuous
and semi-continuous kiln regarded as a whole is of the " hori-
zontal-draught " type, each portion or chamber in such a kiln
may be worked on the " down-draught " principle.

The Newcastle or single horizontal-draught kiln may, in fact,
be regarded as the forerunner of the modern continuous kiln.

Continuous Kilns have the great advantage of using but little
fuel (3 to 5 cwt., as compared with the 12 cwt., of up -draught
kilns for each 1000 bricks). Many continuous kilns are, how-
ever, spoiled by the lack of provision for keeping the fuel
away from the bricks, and many of these are in consequence
spoiled in the firing. Where proper fire-boxes are provided for
the combustion of the fuel, it is possible to obtain bricks equal
in every respect to the best produced in any single kiln and at
a far lower cost in fuel than is otherwise possible.

Brickmakers who have not studied the recent improvements
in continuous kilns have an impression that they can only be
used for common bricks. This is quite erroneous, as several
firms are now regularly producing some of the best facing bricks
in the country in continuous kilns.

Having described the main characteristics of the chief
patterns of kilns briefly, typical kilns of each class may now be
studied in greater detail.

Clamp Kilns are best considered in a class to themselves.
They are seldom employed except for temporary purposes and
for hand-made bricks, and a typical clamp has therefore been
described on p. 61.

The Up- Draught or Scotch kiln is of a simple yet effective type
and is typical of this class of kiln. It consists of four upright
walls forming a rectangular chamber, the two end walls being
sometimes replaced by temporary ones so as to facilitate the
filling and emptying the kiln. These openings are 36 in. wide
with a permanent wall at each side of the opening, but in practice
it is better to make the opening sufficiently wide to admit a
horse and cart, as the bricks can then be loaded direct from the
kiln into the vehicle. When the filling of the kiln is complete,
each of these openings is filled with a temporary brick wall
covered with " daub " or clay paste. The openings may reach
to the ground level or not, as is most convenient.

The floor is often sunk about 4 ft. below ground level, but this

246

MODERN BRICKMAKING

has the disadvantage that a cart cannot be taken into the
kiln.

Along each side of the kiln are fire -holes or openings about
16 in. wide and 2 ft. to 3 ft. high. These openings should be
lined with fire-bricks (which can be renewed when necessary) so
as to reduce their width to about 12 in. They may also with
advantage be arched with fire-bricks.

The whole structure isoisually about 26 ft. long by 16 ft. wide
and 12 ft. to 15 ft. high externally, the side walls being 18 in. to
40 in. thick and the end walls (with "wickets ") 36 in. thick, but
dimensions vary so in different places that no definite sizes can
be stated as being the standard.

The sides of the kiln may be the thickest at the bottom and

may taper (externally) to-
wards the top (fig. 168), as
it is in the lower portion
that the greatest strength
is needed to resist the ex-
pansion action of the heat.
Small chimneys may be
provided on the top, if
necessary, but it is usually
found that they are not

FIG. 168. — End of up-draught kiln (with
extra large wicket).

required. The top of the
kiln may be closed with
ashes, or a permanent arched roof may be employed.

Such a kiln is built of bricks set in clay paste. No ordinary
mortar must be employed, except, possibly, for pointing the
outside of the kiln, as the lime in it is detrimental to the hot
brickwork when the kiln is in use. The walls must, usually, be
supported by buttresses at the angles and, occasionally, at the
sides.

An up-draught kiln of improved type designed by George
Durant (fig. 169) burns 30,000 bricks at a time with an average
consumption of 8 cwt. of fuel per 1000 bricks.

The fire-holes are 19 in. across, and are separated by 20 in. of
brickwork and lined with 4| in. fire-brick linings. Doors and
bars can be fitted to the fire-holes if desired, but these are by no
means always necessary. Between each two fire-holes a smoke
vent 4| in. wide is built, and a short chimney to each vent allows
of the proper regulation of the draught in different parts of the
kiln.

KILNS

247

The foundation of the kiln should be perfectly water-tight, and
in cases of doubt or dampness a layer of concrete 10 to 18 in.
deep should be put down.

An important point in the construction of all kilns is the
jointing of the brickwork, as if this is carelessly done the amount
of loss through cold air leaking in and heat leaking out will be
enormous. If the bricks are carefully dipped in " daub " and
well malleted into position so as to secure a perfectly close joint,
a ' considerable waste of fuel will be prevented. Lime mortar
must not be used for jointing except at the outside facing, as it
cannot stand the action of the heat inside the kiln. When
carefully built and fired, no stays are necessary, though they can
be used if desired. It is a great advantage, both in enabling the

i ii 1 1 i i

FIG. 169.— Plan of up-draught kiln.

fires to burn more steadily and<in keeping the fuel dry, if a lean-
to roof is erected along each side of the kiln. Many users of up-
draught kilns omit this roof, though it is unwise for them to do
so as it soon pays for its cost in the saving in fuel it effects.

The setting of the bricks in such a kiln requires considerable
skill, as the courses must be crossed in such a manner as to
leave continuous openings throughout, in order that the heat
may be properly distributed. On this account flues about 8 in.
wide and 2 ft. to 3 ft. high are left in the lower parts of the kiln
connecting the fire holes in the side walls. One of the most
satisfactory methods of setting such a kiln is to arrange the
bricks in three straight lines, the centre one skintled, running
from side to side, and to fill the kiln completely up to the top.

A circular up-draught kiln is only used to a limited extent
(being preferably replaced by a down-draught kiln) ; there is no

248

MODERN BEICKMAKING

need to describe it in further detail.1 According to E. Dobson,
up-draught kilns of this pattern were largely used at one time
for the burning of Staffordshire blue bricks, consuming about
4 tons of coal for a kiln capacity of 8000 bricks

The Down-Draught kiln, whether circular or rectangular, is the
most efficient and satisfactory of all single kilns, yielding the
most perfect colour and the lowest fuel consumption of any
intermittent kiln.

For many years the most popular form of single down-draught
kilns has been circular in shape, but for ordinary bricks the
rectangular pattern has several obvious advantages and is re-
latively cheaper to construct.

Figs. 170 and 171 show a section and plan of a circular down-

FIG. 170. — Section of down-draught kiln.

draught kiln. For bricks, such a kiln has usually ten pr twelve
fire-holes around its circumference, and the hot gases from these
rise up through a series of pockets or " bags " towards the top
of the kiln, whence they are turned downwards, distributing
themselves through the bricks in the Mm and finally passing
through the central flue to the chimney. In most down-draught
kilns of this pattern the floor is solid with the exception of the
central flue, but in some cases a perforated false bottom is added
so that the gases may be better distributed amongst the goods
in the kiln. The chimney is usually external to the kiln, but may
be placed centrally inside it if desired. Instead of the bags
or pockets through which the fire-gases rise being separated from
each other, it is, in some cases, preferable to use a continuous
flash-wall or screen running completely round the inside of the

KILNS

249

kiln, so as to spread the gases more than is the case when bags
are used.

In any case, the hag, or screen-wall, must be perforated near
to the bottom so that some of the gases may penetrate at once
to the lower part of the kiln. If this is not done, and the walls
are solid throughout, the lower portion of the kiln will probably
be under-fired.

It is usual to connect several kilns to a single chimney, but,
if this is not practicable, each kiln may have its own shaft.
Occasionally, round kilns are connected to each other so as to
form semi-continuous kilns, but such an arrangement is seldom
quite satisfactory.

FIG. 171. — Plan of round down-draught kiln.

The walls of a circular down-draught kiln must be of con-
siderable thickness, and must, usually, be surrounded by iron
bands in order to prevent it being damaged by expansion.

The fire-boxes may be simple openings in the walls of the
kilns fitted with a grate about 14 in. wide, or they may, pre-
ferably, be in the form of a box or hopper as described in con-
nexion with a rectangular down-draught kiln. The box form
has the advantage of giving more regular heating with less fuel,
as it prevents much leakage of air through the fire-holes. The
grates may be flat or sloping, the latter being preferable, as they
expose a larger area of fuel and prevent air-leakage when the
fuel is partly burned.

'250 MODEKN BKICKMAKING

In the ordinary fire-box the most elementary requirements
for the efficient burning of the coal are to a large extent omitted,
with the result that much fuel is wasted and a large amount of
smoke produced.

Most kiln builders appear to forget that when fresh fuel is
fed on to a fire the amount of air needed whilst gas is being
produced is very large and that this air must, for the most part,
be introduced into the gas stream direct and must be shut off
when the production of gas has ceased. For this purpose an
air-flue which can be closed by a door or by bricks should be
constructed some inches above the furnace and should lead
directly into the kiln bag or screen-space. The fire-box must
be of such a shape that the coal will lie on the grate and will
form its own seal, preventing much heat escaping outside the
kiln. To secure this it is necessary to have the grate much
more sloping than is usual, so as to allow the1 fuel to lie at an
angle inside the furnace.

A similar principle is employed in the Gillet fire-box, but in
this case several parallel air openings are provided. A large
iron hopper is also placed on top of the square masonry.

The use of a grate is not necessary with some fuels, but it is
generally an advantage.

If the fire-boxes are made sufficiently deep (above 30 in.) a
species of gas-producer is formed which is very effective and
economical. When using smudgy coal the difficulty sometimes
experienced with so deep a fire-box can be overcome by blowing
steam and air into the fuel near the bottom. This is best ac-
complished by fitting a 2-in. iron or stoneware pipe into the front
of each fire-box, and allowing it to project about half-way inside
the latter. A steam jet $• in. diameter is then attached just
inside the outer end of this tube, so that the steam passing
through the tube carries a supply of air with it. As the steam
must usually be brought a considerable distance, much con-
densation occurs, so that some form of superheater is necessary.
This is easily obtained by fixing a U-shaped iron pipe 2 in.
diameter just above the gas exit of the fire-box, and connecting
the ends of this pipe to the boiler and steam jet respectively. If
the action of the heat on the iron U tube is excessive, a thin fire-
clay slab may be placed beneath it. A larger steam jet than
that mentioned is undesirable, and the superheater must not be
omitted if the best results are to be obtained.

In order to overcome the difficulty experienced in drying and

KILNS

251

warming the lower bricks in a down-draught kiln, and in prevent-
ing the deposition on them of condensation-products from the
upper bricks, E. Thomas has patented the use of a number of sup-
plementary fires placed between the ordinary fire-boxes and
connected to a different pattern of " bag " (fig. 172). These
•supplementary fires are used entirely for the heating of the
lower part of the kiln before, or simultaneously with, the heating
in the usual manner. For this purpose the " bags " are nearly
closed at the top as shown in fig. 173, but are open at the front, so
that the fire-gases are confined to the lower 3 ft. or so of the kiln.
By heating this portion first (instead of last as in the ordinary

FIG. 172. — Special screen (front view).

manner) the bricks contained in it are made better able to stand
the pressure of those above them. They are warmed and so
cannot be spoilt by condensation deposits, the draught of the
kiln is improved and the amount of fuel required is slightly
reduced. These supplementary fires are fitted with doors so that
the heat from them may be regulated, and it is found in practice
that they enable the bottom of the kiln to be finished as-soon as
the top.

The rectangular down-draught kiln shown in figs. 174 and 175
is easier to set than a circular one. It may have a single separ-
ate chimney, or two smaller chimneys, one at each end, or a
series of very small chimneys, one for each fire. The first men-
tioned is the best, though it may be more expensive if only

252

MODERN BRICKMAKING

one kiln is built, the only advantage claimed for the use of a

separate small chim-
ney to each fire being
that a separate con-
trol of the draught is
obtained. This may
be equally well ar-
ranged, when desired,
by inserting dampers
in the separate flues
leading to the main.
The walls should
not be less than 30
in. thick and should
be strengthened by
vertical steel joists
placed at intervals on
each side of the kiln,
and tied together by
1-in. rods to those on

FIG. 173.— Cross section through centre of fig. 172. the opposite side of
the kiln. In order to strengthen the kiln at the springing line of

FIG. 174. — Cross section of down-draught kiln (on line zz, fig. 175.) (Brown).

KILNS

253

the arch, horizontal steel joists should be placed around the kiln
at this level and kept in place by the vertical ones.

The kiln has an arched roof. The fuel is burned on inclined
grates fixed in fire-boxes down two sides of the kiln. These fire-
boxes are so made that a considerable quantity of fuel is con-
tained in them, the gases and volatile matter from the fuel being
drawn downwards and passing over the glowing fuel in a manner
impossible with a flat grate. This not only saves fuel but reduces
the amount of smoke. The inclination of the grates must be
adjusted to suit the fuel used, and experiments may be necessary

otta-c ^

FIG. 175. — Half-plan of down-draught kiln (Brown).

before the correct angle can be found, though it is usually about
60 degrees. The grate-bars should not reach quite to the wall
at the back, a space for pushing down the ashes being desirable.
The air necessary for the combustion of the fuel enters chiefly
through the grate, but an additional supply can be admitted
through an opening in the wall above the fire-box. The admission
of this additional supply of air is of great importance in aiding
the prevention of smoke, and by constructing a series of vertical
flues within the kiln-walls and parallel to the bag-walls a supply
of hot air can readily be obtained. By this means the production
of smoke is almost, if not entirely, prevented. This hot air is ad-
mitted to the bags at a point about 2 ft. above the level of the

254 MODERN BEICKMAKING

fuel at the bottom of the bag, the amount of air entering the kiln
being controlled by a simple damper.

The flame, fire-gases, and air rise through the bags and, after
deflection from the roof, distribute themselves amongst the bricks.
As it is essential that .this distribution of heat should be even,
the " bags " are sometimes replaced by a single wall or screen built
parallel to the sides of the kiln forming a space or trough, into
which the fire-gases are discharged. Cross- or tile-walls may be
used between the fires to bind this wall to the kiln. As will be
seen, the bags or screen-walls rise to the height of the spring
of the arch or even higher, but ample room must be left in the
top of the kiln for the effective combustion of the gases. A few
perforations should be left near the bottom of the bag- or screen-
walls in order to supply some heat to the lower part of the kiln
during the earlier stages of the firing. The supplementary fires
described in connexion with the circular down-draught kiln may
be used if desired.

The floor of this kiln is perforated so that the heat may be
well distributed, each series of perforations leading to a separate
flue. These flues are connected to a series of chimneys or to a
main flue running beneath the kiln floor to the chimney-stack.
If two chimneys are used (one at each end) the sub-floor flues
should be connected to each chimney alternately, so that all the
fires on one side of the kiln will lead to one chimney and those
on the opposite side to the other.

There are no fire-holes at the ends of this kiln, their place
being taken by "wickets" or " door-gaps," through which the
kiln is filled and emptied.

The size of the kiln may be varied to suit special uses, but
one capable of holding about 30,000 bricks, leaving ample space
between them and the arch, will be found to be most generally
useful. If built of ordinary bricks, with the exception of the
bag-walls and the lining of the fire-boxes — which should be of
fire-bricks, a kiln of this size will cost about £250, but if any
independent chimney-shaft is used the cost of this must be
added.

The bricks may be set "five on two," i.e. five headers on two-
stretchers, or in " blades " as preferred. In each case, care must
be taken to allow the gases in the kiln to have access to the per-
forations in the floor, and the first two or three courses of bricks
must be arranged accordingly. The bricks should not be set
much above the level of the bag-walls, and in no case within

KILNS 255

%

15 in. of the top of the kiln, as this space is necessary for com-
bustion and heat circulation.

Down-draught kilns should be built rather low — 16 ft. high
inside is too high for most purposes, and 10 ft. would be far
better.

The Newcastle kiln (fig. 176) is typical of horizontal-draught
kilns. Unlike the up-draught kiln previously described, it is
fired from the end instead of from the sides, with a consequent
saving in fuel. In most Newcastle kilns this firing is from one
end only, the chimney being placed at the other, but in kilns of
20 to 30 ft. or more it is usually necessary to. fire from both
ends.

It is customary in some districts, though not in Newcastle,
to fire through holes in the roof of kilns of this type, the fuel
being received and burned in special '•• pillars " constructed of

•Fio. 176. — Longitudinal section of " Newcastle " kiln.

the bricks to be fired. As this arrangement spoils a certain pro-
portion of bricks it is not to be recommended except in the case
of common goods.

The Newcastle kiln consists of a long rectangular chamber
with an arched roof. It is not usually more than 15 ft. wide in-
ternally and is often much narrower. One end of the kiln is
solid and has a chimney, or three flues leading to a chimney, at
the back of it ; the other has two permanent fireplaces, and a
wicket or door gap about 40 in. wide, in which, when the kiln is
filled, a third fireplace is constructed.

These fireplaces, as ordinarily built, each consist of an open-
ing about 2 ft. 6 in. by 1 ft. 4 in. reaching from the ground,
usually containing a grate, and another arched opening just
above, and of the same width, but only 14 in. high at the centre
of the arch, through which the fuel is fed. These openings
should be partially closed by means of iron sheets or fire-clay
slabs, though in practice they are left quite open in spite of the

256 MODERN BRICKMAKING

waste of fuel which is thus involved. To obtain the best results
they should only be sufficiently open to admit the proper quantity
of air.

A space at least 3 ft. wide at the bottom and 4 ft. at the top
should be left between the bricks to be burned and the inner face
of the end wall of the kiln. This space forms a combustion
chamber, and • when no grates are used for the fuel it forms an
ashpit and bed for the combustible. It is necessary to have this
space in order that the air- and fire-gases may be properly com-
mingled and the fuel thus be perfectly burned.

These gases travel along, chiefly in a horizontal direction, but
distribute themselves through the bricks, finally passing out
through three openings at the farther end of the kiln, to the
chimney. If the kiln is longer than 30 ft. it is desirable to have
exit openings in the side walls and floor of the kiln at intervals,
so that the gases may be taken out as required. This is especially
necessary during the earlier stages of firing, as if the gases be-
come too cool they will cause deposits (scum) to form on the
goods. Very large Newcastle kilns are, however, undesirable, as
smaller ones connected together to form a semi-continuous or
continuous kiln have many advantages and are equally econ-
omical in fuel.

For convenience, and to reduce the cost of building, New-
castle kilns are often erected in batteries of six kilns placed side
by side. When this is the case it will be found much more
economical and satisfactory to erect a semi-continuous kiln of
the same capacity.

The setting of the bricks is similar to that in a continuous
kiln.

Gas-Fired Single Kilns have been made the subject of many
patents, but few have proved really successful. Most patentees
have had an insufficient knowledge of the firing of kilns, and have
attempted the impossible by introducing the gas at the wrong
place, or have tried to keep it alight when supplied with cold air.

For the successful application of gas to intermittent kilns it
is necessary to have several kilns so placed that they discharge
their waste gases into one of two central regenerators or chambers
filled with bricks arranged in a chequer-work fashion. Whilst
the waste gases from a kiln are passing through one of these
regenerators the brickwork becomes heated, and when the
supply of gases is cut off by being diverted into the other re-
generator, air is drawn in the opposite direction through the first

KILNS

257

one ; thus the air becomes heated and is then in a suitable con-
dition for being supplied to the gas used for heating the kiln.
The change of air and waste gas currents through the regenerators
must be made at regular intervals of about thirty minutes, this
being effected by means of a simple reversing valve.

The gas is made in special producers, the construction of
which needs special skill. The gas-burners must also be of
special construction ; most of those who have endeavoured to
apply gas to brick burning in single kilns have failed to burn
the gas satisfactorily.

A typical arrangement for a single kiln fired by gas (fig. 177)
is designed by E. Schmatolla, and found to be specially suitable

FIG. 177. — Intermittent gas-fired kiln.

for use at temperatures higher than can be obtained by direct
firing with coal.

It consists chiefly in the connexion of the heating chamber
with two or more heat collectors, accumulators or regenerators ;
the furnace proper is arranged so that it may be started as a
direct fired grate, and afterwards changed gradually to gas firing,
and on this account it is built centrally to the whole structure,
the regenerators being placed at each side.

The gas generator (c), which is built in a similar way to a
grate furnace, but with a higher shaft, is arranged below the
burning chamber (a), and the two heat collectors or accumulators
reach approximately from the bottom end of the gas generator
to the upper end of the heating or burning chamber. The gas
generator is connected to the chamber at both sides by means

17

258 MODEEN BEICKMAKING

of conduits or flues (d, e,) between which are arranged dampers
(/), the latter making it possible to close the one or the other of
the flues (d). The two heat collectors (b) are connected to the
heating or burning chamber (a) by means of conduits (g) and
openings (h). The heat collectors, which are provided with a
grating of refractory bricks or other material, are connected at
the bottom end to conduits (61, 62, 63, 64), which can be brought
Into communication either with the chimney channel (65) or
with the outer air by means of a device consisting of a box (k).
Assuming that the damper (/) on the left-hand side is closed,
the corresponding damper •(/) on the right-hand side being open,
and the box standing as shown in the drawings ; the conduit
(64) on the right-hand side is in connexion with the outer air,
and the conduit (64) on the left-hand side is connected with the
chimney ; and assuming further that the generator is filled with
coal, and that the whole furnace is already incandescent, the
generator gas will then pass through the right-hand conduit
system (d, e) into the heating chamber (a), and the air through
the right-hand conduit system (64, 63, 62, 61), the grating of the
right-hand collector and the conduits (g, h) also into the heating
chamber (a). Gas and air become mixed at the right-hand end
of the chamber, burn in the interior of the chamber (a), and pass
at the other end through the conduits (h, g) and the heat col-
lectors (6), as well as the conduits (61, 62, 63, 64) on the left
hand, into the chimney. The combustion gases escaping from
the chamber give off the greatest portion of their heat to the
grating of the heat collector arranged on the left-hand side.
When the latter is so highly heated that the combustion gases
begin to escape through the flues (61, 62, 63, 64) at a higher tem-
perature, the box (k) is drawn to the right side, so that the left
channel (64) is open and the right channels (61, 62, 63, 64) are
connected to the chimney. If, then, the right-hand damper (/)
is closed and the left-hand one is opened, the gas will pass through
the left-hand side flues (e) and (g) into the chamber, and the air
will pass through the left-hand side flues (64, 63, 62, 61), the
grating of the left-hand side heat collector, and the right-hand
side flues (g, h) into the chamber. The direction of the flame
will be reversed, and it will pass on the other side through the
flues (g, h) to the heat collector, and after having given off to the
latter the greatest portion of its heat through the right-hand
flues (61, 62, 63), into the chimney. The air is, of course, highly
heated by the previously highly heated left-side accumulator,

KILNS

259

and passes into the chamber with a very high temperature. The
producer gas will also pass into the heating chamber at a very
high temperature, since it has to traverse only a short conduit,
and thus it is possible to increase the temperature in the
chamber to a much higher degree than is possible in the furnaces
generally used — for instance, for burning or heating highly re-
fractory materials. As the direction of the flames can be altered
at given intervals of time, the temperature in the chamber can
be raised as much as desired up to the limit of the dissociation
temperature of carbonic oxide — that is to say, up to 2000° C.

FIG. 178. — Kegenerator and furnace.

An adaptation of this regenerator to a furnace is shown in
fig. 178. In this, the heat accumulators (6) are placed at the side
of the producer (c) as before, but the gas flues (d,-e) are arranged
at each side in the middle of the accumulators (6), separated
from them by thin walls (w), whereby the accumulators are
divided at the top into two branches, which are also filled with
brickwork for accumulating heat and communicating at their
upper end with the combustion chambers (a). In this arrange-
ment the dampers (/) for regulating and reversing the gas and air
are arranged at the level of the heating chamber inlets, and are
controlled from the sides of the furnace instead of from the front.
By means of this arrangement it is possible to look through the

'260 MODEEN BBICKMAKING-

flues direct into the gas producer, and consequently the cleaning
of. the gas flues is quite easy. In this way it is possible to cool
the bottom of the hearth from a water tank (t), a great advantage
when the furnace is used for melting purposes, -or where a fusible
slag is produced. This drawing also shows a design when the
flues (63) leading to a separate reversing box (k), as in fig. 177, are
used as a part of the accumulator by filling them also with brick-
work ; in this they can be covered with plates (p). By this system
the whole of the heat in the waste gases may be recovered, and
experience has shown thatf, whilst the heating chamber is at a
white heat (1700° C.), it is easy to keep one's hand on the revers-
ing valve (k), (fig. 177).

The Mond Gas Producer has also been applied to the firing of
kilns, but as the essential feature of this plant is the recovery of
by-products from the fuel, it can only be used where a very large
number of kilns are employed at a time. In such cases it is
easier and better to use a continuous kiln — either coal or gas-
fired — for burning bricks.

A system of what may be termed " half-gas " firing has been
successfully applied to kilns by A. Woolley and others. This
consists in removing the grates from the ordinary fire-boxes of
the kilns, providing an air-tight door, and blowing in air and
superheated steam below the fuel. A crude gas is produced with-
out any appreciable alteration of the furnaces, and regular heat-
ing is greatly facilitated with a reduction in the amount of fuel
consumed, and a great saving in the labour of firing and of cleaning
out the fire-boxes.

Semi- Continuous Kilns are those in which the unused heat from
one chamber is used in others, the transference being continued
until the end of the series is reached. Semi-continuous kilns are,
therefore, more economical in fuel consumption than are single
kilns, and yet, if rightly constructed, they give equally good
results. Unfortunately, most designers of semi-continuous kilns
have been unduly influenced by their knowledge of the New-
castle (single) kiln and the Hoffmann (continuous) kilns, and have
overlooked the advantages of the down-draught kiln when con-
nected to form a semi-continuous series. On this account many
semi-continuous kilns do not produce bricks of good colour, but
the fault lies less with the underlying principle of semi-continu-
ous action than with its limited applications.

The general structure of a semi-continuous kiln is shown in
fig. 179, though the use of only four chambers would not secure

KILNS 261

a great reduction in the amount of fuel used, and at least six
chambers should be connected. The kiln shown is practically a
Newcastle kiln with fires at one end, to which have been added
three other chambers for which no fire-grates have been provided,
though feed-holes for the fuel are placed in the roof.

Chambers 1 and 2 having been filled with bricks the fires are
lighted and the heat not required in No. 1 is taken through the
five short connecting flues direct to chamber 2. Passing through
this, it escapes to the chimney through underground flues situated
at each side of the kiln. As soon as the succeeding chambers
(3 and 4) are filled, the gases are passed through them before being
admitted to the flue, and, in this way, almost the whole of the
heat in the gases is used. As soon as the bricks in chamber 1
are finished, the firing in the fireplaces is stopped, and the fuel
supplied as required through the roofs of the different chambers.

FIG. 179. — Plan of semi-continuous kiln.

It will easily be seen that whilst the heat from No. 3 chamber is
fully used in heating bricks in other parts of the kiln, much of
the heat from No. 3 and all from No. 4 must pass into the
chimney and be lost, so that the saving in fuel depends very
largely on the number of chambers (i.e. on the length) of the
semi-continuous kiln.

If such a kiln be constructed with fourteen or more chambers,
and these, instead of being in a straight line, are in the form of
a circle or ellipse, the fireplace necessary in the semi-continuous
kiln is no longer needed, and a continuous kiln, in which the
waste above mentioned does not occur, is produced.

Another serious objection to the semi-continuous kiln just
described (where the colour of the goods is of importance) is the
damage done to some of the bricks by feeding the fuel amongst
them through openings in the roof. This may be overcome by
the use of grates or fireplaces in each chamber, whereby the fuel

262

MODEKN BEICKMAKING

is prevented from coming into contact with the goods, and bricks
of an excellent colour may then be produced.

Occasionally, two semi-continuous kilns are built side by side,
one being burned whilst the other is drawn or set. This simplifies

FIG. 180. — Section of semi-continuous kiln.

the construction somewhat, but is awkward in use compared with
the semi-continuous down-draught kiln with one gallery shown
in fig. 180, and is not so economical as a continuous one.

FIG. 181. — Part-plan of semi-continuous kiln.

The Semi- Continuous Down-Draught Kiln shown in figs. 180 and
181 is due to A. E. Brown, but similar principles are used by
other designers of kilns of this style, and many of the better con-

KILNS 263

tinuous kilns can be made into excellent semi-continuous ones by
building a few chambers instead of the whole kiln.

Each chamber in such a kiln can be used independently of
the rest — an important advantage when the supply of green
bricks is short or when the output of the works is reduced.

As shown in fig. 180 a number of chambers (usually six) are
connected with each other by means of a row of openings in the
floor next to the partition walls, so that the fire-gases pass through
these openings to the next chamber. The furnaces, in this case,
are arranged in each corner of each chamber, and direct communi-
cation with the chimney can be made through a damper-con-
trolled flue in each chamber. The chambers may conveniently
hold 7,000 to 15,000 bricks each, and if only six are erected the
whole set should be filled, burned off, and cooled before being
drawn and reset, though with careful working it is possible to set
some chambers at the same time as the others are being fired.

When starting the firing the damper (d) and the flue (D) is
opened and the fire-gases pass through the perforations to the
chimney through the main flue (L). By keeping this damper
open, any chamber can be worked independently, but on closing
it the fire-gases pass into the next chamber through the perfora-
tions and under the partition walls, rising through the openings
in the next chamber up what is practically a "bag". The
chimney damper of this second chamber may be opened, or if
closed that of a later chamber must be opened. When the
firing of a chamber is finished, the fires are allowed to die out,
the openings for admitting fuel are closed, and the finished
chamber only used for the supply of such hot air as may be
needed. Such a kiln with a suitable chimney would cost about
£500 for a chamber capacity of 7,500 bricks and a weekly output
of 15,000, but the saving of fuel on this output would repay
the extra cost of the kiln over single ones within five years.

Continuous Kilns have increased-steadily in popularity during
recent years, and though still misunderstood and mismanaged
by many brickmakers, the prejudice which existed against them
at one time is slowly dying out.

In this country few brickmakers would attempt to use a
continuous kiln for an output of less than 1,000,000 bricks
yearly, though in Germany many small kilns of this type are in
use.

For an annual output of 1,000,000 or more bricks some form
of continuous kiln is very desirable, the precise construction

264 MODERN BRICKMAKING

depending upon the class of bricks to be produced. The first
successful continuous kiln was invented by Frederick Hoffmann
in 1859, and though many improvements have been made since
that day, the general principle he employed is still used, and
many modern kilns are termed "Hoffmann," although they
differ widely from the original one of that name.

For common bricks the original type of Hoffmann kiln is
quite satisfactory, but as it seldom yields as much as two-thirds
of its contents of facing bricks the proportion of those of second
and third-quality is very large. This type of kiln is characterized
by a remarkably low fuel consumption — averaging 3^ cwt. per
1000 bricks as compared with 10 to 12 cwt. for single kilns —
but the first cost is necessarily great, though not so high in pro-
portion as many brickmakers are apt to suppose.

Although many patent continuous kilns are on the market,
it will be sufficient if seven main features are described and
compared, the characteristics of certain other well-known kilns
being mentioned according to the class in which they occur. The
chief features of modern continuous kilns are : —

1. The general principle of continuous action, typified in the
simple Hoffmann kiln. In this the fuel is fed through the roof
and burned amongst the bricks to be fired.

2. The use of grates or troughs for the fuel.

3. The use of flues for supplying the freshly-set bricks with
warm air, in order to dry them and to prevent the deposition of
moisture on them — as in most modern continuous kilns.

4. The use of the down-draught principle — usually in con-
nexion with grates or troughs for the fuel (see 2) — and permanent
partitions so as to divide the kiln into a number of separate
chambers.

5. The means used for removal of steam.

6. The use of gas in place of solid fuel.

7. The use of mechanical (fan) or natural (chimney) draught.
The simple Hoffmann kiln was originally circular in shape,

but it is now frequently made with two straight portions con-
nected together by two semicircular ones so as to form an ellipse
with flattened sides. This later pattern is more convenient in
shape than the circular one. The general construction and
method of working of this, the simplest and oldest type of con-
tinuous kiln, is shown in figs. 182 and 183, from which it will be
seen to consist of a circular tunnel with twelve door-gaps in its
outer circumference and twelve flues in its inner one. The

KILNS

265

door-gaps give access to the interior of the kiln and are closed
with brickwork when those portions of the kiln in which they
occur are being fired ; the flues lead to a central annular flue
connected directly to the chimney, the connexion between the
twelve flues and the annular one being controlled by dampers.

The outer walls of the kiln must be at least 3 ft. thick,
and must be set in buttress form so as to resist the great effect
of the heat upon them. The masonry in the centre of the kiln
is composed of brickwork filled in with rubble or broken bricks,
well stamped down so as to yield a solid mass. The fuel is
supplied through holes in the roof of the tunnel.

The size of the kiln may be varied to suit different conditions,
but it should have at least 14 " chambers " each at least 12 ft.

FIG. 182.— Vertical section of Hoff-
mann kiln.

FIG. 183.— Plan of Hoffmann kiln.

in length or an average tunnel length of 168 ft. It is found that
better results are obtained with an average tunnel length of
about 225 ft., and this the author considers a desirable minimum
for the manufacture of first-class bricks. The earlier kilns, with
only twelve chambers, were too short for obtaining the best
results, and in the best modern continuous kilns sixteen chambers
are considered to be essential.

In considering a Hoffmann kiln it must be remembered that
110 partitions exist to separate the kiln into a definite number of
chambers. The term " chamber " is, however, so convenient
that its use in this connexion is universal.

The whole of the chambers, with the exception of two, having
been filled with bricks which are being heated, the working of
a simple Hoffmann kiln is as follows : " chamber " 1 is empty,

266 MODEEN BRICKMAKING

12 is being filled, and a current of air entering through the
doorway of No. 12 through No. 1 on, gradually becoming hotter
in its journey, thus helping to burn any fuel with which it may
come into contact. No. 11 chamber is the one last filled, and
consequently contains the coolest of the unfired bricks, the
hottest bricks being in Nos. 4 or 5 ; the intermediate chambers
being at varying but progressively increasing temperature.

The air passing contra clockwise round the kiln is, during its-
journey through the hottest chambers, highly charged with flue-
gases, and the mixture so formed is purposely taken through as
many chambers as possible so as to expend most of its heat in
warming the goods. Finally, at a temperature of 150° C., and
nearly saturated with moisture, it passes into the chimney and
is lost. Meanwhile, the bricks in the various chambers are
increasing in temperature as the result of the hot air and gases,
and the fuel fed through the roof of the hotter chambers ; and
when those in (say) No. 4 are sufficiently heated, no further fuel
is supplied to them. This chamber will then begin to cool,
because of the current of air drawn through it as already de-
scribed, and another chamber (say) No. 9, which has hitherto
been heated by the hot gases alone, will be sufficiently hot to be
fed with fuel through the roof.

In such a kiln, therefore, No. 1 chamber will be empty, Nos.
2 and 3 will be cooling, No. 4 will be at full fire and nearly
finished, Nos. 5 to 8 will be under fire and hot, Nos. 9 to 11 will
be being warmed by the "waste gases" from the previous
chambers and No. 12 will be being filled. The partition shown
between Nos. 11 and 12 will be placed between Nos. 12 and 1 as
soon as No. 12 is filled, or as soon as possible after No. 4 is finished
firing.

With some clays the gases become so charged with moisture
that the foregoing procedure must be modified, and the freshly
set goods warmed by special fires in the door-gaps or wickets.
It is to avoid this that hot-air flues (see later) are used.

In the Hoffmann kiln as originally designed, the fuel, fed
through the roof, falls into hollow pillars formed by the bricks
to be burned on account of the special manner in which they
are " set " in the kilns. The ash from this fuel discolours these
bricks and renders them unsightly, but the saving in fuel effected
by the kiln was for a long time considered to outweigh this dis-
advantage. In recent years, however, the demand for a better-
coloured brick than can be produced by the original Hoffmann

KILNS 267

kiln has increased so much that few modern brickmakers would
now erect one of these simple kilns, but would include several
improvements such as those described later. The fact still re-
mains true, however, that the original Hoffmann is the most
economical in fuel of any continuous kiln on the market, none
of the " improved " kilns being able to work with less than 3 cwt.
per 1000 bricks using a clay or shale free from any combustible
matter.

In judging the fuel- consumption of a kiln it is necessary to
ensure that there is no combustible matter in the clay as,»other-
wise, any comparison is useless. For example, the Fletton-shale
contains so much oil as to render only a trifling proportion of
fuel necessary, and a kiln which will burn this satisfactorily with
only \ cwt. of coal per 1000 bricks may need 5 cwt. for a South
Country clay or for a Midland marl.

Where the colour and appearance of the bricks are unim-
portant the simple original Hoffmann principle (fig. 182) is still
the best. ii;

Hoffmann Kilns with Grates or Troughs for the fuel, mark a
distinct step forward in the production of facing bricks in a con-
tinuous kiln, as by keeping the fuel out of all contact with the
goods they eliminate one of the chief causes of discoloration.

In the original " Belgian " kiln the grates are placed trans-
versely— one in each chamber — the fuel being fed through holes
in the roof or through a door at one end of the grate. With this
exception the Belgian kiln is almost identical with the original
Hoffmann one, though it is usually built of an oblong shape
instead of being circular in form, and the chimney is at one side
instead of being placed centrally. Like most modern continuous
kilns the " Belgian " has a large number of chambers, frequently
twenty-two.

In several other kilns this arrangement of grates is employed,
and it has now become a recognized feature of continuous kilns
for facing bricks. These grates may be of metal or of fire-clay,
the former being generally preferable, being stronger.

In kilns designed by Guthrie and by Brown the grate is re-
placed by a trough or gutter in which the fuel is burned. The
hearth patented by A. E. Brown is shown at / in fig. 184 and is-
sloping, the air being admitted to the side instead of below the
fuel. This hearth is placed below the floor level and is found,
in practice, to give results quite equal to the ordinary grate bars
and to be somewhat easier to clean, as but little clinker adheres

268

MODEEN BRICKMAKING

to the air inlet. Flat grates are, however, quite satisfactory with
proper care.

In the arrangement devised by Guthrie the trough has a level
bottom, is somewhat deeper, and has no grate.

The openings through which fuel is fed to the fire-boxes must
be capable of being closed to prevent the use of cold air, but a
sufficient supply of air must be admitted to enable the fuel to
burn properly and to prevent the grate bars (if of metal) from
being melted. The means by which this air is admitted will be
described later.

The advantages of grates, or troughs, running the whole width
of each chamber are so numerous that they may be considered

FIG. 184. — Section of one chamber in Brown's kiln.

an essential feature of all modern continuous kilns, and the
question now facing brickmakers is not whether a grate or trough
is necessary, but whether one is sufficient for each chamber.
For most purposes a single grate or trough for each 15 ft. of tunnel
is amply sufficient, but where unusually high temperatures — as
in fire-brick and blue-brick manufacture — are required, it is de-
sirable to employ two grates or troughs to each chamber. This
arrangement has been patented by Barnett & Hadlington.

Hot Air Flues are essential in the production of well
coloured bricks in continuous kilns, and the chief variations in
modern kilns of this type are due to the different means used to
supply heated air.

Hot air is used for two purposes in the best continuous kilns,
viz. : (1) for facilitating the combustion of the fuel on the grate

KILNS '269

or in troughs or bags, as a better result is obtained when the
fuel is supplied with hot instead of with cold air ; and (2) for
drying and warming newly set goods. In some of the older types
of continuous kilns hot* air is exclusively used for the former pur-
pose.

It has already been stated that if the fire-gases be taken
through too many chambers in succession they will become cool,
and being heavily charged with moisture and other combustible
impurities, will deposit some of these on the goods over which
they pass. For this reason, as soon as the fire-gases in a con-
tinuous kiln reach a temperature of 150° C. they should be taken
direct to the main flue and chimney. The amount of heat then
left in them is very small, and its loss is unimportant compared
with the damage which can be done by the impurities in these
gases. If desired, the fire-gases may be used in a dryer, but they
must be kept enclosed in flues, or pipes, and not allowed to come
into contact with the goods or they will produce scum.

As it is, in practice, inadvisable to use the fire-gases of a con-
tinuous kiln in heating the freshly set bricks up to 120° C.,
some other source of heat must be used. At present three such
sources are available :

(a) Wicket fires may be built or stoves may be placed in the
door-gap of each chamber or connected to the feed-holes in the
roof. In this way the heat from a separate fire is used to warm
a large quantity of air. The disadvantage of this arrangement
is that the products of combustion of the fuel mix with the air
and sometimes discolour the goods.

(b) Air may be drawn over the goods which have finished
firing and which are cooling in the kiln. This air is heated
without any contact with fuel and is, therefore, free from the
disadvantages just mentioned in (a). The amount of heat avail-
able is, however, limited by the rate at which the goods can be
cooled and by the finishing temperature of the kiln. So far as-
it can be used this is the best source of hot air, but it seldom
yields sufficient unless supplemented by heat from other sources.

(c) Air may be drawn through special flues above the arch of
the kiln or below the floor, its temperature being regulated by
the speed at which the air travels and the number of flues used
for this purpose. Heat withdrawn in this way from the kiln
must, in part at least, be replaced by the combustion of a relative
amount of additional fuel, but the arrangement is so convenient,
and the effect of the air on the brickwork by preventing some of

270

MODEKN BEICKMAKING

the loss by radiation which would otherwise take place is so good,
that it may be considered as the second best source of heat and
the best means of supplementing the hot air supplied by the
chambers containing cooling goods. Air drawn through special
flues is, if the flues are in good condition, quite free from objec-
tionable impurities.

The use of wicket fires or stoves needs little description, as it
is familiar to most brickmakers. After a chamber has been
filled with bricks the door-gap is built up, plastered with daub,
and allowed to dry. If a wicket-fire is to be used, two openings
must be left in the door-gap, one to feed in the fuel for the fire
and another to admit air to allow the fuel to burn. Some burners

FIG. 185. — Section showing wicket-fire.

prefer to construct a small fire-box by using a grate on which to
rest the fuel, but the more usual practice is to allow the fuel to
burn on the ground (fig. 185).

A couple of shovelfuls of glowing fuel is now placed behind
the door-gaps and the appropriate damper opened so as to connect
the chamber directly with the chimney, the sides of the chamber
having been, meanwhile, provided with iron dampers, or with
paper pasted on to the bricks or over the openings in the walls
between each chamber. The chamber is thus isolated from the
rest of the kiln and is operated quite independently. The tem-
perature inside it is slowly raised by the addition of more fuel
from time to time, until the bricks are thoroughly dry and of a
temperature of at least 120° C. The side dampers are then re-
moved, the door-gap openings filled in, the damper in the next

KILNS

271

FIG. 186.— Portable stove.

chamber which took the fire-gases to the chimney is closed, and
the newly dried bricks are thus placed in circuit with the rest of
the kiln.

In some cases it is easier to have a portable stove to hold the
fuel and to fit the exit pipe of this to the door-gap of the chamber
to be dried, or to one of the feed-holes in the roof. Opinions
differ considerably as
to which is the best
arrangement, and the
author has made a
considerable number
of tests to solve the
problem. He has found
that if the bricks are
very damp it is better
to use a stove supply-
ing heat near the floor
of the kiln and to open
several feed-holes in
the roof so as to allow
the steam and gases to escape in an upward direction. If, on
the contrary, the goods are not particularly damp they can be
dried more evenly and rapidly by using
several stoves supplying air through the
feed-holes in the arch of the kiln in a
downward direction.

A convenient stove for use on the
ground level is shown in fig. 186. It
consists of a grate enclosed in an iron
chamber and in many respects resembles
a slab-heater (p. 163) but is smaller and
portable.

A stove (fig. 187) for placing in the
feed-holes of a continuous kiln consists
of a cylinder about 12 to 18 in. high,
its lower diameter being slightly less
than that of the feed-hole. The fuel is
placed on the grate and the heated air
passes down into the chamber beneath. FIG. 187.— Stove for top
Several such stoves should be used at a of klln>

time, their number and position depending on the rapidity with
which the bricks can be heated (fig. 188).

272 MODEEN BBICKMAKING

Cooling chambers are usually made to supply hot air by
either temporary or permanent flues. As the air entering these
chambers becomes heated it rises, and such flues are, therefore,
usually placed near the top of the kiln. For temporary flues this
is the best position, but permanent ones should be built as low as-

FIG. 188 — Top stoves in use.

possible in order to counteract the tendency to leakage caused
by the greater movements of the upper parts of the kiln.

Temporary Flues are usually made of sheet metal with an
elbow at each end. They are employed to connect the feed-holes
of one of the cooling chambers with those of one newly filled, but

FIG. 189. — Temporary flue in use.

as these chambers may be a considerable distance apart it is
advantageous to construct a permanent flue the whole length of
the kiln, and to connect this by means of two separate temporary
pipes to the cooling and warming chambers respectively. It is
then possible to avoid the elbows on the connecting pipe and to
make it as shown in fig. 189.

Some burners prefer to cover four feed-holes, and for this pur-

KILNS 273

pose provide a square, bottomless box at one or both ends of the
connecting tube.

The chief objection to temporary metal flues is the serious
reduction of the temperature of the gases passing through them
owing to the loss of heat by radiation. A minor difficulty is the
tendency of the warm air to remain in the top of the kiln, instead
of distributing itself evenly as it does when introduced near the
bottom of the chamber.

Permanent Flues are constructed of brickwork and are an in-
tegral part of the kiln. The loss of heat by radiation is much less
than with metal pipes, but the chance of leakage is much greater,
particularly if the flues are in the upper part of the kiln where
the movement due to expansion and contraction is greatest.

One of the earliest arrangements of permanent flues for the
supply of hot air is that devised by Dannenberg, and shown
diagrammatically in fig. 190 in which A represents the cooling

FIG. 190. — Dannenberg's kiln.

chamber and B the one to be heated. Air enters chamber A
through any suitable opening and becoming heated it rises, passes
through a series of openings in the roof, and through a transverse
flue to the main hot-air duct (c). It passes along this till it
reaches a point near to chamber B, where it enters another trans-
verse duct and is drawn down through openings in the roof of
the chamber, passing out through the floor and the main flue D
to the chimney. It is convenient to use the feed-holes as open-
ings in the roof of the chambers, but care must be taken that no
coal enters the cross flues.

Owing to the tendency of hot air to distribute itself badly
through a chamber to be heated in this way, better results will
be obtained by the addition of a down-take flue connecting the
main hot-air duct with the bottom of the kiln. The arrangement
in fig. 191 shows this down-take flue.

A better means of supplying hot air is that used in the
<£ Vaughan" kiln (fig. 192) in which a flue is constructed immedi-

18

274

MODEEN BRICKMAKING

ately over the arch into which the air heated by its contact with
the bricks in chamber A rises and passes to the centrally situated
flue running the whole length of the kiln.

The hot air next passes through the down -take (also centrally
situated) and under the floor of the chamber B, through the
perforations in which it rises, and after drying and warming the

FIG. 191. — Spitta's hot-air flues.

bricks is taken to the main flue. The temperature of the air
entering chamber B can be regulated by the amount allowed to
pass down the down-take, and by admitting cold air through the
external " cold-air valve," placed at the left of the chamber.
This is very valuable when heating delicate clays. Hot air can
be used for aiding combustion by supplying it to the fuel on the
grates, as well as for warming newly set goods.

FIG. 192.— Vaughan's kiln.

A similar arrangement, but using arched flues instead of a
flat one, is used in the " Manchester " and " Staffordshire " kilns
(fig. 193), but in these the hot air is collected through more
openings and conveyed to a much larger central hot-air flue,
which is situated in much the same place as that occupied by
the "smoke flue" in fig. 192, about 6 ft. 6 in. above the floor

KILNS

275

level. This flue is so placed that it is unlikely to be disturbed
by the movement of the kiln during heating and cooling, and
consequently it is not liable to leak. In both these kilns the
hot air is taken by a flue leading from the bottom of the hot air
flue (damper controlled) down the centre wall, and admitted
through an opening in line with the grate at the end of the
chamber, either over or under the bars. This, alone, is used for

FIG. 193. — Flue arrangement in "Manchester" and " Staffordshire" kilns,
starting the fires, and afterwards the hot air from this flue, sup-
plemented by air of atmospheric temperature, may be used for
combustion purposes. The hot air is also admitted through
openings in the top of the chamber, at points where, in practice,
the vapour has shown any tendency to linger, and thus secures
thorough circulation in every part of the chambers for drying.
The moist gases formed during the stoving, and the combustion

FIG. 194.—" English " kiln.

gases afterwards, are carried through (1) a damper-controlled
flue leading from an opening in the outer wall of the chamber,
and thence under the floor to the central large smoke flue, and
(2) through openings into a flue running right across the centre
of the chamber, with separate connexions to the main smoke flue.
Slight modifications of the foregoing arrangements of flues are
used by several other firms ; a particularly ingenious system being
employed in the " English " kiln used by the London Brick Co.
at Fletton (fig. 194). In this, two hot-air flues run along the top

276 MODEEN BKICKMAKING

of the kiln, each being provided with a down-take to each chamber
and an opening into the top of the chamber. These openings
are controlled by flat valves, and the whole construction is such
that no special valves are needed for the hot air as distinct from
the steam- exit flues. This kiln is, however, designed for burning
only common bricks.

Instead of heating the air in the upper part of the kiln it is
taken from below the floor in Brown's patent kiln, special flues
(as a in fig. 184) being arranged for this purpose, so that the
heated air may be used to supplement that from the cooling
chambers in drying or warming the bricks, or it may be used to
facilitate the combustion of the fuel on the grate.

Chamber Kilns. — The down-draught principle has been applied
to continuous kilns by several patentees, with a view to obtain-
ing a better colour on the goods than is possible' with the original
Hoffmann kiln. Broadly speaking, all continuous kilns employ
grates for the fuel work on the down-draught principle, though
it is only in special instances that a bag- or flash-wall is
erected between the grate and the goods to be heated. It is
also more convenient for ordinary red bricks to remove the
gases from the side rather than from below the sole of the kiln ;
but these variations are only slight, and a careful study of the
directions in which the heat travels in a modern continuous kiln
will soon show the preponderance of an up- and down-draught,
or as it is usually termed a " down-draught ". This is particu-
larly the case in continuous kilns fired by gas.

The advantages of the down-draught principle in single kilns
have already been mentioned ; the most important are evenness
of heating, excellence of colour of the goods, and economy in fuel
consumption. When applied to a continuous kiln this last ad-
vantage is enormously increased whilst the others are retained,
and for this reason continuous kilns in which this principle is
largely used will be found to be best for facing bricks, tiles,
terra-cotta, and other work where colour is of importance and
the output required is large.

In order that the down-draught principle may be effectually
applied it is necessary to divide the tunnel of the kiln into a
number of chambers by means of partitions permanently erected
in the kilns — whence the name " chamber " kilns. Various
forms of partitions have been patented (especially on the Contin-
ent) but they may all be classed under one of the following
heads : —

KILNS 277

(a) Solid walls with no openings.

(b) Walls with openings uncontrolled by dampers.

(c) Walls with openings controlled by iron, fire-brick, or paper
dampers.

Solid partition walls having no openings in them to the next
chamber, are claimed to have been first introduced by several
different persons, and the true originator is unknown. In most
cases the connexion between the chambers is made by flues
under the walls — a method which is open to the objection of
great friction in the passage of the gases, as it is difficult to
construct such flues of a sufficient size without enormously
increasing the cost of the kiln. This method of separating the
chambers is not much used in England, but on the Continent it
has met with considerable favour. British brickmakers prefer
to use small underground flues for the supply of hot air, and to
leave openings in the partition walls which can be closed by
dampers when required.

Iron dampers are easy to place in position when new, but are
apt to warp and become troublesome after some time, so that
paper dampers are often preferred for partition work.

Fire-clay dampers are excellent, if properly designed, but are
heavy to handle. Some good types have been used in kilns
working as high as cone 17. A satisfactory damper may be made
of slabs 12 in. high and 2 in. thick, the iron bolts holding
them being placed in the centre and so fully protected from the
heat.

Paper dampers consist of sheets of suitable paper pasted
over the openings with a little clay slip to which some dextrin
has been added, and in addition to being very cheap and easy
to fix, they have the advantage of removing themselves auto-
matically when the kiln is sufficiently hot to burn them.

The paper used should be sufficiently thin to be cheap, but
must be as free as possible from pin-holes. A light grade of
brown paper is usually best, being stronger than newspaper and,
if carefully selected, less porous. It can usually be obtained in
rolls of a convenient size weighing 1 cwt., and measuring 40 to 75
in. wide.

Toughness and resistance to water are necessary, as other-
wise the paper would tear readily and the damper might break
at a critical moment if sodden with condensed moisture from
the bricks. When the openings to be covered are too large for
a single piece of paper, the pieces used should overlap by 2 in.,

278 MODEEN BKICKMAKING

the joints being well fastened with flour-paste, as leaky joints are
a frequent source of trouble.

Further details as to the use of these dampers are described
in the section on " Setting ".

The use of permanent partition walls greatly improves the
quality of the bricks produced, and enables the chambers to be
worked more or less independently when the supply of bricks is
irregular, but kilns in which such walls are employed cannot be
so economical in fuel as the original Hoffmann kiln, as the heat
spent in raising the temperature of these walls is entirely wasted.
Many attempts have been made to substitute portions of the
walling* by various other materials with greater or less success.
The most satisfactory method is to leave considerable spaces in
the walls, and cover these by dampers, which can be destroyed
or removed when it is no longer necessary to shut off a chamber
from the rest, as when its contents have attained a temperature

FIG. 195. — Beyer's double paper-damper.

exceeding 120° C. When very wet bricks are to be dried in the
kiln, two paper-dampers may be used with an air-space be-
tween them, as suggested by F. Beyer, and working as follows : —

Instead of setting the new bricks close to the paper-damper,
as at present, two blades of bricks are omitted, leaving a space
of about 2 ft. (fig. 195) which is only filled when the smoking of
the chamber is complete. When the chamber is filled, paper-
dampers are fixed to each end of the blades of bricks, and as
there is a space of 2 ft. between these dampers there is ample
room for the burner to step in and examine them as to their
tightness during the smoking, and to repair them if necessary.

As a current of air plays on one side of the paper, this resists
the action of the heat and the moisture much better than the
ordinary form of paper-damper, which is equally heated on both
sides, and prevents it collapsing before the proper time.

When the chamber is completely. smoked and.ready to>beput
into the direct round of the kiln, the space between the dampers

KILNS 279

is filled with bricks which have been previously dried, or it may
even be left empty, if preferred, without in any way interfering
with the working of the kiln, providing the outer wall is bricked
up. The accompanying diagram (fig. 195) shows the position
of the papers, as well as the portions of the kiln filled up with
dry bricks, and included in the -regular run of the firing.

Steam is produced in large quantities in most kilns, as it is
seldom that all the water is dried out of the bricks. This is
particularly the case with bricks made by the stiff-plastic pro-
cess and set direct into the kiln ; many of these will lose one-
seventh of their weight on burning, and the greater part of this
loss will occur below a red heat. For this reason the removal
of steam is an important feature of all the>best continuous" kilns,
and they contain special arrangements for this purpose.

As already pointed out, it is usually necessary to use some
supplementary method of heating, such as hot air, or wicket-fires,
to remove moisture from the goods and to raise their tempera-
ture to at least 120° C. During this heating large volumes of steam
are produced, and if these come into contact with cooler bricks
condensation occurs and the bricks may be spoiled. It is there-
fore essential to remove the steam as rapidly and completely as
possible after it has been produced.

A common method of doing this is to open the feed-holes in
the chamber in which the steam is formed, so that it may escape
through them, but this is only a rough-and-ready method and
unsuitable for many purposes, and in the better kilns some
system of steam-flues is provided.

When unusually dry goods are being fired, the opening lead-
ing from each chamber to the main flue may be used, but for
wet bricks this is too small, or so far removed that condensation
would occur in the bricks in the remoter parts of the chamber,
and subsidiary flues are then essential.

The position of these flues depends upon the direction in
which the heat and steam are expected to travel, some burners
preferring it to travel upwards and others downwards. The
former use wicket-fires or stoves (figs. 185 and 186) near the
ground level, or introduce warm air from other parts of the kiln
to below the floor of the chamber to be warmed (fig. 191), whilst
others use portable stoves fitting into the feed -holes in the roof
of the chamber or flues which introduce warm air at just below
the top of the arch (fig. 187), and others again introduce the heat
at or near the ground level and withdraw the steam at the same

280

MODEEN BBICKMAKING

level, a sufficient number of flues being used to carry off the
steam to the main flue (figs. 196 and 197).

FIG. 196. — Drying and removing steam at one level.

It is essential that some construction be chosen which will
permit the heat in the chamber to be distributed as evenly as

possible and will avoid
large "dead< spaces,"
though some amount of
dead space (fig -189) is
unavoidable in almost
every kiln.

A simple form of
steam-flue (fig. 198) may
be constructed by build-
ing a flue under the kiln
floor and connecting it
to a small flue in the
outer wall of each
chamber, and controlled
by a flat sliding damper
(a). The main flue (b)
is, in this case, shown in the centre of the kiln.

W. H. Ser combe, -in the kiln known by his name (fig. 199),
uses a similar construction for the main fire-gases, but provides,
in addition, one or more steam outlets in the upper part of the
kiln above the arch, so that each chamber has four or more
steam outlets.

In the "Manchester," "Staffordshire," and Vaughaii kilns
also, the steam can be taken out from above or below, or both, as
desired (see pp. 275 and 298).

FIG. 197. — Drying and removing steam at floor
level.

KILNS

281

The value of a flue-system for removing the steam may be
judged by the shortness of the distance the steam has to travel
before it is removed from the chamber. When hot, steam is
lighter than air and may best be removed from the top, but
when near the condensation point it should be taken away from
near the bottom of the chamber, hence two sets of openings or
flues are needed for its efficient removal.

FIG. 198.— Diagram of steam-flue.

The draught of a kiln is usually produced by means of one or
more chimneys, and providing these are of ample size and are
in good order their use is satisfactory for most brick-yards.
Chimneys are, however, subject to variations in drawing power
owing to climatic changes, and it is sometimes difficult to work
steadily with them.

FIG. 199.— Sercombe kiln.

Iii an ideal chimney the weight of gases drawn through it
varies as the square root of its height, i.e. each added unit of
length increases the draught, but to a less extent than its pre-
decessors, so that by doubling the height of a chimney the weight
of air drawn is only two or one and a half times the original
amount.

If the sectional area of the chimney is increased proportion-
ately, so as to double the cross-section, the draught is doubled.

282

MODERN BRICKMAKING

Unfortunately it is not usually possible to enlarge the area of a
chimney without first pulling it down.

The temperature of the gases passing through the chimney
is increased until a mean internal temperature of 300° C. is
reached. Above this temperature the velocity of the gases does
not increase with increase of temperature, and there is no ad-
vantage to be gained by allowing gases to pass to the chimney
at a higher temperature than will give this average inside the
chimney.

A thermometer placed at the base of the chimney, and read
occasionally, ensures the prevention of waste heat passing to the
chimney in unnecessarily large quantities. As the gases at the
base of a chimney are hotter than those at the top this ther-
mometer should never indicate a temperature of 500° C., and
lower temperatures are ^ better if the temperature at the top of
the chimney can be ascertained > and the 'inean>internal> tempera-
ture calculated therefrom.

FIG. 200. — Diagram of chimney draught.

When a fan is used, the gases may be cooled to 150° C. (but
not lower) so that the advantage derived from the use of a fan
lies chiefly in its ability to create a greater and steadier draught
rather than in its actual economy of working as compared
with an ideal chimney. Unfortunately few brickworks' chimneys
approach the ideal.

In an ordinary single kiln the products of combustion are
cooled by the bricks to be burned until these attain a high tem-
perature, when the gases escape in a heated condition. Such
conditions are more favourable to a chimney than to a fan, unless
the gases are passed into another kiln or a dryer.

In a continuous kiln, on the contrary, the object of the burner
is to use all the available heat in the gases, and a fan is then
preferable, as otherwise an abnormally high chimney would be
required to obtain the best results. J. W. Cobb has shown that the
effect of using chimney draught, and mechanical draught on the
sarhe kiln may be shown diagranimatically as in fig. 200, in which

KILNS 283

the dotted line marks the assumed distribution of temperature
along the length of the kiln when the chimney is producing the
draught. On putting a fan into use and raising the draught the
quantity of air drawn is increased, and in order to neutralize the
cooling effect of the excess of air the rate of feeding in the coal
must be also increased. Two effects follow : in the first place
the temperature curve is flattened ; this necessitates more
chambers in use, and shows that the usable draught is limited
by the number of chambers in the kiln. In the second place the
peak of the temperature curve travels more quickly along the
kiln, the chambers are burned more quickly, and the output
increased. The increase in output can be effected with economy
by increasing the draught until the limit is reached which the
size of the kiln determines ; beyond this, higher draught means
waste of fuel. It would be wrong to apply a fan to increasing
the output of a kiln which has already as few chambers as will
work well with natural draught, but by increasing the draught
up to the maximum so determined, economy is effected, be-
cause the radiation and conduction losses from the kiln remain
constant, and so can be made to bear a smaller ratio to the total
heat used.

Biihrer has made excellent use of this principle in connexion
with the kilns of his name (fig. 208).

For the reasons just given, in the case of continuous kilns,
mechanical draught is replacing that obtained by means of a
chimney and (erroneously) termed " natural " draught, a fan be-
ing substituted for the chimney. When rightly designed and
properly cared for, fans give a more powerful draught and one
which can be more easily and accurately regulated even in the
windiest weather, and the result of this steadier working gener-
ally leads to a considerable economy in fuel, because there is no
"waiting " until a sufficient draught is produced, as is frequently
the case with a chimney. They also cost less to construct than
a chimney, but this advantage is to some extent neutralized by
the cost of driving them, though the difference in running cost
between a fan and a chimney is. not so great as is popularly
supposed.

Owing to the general structure of continuous kilns an induced
draught fan is preferable to a blower. Several fans very suitable
for brick-burning are now on the market, the best known being
those made by Matthews & Yates, Ltd. (fig. 201) ; Sutcliffe Ventil-
ating and Drying Co. (figs. 202 and 203) ; Sturtevant Engineering

284

MODEKN BEICKMAKING

FIG. 201.— Matthews & Yates fan.

:

FIG. 202.— Sutcliffe fan.

KILNS

285

Co., Ltd. (fig. 204); James Keith & Blackman Co., Ltd. (fig.
205).

The speed at which a fan is run should not be greater than
that necessary to produce the required draught, as the power
required to drive it increases as the cube of the speed. That is
to^say, if the speed is doubled, eight times the power is required,
or if the speed is trebled, twenty-seven times the power would
be necessary. In other words, small fans at high speed are not
as economical as larger fans revolving more slowly. From this
it follows that the best size of fan is one which at the lowest
speed will be sufficiently large to produce the necessary draught
in the kilns. Fans with inlets on both sides are generally
considered to be better than those with one inlet only, but

f Kiln^A f Kiln J

FIG. 208. — Plan showing connexion of fan, kilns, and dryer.

the difference is not very great if the fan is properly designed,
well mounted, and of sufficient size.

The construction of the fan should be as simple as possible
in order that it may not easily get out of order, or cause un-
necessary delay in waiting for special repairers ; but the designing
and erection of both chimneys and fans must, to a large extent, be
left to those accustomed to this kind of work, for the experience
necessary to successful working is only obtained as the result of
years of practical application.

It is always wise to install two fans and to run them alter-
nately, so that in the event of a breakdown the second fan may
be available, though in a good continuous kiln little or no
damage will be done before the fan can be repaired if only one
is used, providing the dampers of the kiln are kept closed. The
fans may be driven direct from a small engine attached to

286

MODEEN BRICKMAKING

them (fig. 206) or a belt may be used. The separate engine
has the advantage that it can be run at night and on Sundays

FIG. 204.— Sturtevant fan.

and holidays without the necessity of keeping other machinery
in motion. On these occasions they are looked after by the
burners.

Fans can be worked without any chimney, but it is better to

KILNS

287

allow them to discharge their contents into a short stack, or, if

preferred they may discharge into the

tubes or flues of a dryer, though when

this is done care must be taken that

the gases do not come into contact

with the goods to be dried or the bricks

may be discoloured.

Fans are largely composed of metal ;
they must not come into contact with
very hot gases, though a temperature
of 200° C. will seldom do much harm.
Unless it is unusually short no con-
tinuous kiln should discharge its gases
at a higher temperature than this. With single intermittent

FIG. 205. — Blackman fan.

FIG. 206. — Sutcliffe's self-contained engine, boiler, and fan.
kilns the gases may first be drawn through a dryer (fig. 207).

288

MODERN BRICKMAKING

The increased draught obtainable when a fan is used enables
the firing to be carried out more rapidly, and in some cases more
than thrice the normal output of a kiln may be obtained by
this means. Some of the best work in this connexion has been*
done by Jacob Biihrer, of Constance, who regularly burns at the
unusual rate of 4 linear feet per hour in his patent kiln. As
such a rapid rate of burning demands a great length of kiln or
fire-travel, it is 'necessary to make each chamber correspondingly
narrower than usual, and to avoid any inconvenience\caused b1

KILN

DRYER

FAN

FIG. 207. — Kiln connected to dryer.

the unusual length of kiln if it were to be built on the usual
plan, Biihrer arranges his chambers as shown in fig. 208.

This enables him to work with a large number of chambers
(on a length of 25 yds.) in each section — steaming, full fire, and
cooling — and so produces excellent results even with many
delicate clays, though his kiln is best adapted for sandy clays of
an open texture. A typical brick-plant worked on this system
has a kiln tunnel 2 yds. wide, 2£ yds. high, and 100 yds. in length,
and an artificial dryer comprising twenty chambers, 7 yds. long,
2 yds. wide, and 2| yds. high, the draught controlled by a fan
utilizing 10 h.p. running night k and day, and produces 10,000,000
bricks annually.

KILNS

289

The dryer is placed near to the kiln, so that heat radiated
from the latter may be used in the former.

J. Osman & Co., Ltd.,
have recently introduced a
similar kiln termed the
"Excelsior" (fig. 209), for
which they claim an out-
put of 120,000 bricks per
week in a kiln measuring
only 66 ft. by 60 ft. the
capacity for increased out-
put without structural al-
terations, and that it is
cheaper to erect than any
other continuous kiln on
the market though at the
time of writing no kiln of
this design has been built.

There is no reason to
doubt that , as soon as
British brickmakers have
realized the advantages to
be derived from the use of
mechanical draught, they
will employ fans in place
of the present chimneys ;
for continuous kilns the
firms who "have already
overcome the trifling diffi-
culties which occur when
any change of method is
used in a works are highly
satisfied with the improve-
ments and economies re-
sulting in the use of
draught produced by a fan. Quite apart from any other con-
sideration, the increased regularity in the heating of the kiln is
more than sufficient to pay for the installation of a suitable fan.

Some firms have met with difficulties owing to their fans
getting out of order. These arise most frequently when only
one fan is used, and for this reason two should be installed and
run alternately, or one may be used for the boiler fire and the

19

290

MODERN BEICKMAKING

other for the kiln if each is capable of taking care of both in
case one fan should get out of order. It will then be found that
the difficulties experienced in the use of fans will be less than
the damage done to bricks by the climatic effects on a chimney
and by having to let the kiln " soak " because the wind is in the
wrong quarter.

Having thus outlined the main features of the best modern
continuous kilns, five typical ones may be described. The first
is a modern Hoffmann kiln in which the main features of
the original pattern are retained, but which has been altered in
shape. This is suitable for common bricks.

The second has given remarkably satisfactory results in th&

Only short
chimney stack
required.

Engine.

FIG. 209. — Plan of Osman's " Excelsior " kiln.

production of best facing bricks where colour is of great im-
portance. This kiln may also be used-for fire-bricks and other
goods requiring a high temperature. It is a typical chamber kiln.

The third is a kiln specially designed for burning blue bricks
and has proved highly satisfactory for this purpose.

The fourth is a tunnel kiln in which the goods travel along in
cars, the various parts of the kiln each remaining at a definite
temperature.

The fifth is a gas-fired kiln.

In thus selecting one design in preference to others the
author's sole aim has been to choose the ones which, in his
opinion, contain the best features and fewest objectionable quali-
ties. He holds no brief for the particular kilns described and has
no financial interest in their success, but having found them

KILNS

291

succeed where others have failed, and having studied all the best-
known kilns with equal care, he has selected these as represent-
ing, in his mind, the simplest and best design for the purpose yet
published. Those brickmakers who are interested in other kilns
may compare them with the ones described with considerable
interest.

A modern continuous kiln with sixteen chambers, for pro-
ducing common bricks, is shown in figs. 210 and 211. This kiln is

FIG. 211.— Cross section of modern Hoff-
mann kiln.

FIG. 210. — Section of modern Hoffmann kiln.

the one last recommended by Frederick Hoffmann, though there
are numerous variations of this design used in different works.
It consists of an elongated, endless tunnel or " ring " in which
the bricks to be burned are
placed, and a central body
of masonry fitted with flues
connected to a chimney-
stack.

In former times only
twelve chambers were used,
and the kilns were circular in pattern, but these are too short,
and the shape • shown in fig. 212 is now almost universal. This
pattern of kiln can ble built for any desired output from 500,000
bricks per annum upwards.

In the Hoffmann kiln (figs. 210 and 211) the chimney is usually
placed near the centre, each part of the tunnel being connected
to it by means of small flues discharging into a central main
flue, which in its turn discharges into the chimney.

These flues are represented by dotted lines in fig. 212, in which
the chimney is built outside the kiln so as to avoid the necessity
of so massive a block of masonry within the kiln itself. The
older types of Hoffmann kiln (fig. 182) had all the flues arranged
on the central wall of the kiln, but in the one shown two flues
are arranged for each chamber at the end of the kiln — one on
the outer wall, and one in the inner masonry. The additional
flue is useful in reducing the friction of the flue-gases and in
distributing the heat more evenly in these parts of the kiln (in-

292

MODEEN BEICKMAKING

"horse" with
pegs fixed in

cidentally it may be noted that W. H. Sercombe uses this ar-
rangement in each chamber and not only at the ends).

These flues are con-
trolled by conical dampers
to which are attached
vertical iron rods operated
from the top of the kiln.
The extent to which the
dampers are opened is
usually regulated by a
board or
holes in it,

the holes passing through
a ring at the other end of
the damper rod. This ar-
rangement is clumsy, and
far easier regulation is
obtained if the damper-
rod is surrounded by a
collar as shown in fig. 213
working on a hinge in
such a manner that on
lifting, the rod can be
raised easily, but it will
not sink unless the collar
be kept perfectly level by
depressing the " step " on
the other side of the hinge
with the foot. Damper-rod
holders of this type can
be obtained very cheaply
from T. Burnett & Co., Ltd.,
Doncaster.

The fuel is fed into the
kiln through holes in the top into hollow pillars formed of
green bricks when the kiln is being set, the preliminary warming
of the goods being effected by hot air drawn from the cooling
bricks and conveyed by a hot-air flue in the centre of the kiln
and above the main flue, and by a temporary metal flue (m)
to the portion of the kiln to be heated. Other arrangements for
the supply of hot air have already been described (p. 272).

The kiln is provided with sixteen wickets or door-gaps through

KILNS

293

which the goods enter and leave the kiln. These wickets are
built up as soon as the portion of the kiln nearest to them has
been filled. As it is essential that no air should leak through
these, the brickwork used to fill them is thickly plastered with
clay paste or " daub ".

The fire travels steadily forward around the kiln, the gases
passing through a sufficient number
of bricks to utilize the greater part
of the heat they contain, and the
heat from the finished bricks being
utilized to dry freshly set ones by
means of the hot-air flues already
described.

As originally designed, no hot-
air flue was used in the Hoffmann
kiln, though few are now built
without some means of using the
hot air from the cooling chambers.
J. Osman & Co. claim that the use of Fm' 213.-Clamp for damper rod.
this hot air in their kiln " effects a saving of 40 per cent
of fuel over and above the ordinary (i.e. original) Hoffmann
kiln," and other modern kiln-builders make similar statements,
but the saving effected is the result of several factors and not
merely to the use of hot air. The Osman " New Perfect " kiln
is practically a Hoffmann kiln similar to the one shown in
figs. 211 and 212, but the hot air is conveyed through permanent
hot-air flues placed in the upper part of the kiln instead of
through temporary ones, in a manner similar to fig. 189, except
that the hot-air flue is placed centrally in the kiln and the main
or smoke flue is below the ground level on the circumference
of the kiln. As already pointed out, the weakness of this ar-
rangement is the liability to leakage due to the movement of
the kiln, and to avoid this J. Osman & Co. are now placing
their hot-air flue much lower than formerly, and are admitting
the air to the bottom of the chambers to be warmed, its steam
escaping through an up-draught flue connected to the main
flue.

The progress of the fire depends upon the speed at which the
clay can be heated and cooled ; the usual rate is 6 in. to 1 ft.
per hour, but if the kiln is sufficiently long and well managed
double this rate should be reached with normal clays. By the
use of a mechanical draught J. Biihrer is able to use a rate of

294 MODEKN BEICKMAKING

fire-travel four or five times as fast as that usually employed
(p. 288).

The tunnel should be as long as possible, the width being not
more than 16 ft. and preferably much narrower.

The walls and other masonry must be strong and well built
of good materials. Several kilns known to the author are scarcely
fit to use, though they have only been erected a few years,
through failing to comply with these requirements. Brickmakers
should remember, in comparing tenders for a kiln, that the
cheapest is often the least durable.

For ordinary use the kiln may be built of any good bricks,
but for unusually high temperatures a fire-brick lining is
necessary. The arches and door -jambs should be built with
special made arched bricks and bull-noses respectively. The
foundation of the kiln must be dry, or a special bed constructed,
as a damp floor causes a great waste of fuel.

The upper part of the tunnel or ring is usually arched (as
shown), but it may be replaced by a temporary layer of ashes if
required. The arches add considerably to the cost of erection,
but are permanent ; the ash-layer top costs but little, but must
be renewed each time a chamber is filled. Hence for temporary
work an " archless " kiln is to be preferred, but if the kiln is to
be used for several years the usual form will prove to be more
satisfactory, especially where better class bricks are required.

The construction of archless kilns of the semi-continuous
type was patented by Bull in 1876 and of the continuous type
by Bock (in Germany) in 1896. The first of these has long been
used in India and China, in spite of several disadvantages in-
volved in the use of the movable chimneys it employs.

Several British patents have been taken out for " archless "
continuous kilns, one of the most satisfactory being that of H.
Harrison, Manchester. In this kiln the door-gaps or wickets
are sufficiently wide for a horse and cart to enter, and the bricks
are loaded direct. As the ash-layer forming the roof can be
removed in a few minutes the kiln can be emptied easily and
rapidly, as it cools more readily than the arched form. When
a new chamber has been filled with bricks a layer of burned
bricks laid close together is placed on the top, the usual " pot "
holes being left for feeding in the fuel, and the whole is covered
to a depth of 4 in. to 6 in. with ashes.

The cost of this work is very low, as it can be done by two
boys who can also do other work in the intervals. The comple-

KILNS

295

tion of the firing of any part of the kiln can be seen by that
portion of the " roof " being lower than that on the insufficiently
fired portions.

The Harrison kiln also differs from the ordinary Hoffmann
kiln in the disposition of the flues, the main flue running along
two sides of the kiln (as in fig. 220) instead of down the centre,
and in the use of a fan.

All continuous kilns should be covered with a wooden and
glass roof, the space between this and the kiln being match-
boarded anc1 fitted with doors for ventilation. The roof not only
affords ample protection for the workman, but, by keeping the
fuel and top of the kiln dry, it reduces fuel consumption and

FIG. 214. — Dryer built around kiln.

increases the durability of the arches. The cost of such a roof
is often regarded as an unnecessary expenditure ; but it will be
found that it is really economical to have a good one erected.

In Germany it is customary to surround the kiln with a
dryer (fig. 214), but this arrangement is not much used in
Great Britain.

If properly constructed, a kiln of the type just described
should burn 1000 ordinary bricks with a maximum of 4£ cwt. of
good coal, but with certain shales less than half this will be re-
quired. The fuel consumption of some patent continuous kilns
is seriously understated.

For very large kilns with twenty-eight or more chambers two
independent fires and two chimneys '(fig. 215) are often used
and considerable economy is thereby realized.

296

MODEEN BEICKMAKING

KILNS

297

The ordinary Hoffmann kiln is not suitable for the produc-
tion of more than 60 per cent facing bricks, and for bricks con-
taining much combustible matter ; for both these kinds of bricks
chamber kilns (p. 276) should be used.

The "Staffordshire" kiln (figs. 193. and 215 to 217) is emin-
ently adapted for the production of best facing bricks, as it is a
chamber kiln employing grates so as to keep the fuel out of con-
tact with the goods, and has ample facilities for using hot air
and for the removal of steam. This kiln, patented by Dean,
Hetherington & Co., must not be confused with the ordinary
pottery kiln used in North Staffordshire, although such mistake
is natural, considering the title of the newer kiln.

The means of supplying hot and cold air to different parts of

O

c'O7 P / O O D's Q
FIG. 216.— Plan of " Staffordshire " kiln.

the kiln are much more complete in it than in any kiln yet
built, and, as only one face of fire is used in each chamber, this
kiln is capable, under good management, of giving results equal
to the best down-draught kilns with a coal consumption as small
as in continuous kilns. This is brought about by the combina-
tion, in a continuous kiln, of damper-controlled passages leading
from the outer air to flues under the fire-grates in the bottom of
the kiln in each chamber, as shown in the illustrations (figs. 193,
216 and 217), and of similar flues leading from the hot-air flues
and from the outer air in such a way that, by appropriate con-
nexions, air of any desired temperature and in any desired volume
may be admitted to any part of the kiln. The ordinary diffi-
culties experienced in connexion with warped dampers are also
to a large extent eliminated by their position and shape.

298

MODEKN BRICKMAKING

By suitably working the dampers the following results may be
obtained : —

(a) By opening dampers 11 and 18 the whole or part of the
hot air from the finished or cooling chambers may be admitted to-
the chambers containing the freshly set goods, and the steam
resulting from the heating of these goods led away from the top-
through flues 7 and 3 to the chimney.

(b) By opening the dampers 16 of the flue 13 hot air from
flue 5 may be led under the grates 14 to develop the highest
possible temperature in the finishing chamber, or to distribute
hot air uniformly from the hot-air flue 5 to a chamber contain-
ing green goods.

17

Section on line DD in fig. 216.

Section on line CO in fig. 216.
FIG. 217. — Cross sections of " Staffordshire " kiln.

(c) The admission of cold air to a cooling chamber is kept
under perfect control by means of dampers 18 and flues 17.

(d) The temperature of hot air entering a hot chamber from
one that is cooling may be perfectly regulated by the admission
of air through flues 17 and 19.

(e) The volume of air admitted through the various flues
allows a nice adjustment for reducing and oxidizing atmosphere.

(/) The fire and hot gases may pass from chamber to
chamber, through openings 10, whilst cold air only is admitted
to the under side of the grates 14 through flues 17.

(g) Any chamber can be completely sealed by closing all the
dampers, thus allowing of good annealing. This arrangement is-
also of great value where the goods are liable to catch fire spon-
taneously.

KILNS

299

Some further particulars of the hot-air flues will be found
on p. 274. It will thus be seen that in this kiln the whole of
the hot air from such cooling chambers is taken direct to the
main central hot-air flue, and can thus be admitted into any
chamber in any part of the kiln.

The air for combustion purposes, independently of that sup-
plied from the hot-air flue, is admitted at each end of the
chamber, through dampered openings in the top ; thus becoming
heated on its journey to the grate. The temperature of this hot
air can be further regulated by air admitted through a flue lead-
ing from the outside to directly under the fire bars.

The flues of the "Manchester" kiln are similar and are so

FIG. 218.— Plan of " English " kiln.

arranged that certain of them can be equally easily used for the
collection of hot air, or for carrying away the steam as in the
" English " kiln (figs. 194 and 218). The hot air is admitted into
the chambers both at the floor level and through openings in
the top.

In order to adapt them to the special characteristics of
certain clays, the kilns built often differ in minor particulars
from the description just given.

Most chamber kilns — the type most suited for use where facing
bricks are to be made — are built with arches running trans-
versely to the travel of the fire. This has the disadvantage of
losing a certain amount of heat owing to the additional masonry,
but it enables the chambers to be built of almost any size and
much larger than is practicable where the arch is longitudinal,

300 MODEEN BEICKMAKING

when 18 ft. is the maximum width. The travel of the fire is also
more regular in kilns with transverse arches. The London Brick
Co., of Fletton, use what is known as the ".English " kiln, the
chief feature of which is the ingenious system of hot-air flues.
These are placed in two parallel rows on top of the arches, the
dampers taking the form of circular plates or lids (fig. 194), the
position of which determines the direction of flow and the amount
of hot air allowed to enter or escape from any chamber. The fire-
gases pass through openings in the wall between the chambers
(figs. 194 and 218).

This kiln is not intended to produce facing bricks of first-class
colour, but for use with certain shales it is found to give great
satisfaction, producing a great heat with a low consumption of
fuel, the hot-air system being so arranged that very damp bricks
can be set direct into the kiln.

The foregoing kilns can be used at the high temperature
used in blue-brick and fire-brick making, but a special kiln for
this purpose has advantages, as by using two fires the chambers
can be large and the waste of heat due to small chambers can
be avoided. Kilns of this type are well known on the Continent,
but in this country the only one which has proved successful is
that patented by S. Barnett and R. J. Hadlington, Dudley Port,
Staffs, the essential features of which are (1) the use of trans-
verse arches, (2) of two grates or fire-boxes to each chamber, and
(3) the direct connecting flues between each chamber. Kilns very
similar to this have been patented by G. Oakland and others, but
they used one fire-trough, divided into a number of boxes or
bags, in which the fuel is burned on a solid floor as in Guthrie's
patent, and the connecting flues are less suited for careful re-
gulation at the higher temperatures necessary for blue -and fire-
brick burning.

The Barnett and Hadlington kiln may be regarded as a series
of separate chambers with a slight space between each; this
space may be used to contain the connecting flues and dampers
regulating the supply of air. Owing to the desirability of large
chambers the arches are built transversely. The fuel is fed ex-
clusively from the front of the chamber as in the Belgian
kiln.

The gases are not led directly through the partition walls of one
chamber to another as in most continuous kilns, but pass through
perforations in the floor (as in a down-draught kiln) and thence
to the following chamber. The perforations in the floor are at

KILNS 301

one side of the kiln, opposite to that at which the gases enter,
but the main flue (through which pass the gases produced by
the fuel on the grates within the chamber) is in the centre of
the floor.

The use of this second flue at the side of the chamber
farthest from the point of entry of the gases is important, as it
tends to produce a better distribution of tjie warming gases,
whilst the centre flue is to be preferred when fuel is actually
being burned on the grates, because it concentrates the effect of
the flames, and then distributes the gases evenly throughout
the goods during the hottest part of the firing. In other words,
this kiln utilizes the old idea of a grate at one end of a chamber
and a flue at the other during the earlier part of the burning,
but during the last forty-eight or fifty hours the heat from the
two grates is concentrated by shutting off the side flue and using
the centre one.

In this way, it is possible, in so far as respects the products
of combustion of the fuel, to reach a very high efficiency in the
transference of heated air from one chamber to another, and
the successful drawing off of the steam, and its conveyance to
the smoke-shaft.

Steam is removed and the goods dried with regeneratively
heated air (partly from the cooling chambers) which is also uti-
lized for supplying hot air to increase the temperature of the
chambers under fire, or to assist in starting the furnaces of a
chamber into which fuel has just been placed. It is conveyed
through four or more large openings in the sides of the chamber
containing cooling goods, through flues running underneath the
chambers and up through other flues (controlled by sliding
dampers) to the fire-grates of the chamber where it is to be used.
It is then drawn through a special set of flues into the main
leading to the chimney-stack, so that if used for goods con-
taining much moisture the steam produced does not come in
contact with any other goods, but goes direct to the chimney.

The additional air required for supporting the combustion of
the fuel on the grates, or for completing the ignition of any im-
perfectly consumed gases, is supplied partly through the grate
bars (the ash-pit being then kept open to the air) and partly by
means of a small flue connecting the space above the grate-
bars with the hot-air flues from the cooling chambers, and also
with the open air, this open-air port being controlled by a
damper about 3 ft. from the ground. In this way any desired

302 MODEEN BKICKMAKING

mixture of hot and cold air may be supplied to the contents of
a chamber.

These apparently elaborate arrangements for controlling the
air- and fuel-supply and the speed at which the burning takes
place cannot be satisfactorily shown in one or two small illus-
trations, but they are, in reality, far simpler than appears at first
sight, and little difficulty is found in obtaining perfectly satis-
factory vitrified blue bricks or well fired fire-bricks from this kiln.
The accurate burning of the fuel is essential to the production of
a good colour and a proper degree of density or vitrification, and
the author has found that the dampers (even after several years'
constant use) work so accurately that the appearance of the
flame of the hot gases in the chambers can be altered with the
greatest nicety, or smothered out altogether by simply moving
the appropriate dampers. This speaks highly for the soundness
of the construction, and the careful placing of the dampers
where they will work effectively and be least affected with the
heat. These dampers are chiefly in the form of slabs of fire-
clay or of the usual conical pattern. The Bock, Diesener, and
Mendheim kilns, which are greatly used in Germany, are ar-
ranged on the same general principle.

Tunnel kilns are those in which the goods are placed on wag-
ons and travel through a heated tunnel, whereas in the ordinary
continuous kiln the heat travels whilst the goods remain sta-
tionary. Whilst very useful for light goods (pottery, etc.) tunnel
kilns have not become popular in this country, though numerous
patents have been obtained. In France, several are in satisfac-
tory use for brickmaking.

The chief objections urged against them are the jolting of
the goods on the cars and the difficulty in repairing the kilns
without stopping the works, but neither of these objections is as
important as many brickmakers imagine, though the former is
the more troublesome with tender clays.

The great advantages of tunnel kilns are the absence of
" setting " — the bricks, being loaded on to the cars at the machine,
remain on them until the drying and burning is complete — the
small waste of fuel due to its all being delivered at one spot in-
stead of over a larger area as in the ordinary continuous kiln,
and the economy in fuel consumption which is fully equal to, if
not greater than, that of the Hoffmann kiln.

A tunnel kiln for bricks is shown in fig. 219, which represents
a cross-section. The whole kiln should be at least twenty times

KILNS

303

FIG. 219.— Bock's tunnel kiln.

the length of a wagon. As the goods enter the kiln they are

subjected to the heat of the waste gases, and as they pass out

they give up their heat to

the incoming air which,

being pre-heated in this

manner, effects a better

combustion of the fuel.

In the Bock kiln, gas
from a producer enters the
central portion of the kiln,
Tises through the flues, and
enters the burners where it
meets with the pre-heated
air in another chamber.
The goods are placed on a
single deck car, the top of which is a fire-clay slab. It is essential
to use gas as a fuel, as in.no other way can absolutely continu-
ous heating without variations due to the removal of ashes be
obtained.

The chief difficulty to be overcome is the effect of the intense
lieat on the wagon carrying the goods and on the brickwork in the
hotter parts of the kiln. There is also a minor difficulty that air
leaks between the sides of the wagon and the kiln, and prevents
the proper heating of the goods. In spite of their advantages, tun-
nel kilns are scarcely likely to become popular for brick-burning.

Gas-fired continuous kilns have been known for many years,
James Dunnachie having erected one at Glenboig in the year
1881, yet many attempts have been made to apply gas to kilns
which have resulted in disastrous failures. Two principal reasons
for these failures may be given : those attempting to use gas did
not (1) know how to burn it, and (2) permit it to enter the kiln
at the proper point. Subsidiary failures have been due to at-
tempting to use cold instead of hot air for mixing with the gas,
and other equally impractical ideas, the result of ignorance of
the characteristics of the gas used.

It is generally thought that gas-fired kilns are difficult to
manage and that they effect an enormous economy in fuel.
Neither of these ideas is correct. A properly constructed gas-
fired kiln is quite >easy to manage — the difficulty lies in the de-
sign and not in the manipulation — and the fuel-consumption
is practically the same as that of any equally well-designed coal-
fired continuous kiln.

304 MODEEN BRICKMAKING

The real advantages of gas are its greater cleanliness, the
better colour obtained on the goods, greater regularity in heating,
and, above all, the greater finishing temperature which can be
reached when gas is used. This last is of the greatest impor-
tance in fire-brick manufacture, though few British makers of
refractory goods realize this fact.

The number of designs of continuous gas-fired kilns is already
very large, and it must, therefore, suffice to describe only three of
the best known ones. A kiln built according to Schmatolla's
designs has been described already (p. 257) It is much newer
than the Mendheim and the Dunnachie kilns. The Mendheim
kiln is a great improvement on some of the earlier designs, and
is practically a series of down-draught kilns connected to each
other, the gas being burned in " bags " at one side of each
chamber, and the products of combustion, after distributing
themselves through the chamber, pass away through perforations
in the floor to the " bag " of the next chamber or to the main flue.

In the most recent gas-fired kilns by G. Mendheim the gas
enters at the four corners of each chamber and rises up the bag-
walls, the product of combustion then passes out through a
central opening in the floor which delivers them to the bags of
the next chamber or to the main flue. This arrangement has
the advantage of using a minimum number of dampers.

The Mendheim kilns appear to be rapidly increasing in
popularity on the Continent.

The Dunnachie kiln has been chiefly used in connexion with
fire-brick burning, though well adapted for ordinary bricks, but
it has not been the policy of the inventor to encourage the erec-
tion of similar kilns in this country or in Scotland, and conse-
quently the kiln, though well-known by name, is not familiar to
more than a few privileged workers as regards its constructional
details. Abroad (where the possibility of competition does not
exist) a number of Dunnachie kilns have been built, and, when
the original design has been closely followed, have proved quite
successful and economical. It is, indeed, only to be regretted
that more do not exist in this country. The Dunnachie kiln has
a solid floor, thereby overcoming one of the greatest disadvan-
tages of the Mendheim kiln, and the larger flues give a more
satisfactory control as well as more rapid burning of the goods,
and at the same time become much less easily choked.

The gas producer used may be of any type supplying gas at a
pressure of about one-hundredth of an atmosphere (4 in. water-

KILNS

305

column), though at Glenboig the Wilson producers are the ones
actually used.

The Dunnachie kiln presents a very different appearance to
the ordinary continuous kiln because of the great distance

FIG. 220. — Plan of Dunnachie kiln.

between the two rows of chambers. In the ordinary coal-fired
continuous kiln, with sixteen chambers, twelve are placed back
to back close together, and the remaining four are placed two at
each end of the others, so as to form a complete "ring ". In the
Dunnachie kiln (fig. 220) on the other hand, there are only ten

20

306 MODEEN BEICKMAKING

chambers placed in two rows of five, and with a space of 20 ft.
between them, the chambers at the end of each row being con-
nected by underground flues (J and M). In the centre of this
space the gas valves are arranged, and, if roofed in, the space
forms a convenient room for drying goods, being kept warm by
the heat radiated from the ends of the chambers, and the heat
which would otherwise be lost by this arrangement of the kilns
is made use of, to the general advantage of the works. If
•desired, the space above the kilns may also be roofed in, and
used as a making and drying fldor — a custom particularly common
with continuous kilns in Germany, but not so popular in Great
Britain.

The chambers used at Glenboig have a capacity of about
18,000 bricks and measure 17 ft. by 10£ ft. by 10| ft. internally,
and worked at ordinary speed can produce an average output of
400,000 fire-bricks a month.

The chimney is placed at one end of the -, structure, the main
flue leading to it being placed around the sides, as shown in
fig. 220. This plan necessitates some loss of heat in the main
flue, but as the gases passing through it are at a comparatively
low temperature this is not considered to be of much importance,
especially as the chimney-draught can be accelerated to any re-
quired extent by means of a fan. It is certainly better that the
heat should be lost from the main chimney -flue rather than from
the flues conveying hot gas to the kilns, which seems to be the
only other alternative if the present simplicity of arrangement
and accessibility of flues are to be maintained. Under such con-
ditions a blower may be used instead of, or in addition to, the
chimney- or fan-draught, but this requires care, or its use may
become dangerous.

" Steaming " or " smoking " of the goods is effectually carried
out by burning a small quantity of gas mixed with an abundance
of cold air in the chambers to be smoked, or, if there is a suf-
ficient supply, hot air from the cooling chambers is used. Dur-
ing this " steaming," openings in the arched roof of the chambers
(corresponding to the " feed-holes " in the ordinary kiln of the
Hoffmann type) and the ports G (fig. 220), near the floor level of
the kiln, are kept open until the whole of the steam has been
removed, and the goods are distinctly hot ; they are then closed.

The burning then commences by admitting gas at a tempera-
ture of about 600° Fa,hr. from the producers through the flues R
through valves A, hot air for its combustion being supplied at

KILNS 307

the same time from the chamber which has just finished firing.
It is the employment of the heat in the finished goods for heat-
ing the air required for the combustion of the gas which consti-
tutes the principal feature of the Dunnachie kiln, and is the chief
cause of its success. This kiln was, in fact, the first in this country
to combine the advantages gained by the use • of gas as fuel with
the " regeneration " of the air used for its combustion by means
of the waste heat from the burned-off chambers. This principle
of heat regeneration has been recognized for nearly a hundred
years, and was applied with remarkable success in 1856 to the
melting of steel by the late Sir F. Siemens, but the credit of its
successful application to the < requirements of the clay industry
must be given to Mr. James Dunnachie, who first employed it in
the kiln now under consideration. For its application to single
kilns see fig. 177.

The air is heated in a manner very similar to that now
employed in most continuous kilns using coal, by drawing it
through the chambers containing finished goods which are still
very hot (in the case of fire-bricks of best quality the air is heated
to a " blue white heat " before it comes in contact with the gase-
ous fuel). It is conveyed from one chamber to another by
openings in the floor of the chambers leading to a flue beneath,
thence through slits in the brickwork to another flue, and thence
through openings in the arched roof of this latter flue into a
smaller flue, from which it passes at, or slightly below, the floor
level of the kiln into the next chamber by means of a series of
openings, the size of which is calculated so as to supply the
correct proportion of air to the gas. (Usually the capacity of the
air-openings is two and a half times that of the gas.) As these
air-openings extend the whole length of the chamber also, even
heating is thereby effected.

The gas catches fire where it comes into contact with the air
a little below the floor level, and for some distance above it, the
flame rising a considerable height in the chamber in huge sheets
of a clear bright colour, and practically free from smoke if the
air and gas are in the correct proportions. The products of
combustion then pass through the following chambers, heating
the bricks in them, until the heat left in the gases is so small as
to be of little value, when they are turned into the main flue
leading to the chimney.

If, for any reason, a supply of air is required at a higher level
than the floor of the kiln it can be supplied by opening dampers

308 MODEEN BEICKMAKING

in other flues (not shown) which are so arranged as to supply hot
air from the preceding chambers or, by opening dampers at
their ends, cold air can be supplied in any desired amount to
the chambers. These flues are not generally required unless
the firing in the burning chamber is not hot enough, or when the
chamber is too hot and cold air must be supplied to prevent
the bricks melting.

All these air-flues and gas-flues are controlled by dampers
and valves of a simple character, and the supply of hot air or
cold air and gas can be regulated with the greatest nicety to the
changing conditions of the kiln.

The " round of the kiln " when burning fire-bricks is somewhat
as follows : —

No. 1 Chamber — Being emptied. No. 2 Chamber — Open and
cooling. No. 3 Chamber — Red hot, being cooled by air supplied
through flue at its base, and carried on to No. 4 Chamber. No.
4 Chamber — White hot, being cooled by air from No. 3, which is
passed on to No. 5. No. 5 Chamber — In full fire for 36 to 48
hours, being supplied with hot gas from the producers and with
"white hot" air from No. 4. No. 6 Chamber — Very hot, being-
heated by products of combustion from No. 5. No. 7 Chamber
— Heating up to red heat by gases from No. 6. No. 8 Chamber —
Steaming for forty- eight hours. Filled with green bricks. No. 9
Chamber — Filling with green bricks. No. 10 Chamber — Empty,
ready for filling.

The cooling of each chamber takes about seventy-two hours,
though varying with the nature of the goods. It can be accelerated
by the use of a blast of cold air blown into the top of the chamber
during the last day of the cooling. The hot air thus obtained
may be used for the kiln, any excess being employed for heating-
drying sheds, etc.

Though essentially designed for the highest temperatures
used in fire-brick making, the Dunnachie kiln can be equally
well employed with common bricks, for salt glazing (in which
case a perforated floor is used so as to secure a draught inside as
well as outside the goods), and for ordinary pottery purposes,
though its advantages at lower temperatures are less important.
For many purposes, though still capable of improvement, it is
undoubtedly the greatest advance in firing that has been made
since the invention of the continuous kiln by Hoffmann, as the
employment of gas at high temperatures greatly lessens the re-
pairs needed by the kilns, and by reducing the labour necessaiy

KILNS 309

for supplying the fuel it enables the number of men employed
for a large number of kilns to be considerably reduced, and
renders their work more accurate and under better control than
when a coal-fired kiln is used.

There is undoubtedly a great opening for the further applica-
tion of gas to the burning of all kinds of fire-bricks, and the suc-
cess whiclr has attended the Dunnachie kiln ever since its
introduction should give brickmakers an incentive to adapt
their own kilns as far as possible, or to seriously consider the
advisability of erecting fresh ones to be fired exclusively with
gas. The reason why most firms are afraid to make the change
is that they have heard or read of numerous and expensive
failures to apply the gas properly to the kilns — due as already
explained to the belief that it should be introduced near the top
of the chambers — and are afraid to risk their own capital in a
similar venture. This is bad business, because it is looking at
the subject from one side only instead of regarding it from every
point of view. The fact that some kiln-builders recommend a
certain class of kiln is not by any means conclusive evidence
that the facts which tell against their own invention are by any
means fairly represented. This is where the advice of an en-
tirely independent expert comes in, provided that one can be
assured that he is independent.

The success which is being obtained in the adaptation of gas
to the firing of single kilns is drawing considerable attention to
the subject of gas-firing generally, and the application of this
fuel to the general firing of refractory goods is only a matter of
time.

The construction of gas-producers requires special knowledge,
and should not be attempted by the brickmaker except under
reliable supervision. The general principles involved can be
learned from special books on the subject, but practical experi-
ence is essential.

The use of a gas-producer also requires a slight training,
though when this is obtained the work is far easier than the
ordinary stoking of kilns, and the temperature in the latter can
be far more accurately and easily regulated.

Muffle kilns are used when it is necessary to keep the goods
free from all contact with flame or fire-gases. In brickmaking
the use of muffles is confined to some glazed bricks and to the
production of red bricks from certain Staffordshire marls.

The usual form of muffle is an arched chamber placed in-

310

MODERN BEICKMAKING

side a Newcastle or similar type

Fio. 221.— Cross section of muffle-kiln.

of kiln, this chamber or muffle
(fig. 221) being built on flues
and with a space above and at
each side. The front of the
muffle is left open for filling,
but is closed with bricks plas-
tered over with daub before
the firing is commenced. The
flame and fire-gases play all
round the muffle, heating it
evenly and yet keeping the
goods free from ash, dust, and
other harmful influences.

Providing that an even
heat is obtained, the shape
of the muffle is unimportant,
but the design already indi-
cated is as simple and effi-
cient as any. The waste gases
from one muffle kiln may
often be used to heat another
in a manner precisely similar
to that used in continuous
chamber kilns.

KILN CONSTRUCTION.

Errors in kiln construction are often numerous and serious.
A number of the most important ones are enumerated below : —

General instability is a common feature of certain continuous
kilns where the cost of erection has been reduced to below the
proper limit as a result of excessive competition. This defect
usually shows itself first by cracks in the outer walls and in the
flues, though the former may be due to a poor foundation rather
than to indifferent workmanship. It has already been pointed
out that flues should not be built above the keystone of an arch
if they run in the same direction as the arch itself, as the move-
ments of the kiln during heating and cooling render this the
most unstable position in the whole structure.

A form of economy often attempted is to fill large portions of
the masonry with broken bricks, sand, or rubble. If well stamped
down these may be satisfactory, though properly laid brickwork
is far better. Occasionally, burned clay or sand is used, but it is

KILNS

311

apt to dry, leaving hollow spaces. Slag, though better than clay,
is liable to contain unburnt material and so shrink on heating.

The choice of bricks for different portions of the kilns is a matter
requiring a considerable amount of attention, for it is just as
foolish to use best refractory bricks where a lower grade material
at half the price can be used with equal satisfaction, as it is to
endeavour to save expense by using inferior bricks in those parts
of the kiln which require to be most heat-resisting. By a little
thought it is often possible to save considerably in the expense
of erecting new kilns, or repairing or altering old ones, if this
careful choice of different bricks for different positions is made.

The masonry used in the centre of most continuous kilns is
a good example of a case where inferior bricks may be used, as
they are heated but are not exposed to the action of the weather
to any notable extent, and being usually well imbedded, only
need to have sufficient strength for their work, no regard being
paid to their softness or general appearance. The external

I \

1 1 1 1 1

1

FIG. 222.— Wrong bond for bricks.

FIG. 223.— Correct bond for bricks.

work, and that which is subjected to heat, however, must be of
best materials in order that it may stand the existing and prob-
able strains and exposure without the least likelihood of failure.

Of the brickwork which comes in contact with the fire it is
scarcely necessary to say that it should be constructed of the
best materials, and laid with as thin joints and in as skilful a
manner as possible, a small extra cost in the erection more than
repaying itself in the far greater length of time the work will last
as compared with badly built work of less refractory materials.

Another defective arrangement, which is more often noticed
in repair work than in a newly erected kiln, is the wrong bonding
of the bricks. This is carried out in such a way that instead of
breaking joints with the courses above or below, the bricks are
so arranged that the joints coincide as in fig. 222, whereas they
should be as in fig. 223. In this latter case not only is the bond
better and the masonry stronger, but the effect of cracks in the
jointing is much less serious, as these cracks do not extend
nearly as far when t.he joints are broken as when they coincide.

312 MODERN BEICKMAKING

The mortar used will vary in composition according to the
object of the brickwork. For the cooler portions of the work,
where strength and not heat-resistance is needed, the use of
ordinary lime -mortar is satisfactory, but for the more refractory
portions the jointing materials should consist simply of a clay
similar to that of which the bricks are made, mixed with water.
Sometimes a little finely ground burned clay may be added to
reduce the shrinkage of the mortar, but lime and other fluxes
must be most carefully excluded where the masonry has to
withstand great heat.

In the construction of a kiln foundation too much care cannot
be taken, as dampness drawn up into the kiln because of a defec-
tive foundation is not only a source of loss of fuel, but may cause
serious damage to the goods in the kiln. Bricks having a good
colour and a clear "ring " cannot be economically obtained with
kilns which have damp soles.

It will be easily understood that the chimney-draught causes
a very slight vacuum inside the kiln, so that any air, gas, or
vapour outside it, whether below or above, will tend to rush in
through any pores in the soil or masonry. The heat in the soil
beneath evaporates the moisture which reaches it, and tha
vapour inevitably finds its way into the chambers.

The effect of this is seen on the goods nearest the floor,
and a marked effect also is produced on the coal consumption.
Scummed and unsound bricks result, in spite of all ordinary
precautions against these defects.

Brickmakers who have not studied the question carefully
have no idea of the difference in the quality of the goods and
the saving in fuel which results from properly draining a kiln,
and the expense of installing a proper system of drainage is
rapidly returned to the manufacturer who is enterprising enough
to ensure that all the water in the sole of his kiln is removed in a
proper manner, instead of being boiled out by heat which should
be expended in firing the goods.

In erecting new kilns it is seldom that sufficient attention is
paid to the removal of foundation water, although every kiln
builder is fully aware of the necessity of properly draining the
foundations of his kilns. In addition to this, most kilns are not
used during the winter months, and in but few cases are proper
means provided for the efficient removal of rain-water from the
kiln roof; it is generally allowed to run off anywhere, and most
frequently finds its way into the ground immediately around the

KILNS 313

walls. Consequently, the goods are of inferior quality,
and require far more than the normal proportion of fuel, owing
to the Mln and its foundations being soaked with water.

It is a good rule never to build a kiln on ground in which the
subsoil water is within 6 yds. of the surface unless a special
insulation system is used.

It is well known that the heat produced in firing a kiln not
only rises to the upper parts of the kiln, but also sinks into the
foundations, and it is not unusual to find that the first three
rounds at the beginning of a new season produce goods which
are inferior in quality, as it takes some time before the heat can
penetrate to its normal depth of 3 to 4 yds. into the ground.

All the water present in the foundations of a kiln to a depth
.at which the temperature approaches 100° C. must be sooner or
later evaporated and removed through the flues, fan, or chimney
of the kiln. Not only so, but when a higher temperature than
this is present the temperature is lowered by the evaporation
which takes place, thereby causing a serious loss of heat.

It is important that every brickmaker should see that his
kilns are properly drained, as, otherwise, serious trouble will
result. It is equally important to see that the water from the
roof of the kiln and from other buildings is not allowed to soak
into the ground near the kilns, but is conveyed away out of harm's
reach. If it must be allowed to enter the ground near the kilns,
it must be taken to a depth of at least 4 yds. below the kiln sole,
and even then it is apt to be troublesome.

A plan recommended by J. Buhrer and other well-known kiln-
builders consists in laying 12-in. pipes to drain the foundations
of the kiln, and to turn all roof water into these, so that it may
be led right away from the yard. Above these pipes (which
.should be about 3 yds. below the sole of the kiln), a 14 in.
layer of sandstone chips should be laid, as these allow the water
to drain out far better than does a layer of broken bricks or
ordinary earth.

The pipes which collect the water from the roof of the kiln
should be of ample size, and should be taken about a foot deeper
than the drain-pipes just mentioned, as this enables the dirt and
sediment to settle out and lessens the liability of the drain-pipes
under the kiln to choke up with sediment.

It is often convenient to connect the drain-pipes of the kiln
to a small chimney, so that the system can be kept dry by means
of the continual draught of the chimney itself. Connexion may

314

MODERN BRICKMAKING

be made to the ordinary chimney of the kiln, but a supplementary
chimney is often better. The slope of the drain-pipes may be
arranged to suit local conditions, but should not be less than 1 :
100. In some cases where there is much water to be removed a
small well should be dug at the lowest level of the drainage
system, and all the water led to this well, which can be emptied
periodically with a small pump.

Another effective method of draining a kiln is to construct

FIG. 224.— Kiln foundation.

the foundation as shown in fig. 224 in cross-section. The ground'
is excavated to a depth of about 3 ft. and is well rammed, with a
slight fall towards the centre. A bed of large stones, 18 in.,
thick, is formed, with a rough kind of central canal for drawing
away water. This canal must have a proper drainage outlet.
On the stones a layer of gravel is placed, and then a bed of well-
rammed mild clay or loam. On these two layers, which would
be only 2 in. to 3 in. in thickness, is spread a good bed of sand
and over this a paving of hard bricks bedded in clay.

FIG. 225. — Cross section of fig. 224.

In most cases this isolation of the floor will suffice, but when>
water has continual access to the subsoil it is desirable to-
provide a means of independent liberation of the evaporated
moisture which is continually produced. In this instance an*
effective method is to provide a complete canalization of the
floor with inlets at each end of the kiln and outlets at the
middle. Fig. 225 shows the cross-section of this scheme with
brick flues, though 4 in. land drain -pipes may serve equally well-
Over the flues are layers of loam, sand, and paving brick.

KILNS 315

At each end of the kiln a collecting flue is formed, with -a
couple- of inlets from the open air. At the middle, two collecting
flues carry the accumulated moisture to up-cast shafts. By
their draughts these shafts maintain a gentle current of air
which enters at the ends and carries off the water vapour as it is
formed. If the kiln chimney is sufficiently powerful, the draught
may be obtained by connecting the middle flue to it, dampers

Wrong construction. Right construction.

FIG. 226. — Brickwork arch.

being provided to regulate the flow of air, but as already stated,,
a separate chimney is preferable.

The arches and crowns of kilns are often badly designed and
constructed. There is a general tendency to use plain instead
of special bricks for this purpose, with the result that a weak
arch with wide joints instead of narrow ones is produced.

The difference between arches built of plain bricks and pro-
perly shaped wedges is clearly shown in figs. 226 and 227, in

Wrong construction. Kight construction.

FIG. 227. — Arch of double brickwork.

both of which the left-hand side is shown constructed of plain
bricks with excessively thick joints, especially at the outer ring'
of -the arch, whilst the right-hand side shows the thin and evenly
distributed jointing with wedge-shaped bricks. The difference
is more noticeable in smaller arches than in large ones, and in
bricks arranged as in fig. 226 ; but in either case the effect is the
same — an excessively weak arch which must soon be repaired,
and a total loss of some 80 per cent of the total expenditure as
compared with the use of properly shaped wedge bricks. If the

MODERN BRICKMAKING

arch is of very large diameter — over 25 ft. — the taper required
is so small that it may be neglected and ordinary shaped bricks
used. If, 011 the other hand, the kiln arch is less than 25 ft.
diameter the bricks should be arranged to have a taper propor-
tionate to the diameter of the arch.

This taper may be made by cutting the bricks before they
are dry by means of a stiff knife or a specially fitted wire-cutter,
or, as is preferable, they may be produced through a mouthpiece
which gives them the right taper. The taper of the bricks may
most conveniently be calculated as follows : Measure the in-
side diameter of the arch in inches and call it A. Having de-
cided the design of the arch, measure its outside diameter, or
add to the inside diameter twice the web of the arch, and call
this outside diameter B. The taper of the bricks will then be
B : A. That is to say, the widest and narrowest parts of the
wedge-shaped arch brick will be in the proportion B : A. Instead
of calculating the taper of arched bricks, it is generally better to
set out a portion of the arch to full scale on a convenient board
or floor, and to take the measurements direct from this, as the
bricks can thus be tried before many are made, and small errors
(if any) altered.

For most purposes the use of hollow bricks is better than
plain, solid ones for kiln arches, as the former are not nearly so
heavy, and yet are of practically equal strength.

The strength of the arches is a matter often needing special
care, for it must be remembered that the masonry must not only
be sufficiently refractory to withstand high temperatures, but it
must also be possessed of such resisting power that it can bear
the strains set up by the continual contraction and expansion.
Flattened arches are, therefore, to be avoided, as are also those
with a very pronounced point. In almost every case the true
semi-circle is the best form of arch.

In the case Of a continuous kiln it is usually wise to have
the feed-holes through which the coal is supplied to the kiln
made of blocks of fire-clay or at any rate of the most refractory
clay easily obtainable. The number of these blocks in an arch
varies with the number of feed-holes, and in the accompanying
illustration (fig. 228) three blocks are used.

In constructing arches of bricks and blocks, care is needed
to get the shapes of the latter correct so that they fit well to the
bricks, as, otherwise, there is a serious danger of collapse after
the kiln has been in use for some time. In setting out such an

KILNS

317

arch the most important measurements are indicated by the
dotted lines in figs. 228 and 229, in both of which r is the radius
of the semi-circle composing the arch. Where these blocks
can be purchased ready-made the speed of building is greatly

FIG. 228. — Section of chamber of continuous kiln.

increased, but even when they have to be made specially they
soon repay their cost in the additional strength, security, and
freedom from slip which they give to the arches in which they
are used. The wicket arches may be constructed in a similar

FIG. 229. — Section of chamber of continuous kiln.

manner, but where special blocks can be made, they improve
the appearance of the kiln. Such blocks are now supplied ready
for use by several German fire-clay manufacturers, the one
shown in fig. 230 being popular on account of its neatness and
strength. Like the other arches it is of a semi-circular or Ro-
man type. The distance r should never be less than 20 in. so

318

MODEBN BRICKMAKING

as to allow ample room for the men to enter the kiln without

scraping the bricks. Fire-clay blocks used in arch construction

_^_^^_^,_^.^^_^ should be of open material, so as

to respond readily to sudden
changes in temperature without
damage. They must be fired in
such a way that they do not warp,
and if at all twisted must be care-
fully dressed before use.

" Drop arches " are often built
in continuous kilns to prevent the
air travelling along the top of the
inside of the kiln at too rapid a rate. They are primarily in-
tended to act as baffles and are generally desirable though not
indispensable, Their strength need not be great, though they
act as supports for the proper arch. Their shape is clearly
shown in fig. 231.

In single round kilns the whole roof or crown is dome-shaped,
the curvature of the crown usually being part of a true circle

FIG. 230.— Wicket arch.

FIG. 231. — Interior of Osman kiln.

though not a complete semi-circle. This form of crown is much
stronger and in every way preferable to one which is either
more pointed or flatter.

The fire-boxes and bags of a kiln need careful design and con-
struction if the heat is to be economically produced and evenly

KILNS 319

distributed. Usually the fire-boxes are too shallow and allow too
much air to enter above the fuel. The " box " or hopper pattern
where a considerable depth of fuel is present and forms its own
seal, is usually the best for single kilns. In continuous kilns the
depth of fuel on the grate, or in the trough, is of less importance,
and in those of the original Hoffmann type no permanent fire-
boxes are used.

The feed-holes in the top of the kiln must be kept covered
with air-tight caps or bells. In many cases the amount of air
which leaks in through the caps is sufficient to spoil the draught
and prevent satisfactory firing. As the top of the kiln is hot, a
liquid seal cannot be employed, but some form of sand-seal
should be used. The common practice of a simple bell fitting
on to a raised rim is far from satisfactory. The use of a conical
lid fitting into a ring (fig. 232) is but little better, as, whilst air-tight
when new, the effect of repeated heating and cooling makes the

FIG. 232. — Conical cap in feed-hole.

metal twist and fit badly. A simple and durable, but at the
same time air-tight, cap is greatly to be desired, and there is scope
for ingenuity in this direction.

The position of the feed-holes may be seen in figs. 228, 229.

The flues of most kinds of kilns, but particularly those of the
continuous type, need unusual care in regard to their arrange-
ment and construction.

A common error with some kiln builders consists in construct-
ing flues, the sizes of which have no relation to each other or to
the capacity of the kiln ; their dimensions being determined
largely by guess-work. In a kiln with simple flues this may
often prove satisfactory, particularly if all the flues are larger
than is really necessary, but in many cases defective draught is
produced and disappointment is caused when a 15-in. square flue
cannot discharge its contents completely into a 12-in. flue some
distance away, with probably a couple of bends between them.
It is frequently desirable to connect smaller flues to larger ones

320 MODEEN BRICKMAKING

so as to vary the speed of the gases travelling through them,,
but this should only be done when the designer has a definite
object in mind and is fully aware of the consequences. Such
little troubles as are caused by discharging flue gases through
opposite openings in the same flue without any midfeather are
frequently met with, and are a continual source of mystery until
some one finds out what is really the matter. Fortunately, they
can usually be put right when found.

On the Continent, small flues are frequently made of sanitary
pipes carefully bedded, it being considered that they are tighter
than the brickwork flues almost exclusively employed in Great
Britain.

Flues are often made too small and inaccessible as well as-
being placed in positions which are undesirable from the point of
stability. Their walls are often too thin and the connexion with
other flues badly made. The connecting flue of a continuous
kiln should be sufficiently roomy for an ordinary sized man to
get inside it easily for cleaning purposes, and should be provided
with so many openings that, no matter which part of the kiln is
under fire, the flues may be entered in the cooler parts direct
from one of these manholes. The covers for these manholes-
must, of course, be kept air-tight, usually by means of sand and
often by a second cover of wood or iron. Sometimes defective
draught is caused less by the flues than by unsuitable dampers.

All dampers should fit tightly when closed, a " sand-seal "
(similar to a water-seal) being used if necessary. They should
usually be designed and made specially, as home-made dampers
are often unreliable. In continuous kilns the tightness of the
dampers is of very great importance.

Chimneys are often too slightly built, and so lose heat and
draught-producing power. Lined chimneys have a great advan-
tage in this respect.

The attempt to save money by building a chimney which is
only just large enough for the work is really a false economy, as
sooner or later it will result in the gases being turned into the
chimney at too high a temperature, and consequently any sav-
ing 011 the original cost of the stack will be more than counter-
balanced by the unnecessary high expenditure of fuel in firing
the kiln. The chimney must be regarded as a " capital " invest-
ment, and the saving effected by its use must be reckoned as
legitimate interest on the capital spent. If a short chimney is
erected, the fuel wasted by turning hot gases into the chimney

KILNS 321

will represent an annual expenditure corresponding to possibly
25tper cent interest on the additional amount of money originally
required to have made the chimney of the right size. Not only
so, but with ample chimney capacity (in other words with ample
draught) it is possible to " smoke " the bricks far more effectively,
and so not only increase the output of the kiln, but to turn out
a better class of goods, and, consequently, to produce a larger
income for the same amount of expenditure.

For this reason, it is usually desirable to substitute a fan for
a chimney in cases where the capital available is not sufficient
to build a chimney of ample size. The relative advantages of
fans and chimneys are described on page 288.

It has already been pointed out that a roof is essential on all
continuous kilns, and it is desirable to have one erected over single
kilns if the best or most economical results are expected from
the firing. The reason is that all water which is driven off the
top of the kiln by evaporation represents a definite waste of fuel
which could be saved by the erection of a roof or shed over the
kiln. When no roof is provided, the crown or arches of the kiln
begin to sag on account of the rain soaking into the brickwork,
instead of being carried off by a roof ; the fuel is wasted because
the kiln has to be dried after each shower, and because the fuel
stored around or on top of the kiln is, in winter, in a soaked con-
dition. The fireman, too, does his work in a less satisfactory
manner, because he has to be exposed to the cold and rain ;
whereas in a properly constructed kiln both he and the fuel, as
well as the brickwork itself, would be covered by a roof which
would effectually protect them all.

It is curious how many firms will spend £1000 or so in build-
ing a kiln, and yet will not lay down the extra sum required to
keep their kiln in good condition by erecting a cover over it.

In selecting a kiln for a given brickyard it must be remembered
that the pivot upon which the success or failure of a clay -works
turns is 'frequently due, not to the clay but to the kilns employed.
The proportion of the total interest on capital chargeable to the
kilns is very high in many yards, and thus, the choice of a
kiln is of the greatest importance. Besides, the kiln is the final
machine through which the bricks must pass, and, consequently,
if it works unsatisfactorily, all the labour expended in making,
drying, etc., is lost, as well as the loss directly attributable to the
kiln itself.

21

822 MODERN BRICKMAKING

Many brickmakers think that because a certain kiln is suit-
able for a similar clay to their own, it is equally fitted for burn-
ing their own clay, without any modification or adaptation, and
far too many continue to make wares of inferior quality when,
with a little alteration either in structure, setting, or firing, they
might produce a large percentage of well-coloured, -soundly ring-
ing bricks.

The most economical kiln is the continuous kiln of the
Hoffmann type and its many modifications for special clays
and classes of goods, yet such kilns have, unfortunately, a de-
cided limit below which they are not economical, and firms with
-an output of only 500,000 bricks or less per year will be
well advised not to invest in a continuous kiln, statements by
kiln builders to the contrary notwithstanding. There are several
reasons for this, but one of the most important is that it does
not pay to build a kiln which is too large and must be worked
far below its normal capacity.

A further disadvantage of installing a continuous kiln for
small outputs^ or for widely varying outputs, is the temptation it
offers to the foreman and works manager to make too large an
output for the demand. Some brickmakers imagine that it
makes no difference whether one makes a small quantity at a
certain profit or double the quantity at half the profit. This is
a false argument, for it does not include the wear and tear on
plant and kiln due to more rapid working; and whilst the
machinery may be easily repaired at a small cost, what about
the kiln?

On the other hand, it is not wise to select a kiln which is
likely to be too small, though this is far less an evil than too
large a kiln. " Large kilns bring great anxieties, whilst small
kilns bring small pleasures." If times are bad a small kiln
means less loss, but on the other hand, a small kiln is very
annoying in days of sudden good trade, in which there is no
time to erect additional kiln room before the boom has passed.
On this account as fair an average as possible should be used as
the basis on which to determine the size of kiln to be erected,
so that the annoyance of unavoidable loss 011 the one hand and
unattainable profit on the other shall be avoided.

A clamp kiln is rapidly becoming obsolete in many districts
on account of the impossibility of obtaining many facing bricks
from it, some of the bricks being under-fired whilst others are so
b;idly scorched that in some cases they are half melted. It is

KILNS 323

impossible to get all the bricks fired at the same temperature,
but in Kent, etc., architects insist on clamp-bricks.

Clamp kilns are frequently employed in order to obtain bricks
for the erection of a kiln in a newly started work, but, unless
the cartage is likely to prove most unusually heavy, it .is scarcely
any cheaper to make and burn the bricks on the site than -it is
to purchase them from a neighbouring yard, for clamp kilns are
often wasteful in fuel, and the brick trade for several years has
been in such a state that almost any yard will sell bricks at but
little over actual cost, and be satisfied that they have made a
good bargain !

Intermittent kilns certainly cost less to erect than a con-
tinuous kiln, but not when they are of the same capacity as- the
latter. The main advantage offered by single kilns is that a
man can put up two intermittent or single kilns, whereas it does
not pay to erect less than six chambers in a continuous or semi-
continuous kiln,' as so small a number does not give the user
the full benefit of the heat in the waste gases. Consequently,
when only a small output is required, a few single kilns are often
preferred.

If it is expected to increase the output rapidly to above
1,000,000 per annum, it is better to build part of a continuous kiln,
and to work it on the semi-continuous principle rather than to
build separate kilns which will be thrown out of use when a
larger one is built. For certain classes of work, however, it is
still necessary to use single kilns.

Probably the best form of brick kiln is a partially built con-
tinuous kiln, as this, whilst complete in itself, is always avail-
able for extension whenever the increasing trade of the district
demands a larger kiln. When part of a continuous kiln is built
it is not so economical in fuel as the whole kiln, but it is not so
wasteful as are intermittent kilns of the same capacity. At the
same time each enlargement of the kiln increases its economy
of working, and there is no setting aside of kilns which are not
wanted because they have been replaced by a continuous kiln,
as is the case in many yards at the present time.

In the erection of such a partial kiln it is necessary to con-
sider carefully the character of the clay, as when a delicate clay
requiring very slow and gentle warming is to be fired, a much
more complete kiln should be built than if a small output of a
readily fired clay is required.

The size of the kiln must, as already noted, be equal to the

324 MODERN BRICKMAKING

average output, or a trifle larger, as it is better to miss a little
trade in the best years than to be saddled with too large a kiln
during bad seasons. The question whether it is better to have
two moderate sized continuous kilns or one single one of equal
capacity is one which admits of much discussion, though the
actual loss of working a large kiln partially is less than working
a small kiln fully and keeping another of equal size quite idle
except for occasional use. Owing to the heat to which they are
subjected, kilns do not resist the action of the weather well when
out of use for a long time, and it is better to have one rather
than two continuous kilns, but this should not be much larger
than the average output of the works for a period extending over
several years, if the best results are to be obtained.

The length of a continuous kiln should be sufficient to fully
utilize the " waste " heat from the fuel. There is a great tend-
ency to build kilns which are too short, with the result that the
heat which should be obtained from the cooling goods and from
the fire-gases is lost, instead of being utilized for drying and
heating the freshly placed goods.

Where a small output is required the kiln should have . a
narrow tunnel, the width being increased with large outputs,
instead of the usual method — of retaining the width constant and
reducing the length — being adopted.

The width of the tunnel of a continuous kiln is sometimes
the subject of strange criticisms. It is frequently stated that
tunnels not more than 8 ft. 6 in. or 9 ft. are best and that wider
ones are detrimental to the quality of the goods. As a matter
of fact, the width of the tunnel can be made 18 ft. without any
disadvantages arising, provided the kiln be properly built and
fired, and with transverse arches still wider chambers can be
satisfactorily employed where the output justifies their use.

Where very large outputs are required, it will often be found
best to build continuous kilns of a shape similar to one of the
plans shown in fig. 233. These are known as " Shank Kilns," and
owing to their special shape several fires can be kept going in
each with a minimum of labour, and the cost of erection is less
than that of several continuous kilns of equal total capacity. A
considerable number — over 200 — of these shank kilns are in
existence on the Continent with an annual output varying from
5,000,000 to 50,000,000 each.

A continuous kiln can sometimes be enlarged by adopting
the " Shank " principle just described ; such an alteration to an

KILNS

old circular Hoffmann is shown in fig. 234, which is reproduced
from the " British Clay worker ".

In enlarging a kiln in this way it may be necessary to supple/"
ment the chimney-draught by the aid of a fan.

A great advantage to be gained from the enlarging of a kiln

FIG. 233.— Plans of shank kilns.

in this manner is found in the instance of bricks or tiles which
need very careful warming or prolonged heating as, with so long
a fire-canal as is thus produced, it is possible to burn the most
delicate clays with ease. In some cases it is even possible to
dispense with a dryer and to remove the moisture by a some-

FIG. 234. — Plan of enlarged Hoffmann kiln.

what longer steaming in a manner impossible with the ordinary
twelve-chamber Hoffmann kiln. It was, in fact, the necessity of
treating a new clay found in the course of working an old and
almost worked out pit that first compelled a certain brickmaker
to find a method of enlarging his old kiln, and by doing it as

326 MODEBN BRICKMAKING

shown in fig. 234, he was able to work an unusually delicate
clay with perfect satisfaction.

SETTING AND BURNING,

Bricks must be placed (or " set ") in kilns in certain patterns,
according to the nature of the kiln and the kind of bricks to be
produced.

Thus, in an up-draught kiln, the bricks must be arranged
differently to those fired in a down-draught or continuous kiln.
Again, where glaze or colour is of great importance, it is necessary
to so place the bricks that the " face " is protected, whilst for
commoner bricks no such protective arrangement is necessary.
Many firms fail to obtain the best results simply because they
do not set the bricks to the greatest advantage in the kilns,
using a down-draught arrangement where one suitable for hori-
zontal draught is required and vice versa.

Unless dried by the Scott system, or set direct in continuous
kilns after being made by the stiff-plastic, the semi-dry or
dust processes, bricks should be dry when they enter the kilns.
The method or process by which the bricks have been made is
therefore of little or no importance as far as the setting in the
kiln is concerned. A wise brickmaker will, however, insist on
the dampest bricks (if there are any) being placed uppermost in
the kiln so that the moisture in them may escape more readily
and with less liability to damage other bricks. Methods of set-
ting may be divided into four classes : (1) for up-draught ; (2) for
down-draught ; (3) for horizontal-draught, and (4) where special
protection (as in glazed bricks) is needed.

In an up-draught kiln the heat enters, nominally, below the
goods and rises through them, though in practice it chiefly
enters at the sides. The bricks should be set about f in. apart,
with their longest side parallel to the direction in which the hori-
zontal portion of the fire travels — usually from the fire-box to the
centre of the kiln. Less frequently, the bricks are arranged up-
right, each row breaking joint with the row below it. Usually,
but little difference is made between the setting of up- and down-
draught kilns, and providing the conditions already mentioned
are maintained, the methods described for down-draught kilns
may usually be followed. The main points to remember are
that the heat must be able to circulate freely and evenly among
the bricks, and the bricks must be so arranged as not to slip

KILNS

#27

out of place. This latter requirement usually necessitates their
being crossed by bricks running at right angles every few courses.

In a down-draught kiln the heat rises behind a flash-wall or
bag and descends upon the bricks in a downward and sloping
direction. It distributes itself amongst the goods and passes
out through one or more openings in the centre of the kiln.

If, as is often the case, only one exit is provided, the bricks
must be set somewhat closer near the centre of the kiln
and more open (about 1£ in. apart) for the lowest four rows
nearer the sides, so that the outer parts of the floor may be fully
heated ; or the flash- or bag-wall may be perforated near the floor
so as to allow some heat to pass direct towards the centre flue.
When a perforated kiln-sole is used
these precautions are less necessary.

In a down-draught kiln the bricks
are usually placed " five on two " (fig.
235), as this forms a convenient and
easily remembered arrangement and one
of ample strength. With thicker bricks
the nearest to this must be used, the
bricks being set about f in. apart.
Where the bricks are sufficiently stable another row qf bricks
may be set on the five headers, and sometimes a second row of
stretchers is used.

FIG. 235.— Bricks set
"double five on two".

FIG. 236. — Section of lower part of kiln showing perforations (Brown).

The bottom two courses must be arranged so as to leave any
perforations in the kiln sole fully open (fig. 236), after this the

328 MODERN BRICKMAKING

setting may proceed regularly until the kiln is filled to the level
of the top of the bag- or flash-wall. It is unwise to fill it higher,
as the fire-gases require a considerable amount of space for their
proper combustion and distribution, and this is not provided
when the kiln is too full. Down-draught kilns differ from up-
draught ones in this respect.

Some bricks— particularly those burning buff or white — are
better set flat in " walls " or " blades " 9 in. wide, care being
taken to let the bricks break joint, and being about f in. apart,
the " faces " never being in contact as is the case with red
facing bricks. Some white or buff bricks (including most fire-
bricks) are best set in this way, the ends facing the fire.

In setting red facing bricks in a down -draught kiln special
precautions have to be taken, there being a great risk of pro-
ducing a grey stain on the bricks, and many thousands of such
bricks are spoiled annually by an improper method of setting.
To obtain a first-class red facing brick the kiln -floor must be
level and the arrangement of bottom flues already given is
usually satisfactory, though some bricks are better if the set-off
or bottom portion has 9 -in. flues, four bricks deep, and a double
span over, and a tier of bricks to stretch across the top, breaking
the joints of each flue and thus making the bottom very strong
to stand the heat. Care should be taken not to set the bricks
too close in the bottom. From the set-off of the kiln, bricks
made from a semi -dry machine may be set four bricks one on
top of the other, with a double row of stretchers , above ; this
alternation of four headers and two stretchers being repeated
until the kiln is filled. Wire-cuts and sand-stocks will only
stand three headers high. Sand-stocks «. do not stain as much
as semi-dry bricks, on account of the sand on. the face.

Bricks should, usually, be set from side to side in the kiln
in rows or "bolts," and care should be taken by the setter,
after the first double bolt is finished, to keep the heads, or
ends, of the bricks in the remaining bolts in a straight line with
and tight to one another, so that one may look right through the
chamber from the first bolt to the last. This gives the steam and
fire-gases a straight line and a free course without any chance of
staining the faces of the bricks.

In round, down-draught kilns with a centre flue, it is usual
to lay bricks radially from end to end, and so converge the
spaces between the bottom two or three courses towards the
centre. These two or three courses are laid exactly one over

KILNS

329

the other, stretcher faces in contact. On this " foot " the usual
setting is adopted of five bricks side by side over two bricks end
to end. If the bricks are more than 2f in. thick the five bricks
will be correspondingly less in number. This regular setting
above the foot should be started in a way to suit the tying-in of
the radially placed bricks of the foot.

Other arrangements for setting bricks in a down-draught kiln
are known as "2 on 2," "3 on 3," and "5 on 6 " respectively.
The first is used where very open setting is necessary ; the last
is suitable where the bricks are finished at a low heat and where
.an unusual amount of support is needed (fig. 237).

In a horizontal draught or continuous kiln the setting of the
bricks is slightly different. As the draught is not required to
rise, it is possible to lay the stretcher bricks closer together than
in an up-draught or down-draught kiln, and any vertical spaces

Till

"V

]

-:.-•

=

. L

= -"

]x

a b c

FIG, 237. — Brick arrangements.

(a) "2 on 2."

(6) " 3 on 3."

(c) " 5 on 6."

between the rows, " blades " or bolts are of far less importance
in a horizontal-draught kiln.

In setting bricks in a continuous kiln it must be remem-
bered that they will be subjected to a horizontal draught which
will have a natural tendency to travel along the roof between
the top of the setting and the arch. This upward tendency must
be prevented as much as possible, and this is accomplished by
setting the bricks close to the arch, and when the wares are not
of a very combustible nature it is generally advantageous to
pitch, or set closely together, the top two or three courses, thus
diminishing the number of top-draughts or channels.

To keep the cold air from travelling too quickly between the
arch and the brick in the burnt section, drop arches are gener-
ally built in each chamber (this applies only to the Hoffmann
type of kiln). These drop arches, as a rule, answer their pur-
pose well, though excellent results may be obtained by putting
the top brick of the setting into the feed-hole ; if any difficulty

330

MODERN BJRICKMAKING

is found in stopping the, hole, soft clay should be used, the real
object being to prevent the fine coal from dropping to the bottom
of the kiln. This will give a very useful fire on the top of the
brick, which will heat the air if there is too free a passage along
the top of the brick, due to their settling. The usual arrange-
ment is to set a row of bricks 011 edge -£ in. apart in the direction
in which the fire travels, and on these another row. A third or
even a fourth row may be added if desired, though it makes the
setting less stable. Across these bricks a single row is set at

FIG. 238. — View of bricks in continuous kiln.

right angles, and on this another two rows of headers. This
alternation of one row of headers and two of stretchers is con-
tinued until the kiln is filled almost to the top (fig. 238).

Where a somewhat greater flue-space is required, three bricks-
may be arranged on each other as shown in fig. 239. By setting
the bricks in pairs greater stability is obtained than if the flue-
space is left between each set of upright bricks. There should
be ample draught space in the lower portion of the setting, par-
ticularly in the trace-holes. These trace-holes are in the same
direction as the draught during the whole period of burning, as

KILNS

331

FIG. 239.— Trace-holes.

they may become choked with coal or ash. which would merely

retard the progress of

the fire throughout the

kiln.

An important point

to be taken care of is

that of determining the

number of sections of

chambers to be set,

taken on and treated as

one chamber in the

Hoffmann kiln. The

writer has known diffi-
culties to arise from
too large a number

of chambers being
coupled together in this way. Two chambers are quite sufficient
to be coupled together and is as large a section as is consistent
with good management. Each section should have a papered
end unless permanent partition walls exist.

In a continuous or other horizontal draught-kiln there is no
need to stop short of filling completely to the top of the arch, as
the combustion of the gases takes place elsewhere and not, as in a
down-draught kiln, above the goods.

With kilns with a horizontal-draught the combustion space,
or " free " space, must be at right angles to the draught ; in a
Newcastle kiln it is immediately behind the fire-boxes (a space
of 3 ft. or so in width being left on purpose) and in some con-
tinuous kilns it is immediately above and to one side of the
grates, fire -troughs, or bags. Hence in continuous chamber
kilns the goods nearest to the fuel should not be set vertically
but with a distinct slope in the direction of the draught.

When the fuel is fed amongst the bricks in a continuous kiln
(as in the original Hoffmann kiln) the same general arrange-
ment of setting is used, but beneath each of the pot-holes- in the
roof a vertical flue is left in which the fuel can burn. One pat-
tern of such a " flue " is shown in fig. 240, certain bricks being
made to project in such a manner as to form a series of ledges
on which the fuel can rest and burn, only a very small portion
tailing direct to the bottom of the kiln.

For a beginner, the best way to construct one of these flues
is to fix a plank about 1 in. thick and a little narrower than

33*2

MODERN BBICKMAKING

FIG. 240.— Fuel shaft in
Hoffmann kiln.

the pot-hole in the arch of the kiln, vertically below (and

through) the hole, and to set the bricks
alternately close to and away from this
lath on all sides so as to form the verti-
cal space shown in fig. 240 ; the enlarged
space at the bottom of the shaft serves
to contain the ashes from the fuel, and
to enable the burner to estimate the
temperature of the lower part of the
kiln.

Fire-shafts of other shapes are pre-
ferred by some burners — much depend-
ing on the fuel used — and in some parts
of the Midlands they are built by setting
bricks in pairs as headers and stretchers
alternately (fig. 237a). One of the great
disadvantages of the use of such fire-
columns is the liability to errors in
setting which they cause, and such errors are often discovered
only when too late to be repaired. To avoid them it is essential
that the changes in the setting in various parts of the kiln should
be reduced to a minimum, and, however desirable from the
burner's standpoint, the practice of setting the bricks closer to
each other as the arch is approached, and other methods requir-
ing special skill on the part of the setters, cannot be considered
as ideal. For this reason the author has frequently used with
success a method which consists in leaving a space between the
blades or walls, in which " trough," bricks are set in rows on then-
edges as shown in the centre and sides of figs. 241 and 242. This
arrangement provides ample ties for the bricks, and requires no
laths or other guides for the setters to enable them to keep the
flues properly in line, as the joints of the bricks show where the
next layer of bricks is to be placed. The construction of the
fire columns is also simplified, as will be seen from the illustra-
tions, as a single space is left throughout the whole width of
the chamber. This space is 2^ to 3 in. wide, and on the bricks
which partially bridge over the space, some of the fuel will be
retained in the upper part «. of the kiln.

The aperture in each chamber which leads to the main flue is
made by leaving a space about 4 in. wide, and extending the
whole breadth of the kiln. The fourth row of bricks from the
bottom is laid close, so as to form the top of this shallow flue

KILNS 333

which leads the gases direct to the main flue. Various forms of
this " trough " arrangement are much used in France (fowr d
tranches) and in Germany (Heizwdnde).

If the bricks are dried by fires placed at the wicket, a series
of flues is made to carry the heat from these fires as far into
the chamber as possible, as otherwise the direction of the heat
will be from the wicket to the nearest exit and a large portion
of the chamber will always be left cold.

To obtain facing bricks of good colour the setting must usually
be similar to that in down-draught kilns, i.e. two faces are
placed together before they are tied crosswise by two more, and
so continued up to the required height. The flues or passages
are, however, arranged in the same way as when common bricks
are burned.

The most recent method of setting bricks is one exploited by
the American Clay Machinery Co. So far, it has only been used
in the United States for setting stiff plastic and semi-dry bricks
direct into the kiln. A travelling crane carries a hod of 120
bricks from the machine to the place where they are to be set
in the kiln, and deposits the bricks ready for burning. The
arrangement of the bricks on the hod determines the setting, the
bricks being built up in " units " which are stacked on each other.
In the very large open rectangular kilns (scoves) used in the
States, and to a smaller extent in archless continuous kilns, this
method appears to possess advantages over hand-setting for
common bricks, but it can, obviously, only be used in those cases
where an overhead rail or crane can deliver the hods to each
part of the kiln.

After a " chamber " has been set it must be separated from
the remainder of the kiln by means of dampers. Where no per-
manent cross-walls are used it is convenient to fasten sheets of
paper right across the bricks, smearing the edges of the paper
with clay -paste to make the partition air-tight. The special
characteristics required in paper used for this purpose are de-
scribed on page 277. The paper must be joined with good paste
if single sheets of sufficient size cannot.be obtained, as leaks
are very objectionable and waste fuel.

When permanent walls are erected, the paper need only be
pasted over the trace-holes, though permanent dampers of iron
and fire-clay are often used instead. Three chief forms of
damper-leakages are possible and must be considered separ-
ately : —

334 MODERN BBICKMAKING

(a) The damper nearest the kiln fire may leak, and conse-
quently the hot air as it enters will be more or less completely
drawn through it and away to the chimney from the flue in
the chamber nearer the fire, instead of its being drawn around
the goods to be smoked, and after warming them, passing away
through the main flue.

(b) The damper nearest the empty chamber may leak and
the one at the other end of the chamber being smoked may be
tight, with the result that cold air will be drawn into the
chamber to be smoked through the nearest open wicket, and will
not only diminish the amount of hot air drawn around the goods
to be smoked, but will itself take up some of the heat to no
purpose, and may tend to crack the goods by placing them in
contact with cold air.

(c) Both dampers may leak at the same time. In such a case
both the defects previously mentioned will be increased by their
tnutual action on each other, and a particularly unsatisfactory
smoking will be produced.

The chief precautions to be taken to prevent these troubles
depend on the causes of leakage, and are as follows : (1) Leak-
age due to bad workmanship in pasting on the damper, or to the
use of too thin a clay slip, or to a slip made of too fat a clay.
This may be cured by improved workmanship, by seeing that
the slip is a thinnish paste and not a mere liquid, and of the
right composition. In many cases also, the leakage is due to
insufficient margin round the opening. As already explained,
this should be ample in order to secure a tight joint.

(2) Defects in the walling of which the partition is made, and
which suggest partial rebuilding as the most satisfactory cure.
The use of a poor paper would act similarly, and either a more
waterproof paper must be purchased or it should be pasted over
with clay slip.

(3) Insufficient draught in the chamber being smoked, there-
by causing a deposit of condensed steam 011 the paper partition,
which soddens it and causes it to collapse, or which may prevent
its burning sufficiently soon. The draught in the smoking cham-
ber, should, whenever the goods will stand it, be as strong as
that for the remainder of the kiln, and like it should be measured
with continuous reading gauge. Careless regulation of the
draught will sometimes put such a sudden strain on the paper
partition as to rupture it, so that the burner should remove his
flue-dampers with sufficient slowness.

KILNS

335

(4) The stove may be too near the damper, and sparks from
it may set the latter on fire, thereby producing what is to all
intents and purposes a serious leak. A simple bending of the
pipe so that no sparks can possibly get on the paper will prevent
this disaster.

Special Goods such as hollow blocks, moulded bricks, etc., which
must be specially protected in the kiln, are usually burned in'
small chambers built for the purpose inside the kiln ; as long as
these chambers are not large no difficulty need be experienced,
but when considerable space is required special arrangements
must be made.

FIG. 241. — Cross section of temporary muffles.

Where the demand for goods which have to be protected in
the kiln is sufficiently great a muffle kiln should be used, but
when this is not required the arrangement of part of a continu-
ous kiln, as suggested by F. Hoffmann (figs. 241 and 242), will often
be found satisfactory. Fig. 241 shows a hollow chamber on each
.side of a special flue, two such chambers and the necessary flues
extending the whole width of the tunnel or chambers. The
bottom flues are not built with solid walls but in chequer work,
the space between the ends of each brick being 2J to 2£ in. The
;side and centre flues are arranged to act as fire-columns as well
as flues, their construction being shown in cross-section in fig. 241
.and in plan in fig. 242. Full protection of the goods is secured

336

MODEEN BEICKMAKING

by two rows of bricks set close and , smeared with daub, which
form the special chamber. The special goods having been set
in the chambers provided, a front wall of bricks set close is erected
and daubed. It is, however, wisest not to build such a wall at
the end of the " box " but only at the beginning, as in this way
the combustible matter and moisture can more readily escape
than when the bricks are enclosed on all sides. The rest of the
kiln is then filled with bricks set in the ordinary way.

The number of men required depends upon the size of the
kiln and the output of the making shops or machines. If the
kiln is lar^e enough, three or even four men may be employed
in actually setting the bricks, but for most purposes two are all
that can work at the same time, and when the output is low a
single man may be sufficient. Speaking generally, two men work

FIG. 242. — Plan of two temporary muffles.

most effectively with an ordinary 14 or 16 ft. chamber, pro-
vided they have the bricks placed conveniently near to them by
the " wheelers ".

Glazed Bricks must be so placed in the kiln that the glazed
faces are protected from the flame. Muffle kilns may be used
but are costly in fuel, so down-draught kilns are generally
employed.

A good arrangement is that shown in fig. 243, and largely used
by the author since it was published by L. E. Barringer in 1903.
The stretchers or tie-bricks are unglazed, the glazed faces of the
headers being set together with a small space between them.
These narrow spaces are completely covered at the top and ample
protection is afforded to the glaze. To prevent the arrises of
the glazed edges sticking to each other, it is often necessary to
use short bars of clay between the glazed bricks to keep them
J in. apart, or the glazed faces may overhang slightly.

FIRING

337

When the setting is complete the kiln door-ways or wickets
must be built up with bricks covered with clay paste (" daub ")
to keep out the air. Sometimes an opening for a fire is left in

FIG. 243. — Glazed bricks in kiln.

the doorway, particularly with Newcastle kilns, end-fired Scotch
kilns, and in continuous kilns where a " wicket fire " is used for
the drying of the bricks (fig. 185).

FIRING,

The methods used for the " firing " or " burning " of goods in
a kiln depends upon the type of kiln used and on the nature of
the goods, but certain general principles apply to all ordinary
methods of burning bricks.

The chief requisite for the successful burning of bricks is the
steady raising of the temperature to a sufficient height at such a
rate that water and combustible materials may escape without
damaging the goods, and the expansion and contraction which
occur during the heating may take place sufficiently slowly to
prevent the strength of the bricks being diminished. This
appears a simple matter to those who have no practical experience
of brick burning, but in reality it is far more difficult than is
usually supposed. Some idea of the amount of skill required
may be obtained from the fact that an examination of a very
large number of bricks from the most important yards in almost
every well-known brickmaking district has shown that less than
half the bricks examined were fully or completely burned !

There are, in fact, two distinct heat-treatments possible in
brickmaking: (a) baking, and (b) burning. When bricks are
" baked " they are heated sufficiently to rob the material of its
plasticity, but they are not durable under very adverse conditions

22

338 MODERN BBICKMAKING

of climate or use. " Baked bricks " are somewhat soft, and when
two are struck together a dull or flat sound is produced, which is
very different from the ringing tone emitted when two " burned "
bricks are similarly treated. " Rubbers," " cutters," bath-bricks,
and ordinary firebricks are typical " baked bricks ".

" Fully burned " bricks are characterized by a distinct " ring "
when struck, and they do not shrink on further heating except
when heated to such an extent that change of shape occurs or
the specimens adhere to each other. Some bricks cannot be fired
to completion, because the temperature at which they are fully
burned is too near to that at which loss of shape occurs. Fully
burned bricks are less porous than those which have been insuf-
ficiently heated. Engineering bricks and many Midland and
Northern bricks are typical " fully burned " bricks.

In order to ascertain the amount of heat necessary to burn
a brick completely and the temperature to which it must be
raised before it is fully burned, certain tests must be made.
These usually consist in making specimen bricks or tiles,
measuring them accurately and heating them under carefully
regulated conditions to different temperatures. The test-pieces
are then examined for shrinkage, porosity, and change of shape,
and from the results of this examination a fair idea of the most
suitable kiln-treatment can be obtained. In making such tests
it is essential that at least one test-piece shall be over-heated so
that the highest temperature permissible in the kiln may be
known.

A brick is completely burned when it -no longer contracts on
further heating to a higher temperature,1 and when its porosity is
reduced to the smallest possible amount without the brick losing
its shape. There is a tendency amongst certain writers on build-
ing construction to assume that only fully burned bricks should be
used. This is by no means always the case, as certain effects
cannot be obtained with bricks which have been fired to their
maximum temperature, and the opprobrium cast upon " baked
bricks " by such writers is often quite undeserved. At the same
time, it cannot be denied that fully burned and partially vitrified
bricks are usually far stronger and more durable than those
which have been subjected to a less severe heat treatment.

1 Accurate measurements will show that contraction never ceases completely,
but a stage is reached at which its increase, during a large rise of temperature, is
so small that it may be disregarded and the shrinkage considered to have ceased.

FIRING

339

In this connexion it is curious that fire -bricks — which are
primarily intended to withstand the most trying conditions — are
never more than " baked " in this country, though in Germany
they ar*e often fired to incipient vitrification. Fire-brick manu-
facturers would do well to consider this point, which is far more
vital to success than many of them suppose.

The following list of maximum temperatures, originally pub-
lished by Seger, is generally accepted as a standard : —

GOODS.

SEGER CONE.

TEMPERATUBE IN ° C.

Porcelain colours and lustres .

022 to OlOa

600 to 900

Clays rich in lime and iron .

015a to Ola

790 to 1080

Brick-clays ; red-burning shales . , ,

015a to la

790 to 1100

Clinkers, paviours, vitrified bricks

la to 10

1100 to 1300

Stoneware ; salt-glaze

5a to 10

1180 to 1300

Majolica glazes . ;> . V ,,. .

OlOa to 05a

900 to 1000

Glazed bricks (hard fire) .. . ,

6a to 9

1200 to 1280

Fire-clay and porcelain . . '

7 to 20

1230 to 1530

Silica bricks ; magnesia bricks

16 to 26

1460 to 1580

For determining the refractoriness of clays

26 to 42

1580 to 2000

The figures in the last column are only approximate, and it is
always preferable to refer to the number of the cone rather than
to the temperature, especially with the higher numbers.

In most cases of clay-burning the exact temperature reached
is of less importance than the length of time the goods are ex-
posed to a certain temperature, e.g. whether the maximum
temperature is 1250° or 1300° C. matters less than the time of ex-
posure at 1250° C. The essential question is — " Has the heat been
acting for a sufficiently long time ? "

The finishing temperature for most red-burning clays corre-
sponds to cone 015a to la (790° to 1100° C.), the latter being reached
with many red-burning shales. Fire-bricks are usually con-
sidered finished at cone 5a (1180° C.), but cone 14 (1410° C.) is much
more suitable as a finishing point, and far higher temperatures
are attained in some Continental fire-brick works.

The maximum temperature to be reached in the kilns having
been ascertained, it is necessary to consider the stages which
must be passed through before this temperature is reached.

Generally speaking, the burning of bricks must take place in
three separate stages, viz. (a) drying or " steaming " (sometimes
called " stoving ") ; (b) preliminary heating and removal of vege-
table and other combustible, matter ; (c) full fire and completion of

340 MODEKN BEICKMAKING

the burning. There should, however, be no sudden rise in tem-
perature in passing from one stage to another, and many success-
ful burners do not consciously distinguish between the different
stages.

The speed at which bricks can be burned depends on the
time needed to pass through these three stages of firing. The
first retarder is the amount of water (whether free as moisture or
chemically combined) which exists in the bricks when they are
first placed in the kiln. With strong, open clays this water may
be removed rapidly, but with fine, tender clays several days may
be needed for the " smoking " or first stage of burning.

It is not the open or loose clays that dry easiest ; aside from
openness there must be a natural tenacity of the clay. It must
have an inherent strength to withstand the disruptive force of
steam. Hence there are two qualities of the clay that will allow
rapid water-smoking : (1) open structure ; (2) inherent strength.
A clay that possesses only one of these must be dried slowly. A
clay that does not possess either one has to be dried very slowly
indeed.

A further cause of slow firing occurs in the second stage of
burning, and is due to the influence of the carbonaceous matter
in the clay.

In clays which are rich in organic matter — the Fletton knots
for example — great caution is required between the stoving of
the goods, which may be said to finish at about 200° C., and the
temperature of 1000° C., when the firing will be nearly finished.
If the goods are heated too rapidly after the stoving they may
" catch fire " and burn too rapidly, and so become spoiled, or
they may be burned on the outside and remain black within.

This production of a black core is especially noticeable with
certain shales, and with some red-burning clays, and is, in most
cases, due to the heating being of too short duration to enable
all the organic matter in tl^e clay to be burned out, and for all
the iron compounds to have become fully oxidized. It is, indeed,
necessary for the fireman to study very carefully the length of
time during which it is necessary for him to keep his kiln at
one heat — usually at about 900° C., or Seger cone 01 la or 09a — in
order that this black core may not appear when a finished brick
is broken.

If, when the bricks, or other goods, reach a dull red heat the
supply of air to the kiln is insufficient, there is a strong tendency
to form the black coring, as the iron in the clay is being reduced

FIRING 341

instead of being oxidized (as it would be in the presence of suffi-
cient air), and this lower oxide combines with some of the silica
of the clay at comparatively low temperatures, and discolours the
goods considerably. In addition to this, gases are often given out
by the slag thus formed, and the goods are cracked or " blown ".

The pores in clay being very small, and the amount of free
air in the flue-gases not being in large excess, a considerable
time is often required before the black core is all " burnt out,"
and in some of the worst clays the kiln must be kept at or near
900° C. for 100 hours or more before it is safe to allow it to rise
higher and then finish the kiln. Fortunately, the time required
for this stage of firing is not usually so long, but the stage is
usually well marked in most clays, and may, for convenience, be
termed the " second " or " oxidation " stage of the burning, the
first stage being the " smoking " or " stoving ".

If the heat has been carried on to the vitrification point, with-
out sufficient time having been taken at a lower temperature to
burn out the carbon, it would swell the bricks. In the case of one
fire-clay it is necessary to hold the heat at 500-800° C., that is,
several degrees below redness, for seventy hours, before all the
carbon is burned out. A drift-clay or glacial-clay found close by
can be burned out in ten hours under the same conditions. Some
clays will readily permit of the burning out of the carbon, some
require a greatly extended time.

Hence the rapidity with which clays can be burned depends
largely on the clay. Because one man's material may require a
longer time, it does not follow that another cannot burn his clay
in less. In some descriptions of kilns, in which the patentee
claims that he can burn several thousand bricks in one or two
days' time, it will be noted that the specifications invariably
state that they will " finish the burning in two days ". That
means that they have given the clay a pre-heating in order to
burn out the carbon and dehydrate the clay, so .that the time
required " to finish burning " the bricks is spent wholly in " com-
pleting," i.e. in developing colour or vitrification.

The speed at which the fire travels forward in a continuous
kiln canno-t, therefore, be stated with accuracy, though it should
not, in ordinary cases, fall below an average speed of 11 to 12 ft.
per twenty-four hours, or 6 in. per hour, thisuneasurement includ-
ing all the different stages of firing. With a suitable kiln ten
times this rate of fire-travel may be obtained under good con-
ditions.

342 MODEEN BBICKMAKING

The speed of the firing will depend on (a) the nature of the
clay or goods, and (b) the draught or air-supply, and the latter
must be regulated chiefly by the former. If the goods will stand
a quick fire without damage, the more rapidly they are burned
the better they will be, but all attempts to hurry the fire faster
than the goods can stand will end in failure to produce satisfac-
tory goods.

By using a continuous kiln of very great length and small
width (as suggested by Biihrer) it is possible with open clays,
relatively free from vegetable or other carbonaceous matter, to
burn five or even ten times as fast as is usual in this country, but
a highly skilled burner is necessary for this purpose.

Drying or Steaming. — No matter whether bricks have been dried
or not before entering the kiln, they always evolve a large
amount of water before they become red hot. The proportion of
water varies with the amount of clay in the material, but is
seldom less than one^sixth of the total weight of the brick. In
other words, in spite of the most careful drying, a pound of water
must be removed from ordinary bricks before they are heated to
redness. The elimination of this water (some of which being
" combined " with the clay cannot be driven out by drying) is one
of the most delicate operations under the control of the burner,
as, if it occurs too rapidly, the bricks will be seriously weakened by
the excessive pressures caused by the large volumes of steam
produced within the pores of the bricks.

This '" kiln drying " may be accomplished by the use of waste
heat from other kilns or chambers (as in a continuous kiln, where
the heat from the cooling bricks is often employed), or wicket fires
(fig. 185) or stoves may be used. In single kilns the fires are
lighted in the fireplaces and are allowed to smoulder so that the
warming takes place very gradually, the fire being allowed to burn
more brightly after two or three days. A similar procedure takes
place when wicket fires are used in continuous kilns, a small
opening being left in the door-gap into which glowing coals are
placed or in which a small fire is lighted with chips, paper, and
coal.

Instead of a fire lighted in the wicket of a continuous kiln, a
portable stove is sometimes used, whence the term " stoving "
for this operation. Such a stove saves fuel and the trouble of
lighting many fires (fig. 187).

The drying, or steaming, must be continued until the whole
of the combined water has been removed and the goods are

FIKING 343

distinctly hot. With most clays this cannot be considered to be
complete below a very dark red heat, and by the time the bricks
have reached this temperature a large part of the vegetable and
other combustible matter will have begun to decompose, and the
bricks will have entered upon the second stage of burning.

In continuous kilns the first stage is usually considered at an
end when the goods have reached a temperature of 120° C. (as
shown by a thermometer lowered in the kiln) ; but the attainment
of this temperature really only indicates that the goods are suf-
ficiently hot for the waste gases from previous chambers under
fire to be passed through them. This is very different from say-
ing that the goods are really dry or that all the steam has been
removed !

The completion of the " steaming " is usually tested
by placing a long, cold iron bar into the kiln or chamber
and withdrawing it after a few seconds. If much steam
is present the bar will become damp, but the test is a
very crude one and far from being satisfactory.

A much better plan consists in lowering a suitable
thermometer, protected in a metal case (fig. 244), into
the kiln by means of a light chain, and reading the
temperature when the thermometer is again withdrawn.
The metal case serves to show any condensable water
vapour in the kiln, and the thermometer, by indicating
the temperature, shows the burner whether it is safe to
fire more vigorously.

Owing to the large volumes of steam produced during
the first stage of burning, the kiln should have several
openings through which steam may escape. Some
bricks are sufficiently strong to enable the steam to
be drawn away through fhies, but with delicate clays FIG. 244. —
draughts must be avoided as much as possible. mometer

There is much difference of opinion as to whether the
steam should be removed from the upper or lower parts of the kiln.
As the damp air is' specifically heavier than when it enters the
kiln (because the contraction due to loss in temperature is greater
than the increase in volume caused by the water vapour) the
theoretically best method is to withdraw the steam from the
bottom, but as the constant contact of the lower bricks with
moisture tends to soften them (as they have to carry the weight
of the bricks above them) it is, on this account, often necessary
to remove the steam from the upper part of the kiln. In certain

344 MODERN BRICKMAKINa

modern continuous kilns the steam may be removed from several
parts of the chamber simultaneously.

When the bricks are not sensitive to air- currents they can
most safely be dried and heated by passing hot air through the
kiln or -chamber.

Volatilization or elimination of combustible matter forms the
second stage in burning bricks, but the changes which occur in it
are often exceedingly complicated. Thus, it is not merely that
certain materials are volatilized, but the combustion of vegetable
and other matter in the clay takes place at this stage, and the
colour of the bricks is often seriously affected if this portion of
the burning is unduly hurried.

As is well known, the colour of red-burning clays is largely
due to the presence of red iron oxide, a material which is very
sensitive to partially burned vegetable matter. Thus, if mixed
with vegetable matter and rapidly heated with a limited supply
of air, bricks containing much iron oxide will have a bluish or
slag colour when taken out of the kiln, as the vegetable matter
acts as a reducing agent and prevents the formation of the red
colour, unless the conditions required for its production are all
present. Many discoloured bricks and most bluish " cores " or
" hearts " in bricks, which should burn to the same colour
throughout, are due to the presence of carbonaceous matter
which has been heated too rapidly and with an insufficient
amount of air.

To burn a brick to a good colour throughout, it is necessary
to have an ample supply of air in contact with each particle of
the brick, so that any iron compounds present may be completely
converted into the red oxide. With some particularly difficult
clays alternate heating, with and without air, may be necessary
before this red iron oxide can be obtained.

Most burners make the mistake of using too little air and of
heating too rapidly when the goods are at a temperature of 750 °
to 950° C. ; and if a brick when broken shows a distinct core, the
kilns in which other bricks of the same material are burned
should be kept for some hours at a temperature of about 900° C.
(dull red), with an ample supply of air and a clear burningi fuel,
until it is certain that all the core -forming material has been
burned 'out. If once the temperature is allowed to become so
high that partial vitrification sets in, the core can never be
removed by prolonged burning, as the pores of the brick will be
closed and air cannot get to its interior ; for this reason, it is

FIRING 345

essential that the heating should be very steady during the
second stage of the burning.

The time required for this second stage varies greatly with
different clays. With some very open materials it may be passed
in ten hours, but with dense clays containing much iron and
some organic matter it is necessary to keep the bricks at a dull
red heat for four or even five days if cores are not to be formed.
The most difficult clays to deal with at this stage are those (such
as some shales) which contain a certain amount of " fuel " inter-
mixed with the clay.

The method of manufacture has a great influence on the
time taken for this second stage of burning, and a dry -press
brick being often less dense than one made from plastic clay
will be correspondingly easy to fire. Occasionally, however, a
dry-press brick of exceptional density is obtained and is very
troublesome. Probably no clay exists which cannot be burned
properly at this stage, but if the time required is excessive, the
cost of treatment may make it prohibitive from a commercial
point of view.

Clays which contain pyrites, or other iron and sulphur com-
pounds, are particularly troublesome at this stage, as the sulphur
acts as a reducing compound and tends to form an iron slag, un-
less the heating is exceedingly slow and tedious and the clay of
a very porous character. This slag often fills up the pores, and
prevents a well-coloured brick being produced.

Blue bricks are burned with a minimum quantity of air at
this stage, as the formation of a slag is desired in order to bind
the clay particles thoroughly together. This is, however, a
special case.

For ordinary buff- and red -burning bricks, it is highly im-
portant that, during the time in which they are at a temperature
of 750° C. to 950° C., they should have an abundant supply of
air and no smoke, and that the temperature should not be raised
above a dark red heat until it is fairly certain that the iron has
been fully oxidized and all combustible matter removed. Un-
less this is done, and the oxidization is completed before vitri-
fication sets in, the formation of " cores " or " hearts " is almost
certain to occur.

When clays are burned at temperatures approaching 1200° C.,
it is practically impossible to admit any excess of air without a
special regenerator, and consequently it is impossible to pre-
vent an occasional reduction at this temperature. This will not

346 MODEKN BBICKMAKING

matter much if the clay has been properly oxidized at 900° C., or
thereabouts. On the other hand, it may generally be assumed
that goods not oxidized at or near this temperature will never be
oxidized.

In some cases where irregularly coloured bricks are required,
it is usual to heat with and without air alternately. This opera-
tion is known as " flashing " and is begun towards the end of the
second stage of heating. By heating with a smoky flame and but
little air a bluish shade is produced, and this is partly destroyed
and replaced by a red shade when the bricks are heated with
plenty of air. The combined shades are sought by some archi-
tects and builders who do not like the " monotony " of walls
made with evenly coloured bricks. In some yards this alterna-
tion of heating is done more or less unconsciously by the burners,
as in the manufacture of " purple " sand-faced bricks, which lend
themselves readily to such treatment. When blue bricks show
patches of red on them it is a sign that too much air has been
used at some stage of the burning. Clay which has been mixed
with coal or sawdust needs specially careful firing at this stage.

A brick which has been properly fired to the end of the second
stage will, if broken, be of uniform colour throughout the whole
cross -section, but it will be soft and weak. If, on the contrary,
it has been hurriedly fired, or with too little air, it will show a
spot of dark colour on the broken face, the size of this spot
depending on the incompleteness of the air-supply. In some
instances a broken brick shows only a narrow border oxidized,
the whole interior of the brick being unaffected, whilst another,
which has been better treated, may only show an unoxidized spot.

Full Fire is the stage at which the bricks are finally heated,
the object being to cause sufficient vitrification to form a solid
and durable brick. In " baked " bricks (p. 337) this stage is
never reached, as the firing of such bricks is ended at the close
of the second stage, or very early in the "full fire " stage. The
full firing is not complete until the goods have entirely ceased to
contract without losing shape (and would not do so even if heated
150° C. or so higher), and when some amount of fusion of certain
constituents has taken place so that the maximum available
density is reached. This is somewhat lower than the absolute
maximum density, which only occurs after the bricks have lost
their shape, and so is useless for practical purposes.

Thus, if a brick or tile made from a clay is found to absorb
15 per cent of water when fired at cone 022, and only 12 per cent

FIKING 347

at cone 020, and if, no matter how much hotter it is made, the
absorption never sinks below 10 per cent without the clay losing
its shape, it is clear that for all practical purposes the best finish-
ing heat is somewhat above cone 020.

When clays are subjected to a sufficiently high temperature
a certain amount of fusion takes place, some of the ingredients
melting and binding the others together in a more or less vitrified
mass. When this fusion commences, the clay has softened suf-
ficiently to make the grains stick together, but the particles have
not fused sufficiently to close up all the pores of the mass nor
to allow a recrystallization. The broken mass of the clay shows
a dull surface, with laminations more or less distinctly evident
in the mass, with many isolated particles showing no heat effect.
If the burning is arrested at this stage the resultant mass will be
slightly softer than steel, will absorb water quite readily, and will
disintegrate under the continued absorption of alkaline and acid
liquids. It is then said to be in a state, of incipient vitrification.

Under a continual and gradual increase of temperature the
clay granules undergo an additional softening, sufficient to close
up all the pores and render the mass impervious, owing to the
production of a larger amount of fused matter. Clays burned to
this condition show, when broken, an extremely hard surface
with a smooth fracture, having a slight lustre and showing no
laminations. The substance will not be scratched with steel, is
impervious to water, and is completely vitrified. After the vitri-
fication period is passed a sufficient rise in the temperature
causes swelling and softening of the clay, until it leaves its original
form and flows into a viscous mass. Upon cooling, the substance
may crystallize partially, but usually forms a dark, glassy mass.

The speed at which the temperature rises during the period of
full firing may be much greater than during the earlier stages,
providing that it is sufficiently under control for the bricks not
to be over-heated. This qualification is necessary, because in
some clays the finishing point of the firing, and that at which the
bricks lose their shape and are spoiled, are not far apart, and if
the heating of the kiln at the last is very rapid, many bricks may
be spoiled by the inability of the fireman to keep the temperature
within the necessary limits.

Some burners allow the temperature inside the kiln to remain
constant for a long time previous to finishing, and this is desir-
able in some cases. In many instances it is, however, undesirable
and unnecessary, as any such " soaking " should have been done

348 MODERN BRICKMAKING

at a temperature not exceeding that of -a dull red heat (say 950° C.)
and not immediately before finishing the firing. So much depends-
upon the nature of the clay and the effect which it is desired to
obtain by the action of heat that no general rule can be laid down,
beyond the one that the temperature should increase steadily
and its rise must be under complete control.

The firing of a clamp kiln has already been described (p. 65).
When once started, such a kiln needs no further attention as it
burns itself automatically.

Single kilns of all types are started by lighting a fire in the
various fire-places, taking care to allow it only to smoulder for
some time so that the first heating is not too rapid. Later the fires
are stirred so as to open them out, and by more vigorous stoking
they are caused to burn with steadily increasing intensity until the
bricks are finished.

The mouths of the fire-boxes should be kept sufficiently open
to allow the requisite amount of air to enter (unless special air-
ports are provided), but care should be taken to avoid either too
much or too little air. The faulty construction of many fire-boxes
is responsible for much waste of fuel, and as a general rule the
air needed should be supplied exclusively through the grate, with
the exception of that needed immediately after each fresh charge
of fuel. This supplementary air should be supplied through a
special series of openings which can be closed when not required.
The common plan of working without doors and with shallow
fire-boxes is wasteful in fuel and should be changed as soon as
circumstances permit.

The chief precautions to be observed are those already men-
tioned, but when down-draught kilns are being fired the goods in
the bottom of 'the kilns will be under-fired, unless special care is
taken to admit air to the upper portions whilst continuing the
heating of the lower. The reason for this is the peculiar way in
which coal burns. Instead of being a simple matter, as many
burners appear to suppose, the burning of the fuel takes place in
two distinct stages, viz. the burning of the gas and the burning
of the solid fuel. When a fresh lot of coal is placed on a fire the
heat of the fire converts part of the coal into gas and smoke, and
if sufficient air is supplied both these substances will be properly
burned. As soon as the gaseous portion is all driven off, the solid
part of the fuel (coke) needs a smaller supply of air per minute
for its combustion, and unless some arrangement is made for
regulating the air supplied to the fuel, too much air will enter the

FIEING 349

fire-box during the burning of the coked fuel, or too little air will
be supplied during the evolution of the gas and consequently
the kiln will smoke.

To secure the best results, the air supplied should be heated
to at least 500° C., but few kilns have facilities for this purpose.
Yet unless hot air is used, at any rate during the production of
gas from the coal, it is very difficult to avoid the production of
smoke. The author has used successfully a vertical flue running
through the walls of the kiln above each fire-box, the air being
drawn in through an opening near the top of the kiln, its quantity
being regulated by a simple slide-damper. Some arrangement
should be made whereby this hot air can be passed over the sur-
face of the fuel in the fire-box or underneath the grate, the ash-
pit being kept closed.

The distribution of the heat in a down-draught kiln is facili-
tated by using a kiln with a perforated floor. If this has not
been made at the same time as the kiln, it can usually be added
at a trifling cost afterwards.

The chief precautions in firing a down-draught kiln are those
already mentioned in this chapter, as referring to kilns in general,
but there is always a risk in down-draught kilns of the goods in
the lower portion being under-fired, unless special care is taken to
admit air to the upper parts whilst still continuing to heat the
lower ones. This is known as " getting up the bottom," and is an
operation needing much skill.

Broadly speaking, the firing of a down-draught kiln will be
successful in proportion as the burner is able to recognize the
varying temperatures in the different parts, and is able to work
his fires accordingly. To do this effectually he must pay special
attention to the appearance of the different parts of the kiln, but
especially to that of the upper and lower ones. The firing of a
down-draught kiln is, however, an operation which requires so
much practice and judgment that it is impossible to describe it
in detail.

The "finish" or end of the firing of a single kiln may be
accomplished by closing all the fire-place mouths and other
openings with bricks, or slabs, so as to exclude all air except
such as may leak through the brickwork, or the fires may be
drawn out of the fire-places previous to closing these as just
described. The author prefers an intermediate method, and
opens out the fires with a poker immediately the goods are
sufficiently burned, so as to allow the fuel to burn up rapidly

350 MODEEN BBICKMAKING

but with so much air that the temperature of the kiln does not
increase. When the fires have died down he closes the holes,
more or less completely, according to the nature of the goods,
leaving the damper connected to the chimney as widely open as
the circumstances of the case permit. In this way it is often
possible to get a better colour than when the kilns are closed
completely immediately after the firing, and danger of cracking
the goods is negligible if care is taken not to allow too much cold
air to enter at one time.

Bricks can often be improved greatly in colour if, when the
firing is finished and the kiln " closed up," a number of openings
are made in the front of the kiln about two hours after the com-
pletion of the " closing ". These openings should be small and
numerous rather than large and few in number, and they should
remain open for about an hour or ninety minutes, so that suffi-
cient air may enter the kiln to " brighten up " the goods. The
holes are then closed, daubed up with clay, and the cooling of
the kiln allowed to proceed in the usual manner. It is remark-
able what a difference in the appearance of the bricks is pro-
duced when this simple dodge is resorted to with the majority
of clays. The improvement is probably due to the fact that the
discolorations of bricks are mostly due to their being heated in
a reducing atmosphere, whereas when this air-supply is used
after the finishing of the kiln, these discolorations are removed
by the oxidizing action of the air admitted.

Newcastle kilns often differ from other single kilns in having
no grates on which the fuel is fired. Opinions differ greatly as.
to the advantages and disadvantages of grates, particularly dur-
ing the third stage of firing, where the coal is liable to clinker
badly. On the whole it may be said that grates are best when
but little clinker is produced, as they enable the fuel to burn
more economically. Even when much clinker is liable to form,
the presence of a pan of water or a steam jet beneath each grate
will often reduce the amount produced, and in other (bad) cases
the fuel should be fired direct from the ground, the waste of fuel
being less serious than the waste of time involved in removing
the clinker. For burning building-bricks in Newcastle kilns,
grates should invariably be used. For fire-bricks — where the
heat is more intense — grates are often a nuisance, unless the fuel
is burned in a gas-producer.

The burner may know when to cease firing his kiln by (a)-
determining the temperature by means of Seger cones or some

FIEING 851

other pyrometer, or (b) by determining the amount of shrinkage
which has occurred. This latter is the most popular method at the
present time, but progressive burners are utilizing it in connexion
with some form of draught-gauge or temperature recorder as (a)
so as to secure more uniform results.

The usual method of measuring the shrinkage is by means
of a metal rule which is pushed through a hole in the top of the
kiln from time to time, the heating being continued until the
bricks have settled to a predetermined amount which varies
with the clay, but is usually about 1 in. per ft.

Unfortunately, the amount of shrinkage or settling is often
influenced by the proportion of water in the clay paste used for
making the bricks, and can only be regarded as a rough guide
in finishing the kiln. Some firms use small, accurately made
trial pieces which they draw from the kilns, and measure very
accurately so as to determine the shrinkage. This method is
little if any better than the simple use of a measuring rod as
described, as far as firing bricks is concerned. Seger cones are
superior for this purpose when properly used.

The firing of a continuous kiln is a matter requiring special
care and attention, as failure to keep a sharp look-out on what
is going on in each chamber may result in disaster. The num-
ber of dampers and valves in a modern continuous kiln is often
large, and a man of considerable intelligence is needed to pro-
duce satisfactory results.

There is no greater difficulty in firing a continuous kiln than
is found in burning an equal number of separate chambers, and
the labour required is far less, as for the greater part of the
heating of any chamber no attention is required at all, if the
kiln is properly built and is sufficiently long. Hence, when a
burner once gets accustomed to continuous kilns he seldom cares
to fire single ones.

In a continuous kiln the main object is to make as much use
as possible of all the heat available, by passing the products of
combustion from one chamber through a number of others be-
fore admitting .them to the chimney. This arrangement secures
a great saving in fuel but must not be carried too far, or the
goods will be spoiled by " scum ". This scum is caused by the
moisture in the gases condensing on the freshly set goods and
the acid vapours dissolved by the water thus formed. It is,
therefore, essential that hot air, free from moisture and fire-
gases, should be used for drying bricks and raising them to a

352 MODERN BRICKMAKING

temperature of 120° C. in a continuous kiln. When above this
temperature little or no condensation can occur, and the forma-
tion of scum is thus prevented. The precise means used for the
supply of warm air for this purpose depends on the design of the
kilns used ; usually air is drawn through chambers filled with
bricks which have finished firing. The air passing around the
cooling bricks becomes heated and is then taken to the freshly
set chambers, being mixed with sufficient cold air to prevent the
new bricks from being damaged.

When no such supply of warm air is available some form of
stove or a wicket fire must be used, or, if the kiln is one provided
with grates, the fuel may be placed on these. In some modern
kilns, special flues for the heating of air are employed (pp. 272
to 275 and 297 to 299).

As soon as the bricks in a chamber have all reached a tem-
perature of at least 120° C. the special heating is stopped, and,
by an arrangement of dampers, the chamber thus prepared is
placed in the regular circuit of the kiln, the fire-gases passing
through it before entering the chimney-flue. The number of
chambers through which the fire-gases pass should not be less
in total length then 56 to 70 ft., or, say four or five chambers,
each 14 ft. long, unless some very unusual conditions prevail.
No fuel is used in these chambers ; they are heated exclusively
by the waste heat of the fire-gases until they reach a later stage
in the firing.

The use of fuel is confined < to about 40 ft. in length or about
three chambers, so that a successfully fired continuous kiln of
medium length (sixteen chambers) will always have one chamber
being filled, one chamber being emptied, three chambers cooling
and supplying warm air to the freshly set goods, three chambers
supplied with fuel and nearing the end of firing, five heated with
fire-gases only, and three freshly -set chambers heated by wickets
or warm air. If more chambers are available the number heated
with fire-gases and fuel may be increased, and two chambers may
be filled daily instead of only one.

If there are fewer chambers, as, for instance, in a fourteen
chamber kiln, the temperatures in each chamber will be some-
what as follows : —

FIRING

353

o. 1 chamber

2

3

4

5

6

, 7

, 8

9

t

, 10

, 11

, 12

, 13

14

" Smoking"

Heating
i>
»>

Being fired
Cooling

Being emptied]
Being filled

15° to 120° C.

120° to 200° C.

200°
400°
600°
700°
880°
1000°
600°
360°
160°

400° C.
600° C.
700° C.
880° C.

1057° C. (Cone 02ft)1
600° C.
360° C.
160° C.
50° C.
Cold "

The temperature, etc., of each chamber may also be shown
diagrammatically as in fig. 245 which is a slight modification of
an illustration published by J. Osman & Co., Ltd., for their " New
Perfect " kiln, but which is equally applicable to any continuous
kiln with the same number of chambers.

i

14.

13.

12.

11.

10.

9.

8.

Being
filled.

Being
Emptied.

Cool.

Cooling.

Cooling.

Cooling.

Being
fired.

1.

7.

2.

3.

4.

5.

6.

"Smoking";
or ;
"Drying". ;

"Dry."

Hot.

Black
Hot.

Nearly
Bed Hot.

Red Hot.

Being
fired.

FIG. 245. — Method of working continuous kiln.1

The firing of a continuous kiln takes place in three stages,
viz. (a) " smoking " or " drying " ; (b) heating by waste heat from
other chambers ; and (c) full fire, but each of these may be sub-
divided where troublesome clays are burned.

The smoking or drying- in a continuous kiln is not carried so
far as in a single one, for as soon as the contents of a chamber
have reached a minimum temperature of 120° C. they may pass
to the second stage of heating.

" Smoking " may be accomplished by wicket fires, stoves, or
the use of hot air from other chambers in the ' kiln, the last
named being preferable in every way when the supply of hot
air is sufficient, and providing that its temperature can be regu-

1 Some variation of these figures must, however, be permitted, owing to the
widely different treatment required by some clays.

28

354 MODERN BRICKMAKING

lated with sufficient accuracy. To use this hot air (produced by
drawing cold air through the chambers containing bricks which
it is desired to cool, or through special air-heating flues above the
arch or below the floors of other chambers) the necessary valves
or dampers in the kiln are so placed as to deliver the air where it
is needed, a supply of cold air being added if necessary. When
once the dampers have been placed in their proper positions
the bricks are warmed automatically, and the burner has only to
regulate the amount of air admitted, so that the temperature of
the freshly set bricks increases at the desired rate.

The construction and arrangement of these hot-air flues have
been made the subject of numerous patents, and whilst they
differ from each other in many respects, they have many features
in common, and the diagram shown earlier (fig. 193) of the
" Manchester " kiln (Dean, Hethrington & Co., Leek) includes the
chief features of them all. The chief difficulty to be overcome
lies in the enormous volume of steam and air to be drawn through
the chambers during the smoking, and in not a few cases kilns
have failed to work successfully for no other reason than that the
designers did not allow sufficient flue-space for this purpose.

As will be seen from the illustration (fig. 193) the smoking
may take place in either an upward or downward direction,
according to the nature of the goods and the wish of the fireman,
though in this particular instance the air from the cooling-
chambers is only shown as coming from the hot air flue S. From
S the hot air passes to below the grate of the chamber, up through
this — the grate in this kiln being similar to that in the Belgian
and other kilns in which the fuel is kept out of contact with the
goods, by being fired on a special flat grate — into the chamber A,
where it dries the damp goods. The steam and hot air then rise
upwards, as shown in chamber B (which is a section farther along
the same chamber), until it escapes through large holes in the
roof to the space between the two arches with which this type of
kiln is furnished. From the arch the steam passes through a
large flue to the chimney stack, as indicated by the arrows in the
illustration.

This arrangement of a double arch to the chamber enables
flues of ample size to be constructed so that the steam may be
drawn off as rapidly as is desired, and the same arrangement
enables an equally abundant supply of hot air to be supplied
from the cooling chambers to the flue S, from which it may be
transferred to any chamber needing it. When delicate clays are

FIEING 355

being dried or smoked the opening of the " cold air valve " per-
mits of air of any desired coolness being admitted to the chambers.
This admixture of cold air is of enormous value in some cases,
and kilns possessing arrangements for producing it are con-
sequently better than those without it when high-class goods are
being fired.

In many continuous kilns there is no provision for using air
in this way, the air passing over the cooling bricks being used for
the main fire or being wasted. In such cases wicket fires or
stoves must be used, or, if the kiln is provided with internal grates
these may be used instead. Grates may be built in the wicket
if desired, but a commoner plan is to burn the fuel on the ground
(fig. 185), a poke hole (a) and another (6), about 1 ft. square, being-
left through which fresh fuel may be added. The fire must
smoulder or smoke for many hours so as to prevent the bricks
being over-heated at first, the chamber being separated from those
on either side of it by iron or paper dampers, and the damper
connecting the chamber to the main flue being kept open. At
the same time it is often wise to open the feed-holes in the top
of the kilns, unless special flues are provided for the removal of
the steam.

When the bricks have reached the requisite temperature
(120° C.) or when the fireman judges they are sufficiently heated,
the holes in the wicket are built up and the heating is continued
by the breaking down of the paper damper, or the removal of the
iron one, and the consequent admission of hot gases from the
next chamber. The damper connecting the latter to the chimney
is closed.

In many kilns wicket fires are unsatisfactory, because the
heat is so unevenly distributed throughout the chamber and
the amount of unwarmed space (dead space) is often very large.
This objection may be partly overcome by the setters construct-
ing a series of flues through the bricks, but some amount of
unevenness appears to be inevitable.

A better plan (though not as satisfactory as the use of warm
air) consists in the use of a number of small stoves which fit into
the feed-holes in the arch of the chamber (fig. 187) and through
which air, heated by the fuel in the stoves, is drawn down into
the kiln. The number of these stoves needed at one time varies
with the nature of the clay ; in many cases a stove should be
placed in each feed-hole of the chamber to be warmed. As the
chamber dries a row of stoves is taken to the next chamber.

356 MODERN BRICKMAKING

With delicate clays a single row of stoves may be used. One
objection to the use of these small stoves is the condensation of
moisture which is liable to occur on the bricks in the lower part
of the kiln, thus softening and spoiling them. This objection is
more apparent than real in many cases.

In order to ensure the whole of the contents of a chamber
having a minimum temperature of 129° C. it is desirable to use a
thermometer enclosed in a brass tube, in which a slit has been
cut so that the thermometer may be easily read (fig. 244). By
lowering this thermometer into different parts of the chamber by
means of a thin chain, and after a short interval withdrawing it
rapidly and reading it, very satisfactory results can be obtained,
providing that the thermometer is sufficiently slow acting, or has
some self-registering arrangement so that its readings are not
affected by the time taken to withdraw and read it.

Unfortunately the thermometer is often used carelessly, and
many badly smoked chambers result when this is the case, as the
thermometer is not a "regulator " but merely an "indicator " of
what is going on inside the chamber, and if its indications are
disregarded, or if its employment is carried out superficially
instead of thoroughly, well stoved goods cannot be obtained.

The best part of the chamber for testing with such a ther-
mometer is as • close to the sole as is possible without the ther-
mometer actually touching it, but temperature readings should
also be taken at different heights in the chamber, because the
difference in temperature is often very considerable, and particu-
larly so when the goods to be fired are very damp. This is one
reason why goods should not be placed in the kiln unless they
are as dry as possible, as irregular heating, even during the smok-
ing, is not desirable.

The difference in temperature between the sole and top of the
chambers undergoing smoking varies with different kilns, but
there appears to be a definite relation between the height of the
chamber, the draught of the kiln, and the proportion of moisture
evaporated per minute from the goods, though this relationship
has not been accurately determined.

It is a rule, common in many brickyards, that the smoking
must not be stopped until the lowest temperature in the chamber
is 120° C., but when very wet goods are set it is almost impossible
to carry out this rule without seriously delaying the kiln, as until
all the moisture has been driven out from the goods this temper-
ature cannot be obtained, and the temperature at the sole of the

FIKING 357

chamber may easily register 700° C. or even show signs of redness
whilst the upper goods are still at a temperature of only 100° C.
Thus, it is not uncommon to find that a piece of newspaper will
catch fire if thrown into one part of a smoked chamber whilst
another part will (on account of the dampness of the goods) still
have a temperature lower than that of boiling water ! In such
cases the use of paper dampers between the chambers is unsatis-
factory, because the paper is destroyed before the whole of the
chamber is properly smoked, and sometimes the accumulation of
condensed moisture on it is so great that the paper softens and
falls.

It will generally be noticed that the unevenness in temperature
is greatest when the ventilation of the chamber is low, and the
rate of drying or steaming is high, as the moisture causes irregular
currents in the chamber, and the accumulations of water-vapour
which occur are difficult to dissipate unless some vent is given.
In some of the more recent forms of continuous kiln, special
steam vents are arranged for this purpose, but even when these
are absent much may be done by opening the caps of four or five
feed-holes in the arch of the chamber, so as to allow the steam
to escape, or, if the draught of the kiln is strong enough, to draw
a current of air through the chamber.

The second stage of heating in a continuous kiln needs little
comment. The temperature of the bricks must not be allowed
to rise too rapidly and an ample supply of air must be admitted
in order to burn out the carbonaceous matter in the clay, but if
these points are watched, and the precautions mentioned in the
section on firing single kilns from 800° C. to 950° C. are observed,
no difficulty need be anticipated.

The gases used at this stage of the firing are carried forward
through one chamber after another until their temperature is
reduced to about 200° C. or even less. They must not be used
when below 150° C. however, or they will cause condensation
products to form on the goods and they will not rise readily up
the chimney. The temperature at which these gases are admitted
to the chimney will, therefore, depend on the draught required
in the kiln and on the number of chambers available. As the fire
travels forward, the time will eventually come when a fresh
chamber has to be heated by fuel and it thus passes into the third
stage of firing.

The full fire or third stage of burning in a continuous kiln
requires care and skill. The manner in which it is conducted

358 MODERN BEICKMAKING

depends largely upon the construction of the kiln. Thus in the
original Hoffmann kiln small fuel is fed in through the feed-holes
in the arch and lodges on projecting pieces of brick in the fire-
shafts placed there for that purpose. In this type of kiln, there-
fore, the fuel is scattered amongst the bricks to be burned. The
fuel is added in very small quantities at a time, in accordance
with the old maxim to " fire lightly but often ". If the burner
should try any other method to save either himself or the coal,
trouble is sure to result. The bricks should not be fired until
there is sufficient heat in the chamber to ignite the fine coal or
" duff" which is generally used in the burning of continuous kilns.
If care is not taken in this matter, the fine coal will immediately
turn to coke, and choke the trace-holes, stopping the draught and
spoiling the bricks against which the coke rests. The quantity
of coal used per thousand will vary according to the nature of
the clay, but should not exceed 3% cwt. per thousand (common)
bricks in a well-designed kiln.

The author's personal experience is that every continuous kiln
requires careful and regular attention to make good work, and to
get the most out of it. It must be fired very regularly and very
lightly ; by no means must a flue get blocked or have a large
quantity of fuel in it.

To get the greatest quantity out of a kiln a regular draught
should be maintained, and as long a length of fire as the kiln will
allow. The fireman must be constantly feeding ; he should not
put down more in each hole than it will consume by the time he
gets to the last, so that he commences again at the first as he
leaves at the last, and should just keep sufficient up-draught to
burn the bricks on top. He should work in a contrary direction
to that in which the fire travels, or the smoke from the last-fired
holes will prove troublesome.

If a continuous kiln travels slowly, a quantity of coal or cinders
collects in the bottom ; this means black-ended bricks. It is often
as well, if there is anything 011 the bottom, to stir it with a rod
after the bricks have got below burning heat. The back rows
should be left at as near a burning heat as possible, then the
coal will all burn away, and leave the kiln bottom clean and the
bricks free from black ends.

The whole secret of successful burning is 'attention and
regularity.

In the more modern types of continuous kiln a series of grates
running from front to back is used. This arrangement, first iritro-

FIRING 359

duced in the "Belgian " kiln, has become very popular, as it makes
both setting and firing much easier and the heating is more under
control. The fuel may be fed on to the grates through openings
in the front of the kiln or through the usual feed-holes in the arch,
some burners preferring one and some the other method. Air
for the combustion of the fuel may be supplied direct from the
atmosphere to below the grate, or special flues may be used. To
some extent air from the chamber last finished firing may also
be employed.

The fuel on the grate should be kept at one depth, and fresh
fuel should be added in small quantities at a time, as, if too large
a quantity of coal or fuel is added at once, the cooling effect it
produces will cause the violent production of smoke and the waste
of much heat.

When properly fed with a fair quantity of coal, the combus-
tion is so complete that no clinkering is needed during the heating
of the chamber. The small quantity of ash produced may be
removed when the bricks are drawn from the chamber.

By working with a fair depth of fuel the conditions usually
met with in a producer are obtained, and in consequence there is
but little advantage to be gained by the installation of gas-pro-
ducers when a kiln of this type is used.

The accurate control of temperature in kilns has only been
attempted by a small number of brickmakers in this country, and
the majority of burners estimate temperatures by the eye (which is
often defective, though in many cases remarkably accurate), and
decide that when the shrinkage of the bricks has reached a certain
amount it is time to cease firing.

Whilst these " guides " are quite accurate enough for the
manufacture of common bricks from many clays, they are far
from being reliable with more delicate materials, and other means
must be adopted.

For most purposes the use of Seger cones is to be recom-
mended, as these are simple and cheap in use (costing only Id. each)
and are very reliable. Such cones do not register temperatures
so much as the result of heat, action, but as the latter is what the
brickmaker wishes to know, cones are often more valuable to him
than a pyrometer would be, and this in spite of the fact that the
prolonged action of heat at a certain temperature will bring down
a cone which is only rated to fall when subjected to a higher
temperature. " Thermoscopes " are bars which-" sag " on heating.

Seger cones are pyramidal pieces of partially. burned material

860

MODERN BRICKMAKING

resembling easily fused porcelain (fig. 246). They are made from

various mixtures of clay and fluxes
under very careful supervision, and
are rigorously tested before being
sent out. Similar cones by other
makers are occasionally offered for
sale, but should be avoided unless
the conditions of their manufacture
are known or their reliability can be
guaranteed.

FIG. 246. — Method of placing
Seger cones.

Seger cones are so constructed that when one is embedded
in a stiff piece of clay paste to the depth of one-eighth inch or
rather less it stands upright until it has been heated to a given
temperature. It then bends over until its point touches the
clay base, and if still further heated it melts. The temperature
indicated by the cone is that at which its point just reaches the
level of the base (fig. 247). A lower temperature will not cause
it to bend so much as this, and a higher one will cause it to
collapse. The cones are sold to indicate differences of 20 ° C. for

FIG. 247. — Seger cones in " case ".

FIG. 248.— " Case " for
holding Seger cones.

all temperatures from just below the earliest visible red heat to
those at which the most refractory clays melt.

The cones are placed in different parts of the kiln at various
heights in order that they may enable the burner to secure
regularity of heating. At first a larger number of cones will be
required, but later (as the burner becomes accustomed to their
use) three different numbers of cones in each part of the kiln will
be sufficient.

Of these three numbers, one is intended to act as a " warner,"

FIKING

361

showing that the finishing temperature of the kiln is being
approached, the second is intended to show when the kiln has
reached the correct finishing point, and the third is to indicate
(when the kiln is drawn) whether any over-heating has taken
place.

The cones must be so placed that they can be seen through
-.spy-holes placed in the walls of the kiln (these holes being norm-
ally plugged with blocks or pegs sealed with clay paste) and the
•cones should not be too near the outside of the kiln. In most
cases, the arrangement shown in fig. 246 is satisfactory ; but, if
preferred, a " case " (figs. 247 and 248) may be used.

The range of temperature covered by these cones is shown in
the following table : —

No. CENT.

No. CENT.

No. CENT.

No. CENT.

022 600°

07a 960°

9 1280°

29 1650°

021 650°

06a 980°

10 1300°

30 1670°

020 670°

05a 1000°

11 1320°

31 1690°

019 690°

04a 1020°

12 1350°

32 1710°

018 710°

03a 1040°

13 1380°

33 1730°

017 730°

02a 1060°

14 1410°

34 1750°

016 750°

Ola 1080°

15 1435°

35 1770°

015a 790°

la 1100°

16 1460°

36 1790°

014a 815°

2a 1120°

17 1480°

37 1825°

013a 835°

3a 1140°

18 1500°

38 1850°

012a 855°

4a 1160°

19 1520°

39 1880°

Olla 880°

5a 1180°

20 ! 1530°

40 1920°

OlOa 900°

6a 1200°

26 1580°

41 I9600

09a 920°

7 1230°

27 1610°

42 2000°

08a 940°

8 1250°

28 1630°

Electrical and optical pyrometers are used in research work in
•connexion with brickmaking, but are not, so far as the author
is aware, employed as an integral part of the ordinary manu-
facture, as they are delicately constructed, require special skill
in use, and for most brickmakers' purposes have no advantage
over the Seger cones just mentioned.

For firing continuous kilns it is becoming increasingly common
to check the work of the burner by means of a self-recording
draught-gauge (fig. 249). This is desirable, because the main-
taining of a constant draught is essential to success.

The chart shown in fig. 250 indicates the variations in the

1 Nos. 21-25 are not now manufactured as their indications are too close together.

362

MODEEN BEICKMAKING

draught of a kiln in which the fuel was usually added at intervals

of 40 minutes, but by
no means regularly.
Thus, between 12 and 2
o'clock, over an hour
elapsed between the
stokings, and between
3 and 4.30 no addition
of fuel occurred. The
draught varied greatly
apart from this, as
shown by the irregu-
larities in the line.
Such a chart is charac-
teristic of a somewhat
careless fireman.

The great variations
due to wind naturally
lead to serious varia-
tions. The actual regu-

FIG. 249. — Obel recording draught-gauge.

lation of the draught, so as to keep it at a constant value, must

be done by means of
dampers of various
patterns, and by seeing
that there are no serious
leaks in the flues or
walls of the kiln. As a
check or means of con-
trol of these numerous
factors the self-record-
ing draught-gauge is in-
valuable, as will be
readily understood from
the chart reproduced
from the " Tonindustrie
Kalender ". Against all
the usual troubleswhich

FIG. 250. — Chart of kiln draught.

occur at night, when the
firemen are more or less
sleepy, the gauge is a great assistance, as there is no means of
falsifying its record short of breaking the instrument itself.

It is the constant use of an appliance of this kind which en-

FIBING 363

ables a burner to appreciate the advantage of mechanical draught
produced by the aid of a fan.

It is, occasionally, necessary to work at a lower rate of fire-
travel than usual, on account of an insufficient supply of bricks,
or because of the works being closed on Sundays and Saturday
afternoons. Where the older type of continuous kiln is used it
is difficult to damp down for more than twelve hours, but with a
modern chamber kiln, in good order, little trouble is experienced.
The best way, in each case, is to retard the burning as far as
possible by reducing the draught, and feeding at considerably
longer intervals. At the same time a flat face of burnt bricks
should be exposed in the chamber where drawing is in progress,
and this should be papered over completely with the " paper
damper " used generally in barrel kilns. This paper damper
must be watched, and it can be pierced, if found necessary,
near the top to admit some air. As a rule, however, the kiln
walls leak sufficiently to let in the air required. This damper
will prevent too rapid cooling of the fire, and if the same feed-holes
are kept in operation as long as possible the advance of the fire
will be very slow. In some modern kilns the paper may be un-
necessary, as the dampers will shut off all undesirable heat.

Provided a chamber is kept well closed, the amount of heat
lost will not be serious, and the amount of fuel burned will be
inconsiderable. It is, however, unwise to leave a chamber in
which the firing of the goods is almost complete, without finish-
ing it off properly, the other chambers being held back in such
a manner as to prevent any harm occurring to their contents.
Thus, it will not, as a rule, seriously damage goods to be kept
indefinitely at 150° C. below their finishing point, unless they
are glazed^ though it is best to keep the temperature as low as
possible in goods which cannot be finished at the normal rate.

If kept soaking too near the finishing temperature, there is a
tendency for the lower heat to act as the higher temperature
does in a shorter time, and finish the goods before the fireman
expects it. Hence, it is not always possible to place full reliance
on certain forms of heat indicator (such as cones and thermo-
scopes) when the goods are put under the influence of an abnor-
mally long soaking.

Starting again after a holiday or other stoppage is a difficulty
in the older forms of continuous kiln, but in those with grates
running from the wicket to the back of the kiln this difficulty is
not nearly so noticeable, and in several of the more modern

364 MODERN BRICKMAKING

forms of continuous kiln the simple addition of more coal to
that on the grate, or box, is sufficient to restart the burning,
especially if hot air is used to aid the combustion, as it is in the
best forms of continuous kiln.

The essentials for a kiln in which the output is irregular, or
subject to frequent stoppages, are suitable grates or boxes for the
fuel, a good system of hot-air supply for the combustion of the
fuel, and a simple means of completely isolating each chamber
from the rest. These conditions are found in the more recent
forms of continuous kilns.

The following "Don'ts for Firemen," published anonymously
in the " British Clay worker," contain much sensible advice in brief
form : —

" Do not leave your kiln until your mate has arrived at the
end of your shift ; if he is ill or late the kiln may be spoiled.

" Do not forget to tell your mate exactly how matters stand
when he arrives.

" Do not think that a few minutes more or less between the
firings will make no difference with a continuous kiln. Punctu-
ality in firing is worth far more than irregularity and skilled
1 dodging '.

" Do not think that you can make up with heavy baitings for
neglect at an earlier period. Such neglect always leaves its
marks for the man who can read them.

" Do not fail to repair any leaks in the kiln walls, or, if they
are too much for you to manage, do not omit to inform the man-
ager or master. Much coal and labour can be saved by keeping
a kiln free from leaks.

" Do not fail to be informed if damp goods are put into the
kiln, so that you may regulate your firing accordingly.

" Do not hurry the first period of firing. Better a slow kiln
and good results than a quick fire and a large scrap heap.

" Do not omit to clean out the fires properly. Efficient clean-
ing improves the goods.

" Do not admit quite cold air to the part of the kiln to be
heated. There are many ways of supplying warm or hot air in
abundance ; use one or more of them. (See " hot air " in Index.)

" Do not let the heat travel irregularly, especially in a continu-
ous kiln.

"Do not omit to give an eye to the setters, so as to ensure
their work being properly done. Better a little time spent in
this way than hours lost in trying to work a badly-set chamber.

PIKING 365

" Do not forget to look frequently at the dampers ; neglect of
this caution may cause serious trouble.

" Do not use damper-plates which are badly warped or bent.
Get them made right or replaced by new ones. Warped dampers
waste fuel.

" Do not think that no skill is needed with paper dampers.
See that they fit tightly and remain whole until you are ready
for them to break or burn.

" Do not dawdle with the full fire ; but heat as rapidly as the
goods will stand. Slow firing gives dull finishes.

" Do not carry the full fire too near the freshly-set goods in a
continuous kiln, and,

" Do not start firing in a chamber until the goods in it have a
temperature of at least 120° C.

" Do not forget to test the temperature at the end of the smok-
ing or stoving stage with a thermometer.

" Do not think a poker will do instead of a thermometer for
testing for steam in a chamber. ' Poker results ' are often mis-
leading.

" Do not fail to test the draught of the kiln frequently. A
draught -gauge is often the best aid to efficient firing.

" Do not think that the shrinkage of the goods will always in-
dicate that they are finished. It all depends how dry they were
when set.

" Do not finish ' by eye ' alone. Use cones, or trials, or both.

" Do not think that all kilns are alike. Study the ones you
have to work as carefully as possible.

" Do not cool too rapidly ; you may shatter the goods.

" Do not ' soak ' your kiln because it was necessary at your
last place. With a different clay it may be an absolute injury
to the goods.

" Do not hurry off a kiln at the finish, or the goods will be un-
sound, but

" Do not keep the kiln over-long at a top heat ; it may cause a
' crush '.

" Do not forget that the. burner's work is about the most im-
portant of all, for no matter how skilfully the previous stages
may have been carried out a careless burner can spoil the
whole."

Cooling. — The average burner believes that bricks should be
cooled as slowly as possible, whilst his employer considers that-
rapid emptying of the chambers is desirable. Consequently, the

366 MODERN BRICKMAKING

one tends to unnecessary delay and the other to undue haste in
drawing the kilns. Between these two extremes lies the correct
method of cooling.

With single kilns, the cooling is less under control than in
a continuous one, though much may be done by judicious altera-
tion of the dampers, particularly when the kilns are enclosed in
another building. When the kilns are exposed, the cooling must
be slower if there are no facilities for using air at a temperature
but slightly lower than that of the cooling goods, and if rapid
cooling is attempted without these facilities the bricks will crack
and break.

Many tests carried out by the author on a large number of
different clays show that the cooling may be relatively rapid
until a temperature of about 600n C. is reached ; it must be slower
for the next 300° C. or thereabouts, and after this it may again
become more rapid, providing that cold draughts are avoided.
In single kilns it is impossible to cool very rapidly and at the
same time avoid cold draughts, and with such kilns it is, there-
fore, necessary to cool slowly, and whilst no definite rate of cool-
ing c'an be stated, it is wise to allow the cooling to take the same
time as the heating required between the end of the smoking
and the finishing of the chamber, omitting any special time
allowed for prolonged soaking in order to burn out carbonaceous
or other matter, or to completely oxidize the iron.

The best rate of cooling must, however, be determined separ-
ately for each kiln ; and provided the goods are not damaged,
and no serious quantity of heat is lost, the more rapidly the
chambers are cooled the better.

With a large continuous kiln much more rapid cooling is pos-
sible, as the air employed for this purpose may be used at a
temperature but little below that of the bricks, and, consequently,
large volumes of air may be employed without in any way
damaging the bricks.

To cool bricks rapidly requires a continuous kiln of great
length, as at least 60 ft. should form the cooling portion, and
for very rapid cooling twice this distance is needed in some
cases. The bricks will then cool as steadily as they were heated.
One of the most foolish practices in many otherwise well-man-
aged yards is that of having too few chambers in the cooling
portion of a continuous kiln when a rapid output is required.

Attempts have been made at various times to hasten the
cooling by blowing air into the kilns. These have only been

FIKING 367

satisfactory when warm air has been used, and this is commerci-
ally unprofitable in most cases.

The ordinary brickmaker who wishes to cool single kilns more
rapidly than usual, should make openings near the roof of his kiln
and should leave his main dampers fully open. If the kiln has
a flash-wall or bags, the fire-boxes may be opened partially, and
the damper regulated accordingly so as to prevent too rapid a
current of air being drawn through the kiln. Bricks vary so
much in their abilities to withstand sudden changes of tempera-
ture that each maker must decide, by actual trial, what is the
best method of cooling his kilns.

CHAPTER IX.
VITRIFIED BRICKS FOR SPECIAL WORK.

FOR certain engineering work, bricks of exceptional strength
are required, and for this purpose those which are more vitrified
than ordinary building-bricks are selected. The reason for this-
is that in a well- vitrified brick the burning has been carried as
far as possible, and the particles are bound together with a species
of glass into a mass of enormous strength.

The colour of engineering bricks is of secondary importance, but
great strength and accuracy of shape are essential. In different
districts very different kinds of bricks are used for this purpose,
a verifiable red-burning shale being popular in Yorkshire, a
similar buff-burning shale being used in some parts of the Mid-
lands and West, but the most popular engineering bricks are the
" blue bricks " made in Staffordshire.

These blue bricks are really slag-coloured, and are made from
special clays (locally known as " marls ") which occur in great
masses in South Staffordshire, particularly in the neighbourhood
of Dudley. These clays require the use of powerful machinery
as they are difficult to crush, and the kilns must be fired at a
high temperature in order that vitrification may be as complete
as possible. The "blue " colour is obtained as the result of the
reducing conditions in the kilns at the high temperatures used,,
and under-burned bricks made from the same materials are red in
colour. The iron oxide in the clay is reduced to a lower oxide
and formed into a silicate, previous to the end of the firing. A
similar effect is produced in some German works by the intro-
duction of tar and oil into the kilns when they have reached the
maximum temperature and are almost ready for closing.

In making blue bricks from the Staffordshire marls, several
superimposed materials are available, as will be seen from a study
of a geological survey map of the district, which shows this long
bed of " clay " very distinctly. As most of the eight or ten different
layers found are of similar composition, they are mixed together

(368)

VITRIFIED BRICKS FOR SPECIAL WORK 369

for brickmaking, but it is unwise to use the lowest beds, as they
often produce a scum.

The material must usually be obtained by blasting and fell-
ing and is taken by wagons (into which the materials are put in
the proper proportions) to the crushing plant. Here it passes
through several sets of rolls (figs. 46 and 47) and thence into
a mixer and pug-mill. Formerly the bricks were moulded by
hand, but wire-cutting (pp. 76 and 130) is now the most popular
method. For bricks of more than ordinary accuracy repressing
(p. 139) is practised. The bricks are dried on heated floors
(p. 157) or in tunnel-dryers (p. 161), and are fired in up-draught
kilns of rectangular or circular shape.

The use of continuous kilns for blue bricks has only been
successful within the last few years, as very high temperatures
are required and the conditions of burning are peculiar. With a
double-grated chamber-kiln working on the continuous principle
(Barnett's patent, p. 300), perfectly satisfactory blue bricks may
be obtained, using only about half the amount of fuel ordinarily
consumed.

The exact temperature reached in blue-brick burning differs
considerably in different works in the same district, but is
seldom less than 1200° C.

The atmosphere inside the kiln must be strongly reducing, or
alternately oxidizing and reducing, in order to gain the fuh1 advan-
tage of the fluxing power of the iron oxide present. With the
clays most suited for blue-brick manufacture there is no need for
special precautions being taken, providing the kiln is heated
steadily and finished at a sufficiently high temperature, and that
it does not leak excessively ; but with less suitable clays the pro-
duction of good blue bricks demands the consumption of a large
proportion of fuel, and the exercise of considerable skill in the
firing.

In each case, very little air is admitted during the last eight
or ten hours, the dampers being partially closed during this period.
Immediately the firing is completed all openings into the kiln are
closed so as to exclude air until the bricks are quite cold, other-
wise they will be of a reddish colour.

Some burners throw a little salt into the kiln just before the
close of the firing in order to facilitate the vitrification, but this-
is not to be recommended.

Clinkers and Paving Bricks are vitrified bricks of any colour,
their chief characteristic being hardness without brittleness.

24

370 MODERN BRICKMAKING-

They may be made from any material in which the temperature
of vitrification and that at which the brick loses its shape are
not too close together. The manufacture of such bricks calls for
no special description, as the chief precaution to be observed is
that the firing must be sufficient to produce the necessary vitrifi-
cation without making the bricks too brittle or warped.

They are chiefly made from low-grade fire-clays, shales, or other
brick-earths naturally rich in alkalies, but occasionally the ad-
mixture of a refractory clay with an easily fusible one will give
equally good results. It is seldom possible to add a flux (such as
Cornish stone) to a refractory clay in order to produce a good
vitrified brick, as the particles of added matter are too coarse,
Seger having found that, for successful work, the alkalies in the
clay must be so finely divided as to be present in the finest par-
ticles obtained by washing in a Schone's elutriating apparatus.

The standardization of paving bricks has been carried out
far more completely in America than in Europe, the following
requirements and tests being in regular use : —

(a) The size of the brick is known as " block size," and must not
vary more than ^ in. in any block. The preferred size is 8-J in.
by 3-J- by 4 in., exclusive of all lugs or projections ; but bricks of
other dimensions may be accepted for use provided the depth
is 4 in.

(b) Projections or lugs are required.

(c) The brand or mark of the brick, to identify it by name or
otherwise, must be on each brick. No blank bricks are to be
used.

(d) The shape of the bricks must be uniform and regular, and
must not be distorted more than J in., from the straight edge laid
in any direction on them. Edges must be rounded. All bricks
must be repressed.

(e) The material of the bricks must be homogeneous, uni-
form, free from laminations, cracks and voids, only very minute
fire- cracks being allowed. The material must be thoroughly
.annealed, fused, and vitrified to toughness without excessive
brittleness.

(/) The abrasion or rattler test must be made in a standard
rattler by the method of the National Brick Manufacturer's As-
sociation and the American Society of Municipal Improvements
The maximum loss of any one brick shall not exceed 18 per cent of
its original dry weight. The average loss of all bricks tested at one
time must not exceed 14 per cent. The standard abrasion

VITRIFIED BEICKS FOE SPECIAL WORK 371

machine or rattler is a cylinder of 14 staves or sides, J in. apart,
inside diameter 20 in., length 20 in. It has no interior shaft, and
revolves -at 30 revolutions per minute for one hour. It contains
a charge of 300 Ib. of foundry iron shot of two standard sizes ;
and the charge of brick for a test must approximate 1000 cu.
in., which is about nine bricks of the block size. Records of each
brick in each test must be kept.

(g) The modulus of rupture or cross-breaking of any one brick
must not be below 2500 Ib. The average of all bricks tested
must not be below 2700 Ib., by the regular formula M = (3WL)
-f- (2AD) in which L = 6 in. between supports, W = breaking pres-
sure, A = area of cross-section at break and D = thickness of brick.
The bricks must be tested on the side and the pressure applied
half-way between the supports. At least three bricks must be
submitted to this test.

(h) The absorption of water by any one brick must not be
greater than 3 per cent. The average absorption of all bricks
tested must not exceed 2 per cent of their dry weight. The ab-
sorption tests must be made on either abraded or on broken
bricks, by drying them for twelve hours in an oven, then soaking
them for twelve hours in water. The increase of weight due to
water absorbed, divided by the weight of the dry bricks, gives the
percentage of the water absorbed. At least three bricks must be
used for this test.

(i) The density or specific gravity must be determined exclusive
of the porosity of the brick. No bricks must have a density of
Jess than 2-30, and the average density of all bricks tested must
not be less than 2*35.

(j) The hardness is expressed in terms of Moh's scale for min-
erals, in which 100 is the diamond. The hardness of any brick
must not be less than 60, and the average hardness of bricks
tested must not be less than 65 (i.e. between felspar and quartz).

(k) The crushing resistance must not be less than 7500 Ib. per
sq. in. for any brick, and the average resistance to crushing
of all bricks tested must not be less than 8500 Ib. per sq. in.
The crushing tests must be made on about one-sixth middle
sections of brick, with pressure applied in the direction of the
whole thickness of the brick, which is the least dimension of the
brick. At least three bricks must be used for this test.

(I) Chemical tests may be made to determine if there are any
water-soluble substances, such as free lime, potash, soda, etc., in
the bricks ; and if more than a trace is present the entire lot of

372 MODERN BRICKMAKING

bricks from which the sample has been taken must be re-
jected.

There is no immediate prospect of these or any other stand-
ards being recognized by the paving brickmakers of this country,
as the use of bricks for road-making here is not apparently in-
creasing. In countries such as the United States and Canada,
where great extremes of heat and cold are experienced, pave-
ments made of brick possess many advantages over macadam
and other well-known materials.

Acid-proof Bricks are used in large quantities in the manufac-
ture of various chemicals. They must be strong and accurate in
shape and as resistant as possible to any chemicals with which
they may come in contact. Many fire-bricks are sufficiently
acid-proof for most purposes, particularly if salt-glazed, but
when a superior brick is required a ball- or stoneware-clay must
be used. Acid-proof bricks are not usually required to withstand
violent changes in temperature, so that they need not be made
of clay possessing great heat resistance. The best acid-proof
bricks are those containing a considerable proportion of true
clay, the exceedingly fine particles of which fill up the voids
otherwise present, and the brick is made impervious apart from
any vitrification which may have occurred during the firing.

The standard test for determining the value of acid-proof
bricks is to ascertain their crushing strength before and after they
have been soaked in concentrated sulphuric acid maintained at
a temperature of 90° F. for seven days. All the best bricks sold
for chemical works at the present time are quite unaffected by
this treatment.

CHAPTER X.
FIRE-BRICKS AND BLOCKS.

THE manufacture of fire- bricks and blocks has been carried on
for many years in a somewhat rudimentary manner, and it is
only recently that the more important firms attempted to improve
their product and bring it up to date.

In earlier times fire-bricks and blocks were only required to
withstand relatively low temperatures, but, with the increasingly
stringent requirements of modern metallurgists and other users
of furnaces, it is necessary at the present time to make use of
every available assistance which science can render to the fire-
brick maker.

Investigations have shown that various users require widely
different characteristics in fire-bricks and blocks, and a material
which suits one customer well may be entirely unsuitable for an-
other. It is, therefore, necessary to know what characteristics
are required before the value of a fire-clay can be stated.

The materials from which fire-bricks and blocks are made are of
four main classes : (1) fire-clay ; (2) rocks consisting of almost pure
silica ; (3) rocks composed chiefly of silica but containing about
10 per cent of clay and known as " ganister ". Artificial imita-
tions of ganister are also used ; (4) neutral and basic materials
such as chromite and magnesia.

The treatment of the materials depends on their nature, and
the three chief processes used must therefore be described : —

Fire-clay bricks are made from various seams of fire-clay found
in several parts of the country, the most noted deposits being in
West Scotland, Northumberland, Yorkshire, the Midlands (Bur-
ton and Ashby-de-la-Zouch), Buckley, Stourbridge, Shropshire,
Devonshire, and Wales. The materials from these various sources
differ widely in composition and character.

The West Scotland fire-clays (including those of Glenboig) are
noted for their unusual heat-resisting power. They require to

(373)

374 MODERN BRICKMAKING

be fired at a very high temperature, as otherwise they are soft
and weak.

The Northumbrian fire-clays are chiefly found near the Tyiie,
and are richer in alumina than those of Scotland. Unfortunately,
this advantage is more than neutralized in several cases by the
presence of an excessive proportion of fluxing material (alkalies
and lime) which greatly reduces the heat-resisting power of the
bricks. Several seams in Northumberland and Durham are,
however, of excellent quality.

The Yorkshire fire-clays are found chiefly near Leeds and
Halifax, but the material crops up unexpectedly in several other
parts of the county. In South Yorkshire it is associated with
ganister (see later). The fire-clays in Yorkshire are peculiarly
variable in composition, the alumina varying from 15 to 39 per
cent. The clays richest in alumina are found nearer the surface,
but are much more tender than the stronger ones found at greater
depths.

Taken as a whole, the Yorkshire fire-clays are amongst the
most refractory, but they have not hitherto been worked so as
to develop this property to the fullest extent, as they are almost
invariably under-fired and so shrink in use at abnormally high
temperatures.

The Midland fire-clays are more readily vitrified than most
others of equal quality, and are therefore in great demand for the
manufacture of close-grained bricks and sanitary pipes. They
are not usually so resistant to heat as some others, but where
other factors (such as the cutting or corrosive action of dust and
fire-gases) have to be considered, they are very valuable, and
under some conditions prove more durable than more infusible
bricks from other districts.

The Stourbridge fire-clays have a world-wide reputation for
refractoriness. The composition is remarkably constant, though
unexpected variations occur at times. The average proportion
of alumina is about 22 per cent — -thus corresponding to the
Scotch and some Leeds clays — but portions of clay with over 36
per cent of alumina have been found.

The Devonshire fire-clays, like those of the Ashby district, are
relatively easily vitrified, but considerable variations in quality
exist. The most noted fire-clays in this county are found in the
Teign valley, and often contain considerable proportions of under-
composed granite. They are, therefore, used for the manufacture
of vitrified bricks where the greatest resistance to heat is not re-

FIRE-BRICKS AND BLOCKS 375

quired, but where a brick which will stand what is ordinarily con-
sidered to be a high temperature is required.

The Welsh fire-clays in some ways resemble those of Stourbridge
but are seldom so pure, and must, therefore, be worked with
caution. The best deposits in this district are of first-class
quality for refractory work.

The fire-clays are chiefly found associated with the coal
measures and millstone grit, and must therefore be obtained by
mining. Some brickmakers are working in the " rubbish heaps "
of collieries, but the best fire-clays are obtained direct from mines.

The seams vary in thickness, just as do those of coal, but are
less uniform than the latter, and it has generally been considered
that the only seams which can be worked at a profit are thick
ones near the surface or those mined along with coal. Curiously
enough the best fire-clay is often raised from pits containing but
little or no coal.

The fire-clay should be selected or " picked " before use, so
that nodules of pyrites and other unsuitable material may be
removed. It should also be allowed to " weather " as the sub-
sequent crushing is made easier thereby, many shales and fire-
-clays being exceedingly hard when first mined, but becoming soft
on exposure. The picked and weathered material is then crushed
in an edge-runner mill with either stationary (p. 95) or re-
volving (p. 183) pans.

For very hard fire-clay shale the stationary pan-mill is the
more powerful, but if a preliminary crusher or stone-breaker is
used a revolving pan will often give a larger output.

The material is usually passed through a screen having
twelve or thirteen holes per running inch, but this somewhat
crude method of working is now being replaced in the most pro-
gressive works by a double sieve.

Either before or after grinding, the fire-clay is usually mixed
with burnt material of a similar nature (termed " grog " or " burnt
stuff") in order that a skeleton may be formed which shall hold
the brick together during the drying and firing. The use of this
grog is often greatly misunderstood, and in some works it is
omitted entirely.

The mixed clay and grog are next passed into a pug-mill,
usually of the vertical type (fig. 20) where it is mixed with water
and converted into a paste. This paste is sometimes stored away
in a heap to " sour," but many workers do not appreciate the
value of this treatment and so omit it.

376 MODEBN BEICKMAKING

The bricks or blocks are moulded by hand by the slop -mould
process (p. 51), slight variations occurring in different shops.
They are dried on floors heated by steam (p. 158), or flue-gases
(p. 159), and are fired in Newcastle or Scotch kilns (p. 255).

The maximum temperature reached in the kilns varies greatly
in different yards. In some it is as low as cone 2 (1170° C.) and
in others as high as cone 19 (1510° C.) The higher temperatures
used are largely the result of modern investigations and research
and are not used in the smaller works. About a week is usually
occupied in the kiln, but where exceptionally large blocks are
made a much longer time (extending in some cases to two months)
is considered necessary, as such blocks are extremely sensitive
to sudden changes in temperature before they are fired. It will
thus be understood that, formerly, the manufacturer of fire-bricks
had chiefly to see that his material was right and that the men
worked well. A few degrees more or less in the kiln made but
little difference, and so long as his goods were saleable, little
else mattered.

Within the last five or six years, however, a great change has
come over the fire-clay industry. This is due to a variety of
causes, the chief of which is the demand for better bricks and
blocks from various users. This demand is increasing as progress
with high temperature work continues, and the fire-clay worker
of the future must use his best endeavours to meet the demand.
Fortunately, the cost of building and re-building is so high, com-
pared with the cost of fire-bricks, that a good price can be obtained
for a really satisfactory article.

In order to do this it is necessary to know the general direction
in which this demand tends to run, and for this purpose the chief
characteristics needed in a fire-brick or block must be studied.
It is not possible to obtain all these in a single brick, as they are,
to some extent, mutually incompatible, but the worker will know
which to select from the whole. The chief characteristics re-
quired are : —

1. Resistance to high temperature.

2. Resistance to pressure at high temperatures.

3. Non-absorptive power at any temperature.

4. Uniformity in size, shape, and composition.

5. Expansion or contraction in use.

6. Resistance to abrasion by dust, flames, metal, slag, and
other materials.

FIRE-BKICKS AND BLOCKS 377

7. Resistance to reduction or oxidization.

8. Resistance to wear and tear and accidental blows.

9. Resistance to sudden changes in temperature.

As already mentioned, it is seldom that all these character-
istics can be obtained simultaneously, and a selection must be
made for each case.

Resistance to heat is a property possessed by the material
itself and is largely dependent upon the purity of the material and
upon the proportion of alumina it contains. At the same time,
the results of analysis cannot be reliably used to predict the
fusing point of a high-class refractory clay, though in connexion
with a Ludwig chart analytical results are often valuable in this
•connexion.

It is a curious fact that whilst mixtures of pure alumina and
silica usually melt in proportion to the silica present, a critical
composition is reached when such a mixture contains more than
85 per cent silica, and from this point until pure silica is reached
the mixture becomes increasingly refractory, though pure silica
.is more fusible than pure alumina.

Very small quantities of lime, alkalies, titanium and other
•oxides greatly increase the fusibility of a fire-clay so that what,
in other clays, would be considered trifling impurities, are of great
importance in fire-brick manufacture.

Resistance to pressure, abrasion, reduction, and wear and tear
is obtained by heating to such a temperature that partial vitrifi-
•cation occurs. This is difficult with really high-grade clays on
account of the very high temperature required, so that an un-
oisiually strong brick is commonly of second quality as regards fusi-
bility;. In many cases, however, a strong brick of slightly inferior
..clay may prove more serviceable than one made from a purer clay
which is weaker.

On the. other hand, some bricks which are strong when cool,
or only moderately heated because of the binding power of the
vitrified material they contain, are often very soft and weak at.
high temperatures when the vitrified matter becomes viscous.
When this is the case, such bricks are of little value and should
foe replaced by^those of purer clay burned at a correspondingly
higher temperature.

Expansion and contraction in use are reduced to a minimum
"by firing the bricks at a sufficiently high temperature during the
manufacture, though few British firms do this.

378 MODEEN BRICKMAKING

Excessive expansion in use may be due to too much free
silica in the bricks, a fault which is also responsible for " spelling 'r
or splitting under sudden changes of temperature.

Stated briefly, the most severe requirements for fire-bricks will
be met by using as pure a fire-clay as possible containing a high
percentage of alumina,1 providing the sizes of the various particles
of raw clay and grog are properly proportioned, and the whole
brick is fired at a sufficiently high temperature. Unfortunately,
these conditions are far more difficult to attain than appears at
first sight. They involve the careful selection and purification of
the materials, the correct treatment in the mills, screens, and
mixers, and the use in the kilns of a temperature which is far
beyond that ordinarily employed for fire-bricks in this country,
as, to the best of the author's knowledge, only three firms in Great
Britain were firing their fire-clay bricks sufficiently in 1910.

The selection of the materials for a first-class fire-brick is a
matter needing great skill and care. Analysis is useful in order-
to check the use of clay containing an excess of impurity, but
quite apart from this much may be done in routine work by
careful observation of the appearance, colour, and texture of
the materials. Some attempt is made by most fire-brick makers
to avoid the use of " post " and other rocky material, but much
more careful picking is desirable when bricks of the highest
quality are being made.

In selecting clays it is necessary to bear in mind the char-
acteristics required in the bricks arid to choose accordingly. This
will often result in a number of different clays being mixed instead
of a single one being used, as is often the case at present. It is
unreasonable to expect that a single clay — with obvious limited
properties — can be successfully made into crucibles and furnace -
bricks with equal success.

Whatever may have been done in the past the requirements
of the present and future are and will be increasingly stringent,
and fire-brick makers will find it more and more necessary to mix
several clays in order to produce what they require. In some

xThe use of free alumina or bauxite to increase the percentage of alumina in a
clay is not desirable. A mixture of alumina or silica in the proportions in which
these materials occur in a pure clay does not behave in the same manner when fired
as clay would do.

Hence the use of bauxite and other free alumina as grog, whilst useful in some
cases, does not produce a fire- brick of the very highest class.

FIRE-BRICKS AND BLOCKS . 379"

cases, by supplying a limited market, less complex mixtures of
materials may be used.

Hitherto, the usual practice has consisted in crushing the clay
or clays until they are sufficiently fine to pass through a coarse
sieve, but careful investigation has shown that this is not the best
way to work. Particles of true clay are so exceedingly minute that
they are too small to be produced by any machinery. Yet it is to-
these extremely minute particles that clay owes its plasticity and
value, and any method of working that does not make use of this
fact cannot be considered as satisfactory. To use clay in a coarse
state (as is commonly done) is to waste the material and to pro-
duce an inferior article.

The broad principle upon which to work in producing refrac-
tory goods, such as fire-bricks, is to form a " skeleton " of as great
a heat-resisting nature as possible and to bind this, together with
other materials alsoi of a refractory nature, into a mass possess-
ing the necessary strength, resistance to abrasion, temperature
changes, etc. Sufficient room must be left between the particles
to permit them to move freely over each other within certain
limits, so that the brick wih1 not be shattered or cracked when
exposed to sudden changes of temperature. As it is impossible
to allow perfect freedom of movement of the particles, some
softer material must be interposed (in the form of clay) so that
it may yield slightly but not excessively under pressure. The
main portion of the brick must, therefore, be of as porous and
open a nature as possible, any undesirable pores being filled later
with a binding material.

The nature of1 these skeleton-forming and binding materials
has been studied but slightly, and further investigation is desir-
able. The following statements may, however, be accepted a&
substantially correct : —

The " skeleton " or main portion of the brick must be com-
posed of a clay whose chief characteristic is its infusibility .
Such clays when made into the form of a Seger cone should not
bend when heated to any temperature below that corresponding
to Seger cone 35 for the highest grade of fire-bricks, cone 30 for
" first-class " fire-bricks, and cone 26 for second quality or " ordin-
ary " fire-bricks. Although no official British standard exists by
which the value of fire-clays may be tested, the figures just men-
tioned are accepted by the chief experts on the subject in this
country and by the chief fire-brick makers in Germany.

Provided a clay is sufficiently refractory, its lack of plasticity..

7*80 MODERN BRICKMAKING

weakness, and durability are relatively unimportant so far as its
use as a " skeleton " is concerned. These properties must be con-
ferred by the use of other clays (binding clays).

As the particles of the material forming the " skeleton " are
to be bound together by another material — the binding clay —
there is no need to use a plastic clay for this skeleton. It is, in-
deed, a disadvantage to do so, as plastic clays usually shrink
•considerably in firing — a most undesirable characteristic in this
case.

. It is, therefore, best to use for the skeleton a clay which is
extremely pure and, at the same time, is in relatively coarse
particles and of minimum plasticity. Such a material is fur-
nished under the name of " grog," " burnt stuff," or " chammotte,"
which is obtained by burning a fire-clay of the highest grade ob-
tainable, at a bright red heat, and crushing the product, as
will be described later. It has been customary for the terms
just mentioned to be applied to damaged fire-clay goods, fire-
bricks, etc., which are added to raw fire-clay for various purposes
in a more or less haphazard manner. These sources of an in-
ferior "grog" are sufficiently good for ordinary fire-brick manu-
facture, but they should not be used by the maker of the highest
-class of bricks. Glazed materials and slag and potsherds must
be avoided at all costs.

E. P. Page has shown that if the grog is not more refractory
than the clay used to bind its particles together, the brick may
crack on account, of the strains set up and the amount of vitri-
fication which occurs. The cracking may not occur immediately,
but will do so on repeated heating.

Grog should be made of the purest fire-clay procurable which
should be fired in such a manner as to avoid " flashing " or over-
heating. The temperature reached in its manufacture should
not exceed 1450° C. (cone 15), but should seldom be less than
1 180 (cone 5&). The product should be a creamy mass free from
whitish portions and from discolorations. It should be mod-
erately hard, but not excessively so, and should be so refractory
as not to bend below a temperature corresponding to Seger cone
30 when made into the same shape as a Seger cone. Grog can
usually be manufactured by the fire-brick maker, and the neces-
sary precautions as to purity, etc., can be readily observed ; if
purchased, the grog should be subjected to a series of rigorous
tests before acceptance.

Attempts are sometimes - made to use a grog of a different

FIEE-BBICKS AND BLOCKS 381

composition to that just mentioned, by substituting silica-rock
or bauxite for burned fire-clay. Such materials are useful in the
case of ordinary fire-bricks, but should not be used where bricks
of the very highest quality are required. Silica is not so refrac-
tory as the best fire-clays, and its admixture may easily cause a
reduction in the fusing point. The use of bauxite or other forms
of free alumina, on the other hand, whilst useful as giving a
" skeleton " of great heat-resisting power, requires special care
and skill in use, and is apt to be a continual source of trouble.
Most specimens of bauxite are so impure as to seriously reduce
the value of clays with which they are mixed. The addition of
alumina or silica to a clay should, therefore, only be made under
the advice of a really reliable expert who appreciates the diffi-
culties which may arise, and who can study the problem in all
its bearings. As commonly used, these materials may do more
harm than good. (See footnote on p. 378.)

The size of the grog particles to be used in fire-brick manu-
facture is importantj and it is not sufficient to use all that will
pass through a sieve of definite mesh. Very fine grog is useless
and should be avoided, as by the nature of the case, the spaces
between the coarser particles should be filled by a binding
material which should consist chiefly of a plastic clay.

It is therefore necessary, in making the highest grades of
fire-bricks, to crush the grog and sift it with two screens, reject-
ing all that passes through the finer mesh, returning the residue
on the coarser screen to the mill for further crushing and only
using the intermediate portion. The finest "grog " may be con-
veniently used in place of sand for " dusting " purposes.

The mesh of the grog-screens must depend largely on the
fineness and plasticity of the " binding clay " used. A useful
sized grog for preliminary work is obtained by passing the
material through a wire screen having eight holes per linear inch,
and then on to a similar screen with twenty holes per linear
inch, rejecting all that passes through this latter screen. Later
tests may show that the grog thus obtained contains particles
which vary too greatly in size, but this can be easily remedied
by the use of finer or coarser -screens. In some cases, particu-
larly in South Yorkshire, it is desirable to use three screens and
to employ two sizes of grog ; but this is a refinement not usually
necessary in fire-brick manufacture.

In Germany, many of the best fire-brick makers use two sizes
of grog : (a) particles between ^ and ^ in. diameter, and (b\

"382 MODEKN BEICKMAKING

particles between T^ and ^ in. diameter, the relative proportions
of each of these materials depending upon the characteristics
the fire-bricks should possess.

The binding material used to give strength and resistance to
the " skeleton " must be sufficiently fine to enter between the
other particles ; it must be sufficiently plastic to hold the whole
mass together before firing, and sufficiently verifiable to bind the
whole brick into a strong mass with the requisite qualities, whilst
not being so fusible as to seriously interfere with the heat-re-
sisting power of the brick as a whole. The binding material must
not shrink so much in the kiln as to cause deformation or warping
of the brick.

Taking all these qualifications into consideration, it is evident
that the most suitable binding material will be a refractory clay
of moderate but not excessive plasticity. It must not be quite
so refractory as the grog, but must still be sufficiently free from
fluxing materials to enable the brick to withstand great pressures
-at a red heat.

A single clay is seldom found which will meet all the re-
quirements of a binding clay, and two or even three clays may be
necessary for the highest class of fire-brick. For what are at
present generally considered as " best " fire-bricks (but which are
far inferior to what can be produced) a single binding clay can
usually be employed.

When two or more clays are used as binders the leaner ones
should be ground so as to pass through a No. 20 sieve but not
through a No. 100, the fatter clays being ground as finely as
possible.

If several clays are used the proportion of each must be
settled by actual tests.

There are, unfortunately, great difficulties connected with
such tests, and the fire-brick maker who has discovered a really
successful blend of clays has gained a great advantage over his
competitors.

The clays used for binding must be carefully selected, any
unsuitable material being picked out, and the whole mass exposed
to the weather so as to reduce the labour and cost of crushing.

The fineness to which the binding clay should be crushed de-
pends greatly on its nature. Highly >compressed shales need
reducing to a fine powder, but some of the less dense clays are so
readily disintegrated by water that a comparatively rough crush-
ing is sufficient, the final reduction taking place automatically

FIEE-BEICKS AND BLOCKS 383

during the " souring " process. It is seldom, however, that clay
particles larger than -£$ in. diameter should be used in fire-brick
manufacture, as the coarse particles required are best supplied
in the form of grog which cannot become broken up by later
treatment, as frequently occurs with coarse particles of clay.

A single screen may be used for the binding clay, as the finer
the particles of this material the stronger will be the brick, and
in any case clay particles are naturally far smaller than can be
obtained by any mechanical process of grinding.

The grinding of both clay and grog is best accomplished in
edge-runner mills (p. 375) of either the stationary or revolving-
pan type, the latter being preferable for the clay as it effects a
better mixing of the material.

A preliminary crushing between small rolls (p. 86) or in a
stone-breaker often effects a saving in power and in the wear and
tear of the larger mills, and increases the output by making the
supply of material more regular. Edge-runner mills should
never be supplied with pieces more than 4 in. diameter if they are
to work economically, and the present custom of many fire-brick
makers of feeding pieces of all sizes into the mills is against their
best interests.

The preliminary crusher should be arranged to deliver the
material on to a floor from which it can be readily shovelled into
the edge-runner mill. If an automatic feeding device is employed
for feeding the latter the preliminary crusher may deliver direct
into this machine. (See pp. 181 and 183.)

It is often more economical and facilitates the output if two
edge-runner mills are used, both delivering into the same pit.
The first receives the material to be crushed and the second the
4t tailings " from the screen. 'In this way the harder portions are
kept separate, as far as crushing is concerned, and by using mills
of the proper sizes the output is greater than if a single (larger)
mill is used. It is important that >both mills should deliver
to the same elevator so that the material may be kept mixed.

Where several clays are used, each should be ground in a
separate mill, as this is far more satisfactory than (a) mixing the
•coarse materials and grinding the mixture, or (b) cleaning out the
mill each time a change of material is made. Grog should never
be ground in the same mill as the clay unless second-quality fire-
hricks are desired.

The runners should be provided with renewable rims or tires,
and should be sufficiently heavy to do their work well.

384 MODERN BRICKMAKING

The grates in edge-runner mills for fire-bricks should have
holes or slots not more than \ in. in width, and for most purposes
^ in. holes are best. The day when lumps of material ^ in. or
more in diameter were permissible in fire-bricks of good quality
is rapidly passing away, and pieces \ in. wide are the largest
which are now considered satisfactory, and for first-class work only
very few of these are allowed.

Each mill should be "run off" every noon and evening, and
any material on the pans should be collected and thrown aside.
It will usually be rich in nodules of pyrites and other undesirable
impurities in the clay, but should be tested carefully from time
to time.

The nature of the screen used is important ; piano riddles have
not proved successful in grinding fire-clays and grog in many cases,
because the material is so hard and sharp that it wedges between
the wires and so delivers too coarse a product.

The well-known wire-gauze screen may be employed, or a
sloping plate of perforated steel (see " Newaygo " screen, p. 194}
may be used. The size of the holes in the latter corresponding
to the former must be found by experiment, as they differ with
different materials. As a rule a dry fire-clay will behave to such a
screen having J in. holes as it will to a gauze-screen with a -^ in.
mesh, but the perforated metal gives a much larger output.
(See p. 192).

The crushed materials should be stored in a dry place in bins
where they can be kept apart from each other, yet can be readily
measured and mixed before being treated with water.

The best method of proportioning and mixing is to employ
large boxes on wheels, the size of each box being proportionate
to the amount of material to be mixed. Thus if thrice as much
clay as grog is used, the box for the clay will have three times
the capacity of that used for the grog. Each box is filled up and
any excess of material removed by drawing a flat piece of wood,
or strike, across the top. It is better to use boxes of the sizes
suggested than to have all the same size and use (say) three box-
fuls of clay to one boxful of grog, as errors in counting are
frequent with the latter method. The boxes may be mounted on
cars and should run on a light track. Their contents should be
tipped on to a mixing-plate, fixed at a lower level than the bins,
a rough mixture made by means of a shovel, and the material
then shovelled into the mixing mill, or a mechanical feeder
(p. 182) may be employed, and the labour of one man as mixer

FIRE-BRICKS AND BLOCKS 385

be saved. On no account should the material be fed into the mill
without a preliminary mixing having been effected, except in
those cases where an intermittent solid bottom pan-mill is used.

The mixing of the materials with each other and with water
is effected either in (a) a pan-mill (p. 95) or edge-runner mill with
solid revolving pan into which a charge of material is placed,
together with sufficient water, and the two " ground " for about
twenty minutes and then taken out, or (b) in a pug-mill. The
pug-mill is usually of the vertical type (p. 49), but horizontal
mixers and pug-mills are equally effective, though they occupy
more floor space (pp. 103-109).

Whichever form of mixing plant is used the water should be
added gradually and in a series of fine jets or as a spray. It
should not be added in a single stream as is so often the case.
A couple of level pipes each perforated with ^ in. holes about
1 in. apart forms a good water-distributor, particularly if each
pipe delivers on to the edge-runners instead of directly into the
pan.

The paste produced should be set aside in heaps about 4 ft.
high in order that it may " sour ". At one time it was thought
that some kind of fermentation or bacteriological action took
place and improved the quality of the material, but it is now
generally recognized that the effect of any fermentation in this
direction is very small, and that what really occurs is a more even
distribution of the water throughout the mass by means of
capillary attraction and other purely physical forces, this re-dis-
tribution being accompanied by a development of the plasticity
of the material. Hence, no matter how thorough may be the
mixing, this " souring " should never be omitted in the manufac-
ture of the highest grades of fire-bricks.

With some materials the development of the plasticity of the
clay is rapid ; these may be used after once passing through the
pug-mill or pan, but others must usually be mixed again after
" souring," a second pug or pan-mill being used. Some fire-brick
makers dread " overworking " their clay ; this can only occur
when the clay is used where grog ought to be employed, and by
replacing part of the- clay by a suitable grog satisfactory results
will be obtained.

The bricks are made from the paste by hand-moulding, using
brass or brass-lined moulds for ordinary shapes and zinc-lined
ones for shapes which are seldom required. The process is very
similar to the slop-method used for building-bricks (p. 50),

25

386 MODEEN BEICKMAKING

though, like the latter, it varies slightly in different works. The
bricks are carried off between two pallet-boards by a boy or girl
and are set down on a heated floor (p. 157).

Many attempts have been made to use machinery instead of
hand-labour, and some amount of success has been attained by
the employment of machines imitating hand-moulding (p. 68)
and by use of the wire-cutting process (p. 76). The stiff-plastic
and semi-plastic methods have not, hitherto, proved successful,
and hand-made bricks are still considered to be the best. The
great reason for this is the tendency for machines to compress the
clay too much. If the paste remains sufficiently soft (as soft as
in hand-moulding) it is difficult to keep it of the proper shape
during wire-cutting, and the use of a stiffer paste produces a less
satisfactory brick. The temptation to secure greater accuracy of
shape in the brick by mechanical pressure should, on this
account, be avoided, and represses should never be employed for
bricks to withstand high temperatures in actual use. For the
same reason, machine-pressed bricks which are not sufficiently
perfect to be used for glazing are of small value for the highest
temperature work; the pressure to which they have been subjected
to give them greater accuracy of form so necessary in glazed bricks
has reduced their value for furnace-construction. The desira-
bility of accuracy in shape for all fire-bricks must not be over-
looked, but it must not be produced by the use of greater pressure
than is used in a hand-moulded brick. Even if the method dry-
pressing (p. 241) were to become more popular for the manufacture
of fire-bricks, the great wear and tear of the dies, due to the large
amount of grog necessarily present, would probably rob the process
of any saving in manufacture. Yet this is undoubtedly the
direction in which to look for cheapened output with superior
quality.

Blocks and large pieces of fire-clay are moulded by the same
(slop) process, wooden moulds being employed. A portion of the
drying floor is cleaned, dusted with clay dust, sand, or fine grog-
to prevent undue adhesion of the clay, and the wet mould is
placed on the floor so prepared. The maker next throws large
masses of paste with great force into the mould, and by vigorous
"pommelling " with his fist and kneading with his fingers com-
presses the clay as equally as possible. The mould having been
filled, any excess of clay is removed with a strike or wire, and
the mould is removed either immediately or after a short time.
Some blocks are made in plaster moulds.

FIBE-BEICKS AND BLOCKS 387

The drying of fire-bricks offers no special difficulty, provid-
ing it is effected carefully, but larger blocks or slabs need much
attention or they will crack.

Fire-bricks, slabs, and blocks are usually dried on fire- or
steam -heated floors (p. 157), and these are usually satisfactory
but slow, particularly with the larger pieces. It is, in fact, not
unusual for a large 'block or slab to remain on a floor for three
weeks without any heat being applied to it. Such a method of
drying is highly unsatisfactory, and most block manufacturers
would find a study of the principles of clay drying well worth
while.

One of the secrets of rapid and successful drying consists in
not allowing the outside of the brick or, block to dry more rapidly
than the inside. This accurate regulation of the speeds at which
the various portions of a block dry can only be accomplished by
proportioning the amount of air in contact with the article, and
by ensuring that this air contains just the correct amount of
moisture. In using a steam-heated floor, such as is ordinarily
employed, such accurate regulation is impossible ; it can only
be obtained in tunnels to which air is admitted by means of
special valves and moved by means of a fan.

By the careful use of small chambers in which moist air is
used at various temperatures, the earlier stages of the drying
may be considerably shortened without increasing the risks of
cracking, but the subject is not sufficiently closely related to
brickmaking to be described in further detail in the present
book, but see pp. 161-176 and 213-217.

Dipped fire-bricks are used for special purposes, where they are
required to possess characteristics incompatible in the brick as a
whole, such as maximum heat-resistance combined with entire
absence of absorption. They are really a species of glazed brick,
but instead of a true glaze are, in part, coated with a non-porous
material. This coating is applied in a manner similar to that
used in glazing.

Fire-bricks are set in the kiln in a manner similar to that used
for ordinary bricks, but they should not be placed so close to-
gether. Larger blocks must be set near the centre of the kiln,
and according to their shape, so as to reduce the risk of twisting
as much as possible. A chequer-work arrangement, as in fig.
104, is very popular, the bricks being set on their sides and not
flat as shown.

A little grog dust sprinkled between the bricks and blocks

388 MODEEN BEICKMAKING

enables them to be separated from each other more readily when
the kiln is drawn.

When large blocks have been placed in a kiln special care is
needed to keep away draughts and sharp currents of air. A door
should, therefore, be provided for the kiln and used.

The firing of the bricks is usually carried out in kilns of
the Newcastle (p. 255) or round down -draught (p. 248) type,
but continuous kilns (p. 263) may be equally well employed
if a suitable design is chosen. The Dumiachie kiln (p. 304)
lias been successfully used for many years for the purpose.
The heat required is more and the temperature of finishing is
much higher than with ordinary bricks, but in other respects the
same methods are used.

The ordinary fire-brick of commerce is seriously under-fired,
being seldom heated to more than 1250° C. The result is that it
shrinks and becomes loose in use and wears away rapidly, as the
wide joints so produced cause an unduly large surface to be ex-
posed.

Zoellner has shown that all clays when heated to tempera-
tures above 1300° C. (cone 10) dissociate and become crystalline,
with the formation of silimanite (Al2O3SiO2) and a glassy mass
richer in silica than true clay. This latter material may be
removed by hydrofluoric acid, in which it is soluble. Zoellner
states that this " shows the necessity of heating fire-bricks and
other refractory goods to a much higher temperature than is
customary, as the crystals of silimanite form a felted mass which
is harder, more acid proof, and more resistant to sudden changes
in temperature than is clay which has not been partially dis-
sociated by firing at a high temperature ". Most manufacturers
try to avoid crystallization !

For the best grades of fire-brick the finishing temperature
should certainly not be less than is sufficient to bend cone 18
(1500° C.), and for somewhat less important bricks a kiln tem-
perature corresponding to at least cone 12 (1350° C.) should be
reached. For export, where the requirements are not so strin-
gent, cone 5 may be regarded as indicating the maximum tem-
perature necessary, though harder-fired bricks will suffer less
damage in transport, and will be superior in quality.

Fire-bricks are usually more porous than ordinary ones before
firing, and the earlier stages of burning may often be passed more
rapidly. With large blocks the matter is very different, and the
earlier stages are sometimes prolonged to several weeks.

FIRE-BRICKS AND BLOCKS 389

The final heating should be very steady but moderately rapid,
and the cooling — whilst rapid at first to carry the goods past the
"danger zone" (1100-1200° C.) where, under slow cooling, ex-
cessive crystallization may set in — should be steady and some-
what slow in its later stages.

Many fire-brick manufacturers allow the bricks to cool "any-
how," with the result that on passing near the kilns during the
evening when all around is quiet, a sound as of repeated pistol
shots is heard. These are signs of the production of minute
cracks — often too small to be seen — but readily proved to be
present by the reduced strength of the bricks as compared with
those properly cooled.

If single kilns are used, the desirability of introducing hot
air during the cooling should be considered ; in continuous kilns
the cooling is under much greater control.

Fire-bricks are paricularly sensitive to rain and frost, and
must be stored carefully in a dry place, or their strength (as
shown by crushing tests) may be reduced to four-fifths its original
amount.

In short, the manufacture of the highest grades of fire-bricks
is a matter requiring far more study and attention than it gener-
ally receives in this country, as modern users of these bricks are
working at temperatures undreamed of fifty years ago, and with
the tendency to more stringent requirements the difficulty of
manufacture will increase.

For the highest grades, price is of small consideration, and the
manufacturer who wishes to progress will reap the reward of his
experiments in due course. The ultra-conservative manufac-
turer, on the other hand, may have an uncomfortable time if
the proposed " Standardization of Firebricks " comes into force.

Inferior fire-bricks are used for a variety of furnaces, boiler
work, etc., where their heat-resisting power is of secondary im-
portance. The manufacture of such bricks is much easier and
cheaper than that of fire-bricks of the highest grade, and the
material may often be taken direct from the mine, crushed
until it has all passed through a screen with J-in. holes, and mixed
with water and made up into bricks.

If the clay is very fine, "grog" may be used, but it is not
necessary to use high-grade fire-clay for this purpose. Old fire-
bricks, silica rocks, or pure sand may be used with complete
satisfaction, provided that the particles are of approximately the
correct sizes. Such bricks cannot, of course, be used in the most

390 MODERN BRICKMAKING

trying conditions, but they serve a useful purpose in many in-
dustries.

In this class of fire-brick the grog is chiefly used to " open up "
the material, so that the bricks may be dried more rapidly and
with less risk of cracking in the kiln.

It is not used at all for increasing the refractoriness of the
material. The addition of such non-plastic material has a
noticeable influence on the bricks, as is shown by tests made by
F. Kase, who has published the following facts in regard to the
use of fine sand as grog : —

The finer the grains of sand added to the clay, the total per-
centage of sand added being kept constant —

1. The more water will be necessary for mixing.

2. The longer the mixture will take to dry, and the greater
the danger of cracking.

3. The contraction on drying and in the kiln will be greater.

4. The porosity of the fired ware will be less.

5. The " speed of absorption " will be less.

6. The crushing strength will be greater.

7. The material will stand sudden changes of temperature
less easily.

8. The silica in the clay will combine more readily.

The characteristics of the clay will be altered with varying
proportions of sand-grains, all of the same sizes, as follows : The
larger the proportion of sand added to the clay —

1. The less the water required in tempering.

2. The more rapid the drying.

3. The less the contraction both in drying and in the kiln.

4. The less the porosity in under-burnt ware, and the greater
the porosity by fully fired ware.

5. The greater the " speed of absorption ".

6. The less the crushing strength. -: .,

7. The greater the refractoriness.

8. The lighter the colour (with a red-burning clay).

9. The better the ware will withstand rapid changes in tem-
perature.

Silica bricks are often regarded as '-'fire-bricks," though
usually the latter term is confined to bricks made of fire-clay.
Silica-bricks are not as refractory as bricks 'made of the best fire-
clay, but they are often superior to those made of lower-grade
clays or of good clays badly treated in manufacture

The maximum temperature which silica-bricks made of the

FIRE-BRICKS AND BLOCKS 391

purest materials can stand is comparable to cone 34, but most
eommerical specimens cannot resist more than corresponds to
cone 30. Fire-clays which fuse at a temperature corresponding
to cone 36 are commercially obtainable.

Some bricks branded " Dinas " are occasionally offered for
sale which are not true Dinas bricks, being made of a material
rich in fire-clay, whereas true Dinas bricks are quite destitute of
clay. In Germany and Russia the term " Dinas " is applied to all
fire-bricks very rich in silica.

The fusibility of silica is greatly reduced by comparatively
small proportions of iron oxide, lime, magnesia, and alkalies, and
only those materials which contain upwards of 98 per cent of
silica should be used.

The chief disadvantages of silica-bricks are their brittleness,
and liability to " spall "when exposed to sudden changes of temper-
ature. These defects appear to be a characteristic of the
material used, and not to be due to defects in manufacture,
though badly fired silica-bricks spall more than others.

Silica-bricks expand when they are heated, and this increase
in size continues through several heatings, though the first heating
has usually the greatest effect. The total increase is sometimes
very large, but is not usually more than 8 per cent. Allowance
must be made for it in laying the bricks, and to reduce this, some
users insist on being supplied with twice-burned bricks.

The materials used in the manufacture of silica-bricks are
sand and silica-rock, a special variety of the latter found in the
vale of Neath and known as Dinas rock being highly valued,
but other sandstones, when sufficiently pure, are also used.

The rock is crushed between rolls (p. 86) and is afterwards
ground in an edge-runner mill (p. 95) with a solid pan, lime and
water being added. The lime is used as a flux or binding ma-
terial, and about one-fiftieth of the weight of the rock is added.

Hence, good silica-bricks contain 97 per cent of silica, 1$ to 2
per cent of lime, and 1^ to 2 per cent of impurities. On heating,
the lime combines with the silica, forming a viscous mass, which
on cooling binds the particles of the brick together. It is, there-
fore, necessary that the lime should be equally distributed
throughout the mass, and for this purpose an edge-runner mill
with solid revolving pan is the most suitable appliance.

The lime is best added in the form of " milk " made by
stirring up the lime with water, allowing the coarser particles to
settle, and running off the milky liquid through a No. 60 screen

392 MODERN BRICKMAKING

into another tank. The material in the second tank is tested to
ascertain the proportion of lirne it contains, is stirred up, and u
suitable proportion run off into the mixing-pan. Lime-milk varies
so in composition that it is essential to test it if the best results
are to be obtained.

The testing is not difficult if carried out in the following-
manner : 50 cc. of the milk of lime is measured off by means
of a pipette into a basin or tumbler, a few drops of phenolphthalein
solution added, and the mixture stirred vigorously with a glass rod
until it is strongly coloured throughout.

" Normal sulphuric acid " (obtainable from most chemists, but
not to be confused with concentrated or dilute sulphuric acid) is
then added from a burette, drop by drop, with constant stirring,
until the colour of the lime liquid is just discharged. Each 1 cc. of
the acid corresponds to one eleventh of an ounce (-091 oz.) of lime
in each gallon of milk.

Instead of lime, some makers use plaster of Paris, but this is
better avoided as the presence of sulphates is sometimes injurious
to the brick.

Silica-bricks are usually moulded by hand and are dried on
steam-heated floors, and fired in round, down-draught kilns
(p. 248) or Newcastle kilns (p. 255). No particular precautions
are necessary, as the material being non-plastic can be rapidly
fired without much risk of damage.

The finishing temperature of these bricks varies in different
districts, but does not usually exceed 1200° C. ; much better
bricks (with far less tendency to spall and crack) are produced
when the finishing temperature is raised to.cone 17 (1470° C.).

The cooling of kilns containing silica-bricks requires unusual
care, as they are very sensitive to sudden changes in tempera-
ture.

A much better quality of silica-brick than that usually made
can be obtained by using the process ordinarily employed for
sand-lime bricks. In this process the materials are mixed
together in a semi-dry state and are shaped by powerful presses,
such as that shown in fig. 166. They are then " hardened " by
exposure in a steaming chamber for about ten hours, whereby
a partial combination of the lime and silica takes place, and the
bricks can be more readily handled and stacked in the kiln.
In the ordinary lime-sand (or sand-lime) bricks more lime is
used than is desirable in silica-bricks for refractory work.

Although fire-clay bricks made under pressure are inferior to

FIRE-BRICKS AND BLOCKS 398

those made by the ordinary hand-moulding process, silica-bricks
are not so seriously affected, and providing the grading of the
particles of silica is properly arranged, the use of presses does not
appear to be detrimental.

From experiments now being carried out by the author re-
garding the sizes of grains in silica-bricks, the same grading as is
used for fire-bricks appears to be desirable though not essential.
Some separation into "medium" and "very fine" particles
appears to be very desirable, though to the best of the author's
knowledge no maker of silica bricks at present works with this
in view, though several makers of lime-sand bricks are doing-
it. The experiments not being complete, conclusive suggestions
cannot be given, but the results already obtained indicate that
about one quarter of the rock or sand and all the lime should
be ground in a ball-mill to as fine a flour as possible, and this
dust added to the more coarsely ground material previous to
mixing the whole with water and shaping into bricks.

Ganister -bricks are another variety of fire-bricks; they are-
intermediate in character between those made from fire-clay and
from silica.

True gaiiister is a dense siliceous rock containing up to 10 per
cent of clay. It is found in various parts of the country, the
best deposits being in the neighbourhood of Sheffield, Gartcosh
(West Scotland), and Dowlais (Wales). It is a water-deposited
mineral, probably derived from granitic rocks in a manner sim-
ilar to clay, and varies considerably in composition.

The best Yorkshire ganisters contain 95 per cent of silica, of
which about 5 per cent is in the form of clay.

Ganister-bricks are made in a manner similar to silica-bricks,
but lime is seldom added, as the clay in the ganister acts as a
sufficient binder. Indeed, the term " silica-brick " is often
applied to bricks made of ganister or to mixtures of silica and
clay which are intended to resemble ganister.

In some cases, ganister-bricks must be treated very carefully
in drying sheds and in the kilns, just as though they were made
of fire-clay, but most ganister-bricks can be made and fired
rapidly. They should be heated to a temperature corresponding
to cone 16 or 17 and require to be carefully cooled.

Basic bricks are usually made of magnesia or bauxite and
are weak in resistance to pressure, but remarkable for their
resistance to heat. Bauxite is infusible and magnesia practi-
cally so, as it only becomes viscous at about 1950° C.

394 MODERN BBICKMAKING

Bauxite-bricks are made by grinding the material to a moder-
.ately fine powder in edge-runner mills (p. 183), mixing it with
about one quarter of its weight of clay and a little water in a
pug-mill (p. 49), and moulding it by hand by the slop-process,
-so that the process used is similar to that employed for second-
grade fire-bricks. Bauxite -bricks may also be made in a stiff-
plastic machine and dried on a steam-heated floor or in any con-
venient warm place.

The burning presents no special difficulties, except that, as the
bricks are weak, they cannot be stacked very high, and must
therefore be burned in low kilns or on the top of other bricks in
an ordinary kiln. The bricks must be protected from " flash-
ing," and plenty of air must be used in the firing, as otherwise
the iron oxide present in the bauxite will be reduced and will
lessen the value of the bricks. Bauxite-bricks should be fired
at a temperature not less than 1250° C., as a high finishing tem-
perature is desirable, but is difficult to secure without reducing
the iron. The shrinkage of bauxite is so great that bricks of this
material cannot weh1 be used at higher temperatures than that
used in their manufacture.

Magnesia-bricks have conie much into prominence during the
last few years, though the raw material used in them has to be
imported into this country. The manufacture is accompanied
by peculiar difficulties if a really strong magnesia-brick is to be
made from pure materials.

The materials of which ^magnesia-bricks are made are
<1) caustic magnesia, obtained by burning magnesite at a moder-
ate red heat in kilns similar to those used for lime ; and (2) dead
burned, or sintered magnesia, obtained by heating caustic mag-
nesia to a still higher temperature. This must contain a small
proportion of iron oxide (about 4 per cent) as otherwise the sinter-
ing temperature would be too high.

The magnesia is ground to a fine powder in an edge-runner
• mill, a little water (about 5 per cent) being added so as to form a
pasty mass. This is allowed to stand for a few days. Some firms
grind the materials separately with crushing rolls and mix them
by hand, or in an open mixer, instead of both grinding and mix-
ing in a pan-mill. The pasty mass is formed into bricks by
powerful hydraulic presses, a pressure of 300 to 500 atmospheres
being necessary. A good press will deliver 2500 bricks per day.
The bricks are then carefully and 'slowly dried in well -ventilated,
steam-heated sheds, or in drying tunnels. Great care is needed

FIRE-BRICKS AND BLOCKS 395

in moving the pressed but uiidried bricks, as they are very sensi-
tive to slight shocks and vibrations.

Magnesia-bricks may be fired in round down-draught kilns of
;sinall size, but the temperature to be reached is so high that gas-
fired kilns are preferable. In any case the kiln should be lined
with magnesia bricks. It is essential that the kilns shall be
low (not more than 4 ft. 6 in. high internally) and comparatively
-small. The finishing temperature should not be less than that
corresponding to Seger cone 18, and it is usually better to finish
with cone 23, The addition of clay and other binding materials
is undesirable, as it makes the bricks less refractory.

Owing to the tenderness of the unfired bricks, a skilled setter
should be employed to place them in the kilns, and he should be
instructed to bed each brick carefully in magnesia sand. This
" sand " must have been freed from dust before use, the most suit-
able sized grains being JF in. diameter. Fine dust causes the
bricks to adhere to each other during firing.

The bricks, when drawn from the kiln, must be gauged accur-
.ately and sorted according to size, so that, in use, they may be laid
with the narrowest possible joints.

The chief difficulties in the manufacture of magnesia-bricks
.are due to irregular shrinkage of the raw material, the great pres-
.sure required in shaping, and the high kiln temperature. The
first of these is by far the most troublesome, but much can be
done by carefully determining the density of the raw material
.and classifying it accordingly.

Magnesia-bricks possess a remarkable power of resisting the
.action of slag arid limestone, so that their relatively high cost is
.soon saved when they are used in certain types of metallurgical fur-
naces. They are, however, very sensitive to the action of silica.
'Owing to a tendency to expand on repeated heating, they should
not be used in arches.

The " mortar " used in laying magnesia-bricks should consist
of powdered magnesia mixed with one-ninth of its weight of tar.
It must be used hot.

Neutral fire-bricks are usually made of chromite (an ore con-
taining about half its weight of chromium oxide and one-quarter
of its weight of iron oxide) and are difficult to prepare, as the
material is almost destitute of binding power. It is, therefore,
usually mixed with fire-clay or bauxite in such a proportion that
the bricks contain one-third of their weight of chromium oxide,
or chrome ores containing alumina are used.

396 MODERN BRICKMAKING

These chrome bricks are best made by crushing the material to
a powder, and compressing it by a powerful press (p. 223-236).
The bricks are fired at a temperature corresponding to cone 12 or
over.

Briquettes of compressed graphite or other form of carbon are
occasionally used for high temperature work. They are made
by grinding graphite or coke to a powder, mixing it with about 20
per cent of tar, and compressing in hydraulic or other powerful
presses.

The manufacture of similar briquettes from low-grade coal
is greatly used on the Continent to form fuel, but in Great Britain
the price of good coal is not sufficiently high to make briquetting
commercially profitable.

CHAPTER XI
GLAZED BRICKS

THERE is a general impression amongst brickmakers that any kind
-of brick can be glazed, providing that the composition of the glaze
is known. This half-truth has been the cause of much trouble and
loss of money, because few people have yet realized that unless
the brick to which the glaze is to be applied is practically perfect
the glazed brick will be a failure. Trifling defects in a facing-
brick are often overlooked, but even smaller defects in a brick
which is afterwards glazed will render attempts to sell it entirely
abortive. Thus, a few tiny specks of lime in a facing brick may
be passed unnoticed by the purchaser, but, if such a brick be
glazed, the glaze will shell off above each lime-speck and the
brick will be of no value.

Speaking generally, red-burning clays are very liable to defects
which are trifling in themselves, but which render successful
glazing impossible, and, whilst a few firms have succeeded in
building up a good trade in glazed bricks made of red-burning
clay, the majority of those who have attempted to use this
material on a large scale have failed to show any profit.

Glazed bricks, are, therefore, chiefly made of fire-clay, the
second-grade clays with a fusibility corresponding to cone 26 to
30 being used.

A brick to be suitable for glazing must be regular in shape,
exact in size, with clean arrises, and a fine face free from small
irregularities or discoloured spots. It must be sufficiently porous
to absorb the water in the glaze-slip, and must be refractory enough
to keep its shape whilst heated at a temperature which will suit
the glaze.

Such bricks are usually made by the plastic process (p. 76)
and are repressed before being fired, so as to obtain a good shape
and face and to make them accurate in size. Any of the re-
presses illustrated on pages 140 to 153 may be used; that by
Pullan & Mann (no;. 96) has a special measuring mechanism

(397)

398 MODERN BRICKMAKING

which automatically makes all bricks pressed in the same thick-
ness, as any excess of clay is absorbed by making a somewhat
shallower frog than usual.

When made of fire-clay, bricks to be glazed are often hand
moulded, as are fire-bricks (p. 385), and are repressed when parti-
ally dry. Dry -pressed bricks are slowly coming into use for glazing
purposes, but they have not proved popular so far, owing to their
liability to develop tiny surface cracks which are of little or no
importance in unglazed bricks but prevent glaze adhering pro-
perly.

Much difference of opinion has been expressed from time to
time on the desirability or otherwise of burning bricks before
glazing them. It is considered that the cost of burning the bricks
is so much wasted money, as they have to be reburned when
glazed. Experience shows, however, that if the glaze is applied to
unfired (" green ") bricks, the damage suffered in handling makes
a large proportion of the bricks useless when they come from the
kiln. These spoiled, glazed bricks cannot be sold except as
rubbish, as it is obvious that they are damaged. If, on the
contrary, the bricks are first burned without glaze, any defective
ones sorted out may be sold as building bricks of good quality,
or even as fire-bricks at a higher price. The bricks selected to be
glazed are "stronger and less liable to damage, the amount of glaze
wasted is reduced, and the number of unsaleable glazed bricks is
brought to a minimum. These various savings often combine to
make it cheaper to fire bricks twice instead of once.

At the same time, it is often possible with extraordinarily
careful handling to glaze the unfired bricks and put them into
the kilns in a remarkably perfect condition, and if workpeople
who will give sufficient care to the matter can be obtained, it is
quite possible (though seldom realized) to obtain a large propor-
tion of excellent glazed bricks with a single firing.

A mistake often made by the purchasers of glaze recipes > is to
consider that they can buy ah1 the bricks they require from a
neighbouring yard. Such people forget that bricks intended for
glazing need most careful handling, as when chipped at the edges
they are rendered useless. As few bricks which have been carted
from one yard to another are not slightly chipped, it is practically
impossible to buy bricks for glazing unless the glazer is allowed
to work on the same premises as the brickmaker.

The glazed-brick manufacturer cannot be too stringent or
careful in the selection of his bricks.

GLAZED BRICKS 399-

The glazes used for bricks must be sufficiently durable to
withstand ordinary climatic changes without " crazing " or form-
ing hair-like cracks. They must be sufficiently hard to withstand
accidental blows, and must adhere to the brick so completely
that they will not chip, or peel off. Glazes which melt at low
temperatures (below 1000° C.) do not usually possess these neces-
sary characteristics when fired on a porous body, but tend to
craze or peel. Glazes fired at a higher temperature are therefore
employed for glazed bricks, as the higher temperature enables a
mixture of material to be used which produces a mass more
nearly resembling the brick itself. Low-temperature glazes are
frequently termed "soft-fired" or "soft," and high-temperature
ones are spoken of as " hard-fired " or tl hard " ; the terms " hard "
and " soft " when applied to glazes have no necessary connexion
with the softness or hardness of the glaze.

It is seldom that a glaze can be applied directly to a brick, a&
the colour of the brick itself will usually spoil the colour of the
glaze. It is, therefore, customary to cover the face of the brick
with a " body " composed largely of white -burning clay and to-
apply the glaze to this body.

For dark- coloured glazes, particularly green ones, the glaze
may often be applied direct to the brick without any intermediate
"body," and the use of a white opaque glaze permits the
omission of the intermediate " body " when white bricks are
needed. Owing, however, to the difficulties connected in pre-
paring white opaque glazes, it is, at the present time, customary
to use a white body and a transparent glaze in the manufacture
of white-glazed bricks. Opaque glazes are becoming increasingly
popular, and have many advantages dn spite of the difficulties
involved in preparing them.

The clay being suitable for the purpose of making a clean, well-
shaped brick, the most important part of the manufacture is the
pressing. The presses should be placed conveniently near to the
second drying floor, or to the dripping sheds, according as the
bricks are burned or glazed in the green state, as a little rough-
ness in handling the unpressed bricks will do no damage, but the
pressed bricks must be handled as little as possible and carried
as short distances as possible.

Two serious errors arise in pressing, and must be prevented
at all costs. The first is due to the use of worn moulds or dies,
whereby the bricks are formed with an " arris " or rough edge on
them, and a clean edge is then impossible if the arris is not re-

400 MODERN BRICKMAKING

moved. The second is where the press -man fails to clean out
the die completely, with the result that succeeding bricks have
small pieces of clay forced into their faces and these rise during
the dipping and later cause the glaze to peel.

Pressing bricks for glazing is necessarily a slow operation (about
four bricks per minute being the maximum), and any attempt-
to hurry the press-man may result in the loss of several hundred
bricks, because these are spoiled by loose arris getting on to the
faces of the bricks, or in other ways.

Glazed bricks must be laid with the thinnest possible joints,
and, for this reason, must be pressed accurately. Any good press
may be used for this purpose, but it is sometimes a convenience
to use one in which the die can be drawn out on slides to the
front of the press in order to discharge the brick, and enable the die
to be cleaned before pressing another brick. When the die is
movable in this way, it is much easier for the workman to see
that it is properly cleaned and oiled than when a die fixed per-
manently beneath the plunger is used. It is, however, essential
that the slides on which the die moves are kept perfectly clean,
or the male part of the die will not fit accurately into the other
portion and the die will be damaged.

Bricks which are glazed previous to burning require to be set
in the kilns with the greatest care to prevent chipping, and the
temperature throughout the kiln must be as even as possible or
the bricks will be unevenly glazed later. Bricks to be glazed in
the green state are often first " clapped " with a flat wooden blade
to close up the face, but with a good press and careful man this
operation is not necessary.

The bricks to be dipped are placed on a large off-bearing
barrow with ample springs to prevent undue vibration, and are
taken to the dipper, who has a small wagon to carry his tub of
slip.

If the bricks are to be dipped before firing they are placed
directly they come from the press on to the barrow already
mentioned, a sufficient number of these barrows being provided
to allow the bricks to dry somewhat after they have been pressed.
This is better than placing the bricks on the floor as they come
from the press, as the double handling thus necessary is certain
to damage them, and the cost of a few additional barrows is not
usually prohibitive.

The barrows with the bricks on them may be run into a warm
shed so as to allow the bricks to stiffen and dry sufficiently with-

GLAZED BEICKS 401

in two or three hours, or they may be left overnight, bricks
pressed one day being dipped on the next. The bricks must not
be so dry as to show a lighter colour at the edges. Some firms
dip the bricks after they have been dried "white hard," but this
is seldom (satisfactory as the sudden soaking of the dried face
often cracks it.

When fired bricks are to be dipped they should be sorted at
the kilns, and good bricks placed on the barrows described and
taken to the dipping shop.

The dipping shed is provided with rows of temporary shelves,
and the man places each brick on one of these shelves as
soon as he has dipped it. As already mentioned, it is usually
necessary to cover the face of the bricks with " body " before
applying the glaze, this process being commonly known as " body-
dipping "or " bodying ".

The process of " body-dipping " varies somewhat in different
localities, but the following description of the method used by
the author and many others can be relied upon as being satis-
factory. It requires the services of a man and a big boy, an
extra lad being advisable when special bricks are being treated.

The first lad (termed the " brusher ") is provided with a basin
of " first dip " (see later) into which he dips a broad brush with
soft bristles about 2 in. in length, and by lightly passing the
brush over each of the bricks on the barrow, a uniform coating
of " dip " is applied to each. It may, sometimes, be necessary
to go over the edges of the bricks a second time, any surplus
material being removed by the brush at the same time. It is
necessary that this first coating should be as even as possible,
and that it should extend slightly over the edges of the face of
the brick.

After each brick has been " brushed " in this way, it is
" dipped " into a tub of " body " by the man, being immersed
sufficiently to cover the face of the brick and but little more.
This dipping requires some amount of skill in order to get satisfac-
tory results and to produce an even coating free from streaks.
The bricks should be taken up by both hands, held with the
face downwards at a slight angle, and in this position should be
dipped into the body with a single, sweeping motion. The move-
ment of the brick in the liquid should be very slight, as a long
sweep is liable to cause streaks. The correct movement is ob-
tained when the end of the brick which first enters the liquid
emerges at not more than a foot from the place where it enters.

26

402 MODEBN BBICKMAKING

though for some clays even this sweep is a couple of inches too
long. The dipped brick is then placed on a shelf to dry.

Bricks which have two faces dipped require even more skill,
but the process is the same, the only difference being that a shelf
narrower than the brick must be used, so that the glazed portion
does not come into contact with it during the drying. Some-
times the bricks are dipped twice in the body after an interval
of a couple of hours, but with a good body this is seldom neces-
sary.

The dipping shed should be kept moderately warm (65° F.),
but must not be so hot as to cause the body or glaze to peel off.
The heat may most conveniently be supplied by steam-pipes
about 1 in. diameter near the floor and below the shelves on
which the dipped bricks are placed.

Some firms prefer to burn the brick after it has been dipped
in the body, but this is not advisable as any slight variation in the
heat will prevent the bricks glazing evenly, and discoloured bricks
are more frequent than when the bricks are finished before firing.

The glaze is applied by dipping in precisely the same manner
as the body, but it is usual to let the other end of the brick first
enter the glaze.

Most unfired bricks are dipped in glaze within two hours or so
of their being " bodied," but the interval between the operations
depends upon the brick. The glaze may usually be applied as soon
as the body has become dull in appearance and no longer appears
to be wet, although it is really so. Fired bricks are ready for
glazing within a few minutes after being dipped in the body.

Any surplus glaze is removed (after drying) by means of a
fine wire brush, or a sharp knife. The bricks are then ready for
the kiln.

The materials used in the preparation of glazed bricks are
very numerous, and would require a large volume to describe
them fully. For temperatures near 1000° C, they are similar to
those used by potters, but for the higher temperatures less fusible
glazes are employed, and these are usually composed of felspar,
Cornwall stone, flint, and whiting, the corresponding bodies being
composed of china clay, ball clay, Cornwall stone, and flint, a little
of the brick clay being often used in the " first dip ".

Other materials such as barytes, zinc oxide, soda, and plaster
of Paris may be added at the discretion of the glaze maker, and
the 'materials must, in some cases, be fritted into a kind of glass
and ground before use.

GLAZED BRICKS 403

Lead compounds are seldom necessary in hand-fired glazes,
and their use should be avoided whenever possible for several
reasons.

Coloured glazes are usually made by adding 1 to 5 per cent of
one or more of the following metallic oxides to either the body
or glaze : —

For ivhites — Arsenic, oxide of tin, tin ashes, oxide of bismuth.

For browns — Iron and manganese oxides, coloured clays (sien-
nas and ochres) and umber.

For yellows — Titanium, antimony, and iron oxides, lead
chromate, and (for orange yellows) uranium oxides.

For reds — Ferric oxide, or red copper oxide, or gold under
strong reducing conditions.

For pinks — Chromium and tin oxides mixed.

For blues — Cobalt oxide or phosphate, with or without opacity -
producing materials like zinooxide.

For greens — Chrome oxides, bichromate, copper oxide, cobalt
oxide, and yellow clays.

For blacks — cobalt and manganese or iron chromate (mixed).
A perfect black glaze is unknown.

For gold — The metal gold is applied in various forms, but can
only be used at very low temperatures.

For silver — platinum and some of its compounds.

These materials may be purchased from dealers in potter's
materials in the form of " chemicals " or as prepared glazes,
bodies, or colours which only require to be mixed with water to
make them ready for use on certain clays, though, usually,
the composition of bodies and glazes must be altered to suit
the particular bricks to be used, so that no general recipe is pos-
sible for all cases. The following recipes are, however, given
here as indicating the general type of body and glaze which (after
adaptation) will be found most suitable for general work :—

FIRST DIP.

China clay . . . . 70 Ib.

Ball clay . . • . . 15 Ib.

Cornwall stone .• . . 10 Ib.

Flint . . ... 5 Ib.

Water, about . . . . . 10 gals.

Part of the clay may be replaced by the clay of which the
bricks are made, but this is not usually desirable, and in the case

404 MODERN BRICKMAKING

of some fire-clays is impracticable on account of the shale-oil they
contain.

The amount of water depends largely on the nature of the
bricks, and may be as low as 8 or as high as 15 gallons.

The materials should be weighed out accurately, placed in a
clean tub, stirred up well and passed through a No. 80 sieve, any
material remaining on the sieve being thrown away.

Some workers prefer to use a " first dip " made by adding more
water to the ordinary body ; where this can be done it saves the
trouble of making a special mixture.

WHITE BODY.

China clay . . , .60 Ib.

Ball clay - . . ••-. • . 10 Ib.

Cornwall stone ... , .20 Ib.

Flint . , ' . • . . 10 Ib.

Water, about . . ... 10 gals.

These materials should be thoroughly mixed together — a
mechanical blunger being used when the quantities to be mixed
at a time are sufficiently large — and passed through a No. 60 or
80 sieve. If a blunger is used, the ball clay, flint, and water should
be added together, the remaining materials being added when the
former have been well mixed. The blunger should be emptied
and cleaned out as soon as the paddles have been stopped, or
trouble may occur with the materials setting hard.

COLOUKLESS GLAZE (CONE 8).

Felspar . . . . ' . 20 Ib.

Cornwall stone . I . 60 Ib.

Flint . . . . . 5 Ib.

Whiting . . -. . • . .15 Ib.

Water, about . ''..'. .10 gals.

This is prepared in a similar manner to the body. It may
have 5 per cent of ball clay or 3 per cent of barytes in place of
5 per cent of the stone. It is better than a purely felspathic
glaze, as, being more adhesive, it is less liable to be chipped
or to fall off.

Majolica glazes are used for all those clays and colours which
cannot be produced at higher temperatures. The bricks must>
with majolica glazes, be fired in muffle kilns, and must have been
fired before being glazed.

GLAZED BEICKS 405

The glaze (usually opaque) is applied by dipping in the
manner already described, it being used direct or preferably on a
body.

Owing to the low temperature in the glaze kiln the glazes
must usually have been fritted before use, or some portion of
them must have been submitted to this process.

A typical fritt for glazed bricks is composed of red lead, Corn-
wall stone, borax and soda, with china or ball clay, the propor-
tions varying with the temperature to be reached. Owing to the
trouble of preparation, brickrnakers usually buy their fritts and
colours in such a state that they only need mixing to be ready
for use. The larger works employ men who have made a special
study of majolica glazes — a subject requiring almost a life's work
before perfection can be reached.

The raw materials, as well as the body or glaze slips, must be
stored in a clean dry place, which is cool in summer and not cold
enough for the slips to freeze in winter. The roof or ceiling must
be of such a nature that nothing will drop from it into the slips,
and these slips should be kept covered.

Large wooden bins are most suitable for the material. The
slips are best kept in glazed cisterns or tanks, set about 3 ft. above
the ground-level and fitted with an outlet in the bottom. They
should not be too deep for a man to be able to stir their contents
easily with the aid of a bat about 2 ft. 6 in. long. Before with-
drawing any slip, the liquid must be thoroughly stirred up so
that no deposit remains on the bottom.

The slip should be taken to the dipping sheds in glazed
earthenware bowls. These can be obtained cheaply, and are far
less liable to discolour the bricks than are cans made of zinc or
galvanized iron. Iron and brass cans must on no account be
used, and enamelled iron is also unsatisfactory.

During the dipping, the glaze and body must be kept in con-
stant motion, and should be frequently passed through a No. 80
sieve to remove foreign particles and>to aid in the mixing.

The setting and firing of the glazed goods are matters requiring
great care. The bricks must be placed in such a manner that
they do not run any risk of chipping, nor of being discoloured or
otherwise damaged by the flame. One satisfactory method of
setting glazed bricks is shown on p. 336, though some firms
have found continuous (chamber) kilns excellent and economical.
Muffle kilns are not necessary if the bricks are placed properly.

Coloured glazed bricks must be kept apart from each other

406

MODERN BBICKMAKINU

and from white bricks, as a certain amount of " volatilization "
of colour always occurs.

The glazed faces of bricks must also face other glazed faces,
or otherwise they will be dulled.

The manner of heating will depend on whether the bricks have
been fired before being glazed. If not, they must be heated as
cautiously and steadily as possible, all the precautions mentioned
in section on burning (p. 337 to 367) being observed. When
the bricks have reached a bright red heat and are fully oxidized,
the heating should be continued somewhat more quickly than
when unglazed bricks are fired, as prolonged heating tends to dull
the glaze.

The " finishing point " of the kiln is ascertained by drawing
out glazed test-pieces (fig. 251) and by examining these ; a fairly

accurate idea of the temperature is
also obtainable by the use of Seger
cones. The full temperature re-
quired having been reached, the
fires are poked up, sufficient air
being admitted to let them die down
rapidly (to prevent overheating)
and the openings in the kiln are
then all closed and made air-tight
with clay paste.

Kilns containing glazed bricks
should be cooled fairly rapidly at
first — until the glaze is too cool to
de vitrify or crystallize — but as soon
as they have reached a temperature
usually of 900° C., they should be

o

FIG. 251.— Glazed trial-piece.

at which this cannot occur
cooled much more slowly.

When the glaze is applied to bricks which have been fired
previously, the heating of the kiln may be fairly rapid, but the
cooling must be cautiously carried out.

Salt-glazed bricks are in great demand where a cheap but
reliable glazed surface is required. Owing to the special manner
in which the glaze is formed, it is less liable to defects than
ordinary glazed bricks. Water and frost do not affect them in
any way. There is a greater demand for light glazed bricks than
dark ones. Unfortunately the number of colours available is
very limited and white salt-glazed bricks are exceedingly difficult
to produce.

GLAZED BRICKS 407

Ordinary salt-glazing produces a dark brown glaze (similar to
that on drain pipes), but many makers " improve " upon this by
first dipping the bricks in a body.

Salt-glazing differs from other methods of glazing in that no
glaze is applied direct to the bricks. The bricks are placed in a
down-draught kiln and, when sufficiently heated, salt is thrown
into the fire-holes and automatically glazes the exposed portions
of the bricks.

In simple glazing with salt, the glaze is really formed from
part of the salt combining with part of the clay, so that the glaze
is necessarily far more adhesive than when all the constituents
of the glaze are mixed together and applied in the form of a slip
or spray. For many years the composition of the salt-glaze pro-
duced on fire-clay was unknown, but Maeckler has investigated
the subject very thoroughly and his conclusion that it has a com-
position corresponding to 20 per cent alumina, 54 per cent silica,
and 26 per cent soda and other oxides is now accepted, though
the reactions which result in its formation have not been fully
explained.

All clays are not suitable for glazing with salt, as it is found
that a certain temperature (corresponding to cone 2 but more
usually cone 7) is essential for the full development of the glaze,
and that the proportion of alumina and silica must be within
comparatively narrow limits. L. E. Barringer has shown that
the most suitable clays are those containing about 63 per cent
silica and 23 per cent alumina, but provided there is not less than
3 Ib. or more than 8 Ib. of silica to each Ib. of alumina in the clay
a good glaze may be obtained. Some clays outside these limits
can be salt-glazed, but will not give really good results. The
state in which the silica is present does not appear to be import-
ant, and some clays which, alone, cannot be salt-glazed will give
excellent results when mixed with very fine sand, but coarse or
medium sand cannot be used for this purpose.

The best results are obtained with clays which begin to vitrify
at the temperature >at which the salt is added, but which do not
lose their shape until a far higher temperature is reached.

For this reason, some firms have obtained very excellent
results by the use of ball clays to which sufficient sand or grog (11011-
plastic material, see p. 18) has been added to reduce the other-
wise excessive shrinkage, or by adding some ball-clay to a fire-clay,
shale, or other lean clay. Occasionally, a mixture of several
clays and grog is employed, the object being to form a " skele-

408 MODEKN BRICKMAKING

ton " of lean clay or grog, and to use the fine clay to bind the
other particles together and to help the vitrification.

Bricks for salt-glazing can be made by any of the processes
already described, but they should be pressed (p. 139) or repressed
so as to give them a sharp, clean-cut appearance. The methods
used for the manufacture of glazed bricks (p. 397) should there-
fore be used, but the bricks, instead of being " dipped " when
partially dried, are dried completely and then taken to the kiln.

Bricks made from a ball-clay mixture must not be permitted
to dry too quickly ; if they are forced in drying they will be cer-
tain to crack. Two or four days is the average time taken to dry
such bricks after being pressed, before they are in a condition
suitable for placing in the kiln. If drying space is limited, the
bricks can be stacked in rows to dry two days after being pressed,
and the space thus vacated may be refilled with fresh bricks.

The bricks must be thoroughly dry throughout before being
set in the kiln, otherwise the steam contained in them will
cause them to crack.

A " salt dip " or coating for using upon the brick is often
necessary to give the surface of the bricks a uniform, smooth sur-
face, which will assist the salt to produce a bright, good-coloured
glaze. This salt-dip, or body, is composed chiefly of washed
clay (passed through a No. 60 sieve), and it is best to use the
same clay for the dip as is used for making the bricks, providing
that the clay contains a very small percentage of impurities.

If the clay contains much iron sulphide it is very unsuitable
for use as a body-dip, because the iron will cause the surface of
the bricks to contain rough, black specks resembling small
cinders, and the bricks will not be suitable for good work.

When the clay used for the dip does not produce a good,
deep-coloured glaze, it should have mixed into it a small quantity
of English or French ochre, or if one sort does not furnish the
desired tint, a small proportion of each ochre may do so. .When
using the ochres great care must be taken that they are thoroughly
mixed with the clay, or dip, so that the colour will be uniform
on all the bricks. If too much colouring matter is employed
it will destroy the soundness of the dip, so that care should be
taken to use only as small a quantity of colouring matter as will
give the desired shade. In all cases the dip must have a shrink-
age equal to that of the brick.

In cases where the bricks are fired to a temperature of 1210°
to 1230° C. (indicated by Seger cones Nos. 4 and 5 respectively)

; GLAZED BRICKS 409

it will be advisable to use a dip composed of good fire-clay and
ball clay ; a few trials of different proportions will soon determine
the quantity of each required for a dip which will adhere well to
the bricks. All the materials used for dips should be thoroughly
soaked in an equal weight of water (1 gal. to every 10 Ib. of
clay) before being sifted, and if they are soaking for two or three
months they will work all the better. No dip should be used a
few hours only after it is wetted, as small air bubbles will come
out on the surface and cause small holes or " pinholes ". After
the dip has been sufficiently soaked it is sifted twice through a
No. 30 or 40 mesh sieve.

The dip should be used as thin as is consistent with a perfectly
sound surface ; the thicker the dip the greater its chance of peel-
ing off or becoming otherwise unsound upon the brick's face. As
a rule, five gallons of dip are sufficient to coat about 1000 bricks
on one side.

The kilns used in salt-glazing may be single or continuous
.(chamber) kilns, though there are disadvantages in the latter un-
less they are used exclusively for salt glazing. In most work it
is, therefore, better to use separate down-draught kilns (p. 248)
with a perforated or false bottom. There must be ample grate
.area in the fire-boxes, and the generally accepted rule amongst the
builders of salt-glazed kilns — viz., 6 sq. ft. kiln area for each fire-
box— is generally satisfactory.

As the damper in the main flue of the kiln is of great impor-
tance in salt-glazing, care should be taken that it fits well and is
kept in good order. The brickwork must be tight, as a good,
sharp draught is needed during some parts of the firing.

The goods are placed so that there is ample room for the salt
to reach the faces to be glazed, but apart from this they are set
just as if they were ordinary glazed bricks.

To some extent the method of setting depends upon the
number of headers and stretchers required to be set.

If 25 per cent of headers are required, the bricks may be set
in the following manner : lay a straight edge on the floor at the
back of the kiln and set the shortest row of bricks from screen
wall to wall, beginning the row with headers. Three rows of
headers are next set on edge end towards, and upon the top row
of headers the stretchers are set end downwards, face upwards,
in a double row back to back, so that the faces of stretchers and
headers stand perfectly upright and level. The stretchers should
*be up four rows high, breaking joint in each row, so that the walls

410 MODERN BEICKMAKING

will be firm and the bricks prevented from tipping during the
burning.

Upon this row of stretchers, headers are again laid end out-
wards, to form a tie to the double wall of stretchers. Every two
rows should be tied together with burnt bricks to keep the walls
erect. Upon the headers thus set, bull-nose, double stretchers, and
other bricks having two or more slyied faces are set up in 9 in.
columns leaving a space of 2 in. between each. These are stacked
up about ten to fifteen bricks high according to the strength
of the clay used, so that the bottom bricks will be strong enough
to carry the weight of the others set upon them. When the kiln
has been filled, the wicket is built up smeared over with clay
paste so that when this is dry the kiln is ready for lighting.

'The firing must be steady. When a good red heat has been
reached it should be fairly rapid, a- good " body of heat " being-
reached before the salt is added. This is necessary, because
the decomposition of the salt is accompanied by a sudden drop
in the temperature of the kiln (sometimes as much as 300° C.),
and if the bricks are not hot enough the glaze will be dull and
scummed.

It is possible to glaze with salt when the temperature is as low
as cone 1, but the bricks produced are seldom of first-class quality,
and it is far better not to add the salt before cone 7 has been bent
over in the cooler parts of the kiln.

As cones are useless when salt is present, many burners-
dispense with them and heat the kiln until vitrification sets in
before salting and the goods have a slight gloss or " flash " on the
surface. Some fire-clays give no indication of this kind and cones
are then necessary for reliable work.

The working of the kiln when salting varies with different
men, but the usual and best plan is to get the fires clear and free
from smoke — the bricks being at the right temperature as already
indicated — and then to drop the damper to within a few inches
of its lowest point. A shovelful of salt is next put deep into each
fire-hole in turn and the hole closed with slabs or doors.

, After a quarter of an hour or rather longer, the damper is raised
and the fires fed with coal, the object being to raise the tempera-
ture of the kiln to what it was before salting. When this tem-
perature has been reached the damper is again lowered and
another shovelful of salt is placed in each fire-hole, as before. A
final firing (with the damper raised) will usually complete the
glazing, but this should be confirmed by drawing trials (fig. 251)

GLAZED BRICKS 411

which will show whether the glaze is sufficiently thick and
glossy.

It is wise to draw trials before adding the second batch of salt,
as occasionally the temperature falls more than is expected and
a longer period of firing is then necessary. In any case it is
useless adding more salt until the bricks are hot enough to de-
compose it.

Some men habitually add salt three times, but this is seldom
necessary, and the use of trials drawn after each firing will show
whether a third dose of salt is desirable. Most fire-clays require
10 oz. to 20 oz. of salt per cubic foot capacity of the kiln. The
salt may be damped if necessary, but the moisture in the coal is
usually sufficient to provide all that is needed.

The colour of the glazed bricks will depend on the clay of
which they are made, or the " dip " if any is used, and also on
the extent to which the kiln damper is kept open. A partly
closed damper will introduce reducing conditions during the firing
and will cause the glaze to darken. Light-coloured glazes need
plenty of air and a widely opened damper. The ordinary colours
are yellow to dark red-brown, or occasionally a brownish black,
but if a " body " is applied, the colour produced may be blue,
brown, yellow, or green according to the oxides present in the
body-slip. In such cases, the damper must be kept fully open
and the fires very clear.

The kiln must be cooled fairly quickly until the goods are at
a dark-red heat, but the elaborate precautions taken by some
burners are seldom needed. The fires should be kept clear by
frequent and light stoking, so that when the kiln is finished they
may be allowed to die down without any danger of developing
" sulphur ". As soon as the fires are sufficiently cooled, the fire-
holes may be stopped up with slabs and made tight with clay-
paste.

" Scummed bricks " are due to insufficient firing before or after
adding the salt, and can usually be cured by re-firing at a higher
temperature.

Rough and blistered bricks are due to over-heating the clay,
especially with insufficient air. This causes it to swell and blister.
The defect is caused before salt is put into the kiln, but is more
readily observed when the bricks are glazed. The remedy is to
fire more slowly at a dark-red heat, with an ample supply of air,
until all the carbon has disappeared, or to use a more refractory
clay.

CHAPTER XII

PERFORATED, RADIAL AND HOLLOW BRICKS AND BLOCKS.
PARTITION BLOCKS AND FIRE-PROOF FLOORING.

THE manufacture of hollow or perforated bricks and blocks has
increased greatly during the last few years, particularly in the
manufacture of partition -walls and flooring of a fire-proof nature
for modern building. The manufacture of hollow blocks is really
very old, but it was only during the last century that extended
use was made of this valuable form of architectural work.

" Perforated bricks " have a series of small holes transversely
through them, these holes being not more than f in. diameter.

" Hollow blocks " have much larger holes running through
them. The hollows or "tubes" may run either lengthwise or
transversely through the blocks, the former being the more usual

FIG. 252. — Hollow blocks.

(figs. 252 and 253), and the exterior of the blocks can be of any shape
which can be produced from a mouthpiece connected to a pug-
mill or similar press. Thus, for fire-proof flooring the blocks are
often somewhat bent, so that when put together they have a
distinct "camber." Such blocks are in great demand in con-
nexion with various systems of " reinforcing ".

The shape of the hollows is a matter of some importance to
the block manufacture, as it is far easier to produce circular or
elliptical ones than those of square or angular section, as the latter
require more power and the cores must be frequently renewed
as they wear rapidly. The shape of the ends of these cores
determines that of the hollows, but the cores must usually taper

(412)

PERFORATED, RADIAL AND HOLLOW BRICKS AND BLOCKS 413

towards the back of the mouthpiece (fig. 254) in order that the

FIG. 253. — Hollow fire-proof flooring.

clay may not be strained and cracked as it issues from the

machine.

Hollow blocks with closed ends may be made by using hollow

cores which can be closed inter-
mittently by mechanically oper-
ated shutters. The resulting
clay-band then consists of a
series of alternating solid and
hollow portions, the lengths of
each depending on the time the
shutters remain closed. The
clay -band is then cut, by wires,
into separate blocks.

FIG. 254. — Back of mouthpiece.

Radial bricks are used for chimney construction and are
frequently perforated. They are best
made thicker than ordinary bricks,
the cutting wires being placed 3-J in.
apart, as this saves labour in brick-
laying and, by reducing the number
of joints, it increases the strength of
the chimney. Perforated bricks are

preferable to solid ones in chimney Fm. 254a.-« Cella " die
building, as the workman can place for hollow blocks,

his fingers in the perforations if these are large, and can thus
use wider bricks than could otherwise be employed. Hollow
and perforated bricks are also poorer conductors of heat than
are solid ones, and this is a further advantage.

For each change in the diameter of the chimney a fresh mouth-
piece will be required, as the fitting of temporary liners has
seldom proved satisfactory.

Both perforated and hollow bricks are valued on account of
their lightness, but to a small extent they are made in order to-

414 MODEEN BBICKMAKING

save material. Their lightness compared with solid bricks effects
a great saving in freightage charges, and enables floors, ceilings,
and partition walls to be erected in places where solid blocks would
be too heavy. Some Continental brickmakers prefer to use
perforated bricks for glazing and facing work, because, unlike
solid bricks, they are not lifted by hand from the press, but are
received on a "fork," the prongs of which engage in the per-
foration, so that there is little or no danger of the faces of the
bricks being damaged.

From a technical point of view, hollow bricks have the advan-
tage of drying more rapidly and thoroughly and of requiring less
fuel for burning. On the other hand, trifling defects in a solid
brick become more easily visible in a hollow one, and errors in
the adjustment of a machine which would pass unnoticed when
solid bricks are being made, require prompt attention when
hollow bricks are produced.

Perforated bricks are usually made by fixing bars the size of
the perforations in the mouthpiece of the pug-mill, so as to form
a series of cores, or in the lower part of the die when the semi-
dry or dry-dust process is used.

Hollow blocks are frequently made from a mixture of clay
and sawdust ; the latter burns out in the kiln and produces a
much lighter material than would otherwise be the case. This
material has also an advantage in that it enables nails and screws
to be driven into it, a property much appreciated by housewives.
The proportion of sawdust which may be used depends to some
extent on the plasticity of the clay employed, but it seldom ex-
ceeds one-quarter of the weight of clay.

Coal and peat are sometimes used instead of sawdust, but
the former is not to be recommended as it is liable to cause
over-heating of the material in the kilns.

Hollow bricks are made almost exclusively by the plastic or
stiff-plastic process in a pug-mill with mouthpiece (p. 108) when
large numbers are needed. When only a few are required, and
for ornamental patterns, plaster moulds are used.

The clay is mixed into a paste in a pug-mill and forced
through a mouthpiece (p. 113) provided with one or more cores.
The clay-band produced is then cut into suitable lengths on a
cutting table, and these are set on a warm floor or on shelves to dry.

In making hollow blocks, the clay must be very thoroughly
mixed, as if of uneven composition the paste will crack or tear
on issuing from the mouthpiece or on drying. For this reason

PEEFOEATED, EADIAL AND HOLLOW BEICKS AND BLOCKS 415

they are frequently made in a machine separated from the pug-
mill or mixer, the clay being forced through the mouthpiece by
means of a plunger.

For some of the larger blocks plunger machines or " stupids "
are employed. These are of various types, but, unlike the ordin-
ary pug-mill with a mouthpiece, they do not work continu-
ously, though by using two plungers an almost continuous
output can be obtained. A typical machine of this kind is shown
in fig. 255. It consists of a case or charging box containing the
clay paste, and a plunger which is forced forward by steam pres-
sure which acts directly on the end of it, the steam entering
through a 2 in. pipe into the cylinder at one end of the machine,
the amount of steam admitted being controlled by a hand lever
at the mouthpiece end. As the plunger travels forward under
the pressure of the steam it pushes the clay before it and forces
it through the mouthpiece. The pressure exerted may be much
greater than that obtained with an auger machine or pug-mill,
and as there is no possibility of the clay working backwards (as
when knives are used) such a machine is well adapted for use
Avhere very large hollow blocks are made. Many brickmakers
find such a machine useful for all kinds of " odd work " such as
copings, invert blocks, and various special or ornamental bricks,
drain-pipes, etc.

The machine shown in fig. 256 is driven by hand instead of
steam power, and is, therefore, convenient in many works. The
lid of the clay box is fitted with weights and chains so that it
can be readily lifted, and the fastenings are simple and strong.
A cutting-table is placed in front of the mouthpiece of the
machine, when in use, but is not shown in the illustration.

Suggestions regarding the construction and use of mouth-
pieces will be found in the section on the wire-cut process
(pp. 108, 129), but the insertion of one or more metal cores (to
form the hollow) makes additional precautions necessary.

In the first place, the cores must be exactly central or the
walls will be cracked or torn as the clay issues from the machine,
and they must be tapered away from the front of the mouth-
piece so that the clay may become steadily more compressed in its
passage through the mouthpiece. In order that these conditions
may be fulfilled the cores must be attached to a metal " bow "
or frame at the back of the mouthpiece, this frame being slotted
so that the cores may be moved vertically and horizontally as
shown in fig. 254. which shows two cores fixed ready for use. The

416

MODERN BRICKMAKING

PEEFOEATED, EADIAL AND HOLLOW BEICKS AND BLOCKS 417

framework and cores must be very strong as the pressure of the
clay on them is very great, and unless they are sufficiently well
built, they will be bent by the clay paste in its passage.

Hollow and perforated bricks and blocks are burned in the
usual manner, though they must usually be heated very carefully
during the earlier stages up to a bright red heat, particularly
when sawdust and other combustible material is mixed with the
clay. Unless this material is allowed to burn out slowly with a
sufficient amount of air to oxidize it, yet not enough to cause over-
heating, the bricks will be discoloured and irregularly burnt.

FIG. 256. — Hand-driven running-out machine.

It is a curious fact that many hollow blocks have a crushing
strength quite equal to that of solid blocks of the same size. It
has been suggested that this is due to the much more thorough
mixing of the material which is necessary when hollow blocks are
made, and to the custom of burning hollow blocks more thoroughly
than ordinary bricks.

When laid in cement mortar and "reinforced," hollow blocks
form one of the strongest forms of building material at present
known.

Glazed hollow blocks or tubes of a shape similar to that
shown in fig. 252 are much used as conduits for electrical pur-
poses. They partake more of the nature of pottery than of
bricks, and so are beyond the scope of the present work.

27

CHAPTER XIII
MOULDED AND ORNAMENTAL BRICKS

ORNAMENTAL slabs and bricks are generally made by hand, unless
the nature of the ornamentation permits them to be made by the
wire-cut process. For very simple designs, metal-lined moulds
may be used, but for more ornate work plaster moulds — sometimes
in several pieces — must be used.

A brick of the required design is first carved in plastic clay a
little larger than the size of the finished brick, so as to allow for
contraction in drying and firing. This " model " must be very
carefully and accurately made, as any defects in it will be repro-
duced in future bricks. As soon as the modeller has completed
his work the mould-maker places it on a board and brushes it
over with a solution of soft soap in water to which a little tallow
has been added, the boards being very similarly treated. He-
next places several boards or a piece of linoleum around the
model, carefully stopping up any holes with clay paste, so that a
case is formed into which the liquid plaster can be poured with-
out any leaking away. Plenty of clay paste should be used, as a
leak is very troublesome, and, for added strength, the boards or
frame used should be fastened together with nails or cord.

The inside of the case is brushed over with soap solution, and
the mould-maker next mixes a quantity of " superfine " plaster
of Paris with water in a bucket, so as to obtain a thick slip, and
stirs this well with his hands, so as to mix it thoroughly. The
amount of plaster needed must be judged by experience, the
beginner will not go far wrong if he half fills a bucket with water
and sprinkles the plaster rapidly into it until it no longer sinks
into the water, but the proper proportions can only be ascertained
by trial.

The plaster-slurry must be worked with the hands until it is
free from lumps and is of a smooth, creamy consistency ; it is
then poured slowly and steadily into the case by an assistant,
whilst the mould-maker uses one or both hands to stir it slightly.

(418)

MOULDED AND ORNAMENTAL BRICKS 419

and prevent air-bubbles forming between the model and the
plaster. Sufficient plaster must be poured in to cover the model
to the depth of about 2 in. or 3 in. The whole is now left until
the plaster has set, after which the casing is removed, the
plaster* mould turned upside-down and the clay cut out with a
knife or torn out with the fingers, great care being taken not to
damage the mould. Sometimes the model will drop out whilst
the mould is being turned, but if it does not do so it must be
cut out. The mould is then set aside to dry and harden before
it is used. When complex designs are required, it may be
necessary to make the mould in several pieces.

To reproduce bricks in such a mould, it is laid on a bench and
a piece of clay paste thrown into it with considerable force and
pressed well into the crevices of the mould. More paste is thrown
in and pressed in until the mould is full. Any excess of clay
is removed by drawing a strike or a stretched wire across the
face of the mould, the clay being then smoothed (if necessary)
with a large, flexible -bladed knife. The mould with its contents
is then set aside until the clay is sufficiently dry for it to be
turned out of the mould. If the mould is properly made and
filled, the bricks should not require any further finishing, but it
will often be found necessary to "touch them up" slightly with
a modelling tool before setting them, aside to dry completely.
When very large blocks are made in this way, the drying re-
quires much time and care, but ordinary sized bricks offer but
little difficulty in this connexion. The burning may be carried
out in any ordinary kiln, but as the colour of ornamental bricks
is usually important, they should be so placed in the kiln as not
to be discoloured by dust or flame.

Glazed blocks and slabs for fire-places are usually made in
this manner from fire-clay or shale. The glaze used should, pre-
ferably, be hard-fired to prevent crazing, but as few firms have
been able to create a sufficient variety of colours with hard firing,
': majolica " or low temperature glazes are commonly employed.
A description of this class of glazed ware to be complete would,
alone, require a large volume.

CHAPTER XIV.

DRYING RAW CLAY.

IT not infrequently happens during the winter months that the
clay obtained is so wet that it cannot be properly treated by plant
which is primarily designed for dry materials. In such a case,
some means of drying the clay is necessary, and it will often be
found that materials which are difficult to grind when in a plastic
or sticky state will be greatly improved by being dried before
treatment in the mills.

When ample time can be spared for the drying, or when it is

the practice of the firm to
gather dry clay and store it
under cover, the arrange-
ment shown in fig. 257 will
be found satisfactory. This
kind of shed, constructed
of Venetian shutters and
chequered brickwork with
a light roof, is readily and
cheaply built, and will keep
clay dry, or dry it slowly,
at a trifling cost. The
author has seen several

FIG. 257. — Shed for drying clay.

sheds of this kind in active
use, and in Germany,
where the weather is warmer than it is in this country, it is all
that is required in many yards. No heating arrangement is used,
but every effort is made to allow access of air and to keep out the
rain; consequently, on the most exposed side weather-boards
are used instead of the open brickwork.

When a heated dryer is needed for the clay, two distinct forms
are available, viz. the hot floor and the cylindrical or tubular
dryer ; the latter being usually the most economical.

A hot-floor dryer for raw material consists of a shed, the floor

(420)

DEYING RAW CLAY § 421

of which is built over flues heated by fires or steam. Steam -
heated floors have the advantage that they cannot spoil the
material on them ; but they are slow in action and fire-heated
dryers are therefore more generally used.

The material is taken to the hot floor in wagons which run on
a track down each side of the shed. The material to be dried
is then tipped on to the floor and spread about with rakes
or shovels. The portion on which the material is dried is pre-
ferably covered with iron plates which fit over the flues. Two
or more flues may be used, each being abou;t a yard in width and
depth, with sufficient solid ground between tjo allow a wagon of clay
to travel over it. The flues are heated by fires placed at one end
of the shed, a transverse connected flue ai the other end being
connected to a chimney to produce the neqessary draught. The
fires should be arranged so that an ample supply of cold air can
be admitted if required, in order that the temperature of the
clay may not be excessive. To avoid unjdue risk of excessive
heat, the first 3 yds. of each flue may be covered with brick-
work instead of the iron plates used for the remaining portion of
the flue. It is essential that the flues should be sufficiently long
to utilize the heat from the fuel efficiently : 70 ft. is a suitable
length for most clays.

Whilst drying, the clay should be turned over and moved about
occasionally, and the roof of the shed must be well ventilated so
as to carry off the steam. Clay which is almost dry should be
kept away from the fire end of the flues.

Though simple in construction, floor dryers are far from
economical, and tunnel dryers are, therefore, preferable. The
latter are, indeed, the most suitable of all if the clay is to be
dried in blocks or " balls ". A typical dryer of this type, in
addition to those described in a previous chapter (p. 161) is
shown in fig. 258, and is equally suitable for drying bricks. The
clay blocks or balls are placed on cars fitted with shelves, and
travel slowly through the tunnel. The air enters the heater (H)
and is forced into the tunnel by the fan (F) so that it travels in
the opposite direction to the clay, as shown by the arrows.

Such a dryer is especially convenient where the clay must be
dried with " pure air," on account of its colour being spoiled by
fire-gases.

In tubular dryers, the clay passes down through a hollow
metal cylinder (fig. 259) placed at an angle, hot gases passing
along it at the same time. If the clay is very sensitive it may

MODEEN BRICKMAKING

be necessary to keep it out of contact with these gases by using
pure air heated in a recuperator, or by surrounding the tube by
another and passing the hot gases between them. To facilitate
the drying the tube is usually made to revolve slowly, baffle plates

being fixed in its inside to prevent the clay passing out too
rapidly. Instead of hot air or fire gases, steam may be used,
but only for small outputs, though a level cylinder fitted with
steam pipes and a spiral worm conveyer will often -be found to
be far more satisfactory than a fire-heated dryer of this type.

DRYING EAW CLAY

423

Moeller and Pfeiffer's clay-drying drum is shown in section in
fig. 260, the drum (h) being rotated by gearing not shown, whilst
the clay enters through the hopper (g), and air heated by the
products of combustion from the fuel on the bars (/) is delivered
from a fan (e) which draws it from the farther end of the drum,
and so uses part of it repeatedly, the remainder escaping through
the chimney (p).

A good rotary dryer is somewhat costly to instal, but, if suf-
ficiently long to utilize the heat properly, it will soon repay for
itself in cases where it is required. Large lumps should, if
possible, be broken up, as they dry very slowly and irregularly, and
the greatest output is secured by feeding regularly and only small
pieces.

Where exceedingly large quantities of clay have to be dried a

FIG. 260.— Moller & Pfeiffer's clay-dryer.

special form of shaft kiln may be used; such "tower-dryers"
are, however, seldom used by British brickmakers.

If the material contains less than 5 per cent of moisture
on leaving the dryer it will be satisfactory ; there is no need to
dry it completely and there is a considerable risk involved in
doing so. Care is necessary to prevent any part of the clay
from becoming over-heated and so losing its plasticity.

It is generally understood that 100° C. is the maximum
temperatvire permissible in drying clay, but Bleininger has found
that highly plastic clays kept at 200° O. for some time become less
sticky and are far easier to work. This super-drying is of great
importance with surface clays and with materials similar to
" London clay ".

CHAPTER XV.
SOURCES OF DIFFICULTY AND LOSS.

THE difficulties and losses met with in the manufacture of bricks
are numerous and varied, yet they may be traced to four main
sources : (a) improper materials or site ; (b) unsuitable methods
of manufacture ; (c) lack of capital, and (d) defective accounting.
Any one of these may be sufficient to wreck an otherwise satis-
factory business, and it is, therefore, useless to suggest that one
is more important than the rest.

Improper materials or site. Under this term may be included all
those errors of judgment which have resulted in the establish-
ment of brickworks too far removed from good markets, or on
land which can, at best, produce only an inferior quality of bricks.

Brick manufacturers are particularly prone to erect works
without any regard to the position of the railway or of the market
to be supplied, and the author is acquainted with a number of
instances where a small knowledge of geology would have saved
the firms concerned many hundreds of pounds per annum in
cartage alone. Not having this knowledge, works have been
erected at one part of a clay deposit at some distance from the
road or railway, whereas the same deposit extends close to the
railway line. Instances of works constructed on unsuitable sites
are far more common than is usually supposed, and the average
brickmaker would be wise to obtain independent and expert
advice before completing the purchase of land or works, particu-
larly when new works are to be erected.

There are many clay beds which are notoriously difficult to
work, and from which the inexperienced brickmaker should be
warned, did he but accept impartial advice before it is too late.

Two of the best known deposits which are responsible for
many " failures " are the " London clay " and the various " drifts "
or " boulder clays " which occur in Lancashire and several other
counties.

The first of these is treacherous because it is strong and sticky

(424)

SOUKCES OF DIFFICULTY AND LOSS 425

without being truly plastic, and is of such an inferior nature that
it can never be used alone for good work. The second material
is so variable in its composition as to require constant care on
the part of some capable and responsible person, or material of
a nature quite unsuitable for brickmaking, and yet not easily
distinguished from clay, may be sent to the mills and cause a
serious amount of damage. Boulder-clay is used successfully
by many careful manufacturers for the production of common
bricks, but they are ever on the alert to prevent unsuitable
material being dug and used. Were a bed of boulder-clay to be
worked by steam navvies (as the Peterborough clay), the irregular
composition of the material would bring about the financial ruin
•of the manufacturer unless the deposit was unusually " clean ".

Other clays, in other districts, must also be carefully studied if
satisfactory results are to be obtained, and those sites carefully
avoided where the clay is of an unsuitable character.

The value of a clay bed can only be ascertained as the result of
extensive tests, involving the use of at least several hundred-
weights of material. Opinions based on the examination of a few
-ounces of clay may be accurate, or otherwise, according as the
sample truly represents the whole bed, or is only equivalent to the
worse or better portions of it.

Imperfect tests toften lead to serious trouble for all concerned,
and the opinion of a foreman or of a public analyst should never
be accepted as sufficient, unless confirmed by tests on a relatively
large scale. Even the opinion expressed by a specialist in clay-
working may be erroneous if he is not placed in full possession of
the facts, though he is, by virtue of his special knowledge, less
liable to serious error than are others who give an opinion based
on a more limited experience.

Unsuitable methods of working are an exceedingly common
.•source of difficulty and loss. Many brick manufacturers are led
-fco put down plant without due consideration of the character-
istics of their clay, and later are tempted to replace it by other
plant equally unsuitable. In one case known to the author, a
firm purchased no less than four different sets of machinery,
•each by different makers, and were contemplating experiments
with a fifth when they were persuaded to take independent
advice and to utilize various pieces of machinery in their pos-
session. The difficulty in this instance lay in the peculiar
nature of the material ; but instances of grinding-mills or brick -
making-machines being replaced by those of other makers, for

426 MODERN BRICKMAKING

reasons which are quite insufficient and only show the ignorance
of those concerned, are by no means uncommon.

Erroneous methods of working can only be put right by those
having sufficient knowledge of the clay used, and are so situated
as to be able to give impartial advice. A machinery maker i&
obviously not in this position, and it is only in the employment
of an expert who, it is known, never accepts commissions or other
" remuneration " from the sellers of particular machines or kilns,
that a reliable means of overcoming the difficulty -can be obtained.

Unfortunately, the average brickmaker is fond of asking advice
of all and sundry without placing the information so received at
its proper value. He is, therefore, often in the unpleasant
position of having paid an excessive price for a simple piece of
plant (such as a riddle) or of having purchased a machine which
he learns, later, is quite unsuited to his needs. Either position
is regrettable, but can only be avoided by using the means sug-
gested, and, to a certain extent, by independent study of the
subject.

Lack of capital is stated to be the cause of three-quarters of
the failures of various brickmaking firms. Whilst it is not im-
possible that some of these business failures are really traceable
to other sources, the fact remains that it is generally risky
to start without sufficient capital to pay for all the plant and to
keep the place going for at least six months, and preferably for
a year, without any bricks being sold during that time. In
some branches of brickmaking a larger capital is desirable. It
is not always necessary that this large capital should be invested
in the business, but it must ,be available in time of need if the
firm is to be reasonably safe from premature stoppage and failure.

The fact that some 'years ago certain well-known brickmakers
started with but a few hundred pounds and proved highly suc-
cessful is not a sufficient reason for repeating the experiment
at the present time, except in those places which are growing
rapidly and competition is not likely to be felt for some years to-
come. A large number of such places exist on the outskirts of
some of our smaller towns and near some of the larger ones, but
great circumspection is needed before commencing work under
such conditions.

Special care is necessary in the purchase of old works, as there
are many of these in existence which ought never to have been
erected, and a large number of others for the sale of whose
goods no market exists. Such works are dear at any price, and

SOURCES OF DIFFICULTY AND LOSS 427

whilst " bargains " may occasionally be obtained, they are dis-
tinctly rare, and should only be purchased after reliable and
full information has been obtained. It is never easy to ascertain
the true cause of the failure of the previous occupier, but unless
this can be satisfactorily explained the yard may prove anything
but a source of profit. The services of a specialist having a
previous knowledge of the works in question are often valuable .

In any case ample capital — either direct or in the form of
reliable credit — should be available before a brickworks is started
or purchased.

Defective accounting prevents many brick manufacturers from
realizing their true position as soon as they should do, yet this
disadvantage is comparatively easy to overcome.

As ordinarily carried out in small or medium-sized yards the
manufacture of bricks requires the simplest form of book-keep-
ing, yet many manufacturers fail to keep even this necessary
minimum in a proper manner, with the result that when trade
falls slack they are compelled to make special arrangements
with their creditors, and to suffer discomforts which might have
been avoided had they known earlier the results of their work.

It is essential that the proprietor, manager, or lessee of any
brickyard should know how much his bricks are costing per 1000
from week to week. To wait until the end of the year is in
many cases to postpone the consideration of the subject until it
is too late.

Each week, therefore, a summary should be prepared showing
the following : —

Stock — Brought forward, made, sold, rubbish, in hand.

Accounts — -Owing, receivable.

Cash — Brought forward, received, paid, in hand.

This account should further be divided so as to show the
main items of expenditure under the following heads : wages
for manufacture, wages for repairs and other work, cost of repairs
and renewals, cost of fuel, cost of oil and other supplies, other
expenses (detailed).

From the foregoing should be calculated the figures per 1000
bricks as follows : (a) labour (including foreman) for manufac-
ture ; (b) fuel ; (c) non-productive labour, and materials for
manufacture, alterations and repairs ; (d) oil and other supplies ;
(e) rent and royalty, or equivalent, and taxes, depreciation and
office expenses ; (/) exceptional expenses ; (g) average net selling
price.

428 MODEEN BKICKMAKING

This summary should be studied week by week with a view
to increasing the profit to be realized from the works, and care-
ful comparison should be made of the different summaries. In
some instances, more detailed statements are desirable (e.g. the
number of bricks set in and drawn off from each kiln), but those
mentioned are sufficient for an ordinary yard.

Certain figures will have to be averaged as they are paid for
at long intervals, but with care this need occasion no difficulty,
and little or no inaccuracy.

In making these comparisons from time to time it is essen-
tial that a broad-minded policy should be adopted, or the amount
set aside for depreciation must be increased. Thus it is foolish
to reduce the expenditure on repairs and renewals below a suit-
able limit, as this would result in the production of an inferior
brick for which a lower price would be obtained, or the wear and
tear of the machinery would involve a relatively greater expense
later.

When a yard is sufficiently large to justify the expense it is
far better to have the whole stock and plant valued by an inde-
pendent valuer of established reputation in this class of work,
than to adopt the customary plan of writing off 5 or 10 per cent
each year for depreciation.

It is also important that the sums so set aside should be
kept quite distinct from the business and should be invested in
other securities. Otherwise it may again be found, as has hap-
pened on many previous occasions, that the " reserve fund " has
no real value, as it has all been absorbed by the losses of the firm.

INDEX.

Abrasion, 370, 376, 377

Absorbent bricks, 13

Absorption, 371

Accidental blows, 377

Accounting, defective, 427

Accrington, 5, 9, 14, 212

Accumulators, 259

Acid-proof bricks, 372

Adams, A., 194, 221

Advice, necessity of impartial, 426

Aerial ropeways, 36

" Aero " dryer, 164

Air, 266, 269, 270

— bricks, 17, frontispiece

— heat-carrying power of, 168

— heater for dryer, 163

— in dryers, 163, 166

— in drying, 175

— flue, 250

— for blue bricks, 369

— for combustion, 253, 359

— insufficient, 340

— leaks, 303

— supply, 342, 344, 348, 349
Alkalies, 377, 391
Alumina, 6, 378
Analysis, 378

Anglo-American machine, 73
Annealing, 298

Arch, longitudinal, 299

— brick or wedge, frontispiece

— bricks, 316
- flues, 274

Arches, 315

— flattened, 316

— pointed, 316

— strength of, 316

— transverse, 299

" Archless " kiln, 294,333
Arrises, 12, 231, 232, 239, 241, 399
Artificial dryers, 154
Ashby, 373, 374
Ashes, 10, 43
Auger machines, 108
Automatic feeding, 383

B

Back-thrust, 110

— pressure, 114, 174
Badly-shaped bricks, 114
Baffle plates, 193, 194

Bags, 249, 251, 253, 254, 269, 318

Bagshot, 10, 18, 40

Baked bricks, 337, 338, 346

Baking, 337

Ball-clay, 407, 409

Bar tests, 343, 359, 365

" Bargains," 427

Barnett & Hadlington, 268, 300

Barringer, 336

Barrows, 38, 54, 210, 215, 236, 400

Barton mould, 55

Barytes, 402

Basic bricks, 393

Bath bricks, 14, 338

Bats, 17

Bauxite, 378, 381, 393

— bricks, 394
Bearings, 105
Bechtel dryers, 214, 216

— barrow, 215
Bed-clay, 2

Belgain kiln, 267, 300, 359
Belt, 176, 212, 215

— conveyor, 220

— elevator, 191
Bennett & Sayer, 108, 138
Berkshire, 9

" Best front " bricks, 125
Beyer's damper, 278
Binding clays, 379, 380, 382

— material, 382
Black, 340

— bricks, 12

— core, 340

ended bricks, 358

— glazed bricks, 403
Blackman Ventilating Co., 163, 165
Blades, 104, 105, 106 (see " Knives "),

110, 111, 328
Blake, Marsden, 181
Blasting, 20

(429)

430

INDEX

Bleichert, A., & Co., 36, 38
Bleininger, 175, 423
Blister, 411
Blistered bricks, 411
Blocks, 373, 387, 388

— refractory, 386

— for feed-holes, 316
" Blowing," 9, 23

— air, 366

" Blown," 341
Blows, 377

Blue bricks, 12, 268, 300, 345, 346, 368,
369

— glazed bricks, 403

— colour, 368
Bluish bricks, 344
Blunger, 404
Bock, 294, 302, 303
Body and bodies, 399, 403

— dipping, 401

Body materials, 403, 405

— dip, 408
Bodying, 401
Bohn's clay cleaner, 24
Bolts, 328

Bond for bricks, 311

Book-keeping, defective, 427

Boulder-clays, 2, 4, 102, 179, 424, 425

Bovey Heathfield, 4

Box moulds, 55

Bracknell, W., 54

Bradley & Craven, 96, 144, 147, 201, 202

Breaking, 366

Breeze, 10, 18, 66, 67

Brick-earth, 1

— car, 172

— conveyor, 213

— counter, 211

— kiln, 243

— machinery, 68, 177, 240, 416
Bricks (see also under adjectival liead-

ings)—

— Accrington, 14

— air, 17

— arches, 316

— badly-shaped, 114

— baked, 337, 346
- Bath, 14, 338

— black, 12

— blue, 12, 345, 346, 368

— brown, 12

— buff, 328

— " catch fire," 340

— channel, 17

— clamp, 16

— clinker, 16

— coarse, 232

— coping, 17
— cutters, 15

— dust, 14

— engineering, 16, 368

Bricks, facing, 15, 125, 209, 297

— fire, 16, 41

— Fletton, 14

— floating, 16

— general manufacture of, 20

— glazed, 7, 16, 336

— grey, 12

— Hand-made, 41

— hollow, 316

— impervious, 239

— malm, 17

— marl, 15

— moulded, 335

— paving, 16

— perforated, frontispiece, 125, 412, 413

— place, 17

— plastic, 15

— plinth, 17

— polished, 16

— pressed, 15

— purple, 346

— red, 9

— rubbers, 15

— sand-faced, 15

— sand-moulded, 52

— sandy (see " Rubbers "), 15

— selection of, 311

— semi dry, 14

— semi-plastic, 14

— setting, 254

— slop-moulded, 15, 51

— soft, 13

— soft-ended, 232

— spoiled, 347

— stiff plastic, 15

— stock, 17

— Suffolk, 8

— swelled,' 341

— tubular, 125

— weak, 232

— weak corners, 114

— white, 8, 328

— yellow, 9
Bridgewater, 14

" Brighten up " the goods, 350
Brightside Engineering Co., Ltd., 27,

47, 71, 88, 134
Briquettes, 396
Brittleness, 391
Brown, A. E., 44, 46, 57, 156, 163, 168,

169, 252, 262, 267, 276
Brown bricks, 12

— glazed bricks, 403
Brushing, 401

Buchanan, J., & Son, Ltd., 72, 75, 92,

93, 100, 119, 139, 145, 189, 198
Bucket elevators, 191
Buckets, 191
Buckley, 313
Buff-coloured clay, 5

— burning bricks, 328, 345

INDEX

431

Buff-coloured burning shale, 368
Buhler's mill, 190
Biihrer, Jacob, 288, 293, 313, 342
Building bricks, 350
Built-up dies, 151
Bull, 294
Bullnoses, 17

Burnett, T., & Co., Ltd., 292
Burning, 250, 306, 326, 337, 369, 394
405, 410

— firebricks, 376

— rate of, 288, 293
- stages of, 339

•" Burnovers," 66
" Burnt stuff," 375, 380
•' Burrs," 13, 66
Burton, 373

« Callow," 220

Cambridgeshire, 9

Cam motion, 230, 232, 237

Capital required, 426

Caps for feed-holes, 319

Carbonaceous matter, 339, 343, 344

Carrying off, 210

Cars, 170, 302

Cease firing, 350

Chain haulage, 29

elevator, 191
Chalk, 9, 19

Chamber kilns, 276, 299
Chambers, 317, 352

— too few, 366
Chamotte, 19, 380
Changes of temperature, 367
Channel bricks, 17, frontispiece
Chart of kiln draught, 362
Checking, 214

— fire, 363
Chimney bricks, 413

— draught, 282

— gases, 282

Chimneys, 243, 246, 248, 251, 254, 281,

295, 320, 413
China clays, 2
Chip, 399

Choice of bricks for kilns, 311
Chrome ores, 395

— bricks, 396
Chromite, 373, 395
Chromium oxide, 395
Circuit of kiln, 352
Circular kiln, 247, 248
Clamp bricks, 16

— kilns, 62, 213, 245, 322, 348

— for damper rod, 292
Clapping, 58, 400
Clay, 1, 369

Clay, binding, 379, 380, 382

— blasting, 20

— boulder, 102

— burning, 339

— cleaners, 41

— cleaning, 40
— crushing, 41

— deposited by rivers, 3

— deposited in a lake, 3

— deposits, 3

— digging, 20

— drying, 420

— exposure of, 22

— fluviatile, 3

— for hollow blocks, 414

— hard, 100

— lacustrine, 3

— London, 3, 39

— marine, 3

— mixing, 41, 43

— plastic, 238, 240

— preparation of, 40

— purifiers, 23, 24

— red, 2

— rock, 42

— soft, 100

— sticking, 199

— sticky, 41, 98

— strong, 10, 39, 102, 129

— substance, 2

— tender, 154, 159

— tough, 104, 125

— value of, 425

— weathering, 22
Clayton, H., 26, 119
Cleaning clay, 40
Clinker, 350, 359, 369

- bricks, 16
Clinkers, 66
"Clot," 177, 196,225
Clot-making machines, 197
Coal in bricks, 346

— burning, 348
Cod oil, 150

" Cog " clot mould, 206
Coke-heater, 166

heated dryer, 159

Cold air, 355, 364

air valve, 274

Collar for brick-machine, 114

Colloids, 238

Colour, 213, 261, 302, 304,333, 344, 346,

390, 399, 411
Colour of bricks, 8
Coloured bricks, 405

— glazes, 403
Colours, 403
Colza oil, 150
Combined water, 342
Combustible matter, 343, 344

— removal of, 339

432

INDEX

Combustion chambers, 256

— products of, 282, 301
- space, 331

Commissions, 426

Compression, excessive, 386

Concrete, 240

Condensation products, 251, 269, 351

Condensable water, 343

Conduction losses, 283

Cones, Seger, 350, 351, 359, 363, 406

— temperature equivalent, 361
Conical runners, 189
Connecting kiln, 249

— chamber, 277

— flues, 300

Continuous kiln, 62, 217, 243, 245, 261,
263, 282, 291, 294, 297, 317, 322,
324, 329, 335, 369

— tunnel dryer, 161
Contraction, 376, 377, 390
Control of temperature, 359

— draught, 362
Conveyor belt, 209
Conveyors, 176, 213, 215, 221
Cool, 365, 389

Cooling, 308, 365, 366, 392, 406, 411

— chambers, 272

Coping bricks, 17, frontispiece, 415

"Core cracks," 125

Core preventer, 204

Cores, 340, 341, 344, 412, 415

Coring, 203

Corner cracks, 121

Corrugated rolls, 93, 94

Cost, 427

" Counter," 211

Cracking, 168, 175, 203, 390

Cracks, 122, 124, 153, 170, 207, 225, 341,

366, 389
Craddock, 31
Crazing, 399, 419
" Crowding " barrow, 210
Crown, 318

— of kilns, 315
Crozzles, 17
Crucibles, clay, 43
Crush, 365

Crushing clay, (see " Grinding")

— resistance, 371

— tests, 389

— rolls, 76, 79, 86

— strength, 390, 417
Crystallize, 347
Culm, 67
Cumberland, 6
Curvature, 124
Cutters, 11, 15, 338

Cutting tables, 77, 78, 79, 80, 81, 82, 83,
84, 129

— wires, 137
Cylindrical clot, 196

Damp bricks, etc., 300, 364

— material (screening), 195
Damper holders, 292

Dampers, 277, 292, 297, 298, 320, 333r

334, 351, 365, 409, 410
Dannenberg's kiln, 273
Dark colour, 346
" Daub," 245, 337
Dead-burned magnesia, 394
" Dead spaces," 280, 355
Dean, Hetherington & Co., 297, 394
Defective filling, 203

— accounting, 427

Defects, 225, 334, 391, 397, 399

— in shape, 124

Delicate clays, 274, 323, 343, 354, 356-
Dense clays, 345
Density, 302, 345, 346, 371
Deposits, 3, 256
Depreciation, 428
Derbyshire, 6
Developing colour, 341
Devonshire, 6, 9, 11, 373

— fire-clays, 374

Diamond stretcher, frontispiece

Die-boxes, 151

Dies, 114, 125, 151, 239, 400

Diesener, 302

Difficulties, 424

Digging, 20, 21, 42

Dinas, 7

— bricks, 391

Dip for salt glaze, 408
Dipped, 400
Dipped firebricks, 387
Dipping, 401, 402, 405, 408
Dips, 409, 411
Direct haulage, 29
Discoloration, 269, 350
Discolours, 266, 341
Disintegrator, 72
Dobson, E., 63

Dog tooth stretcher, frontispiece
" Don'ts " for firemen, 364
Door-gaps, 265, 266, 269
Dorsetshire, 9
Double-shafted mixers, 105
Dowlais, 73, 93
Down-draught, 264, 276

— kilns, 217, 244, 248, 255, 327, 409

— kilns, firing, 348, 349

— semi-continuous kiln, 262
Down-take flue, 273
Draining a kiln, 312, 313

Draught, 281-3, 288, 312, 320, 329, 334 r
342, 356, 358, 362, 366

— gauge, 351, 361
Drawing, 366
Drift clay, 341, 424

INDEX

" Drop arches," 318, 329
Dry-dust, 177

- bricks, 14

Dryer and fan, 285, 287

— connected to kiln, 288
Dryer, choice of, 175

— floors, 157

— rails, 172

— testing, 174

Dryers, 56, 57, 154, 161, 213, 289, 295,

420
Drying, 56, 154, 213, 238, 239, 339, 342,

390
Drying firebricks, 376, 387

- kiln, 247, 423

— raw clay, 420
Dry process, 240
" Dudley," 368
Dull glaze, 406
Dunnachie, James, 303, 304
Durant's kiln, 246
Durham, 6, 374

Dust process, 240

£

Eccentric represses, 144
" Economic " moulds, 151
Eddington moulding machine, 72
Edge-runners, 94

- -runner mills, 179, 184, 383
Electrical conduits, 417
Electrical pyrometer, 361
Elevating, 191
" Emperor " press, 233
Emptying, 365
End of firing, 349
Endless rope haulage, 30

— chain haulage, 36
Engineering bricks, 16, 368
"English" kiln, 275, 299, 300
Enlarging kiln, 325
Erroneous methods, 426
Errors in kiln construction, 310
Essex, 9

•'Excelsior" kiln, 289
Excessive burning, 340
Exhaust steam in drying, 157, 168
Expanding mould, 72
Expansion, 366, 377, 391

— of clay, 124
Expression attachment, 235

— rolls, 78, 124

— roller machines, 124

F

Facing bricks, 15, 125, 209, 297, 328, 333
burning, 245

Failures, 424

Fan, 282, 283, 285, 286, 287, 288, 289,
306, 321

— for dryer, 170, 174, 285

— speed of, 285

— size of, 285

— Sutcliffe Ventilator and Drying Co.,

283
Fawcett, T. C., Ltd., 72, 73 102^ 127,

129, 136, 143, 145, 146, 184, 193,

194, 198, 206, 211, 212, 225, 226,

227, 228, 229
Feed-holes, 316
Feed-hole caps, 319

— plate, 193

— tray, 180

Feeding appliances, 82-4, 103, 180, 182

Fermentation, 385

Fine grinding, 185

Fingers for lifting, 232

Finish of firing, 349, 388

Finishing heat 347

— point, 347, 406

— temperature, 339, 349, 388, 392, 395
Fire blocks, 373

Fire-boxes, 249, 250, 253, 255, 268, 300

318, 348
Fire-bricks, 16, 41, 43, 244, 268, 300, 304,

308, 309, 339, 350, 373, 379
Fire-brick lining, 294
Fire-clay, 2, 6, 22, 85, 341, 370, 373, 397,

407

— working, 375

— dampers, 277

— blocks, 318
— columns, 332

Fire gases, 269, 357
holes, 246, 249

— pillars, 255

— places, 261

— proof flooring, 412, 413

— shafts, 332

- travel, 341 (see " Speed ")

- trough, 300

Firing, 65, 250, 306, 308, 331, 337, 348,
369, 376, 388, 394, 395, 405, 410, 417

- a clamp, 65, 348

— fire-bricks, 376, 388

— hollow blocks, 417

— with gas, 306, 308
First dip, 401, 403

— stage of burning, 343
"Five on two," 327
Flashing, 346, 380, 394, 410
Flat grate, 253
Flattened arches, 316
Fletton, 14, 219, 267, 340

— bricks, 14

— knots 340
Floating bricks, 16
Floor of kiln, 254

28

434

INDEX

Floor dryer, 420
— drying, 157
Flues, 319

— for hot air, 268

— for steam, 279, 280

— metal, 273

— permanent, 273

— temporary, 272
Fluviatile clays, 3
Footstep, 98, 186
Forced draught, 250
Formation of clay, 2
Foul clays, 10, 43
Foundation of kiln, 247, 312

— water, 312
Four a tranches, 333
Freshly-set bricks, 269
Frit, 402, 405

Frog, frontispiece, 144, 178
Frost (see "Weathering"), 389
Fuel, 66, 67, 250, 359

— consumption, 264, 295, 348
Full fire, 339, 346, 357, 365
Full shaft, 332

" Fully-burned " bricks, 338
Fusibility, 377, 379, 391
Fusion, 347

Ganister, 7, 373

— bricks, 393
Gartcosh, 7, 393

Gas advantage, 304, 308

— causes of failure, 309
Gas-fired kilns, 256, 303

— continuous kilns, 303

— tunnel kiln, 303
Gas-producer, 250, 257, 303, 304, 309
Gases admitted to chimney, 357
Gault, 8, 40

Gillet fire-box, 250

Glacial clay, 341 (see " Drift ")

Glasgow, 6

Glazed bricks, 7, 16, 336, 397

— blocks, 419

— hollow blocks, 417
Glaze materials, 402, 405

— recipes, 398

— trials, 406

Glazes, 399, 402, 403, 404

Glenboig, 303, 306, 373

Gold-glazed bricks, 403

Granulate, 104

Granulation, 232, 237

Granulator, 103

Graphite, 396

Grates, 250, 253, 255, 260, 261, 264, 267,

268, 276, 300, 348, 350, 355, 358
Gravel, 23, 40

Green bricks, 398
Green glazed bricks, 403
Grey bricks, 12
Grey stocks, 17
Griessmann & Co., 112
Grinding, 221, 383

clay, 41, 83, 94, 179, 183, 221, 383

— grog, 383

— mills,

83, 84, 94, 179, 183
Grizzles, 17

Grog, 18, 375, 380, 383, 389
— size of, 381
" Groke," 122
" Guthrie," 267, 268, 300

H

Hack drying, 60

— ground, 56
Hacks, 56

" Haendle," 182

Haircracks, 12

Half-gas firing, 260

Half-moon stretcher, frontispiece

Halifax, 374

Halsband & Co., 122, 123

Hampshire, 9

Hand-brickmaking, 39

— made bricks, 41, 69

— moulds, 39

— moulding, 41
Hard clays, 100

— glaze, 399

— material, 95

— water, 19
Hardness, 371
Harrison, H., 294
Haulage, 29, 180

Heart (see " Core") 340, 341, 344
Heat accumulators, 259

— necessary to burn, 338
— regeneration, 307

Heizwande, 333
Herve, T., 115, 119
Hexagonal'screen, 195
Highly plastic clays, 104
High temperature, 376
Hoffmann kilns, 264, 291, 297, 358
Hollowness, 124
Hollow blocks, 335, 412
with closed ends, 413

— bricks, frontispiece, 316, 412, 413
Homogeneous, 42, 43, 110, 124, 225
Homogenization, 104
Horizontal draught kilns, 244, 329
Horsham Engineering Co., 48

Hot air, 253, 269, 293, 297, 298, 301, 306,
307, 308, 344, 349, 352, 354

flues, 266, 268, 274

for combustion, 274, 275, 299, 301

INDEX

435

Hot floor, 157, 160, 421
Hughes, W. B., 214
Hunter & Co., 78, 126
Hurried firing, 346
Hydraulic balance, 207

Impervious brick, 239
Improper materials, 424

— site, 424

Improved Hoffmann kilns, 267

Impurities, 22

Incipient vitrification, 339, 347

Inclined grates, 253

Inferior fire-bricks, 389

Instability of kilns, 310

Intermittent kilns, 243, 256, 323

Invert blocks, 415

Irish fire-clays, 6

Iron compounds, 340

— dampers, 277

— oxide, 344

— reduced, 340

— sulphide, 408
Irregularities, 199
Isle of Wight, 4
Isolation of kiln floor, 314

Jamb, frontispiece, 17

Johnson & Sons, Ltd., 129, 130, 132, 203,

228, 231
Johnston, 198
Jones & Sons, Ltd., 116, 151

Kaolins, 2

Kase, F., 390

Keith J. & Blackman, Co., Ltd., 285

Kibbling rolls, 93

Kilmarnock, 6

Kiln, circuit of, 352

— connected to dryer, 288

— construction, 310

- dryer, 157

- foundation, 312

— selecting, 321

— size of, 323

— thermometer, 343
Kiln-gases in tunnel dryer, 166
Kiln-walls, 294

Kilns, 61, 176, 213, 217, 236, 243, 409

— " closing," 350

— connected, 249

— drying, 342

Kilns, enlarging, 325

— for small output, 324

— roof for, 295

— too short, 324

— with grates or troughs, 267
- with two fires, 295, 300

Klemp, Schultze & Co., 33
Knee-joint presses, 147
Knives, 103, 105, 110
Knotts clay, 6
Koppel, A., 170, 171, 172, 173

Lack of capital, 426

Lacustrine clays, 3

Lake deposited clays, 3, 4

Laminated mouthpiece, 122

Lamination, 125, 148, 197, 236, 237, 241,

347

Lancashire, 9, 12
Lane, P., 112
Lead compounds, 403
Leakages, 247, 333, 364
Leeds, 374
Leicester, 6, 9
Leighton Buzzard clay, 3
Length of kiln, 324
Light blocks, 414

— coloured glazes, 411
Lime, 5, 9, 102, 377, 391, 397

— milk, 391

— sand, 240, 392
Limestone, 23
Limey clays, 101
Lined dies, 119
Liners, 199, 235

Lining of mouthpiece, 121

Loading clay, 21

Loams, 10, 78, 179 "*

Loamy, 10 ••;'

London clay, 3, 39, 423, 424

— Brick Co., Ltd., 220, 221, 222, 224,

275, 300

— bricks, 62

— stocks, 14, 62 :
" Loos," 57

Loose clays, 340

Loss of shape, 347

Losses, 424

Lubrication, 60, 117, 122, 149, 199, 208,

241
Lumps, 87, 180

Machine moulding, 68
Magnesia, 373, 391, 393
— bricks, 394

436

INDEX

Magnesia " sand," 395

Magnesite, 39*

Main and tail haulage, 30

Majolica glazes, 404

Malm bricks, 17

Malms and maiming, 8, 17, 23

" Manchester " kiln, 274, 280, 299, 353

Marcasite, 5

Marine clays, 5

Marl facing bricks, 15

Marls, 8, 84, 368

Masonry, 294, 310, 311

Matthews & Yates, 284

Maximum temperature, 339, 390

Maxted & Knott, Ltd., 69, 70

Measuring rod, 351

— mould for bricks, 397
Mechanical draught, 283, 289, 293
Mendheim, 302, 304

Metal flues, 273
Methods, unsuitable, 425
Midland fire-clays, 374
Midland marls, 22, 267
Midlands, 6, 10, 40, 368, 373
" Mild." 10
Milk of lime, 391
Mill-feeder, 82, 103, 180, 182

— with conical runners, 189

— with multiple runners, 191

— with two stages, 190

Mills, 83, 84, 94, 179, 183, 221, 383
Mining, 20
Mixers, 82, 103, 227
Mixing, 43, 103, 385

— clay, 41

Moisture, 279, 301, 340, 343, 351

" Mceller & Pfeiffer," 170, 423

" Monarch " machine, 69

Mond gas-producer, 260

Mortar, 246, 312

Moulded bricks, 335, 418

Moulding, 50, 419

Mould-making, 418

Moulds, 54, 151, 199, 203, 235, 239, 386,

419

Mouthpieces, 77, 108, 113, 413
Muffle, 309

— kilns, 309, 335
Multiple roller machine, 127

— runner wheel, 191

" Murray" machine, 125, 126

N

Natural draughts, 283
Neath, 7

Neutral firebricks, 395
Newaygo screen, 194, 225
Newcastle kiln, 217, 244, 255, 261, 331,
337, 350

"New Era" machine, 207

"New Perfect" kiln, 293, 353

Newton Abbot, 4

Nodules, 39

Non-absorptive power, 239, 376

Norfolk, 9

" Norris," 71, 72

Northumberland, 7, 373

Northumbrian fire-clays, 374

North Wales, 6

Nottinghamshire, 8

Number of chambers, 352

Nuneaton Engineering Co., Ltd., 230

Oakland, G., 300

Ochre, 408

Oil, 150, 368

Oijy shale, 220, 267

Old works, purchase of, 426

Open base mill, 187, 188

— clays, 340

— mixer, 108, 110

— mould, stiff plastic machine, 206

— up, 390

Opinions, erroneous, 425

Optical pyrometers, 361

Organic matter, 340

Ornamental bricks, 415, 418

Osman, J., & Co., Ltd., 289, 293, 353

Output, 324

Over-driven mills, 184

" Overworking," 385

Oxford, 40

— clays, 5

Oxidation, 41, 341, 345, 369, 377
Oxide, red, 344, 368, 377, 391, 395
Oxidized, 340, 341, 345
Oxidizing, 41, 369
Oxley Bros., Ltd., 135

Pallet boards, 171

" Pan mills," 95, 179, 185

Paper dampers, 277, 278, 356, 363, 365

Partial kiln, 323

Partition, 276, 278

— blocks, 412

Paste, plastic, 104, 108, 110
Paving bricks, 16, 369
Paviors, 370
Peat, 414
Pebbles, 23
Peel off, 399, 402

Perforated brick, frontispiece, 125, 412,
413

— floor, 254

INDEX

437

Perforated pan mills, 184

— screen, 193

— steel plate, 192
Permanent flues, 72, 273
Peterborough, 5, 6, 14, 219
Piano- wire screens, 194, 221
Picking, 375

" Pillars" for fuel, 255, 266, 292, 331
Pink glazed bricks, 403
Place bricks, 17, 66
Placing (see " Setting "), 326
Plain brick, frontispiece
Plaster of Paris, 392, 402
Plaster moulds, use of, 419
Plastic bricks, 15, 238

— clay, 15, 240

— clays, super-drying, 423

— moulding by machinery, 68

— paste, 104, 108, 110

— process, 68

Plasticity, 1, 100, 238,240, 247, 379,385

Platt Bros. & Co., Ltd., 232, 233, 234

Plinth bricks, frontispiece, 17

Pointed arches, 316

Poker, 365

Poker-test, 365

Polished bricks, 16, 58

Poole, 11

Pores, 341, 344, 347

Porosity, 338, 390

Porous, 338, 388, 397

Portable stove, 271

" Post," 378

Power-driven presses, 142

Precautions in cutting, 137

— in firing, 348
Preliminary heating, 339

— mixing, 112
Preparation of clay, 40
Press oil, 150, 177, 225
Pressed bricks, frontispiece, 15
Presses, 60, 108, 140, 177, 225, 232

— hand-driven, 140

— knee-joint, 147

— portable, 140

— power-driven, 142

— screw, 140, 144

— toggle-lever, 146
Pressing, 59, 399

— in plaster moulds, 419
Pressure, resistance to, 376, 377
"Price," 204

Primary clays, 2, 3

Products of combustion, 301

Protection of goods, 335

Pugging and pug-mills, 43, 69, 77-84,

103, 108

" Pullan & Mann," 77, 144
Pump, 20

Purchase of old works, 426
Purple bricks, 346

Putrefaction, 42
Pyramid tests, 359
Pyrites, 5, 23, 345
Pyrometer 351, 361

Racks, 171

— for drying, 154
Radial bricks, 413
Radiation losses, 283
Rail-gauge, 171
Bails, 171, 173
Rain, 389

— effect of, 312, 313, 321, 389
Rain-water, 19

— removal of, 312
Rapid burning, 340
Rattler test, 370
Raupach, R., 131

Rawdon Foundry Co., Ltd., 142

Raymond & Co., Ill

Raynor, H., 164

Reading, 4, 40

Recorder, 211

Recrystallizatioo, 347

Rectangular down-draught kiln, 248,

251
Red bricks, 9

— glazed bricks, 403

— heat, 348

— marl, 12

— oxide, 344, 368, 377, 391, 395
Red-burning bricks, 345

— burning shale, 368

— clays, 10, 339, 340, 344, 368, 397
Reducing, 345, 369, 377

— compounds, 345

— conditions, 368

— piece, 114

Reduction, 309, 345, 368, 377
Refractoriness, 390

Refractory clay, 7 (see " Fire-clay")

— goods (see " Fire-bricks "), 309, 376,

379

Regeneration, 256, 301, 307, 345
Regeneratively heated air, 301
Regenerators, 256, 257, 259, 301, 307,

345

" Reinforced," 417
Reinforcing, 412
Relined, 235

Repairs and renewals expenditure, 428
Repress, 69, 139, 177, 208, 229, 236
Repressing, 139, 177, 208, 236
" Reserve fund," 428
Resistance to abrasion, 376

accidental blows, 377

heat, 377

— high temperature, 376

438

INDEX

Resistance to oxidation, 377

pressure, 376

reduction, 377

slag and limestone, 395

sudden changes, 377

wear and tear, 377

Retort clay, 43
Revolving drum, 203, 422

— screen, 195

— table machine, 201
Riddles, 181, 192
Ring kiln, 291, 305
Rise of temperature, 347
River deposits, 3

Rock clays, 5, 42
Rolls, 80-84, 86, 124
Roller-bearings, 171
Roof for kilns, 295, 321

— water, 313
Rope conveyor, 213

— haulage, 29
Rotary clay dryer, 422
Rough bricks, 411

— stocks, 17

Round kilns, 247, 248, 249

— of kiln, 308, 352, 353
Ruabon, 9, 11
Rubbers, 11, 15, 338
Running-out machine, 417

s

Salt, 369

— glazing, 308, 372
Salt-dip, 408
Salt-glazed bricks, 406
Sand, 18, 40, 390, 391

— -faced bricks, 15, 68
folds, 53

- -lime bricks, 392

— -moulding, 50
" Sand-seal," 320
Sandstones, 391
Sandy, 10, 13

Sanspareil machine, 225, 230

Sawdust, 346, 414

Scale-lined mouthpiece, 122

Schmatolla, E., 257, 304

Scholefield, R., 205, 225, 230

Scotch kilns, 245, 337

Scotland, 6

Scott, 213, 215, 326

" Scove " kilns, 217, 333

Scrapers in mills, 187

Screens, 176, 192, 221, 251, 375

Screen-wall, 249

Screw-presses, 140, 144

Scum, 213, 238, 256, 269, 351, 369, 411

Sea-deposited clays, 3, 5

Sealing chambers, 298

Secondary clays, 1, 3

Seconds, 17

Second stage of firing, 341, 343, 344, 357

Seger cones, 350, 351, 359, 406

Selecting a kiln, 321

pug-mill, 110

Selecting clays, 378
Selection of bricks, 311, 398

materials for fire-brick, 378

plant, 85

stiff -plastic machines, 200

Self-delivery wet-mill, 102
Semi-continuous kiln, 62, 243, 244, 260,

294
" Semi-dry" process, 177, 219

— bricks, 14
Semi-plastic process, 177

— bricks, 14

Sercombe, W. H., 281, 292
" Set," 150, 153

Setters, 364

Setting, 213, 247, 254, 266, 302, 326, 387,

405, 409
Settling, 351

— tanks, 26
Seven Oaks, 3

Shakes, 17 • "-.

Shales, 2, 5, 10, 84, 85, 179, 220, 240,

267, 300, 345, 370, 375, 382, 407
" Shank " kilns, 324
Shattering, 365
Shed-dryer, 154
Sheffield, 393
Shell, 5
Shovel, 38
Shrinkage, 175, 176, 351, 394, 395

— rod, 343, 361
Shropshire, 373
Shuffs, 17
Sieves, 192
Silica, 6, 7, 390

— bricks, 7, 390, 393

— rocks, 373, 381, 391
Silver glazed bricks, 403

Single kilns, 243, 276, 282, 318, 342, 348,
366, 389

— shaft mixers, 104
Sintered magnesia, 394
Site, 424

Size of kiln, 323
- of grog, 381
Skeleton, 379
"Skerry," 23
Skintling, 59
Slab-heater, 163, 164, 168
Slabs, drying, 387
Slag, 341, 345

— colour, 344
Slate, 6

Sliding-die brick machine, 207
Slinging, 43

INDEX

439

Slop-moulded bricks, 15

Slop-moulding, 50, 51

Slots, 185

Slow- firing, 340, 363, 365

Slurry, 26

Smith, G. T., 203

Smoke, 250, 253

Smoke-flue, 274

Smoking, 217, 306, 321, 340, 353

Smoky flame, 346

Smooth rollers, 92

Soaking, 42, 347, 363, 365

Soda, 402

Soft bricks, 13

— clays, 100
Soften, 343
Softening clay, 347
Soft end, 232

— glaze, 399
Soil, 18, 23, 28
Soiling, 28
Sole, 356

Souring, 42, 375, 383, 385
Spades, 38

Spalling, 225, 378, 391
Specific gravity, 371
Speed of burning or firing, 340, 341, 345,
358, 363

pug mills, 112

Spiral conveyors, 221

" Spitta," 274

Splitting, 378

Spoiled bricks, 347

Spot, 346

Spy-holes, 361

" Squat," 124

Squints, frontispiece, 17

Stable brick, frontispiece, 368

Staffordshire, 8, 12, 84, 368

— kiln, 274, 280, 297
Stain, 328

Stanley machine, 230, 232
Stationary screens, 192
Steam, 279, 301, 343

— as lubricant, 121

— floor, 158

— flues, 279, 280

— heaters, 165

— -heated dryer, 157

— jet, 250

— navvies, 220

- removal of, 343, 354

— vents, 357
Steaming, 306, 339, 342
Steatite, 240
Stickiness, 240
Sticking, 149, 199, 240

Sticky clays, 41,92, 94, 98, 149, 199, 240,

424

" Stiff plastic" machines, 177, 196
bricks, 15

' Stiff plastic " process, 177
Stocks, 17

— London, 14
Stone-breaker, 180
crusher, 180

Stones, 4, 23, 40, 76, 78, 89, 94, 100, 102,

124

Stoneware-clay, 372
Stony clays, 94
Stool pallets, 171
Stop brick, frontispiece
Storing, 389
Stourbridge, 6, 373

— fire-clays, 374

Stoves, 269, 270, 279, 335, 342, 355

Stoving, 275, 339, 340, 342

Streaks, 401

Strengthening kiln, 252

String course bricks, frontispiece

Strong clays, 10, 39, 84, 102, 129, 340,

424

Structure, 150, 153
Stull, B., 121, 123
" Stupids," 415

Sturtevant Engineering Co., Ltd., 283
Subsoil water, 313
Sudden changes, 377, 390
Suffolk, 9
Sulphur, 29, 411
— compounds, 345
Super-drying, 423

heater, 250

Supplementary fires, 251, 254
Surface clays, 2, 10, 40

— water, 19

Sutcliffe, Speakman & Co., Ltd., 89, 97,

146, 148, 151, 203, 207, 233, 234
Sutcliffe Ventilating Co., 164, 165, 422
Swelling, 341, 347, 411
Swinney Bros., 113, 125, 127, 185

Tamworth, 11
Taper bricks, 316

— mouthpiece, 124
Tar, 368

Teign valley, 6, 374
Temperature, control of,

— high, 376

— in blue brick burning,

— maximum, 339

— of gases, 282

— recorder, 351

— rise, 347

— (scale), 361

— testing, 365, 425
Tempering, 42
Temporary flues, 272

— kiln, 294

440

INDEX

Temporary muffles, 335
Tender clays, 154, 159, 175, 340
Tenderness of magnesia bricks, 395
Terra-cotta, 11

clays, 11

Test for acid-proof bricks, 372
Testing burning temperature, 338

— during drying, 174

— lime liquor, 392
Thames clay, 3
Thermometer, 282, 343, 356
Thermoscopes, 359, 363
Thickness regulating, 398
Thirds, 17

Third stage of burning, 357
Thomas's kiln, 251
Thrust bearing, 112
Tipping frame, 33

— waggons, 33
Tippler, 180
Titanium, 377
Toggle-lever presses, 146, 225

— machines, 238
Toothed rolls, 93
Tough clays, 104, 125
Tower-dryers, 423
Trace-holes, 330
Track, 211
Transfer car, 172
Transport, 176, 236
Transverse arches, 299
Treacherous clay, 424
Treading, 43
Treatment of clay, 23
Trial pieces, 351, 406
Trough, 267, 268, 269, 332
Troughs for fuel, 264
Tubular bricks, 125

— dryers, 421
Tunnel-dryers, 161, 421

— kilns, 302
Turn-tables, 32
Twisting, 124
Two-stage mill, 190

U

Under-burned bricks, 13, 66, 368

— -driven mills, 184

Unevenness in temperature, 356, 357

Uniformity, 376

Unoxidized spot, 346

Unsuitable methods of working, 425

Up and down draught kiln, 244

Up-draught kilns, 243, 245, 326

Value of a clay bed, 425
Variations in size, 152

Vaughan's kiln, 273, 280
Vegetable matter, 343, 344

removal of, 339

Ventilation of kiln, 357
Ventilator brick, frontispiece
Vertical flue, 331
Viscous mass, 347

Vitrification, 209, 302, 341, 345, 347,
360, 368, 374, 407

— period, 347

— point, 341
Vitrified bricks, 368, 374
Volatilization, 344

" Vulcan " mill, 48

w

Waggons, 29, 170, 180, 302
Wales, 6, 373, 393
" Walk flatting," 53
"Walls," 328
Warm air, 352
" Warner," 360
Warping, 168, 175
Wash- backs, 25, 42

mill, 25

Washed stocks, 17
Washing, 25, 40
Waste gas dryer, 159

— gases, 159^, 256

— heat, 324, 342, 352

Water, 19, 56, 176, 177, 340, 351, 385,
390, 404

— as lubricant, 121

— removal of, 312, 354

— smoking, 217, 340
" Watkinson," 189
Weak (bricks), 232, 236

— arch, 315

— corners in bricks, 114
Wear and tear, 377
Weathering, 22, 41, 375
Wedge-shaped bricks, 316
" Well," 178
Welsh fire-clays, 375
West Scotland, 373, 393
Western clays, 10
" Wet pans," 94, 95
Wheelbarrows, 38
Wheeling, 21, 211
Whinney Hill, 5
White bricks, 8

— burning bricks, 328

— body, 404

— glazed bricks, 403

Whitehead, J., & Co., Ltd., 62, 88, 118,
134, 135, 141, 187, 190, 417

Whittaker & Co., Ltd., 31, 48, 49, 93.
98, 117, 131, 188, 194, 196, 207, 222,
223, 224

INDEX

441

Wicket, 246, 254, 256, 293, 355

— arches, 317

— fires, 269, 270, 279, 333, 337, 342
Wills, W. & F., Ltd., 91

Wind, 362
Wire-cut, 69

bricks, 76

process, 76, 180

— gauze screen, 192
Wires for cutting, 137

Wolff Dryer Co., 165, 166, 169, 170

Woolley's fire box, 260

Wootton Bros., Ltd., 125, 128, 132, 133,

203
Working continuous kiln, 353

Works, purchase of, 426.

Worm, 110

Wrong bonding, 311

Yellow bricks, 9, 403
Yorkshire, 6, 368, 373, 393
— fire-clays, 374

Z

Zinc oxide, 402

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Catalogue

OF

Special \9ee6nieal J3ooks

INDEX TO SUBJECTS.

PAGE

PAGE

PAGE

Adhesives 10

Evaporating Apparatus ... 25

Pottery Clays 14

Agricultural Chemistry 10

Fats . ...5,6

Pottery Decorating ... 14

Air, Industrial Use of ...11

Faults in Woollen Goods... 20

Pottery Manufacture ... 13

Alum and its Sulphates ... 8

Flax Spinning 23

Pottery Marks 15

Ammonia ... ... ... 8

Flint Glassmaking 16

Power-loom Weaving ... 18

Animal Fats and Oils ... 6

Food and Drugs 30

Preserved Foods 30

Anti-corrosive Paints ... 4

Fruit Preserving ... .. 30

Printers' Ready Reckoner 31

Anti-fouling Paints ... 4

Fungicides 28

Printing Inks 3,5

Architecture, Terms in ... 29

Gas Firing 24

Reagents 9

Architectural Pottery ... 14

Gearing 26

Recipes 2

Artificial Perfumes 7

Glass Painting 15

Resins 9

Balsams 9

Glue Making and Testing... 8

Ring Spinning Frame ... 23

Bleaching 22

Glycerine 6

Risks of Occupations ... 11

Bleaching Agents 22

Greases 5

Riveting China, etc. .. 14

Bone Products 8

Gutta Percha 12

Sanitary Plumbing .. 27

Bookbinding 31
Brick-making ... 13, 14
Burnishing Brass ... ... 27

Hat Manufacturing ... 19
Hemp Spinning 23
History of Staffs Potteries 15

Scheele's Essays 8
Sealing Waxes 10
Shale Oils and Tars .. 9

Carpet Yarn Printing ... 20

Hops 27

Sheet Metal Working .. 27

Casein 4

Hot-water Supply 27

Shoe Polishes 5

Celluloid 31

How to make a Woollen Mill

Silk Throwing 21

Cement Work 29

Pay 21

Smoke Prevention 24

Ceramic Books ... 13, 14, 15

India-rubber 12

Soaps 7

Chemical Analysis 9

India-rubber Substitutes 5

Spinning Calculations ... 20

Chemical Essays 8

Industrial Alcohol 9

Spirit Varnishes ... ... 5-

Chemical Reagents ... 9

Inks 10

Staining Marble, and Bone 3ft

Chemi?al Works 8

Insecticides 28

Standard Cloths 17

Chemistry of Pottery ... 15

Iron-corrosion 4

Steam Drying 11

Clay Analysis 14

Iron, Science of 24

Sugar Refining 32

Coal-dust Firing 24

Japanning ... ... ... 27

Steel Hardening 24

Coal-Gas By-Products ... 9

Joint Wiping 27

Sweetmeats 30

Colour Matching 21

Jute Spinning 23

Technical Schools, Hand-

Colliery Recovery Work ... 24

Lace-Making 19

book to the 32

Colour-mixing, Textile ... 21
Colour Theory 21

Lacquering 27
Lake Pigments 2

Textile Colour Mixing ... 21
Textile Design 19

Cotton Combing Machines 22

Lead and its Compounds... 10

Textile Fabrics ... 17, 18, 19

Compounding Oils, etc. ... 5

Lead Burning 27

Textile Fibres ... 17, 18, 19

Condensing Apparatus ... 25

Leather Dressings ... 5

Textile Materials 19

Cooling Apparatus 25
Cosmetics 8

Leather-working Materials 13
Linoleum Manufacture ... 5

Textile Soaps and Oils ... 7
Timber 29

Cotton Spinning 22
Cotton Waste 22

Lithographic Inks 5
Lithography 31

Toilet Soapmaking . . 7
Turbines 26

Damask Weaving 19

Lubricants 5

Varnishes 5

Dampness in Buildings ... 29

Manures 8, 10

Vegetable Fats and Oils. . 6

Decorators' Books... 3, 4
Decorative Textiles ... 19

Meat Preserving 30
Mineral Pigments 2

Vegetable Preserving . . 30
Warp Sizing ... . . 20

Dental Metallurgy 24

Mineral Waxes 5

Waste Utilisation 9

Detergents 22

Mine Ventilation 24

Water, I ndustrial Use 11,12

Disinfectants 9

Mining, Electricity ... 24

Water-proofing Fabrics ... 20

Driers, Solid and Liquid ... 5

Needlework 19

Waxes 5

Drugs 30

Oil and Colour Recipes ...2,3

Weaving Calculations ... 20

Drying Oils 5

Oil Boiling and Crushing... 5

Weed Killers 28

Drying with Air 11

Oil Colours 3

White Lead and Zinc ... 4

Dyeing 21, 30

Oil Engines 25

White Zinc Paints ... 4

Dyers' Materials 21

Oil Merchants' Manual ... 6

Wiring Calculations ... 28

Dye stuffs 21

Oils ... 5

Wood Distillation ... . 29

Edible Fats and Oils ... 6

Ozone, Industrial Use of... 11

Wood Waste Utilisation!." 29

Electric Lamps 27

Paint Manufacture ... 2

Woollen Goods, Faults ... 20

Electric Wiring 28

Paint Materials 2

Worsted Spinners' Hand-

Electricity in Collieries ... 24

Paint-material Testing ... 4

book ... 20

Emery 32

Paint Mixing 3

Woven Fabrics 20

Enamelling 17

Paper-Mill Chemistry ... 16

Writing Inks 10

Enamels 18

Paper Treatment 16

X-RayWork ... .... 18

Engineering Handbooks 25,26
Engraving 31

Pigments, Chemistry of ... 2
Pipe Bending 27

Yarn Numbering ... ... 17
Yarn Sizing 20

Essential Oils 7

Plumbers' Books 27

Yarn Testing 19

PUBLISHED BY

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THE CHEMISTRY OF PIGMENTS. By ERNEST J. PARRY,
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Primary and Complementary Colours — Coloured Bodies — Absorption Spectra — The Appli=
cation of Pigments. Uses of Pigments: Artistic, Decorative, Protective—Methods of
Application of Pigments: Pastels and Crayons, Water Colour, Tempera Painting, Fresco,
Encaustic Painting, Oil-colour Painting, Keramic Art, Enamel, Stained and Painted Glass,
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tion. Linseed Oil. — Extraction of the Oil — Classification — Mechanical Purification —
Adulteration— Boiled Oil— Preparation of Boiled Oil— An Alternative Process. Varnish.—
A Vehicle and Essential Component — A Reference to Lithography — Baltic Oil — Preparation
of Varnish — The Modern Method — An Old Argument — Letterpress Varnish — A Cheaper
Medium — A Suggestive Recipe — Fire Risks — Gradations of Varnish. Dry Colours. — A
Recommendation — An Endless Variety of Materials — Earth Colours — Mineral Colours —
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— Characteristics — Lake Derivatives — A Point of Importance — Red Lakes — Madder —
Cochineal and Carmine — Brazil Wood— Alizarine a Coaltar Derivative — Yellow Lakes — Blue
Lakes— Green Lakes. The Grinding of Printing: Inks.— Ink-grinding Machinery— Ink-
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of Proportion— Approximate Calculation — Soap — Saturation — Friction Heat — Consistent
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Blues — Working Consistency — Reducing Medium — Letterpress Inks — Gloss Inks — Three-
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Bronzing. — A Brief Justification — Bronze Printing Inks— Bronze Powders — The Process of
Manufacture — Preparation of the Leaf— Grinding and Grading — Bronzing Mediums — Requisite
Qualities — Wax Varnish. "Things Worth Knowing."— A Record of Notes and
Experiences — Index.

(See also Writing- Inks, p. 10.)

THREE HUNDRED SHADES AND HOW TO MIX
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HOUSE DECORATING AND PAINTING By W.

NORMAN BROWN. Eighty-eight Illustrations. 150 pp. Crown 8vo.
Price 3s. 6d. net. (Post free, 3s. 9d. home and abroad.)

A HISTORY OF DECORATIVE ART. By W. NORMAN
BROWN. Thirty-nine Illustrations. 96 pp. Crown 8vo. Price Is. net.
(Post free, Is. 3d. home and abroad.)

PAINTS, COLOURS, ETC.— continued.

WORKSHOP WRINKLES for Decorators, Painters, Paper-
hangers and Others. ByW. N. BROWN. Crown 8 vo. 128pp. Second
Edition. Price 2s. 6d. net. (Post free, 2s. 9d. home; 2s. lOd. abroad.)

CASEIN. By ROBERT SCHERER. Translated from the German
by CHAS. SALTER. Demy 8vo. Illustrated. Second Revised English
Edition. 160 pp. Price 7s. 6d. net. (Post free, 7s. lOd. home ;
8s. abroad.)

SIMPLE METHODS FOR TESTING PAINTERS'
MATERIALS. By A. C. WRIGHT, M.A. (Oxon.), B.Sc.
(Lond.). Crown 8vo. 160 pp. Price 5s. net. (Post free, 5s. 3d.
home; 5s. 6d. abroad.)

IRON - CORROSION, ANTI - FOULING AND ANTI-
CORROSIVE PAINTS. Translated from the German of
Louis EDGAR- ANDES. Sixty-two Illustrations. 275 pp. Demy 8vo.
Price 10s. 6d. net. (Post free, 10s. lOd. home; 11s. 3d. abroad.)

THE TESTING AND VALUATION OF RAW
MATERIALS USED IN PAINT AND COLOUR
MANUFACTURE. By M. W. JONES, RC.S. A Book
for the Laboratories of Colour Works. 88 pp. Crown 8vo. Price
5s. net. (Post free, 5s. 3d. home and abroad.)

THE MANUFACTURE AND COMPARATIVE MERITS
OF WHITE LEAD AND ZINC WHITE PAINTS. By

G. PETIT, Civil Engineer, etc. Translated from the French. Crown 8vo.
100 pp. Price 4s. net. (Post free, 4s. 3d. home ; 4s. 4d. abroad.)

STUDENTS' HANDBOOK OF PAINTS, COLOURS, OILS
AND VARNISHES. By JOHN FURNELL. Crown 8vo. 12
Illustrations. 96 pp. Price 2s. 6d. net. (Post free, 2s. 9d. home and
abroad).

PREPARATION AND USES OF WHITE ZINC PAINTS.

Translated from the French of P. FLEURY. Crown 8vo. 280 pages.
32 Tables. Price 6s. net. (Post free, 6s. 4d. home ; 6s. 6d. abroad.)

Contents.

First Part. Chapters I., General Remarks.— Technical Principles. II., Painting- on
Woodwork.— Ordinary Outside Work— Inside Work. III., Better Class Painting on
Woodwork. IV., Painting on Plaster, on Mortar, and on Soft and Porous Ceilings.
V.. Hints on Painting with White Zinc. VI., Testing Commercial Zinc Whites.
VII., The Experiments of the Dutch Commission Officially Entrusted to make Com-
parative Trials between White Lead and White Zinc. VIII., Results and Criticisms
of the Experiments of the Dutch Commission. Final Report of October 5, 1909.

Second Part. Chapters IX., Manufacture and Different Treatments of White
Zinc— Its Modifications and Improvements. X., The Legislative History of White
Zinc Paint. XL, Legislation. XII., Methods of Qualitative Analysis.— Examination of
Paints. Fixed and Essential Oils. Waxes. Formulas for Encaustic and Waterproof Paints.
Analysis of Paints. White Paints. Analysis of White Lead. Analysis of White Zinc. Blacks.
Red Pigments. Carmine and Lakes. Yellow Colours. Green Pigments. Blue Pigments.
Brown Colours. Analysis of Binders or Liquids. Testing Preservation and Improvement of
Varnishes by Ageing. Analysis of Yellow and White Wax. Selected Furniture Polish Recipe.
Normal Polish for Floors, Parquets, and Woodwork. Virgin Wax Polish for Flattening of
Paints or Polishing of Varnishes. Formulae for a Waterproof Composition for Plaster and
Stone and Damp Walls. Special and More Economical Formulae for Waterproofing Plaster,
Copious Index.

(Varnishes and Drying Oils.)

THE MANUFACTURE OF VARNISHES AND
KINDRED INDUSTRIES. By J. GEDDES MC!NTOSH.
Second, greatly enlarged, English Edition, in three Volumes, based on
and including the work of Ach. Livache.

VOLUME 1.— OIL CRUSHING, REFINING AND BOIL-
ING, THE MANUFACTURE OF LINOLEUM,
PRINTING AND LITHOGRAPHIC INKS, AND
INDIA-RUBBER SUBSTITUTES. Demy 8vo. 150
pp. 29 Illustrations. Price 7s. 6d. net. (Post free, 7s. lOd. home ;
8s. abroad.)

VOLUME II. — VARNISH MATERIALS AND OIL-
VARNISH MAKING. Demy 8vo. 70 Illustrations.
220 pp. Price 10s. 6d. net. (Post free, 10s. lOd. home ; 11s. 3d. abroad.)

VOLUME III. — SPIRIT VARNISHES AND SPIRIT
VARNISH MATERIALS. Demy 8vo. Illustrated.
464pp. Pricel2s.6d.net. (Post free, 13s. home; 13s. 6d. abroad.)

DRYING OILS, BOILED OIL AND SOLID AND
LIQUID DRIERS. By L. E. ANDES. Expressly Written
for this Series of Special Technical Books, and the Publishers hold
the Copyright for English and Foreign Editions. Forty-two Illustra-
tions. 342 pp. Demy Svo. Price 12s. 6d. net. (Post free, 13s. home;
13s. 3d. abroad.)

(Oils, Fats, Waxes, Greases, Petroleum.)

LUBRICATING OILS, FATS AND GREASES: Their
Origin, Preparation, Properties, Uses and Analyses. A Handbook for
Oil Manufacturers, Refiners and Merchants, and the Oil and Fat
Industry in General. By GEORGE H. HURST, F.C.S. Third Revised
and Enlarged Edition. Seventy-four Illustrations. 384 pp. Demy
Svo. Price 10s. 6d. net. (Post free, 11s. home; 11s. 3d. abroad.)

MINERAL WAXES : Their Preparation and Uses. By

RUDOLF GREGORIUS. Translated from the German. Crown Svo. 250

pp. 32 Illustrations. Price 6s. net. (Post free, 6s. 4d. home ; 6s. 6d.

abroad.) Contents.

Ozokerite— Ceresine— Paraffin— Refining Paraffin— Mineral Wax— Appliances for

Extracting, Distilling and Refining Ozokerite— Uses of Ceresine, Paraffin and

Mineral Waxes — Paint and Varnish Removers — Leather and Piston=Rod Greases —

Recipes for Silk, Cotton and Linen Dressings— Candles.

THE PRACTICAL COMPOUNDING OF OILS, TAL-
LOW AND GREASE FOR LUBRICATION, ETC.
By AN EXPERT OIL REFINER. Second Edition. 100 pp. Demy Svo.
Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. abroad.)
Contents.

Introductory Remarks on the General Nomenclature of Oils, Tallow and Greases
suitable for Lubrication — Hydrocarbon Oils — Animal and Fish Oils — Compound
Oils— Vegetable Oils— Lamp Oils— Engine Tallow, Solidified Oils and Petroleum
Jelly — Machinery Greases: Loco and Anti-friction — Clarifying and Utilisation
of Waste Fats, Oils, Tank Bottoms, Drainings of Barrels and Drums, Pickings
Up, Dregs, etc.— The Fixing and Cleaning of Oil Tanks, etc.— Appendix and
General Information.

THE MANUFACTURE OF LUBRICANTS, SHOE
POLISHES AND LEATHER DRESSINGS. By

RICHARD BRUNNER. Translated from the Sixth German Edition by
CHAS. SALTER. 10 Illustrations. Crown Svo. 170 pp. Price 7s. 6d.
net. (Post free, 7s. lOd. home; 8s. abroad.)

6

THE OIL MERCHANTS' MANUAL AND OIL TRADE
READY RECKONER. Compiled by FRANK F. SHERRIFF.
Second Edition Revised and Enlarged. Demy 8vo. 214 pp. 1904.
With Two Sheets of Tables. Price 7s. 6d. net. (Post free, 7s. lOd.
home ; 8s. 3d. abroad.)

ANIMAL FATS AND OILS: Their Practical Production,
Purification and Uses for a great Variety of Purposes. Their Pro-
perties, Falsification and Examination. Translated from the German
of Louis EDGAR. ANDES. Sixty-two Illustrations. 240 pp. Second
Edition, Revised and Enlarged. Demy 8vo. Price 10s. 6d. net.
(Post free, 10s. lOd. home ; 11s. 3d. abroad.)

VEGETABLE PATS AND OILS: Their Practical Prepara-
tion, Purification and Employment for Various Purposes. Their Proper-
ties, Adulteration and Examination. Translated from the German of
Louis EDGAR ANDES. Ninety-four Illustrations. 340 pp. Second
Edition. Demy 8vo. Price 10s. 6d. net. (Post free, Us. home;
11s. 6d. abroad.)

EDIBLE FATS AND OILS : Their Composition, Manufacture
and Analysis. By W. H. SIMMONS, B.Sc. (Lond.), and C. A. MITCHELL,
B.A. (Oxon.). Demy 8vo. 150 pp. Price 7s. 6d. net. (Post free,
7s. 9d. home; 8s. abroad.)

Contents.

Introduction. — Physiological Considerations— Constitution of Fats and Oils — Trygly-
ceride — Glyceride — Butyrin — Isovalerin — Caproin — Caprylin — Caprin — Laurin — Myristin —
Palmitin — Stearin — Olein— Ricinolein — Stearic Acid Series — Oleic Acid Series— Linolic Acid
Series — Linolenic Acid Series — Ricinolenic Acid Series. Raw Materials used in the Manu-
facture Of Edible Pats and Oils.— Tallow— Mutton— Beef— Lard— Lard Oil— Cocoanut Oil
— Maize Oil — Cotton-seed Oil — Cotton-seed Stearine — Olive Oil — Arachis Oil (Earthnut or
Pea-nut Oil)— Sesame Oil— Palm Nut Oil (Palm Kernel Oil)— Sunflower Seed Oil— Cacao
Butter or Oil of Theobroma— Palm Oil— Soya Bean Oil— Shea Butter— Mowrah-seed Oil—
Margosa Oil. Bleaching, Deodorising, and Refining Fats and Oils.— Physical Methods
— Washing, Freezing, Filtration, Treatment, Steaming — Removal of Stearines — Methods of
Filtration — Chemical Methods — Caustic Soda — Sodium Carbonate — Alkaline Earths — Fre-
senius — Bleaching of Oils — Charcoal— Fullers' Earth — Ozone — Hydrosulphites — Sodium Bi-
sulphite— Sodium Hydrosulphite Formaldehyde — Organic Peroxides — Deodorisation of Fats —
Treatment of Rancid Fats. Butter.— Butter Fat— Water— Salt— Curd— Keeping Properties
of Butter — Rancidity of Butter — Renovated Butter — Preservatives in Butter — Physical Char-
acteristics— Solubility — Refractorative Examination— Chemical Characteristics— Hehner &
Reichert Values — Influence of the Food of the Cows — Cocoanut Oil in Butter— Artificial
Colouring Matters. Lard. — Lard Oil — Rendering of Lard — Commercial Grades : (1) Neutral
Lard ; (2) Leaf Lard ; (3) Choice Steam Lard or Choice Lard ; (4) Prime Steam Lard ; (5) Guts
— Lard Crystals— Influence of Food— Acidity of Lard— Water— Polenske— The Iodine Value—
—Lard Oil. Margarine and Other Butter Substitutes.— Margarine, Oleomargarine or
Artificial Butter — Invention and Development — Modern Processes and Formulae — Vegetable
Butter — Modern Process —Vegetable Butter — Palm Oil. Salad Oils. — Oils used for Culinary
and Confectionery Purposes — Chocolate Fats — Olive Oils— Sesame Oil — Cotton-seed Oil —
Sunflower Oil — Poppy Oil — Maize Oil -Chocolate Fats — Cocoanut and Palm Kernel Oil Stear-
ines-Other Vegetable Fats. Analysis of Raw Materials and Finished Products.— Raw
Materials — Specific Gravity — Free Fatty Acids — Saponification Value — Saponification Equiv-
alent— Iodine Absorption — Wij's Method — Bromine Absorption -Titer or Solidifying of the
Fatty Acids— Refractive Index— Unsaponifiable Matter— Valenta's Acetic Acid Test— Mau-
mene's Test— Bromine Thermal Value— Baudouin's Test— Tocher's Test— Olive Oil— Cotton-
seed Oil — Halphen's Test — Arachis Oil — Butter — Water — Examination of the Fat — Refractive
Power- Soluble and Insoluble Fatty Acids — Insoluble Fatty Acids — Casein— Curd — Colouring
Matters — Boron Compounds — Fluorides — Margarine, Vegetable Butter or other Butter Sub-
stitutes— Lard — Cheese — Water — Ash — Fat — Nitrogen — Chocolate — Unsweetened Chocolate
— Sweetened Chocolate — Granulated or Ground Chocolate — Chocolate Covered Goods — Milk
Chocolate Fat — Palm-nut Stearine — Dika or Gaboon Fat — Borneo Tallow or Tankawang Fat
— Illipe Fat— Fibre— Total Nitrogen— Sugar. Statistics of the Trade in Edible Oils.—
United Kingdom Trade— Exports— Italian Trade in Olive Oil— Spanish Oil Trade— Vegetable
Oil Trade of France — Cotton-seed Oil in the United States.

(Glycerine.)

GLYCERINE. By T. W. KOPPE. Translated from the Second
German Edition. Crown 8vo. 260 pp. 7 Illustrations. Price 7s. 6d.
net. (Post free, 7s. lOd. home; 8s. abroad.) [Just Published.

(Essential Oils and Perfumes.)

THE CHEMISTRY OF ESSENTIAL OILS AND ARTI-
FICIAL PERFUMES. By ERNEST J. PARRY, B.Sc.
(Lond.), F.I.C., F.C.S. Second Edition, Revised and Enlarged. 552 pp.
20 Illustrations. Demy 8vo. Price 12s. 6d. net. (Post free, 13s. home;
13s. 6d. abroad.)

(Soap Manufacture and Glycerine.)

SOAPS. A Practical Manual of the Manufacture of Domestic,
Toilet and other Soaps. By GEORGE H. HURST, F.C.S. 390 pp.
66 Illustrations. Demy 8vo. Second Edition. Price 12s. 6d. net.
(Post free, 13s. home ; 13s. 6d. abroad.)

TEXTILE SOAPS AND OILS. Handbook on the Prepara-
tion, Properties and Analysis of the Soaps and Oils used in Textile
Manufacturing, Dyeing and Printing. By GEORGE H. HURST, F.C.S.
Second Edition. Revised and Partly Re-written by W. H. SIMMONS,
B.Sc. (Lond.). Demy 8vo. 200pp. 11 Illustrations. Price7s.6d.net.
(Post free, 7s. lOd. home ; 8s. abroad.)

THE HANDBOOK OF SOAP MANUFACTURE. By

' WM. H. SIMMONS, B.Sc. (Lond.), F.C.S. and H. A. APPLETON. Demy
Svo. 160 pp. 27 Illustrations. Price 8s. 6d. net. (Post free, 8s. lOd.
home ; 9s. abroad.)

Contents.

Definition of Soap.— Properties— Hydrolysis— Detergent Action. Constitution of Oils
and Fats, and their Saponification. — Researches of Chevreul and Berthelot— Mixed
Glycerides — Modern Theories of Saponification — Hydrolysis accelerated by (1) Heat or
Electricity. (2) Ferments, Castor-seed Ferment. Steapsin Emulsin and (3) Chemical
Reagents, Sulphuric Acid, TwitchelPs Reagent, Hydrochloric Acid, Lime, Magnesia, Zinc
Oxide, Soda and Potash. Raw Materials used in Soap-making.— Fats and Oils— Waste
Fats — Fatty Acids — Less-known Oils and Fats of Limited Use — Various New Fats and Oils
Suggested for Soap-making — Rosin — Alkali (Caustic and Carbonated) — Water — Salt Soap-
stock. Bleaching and Treatment of Raw Materials Intended for Soap-making. —
Palm Oil— Cottonseed Oil— Cottonseed "Foots"— Vegetable Oils— Animal Fats— Bone Fat-
Rosin. Soap= making. — Classification of Soaps — Direct combination of Fatty Acids with
Alkali — Cold Process Soaps — Saponification under Increased or Diminished Pressure — Soft
Soap — Marine Soap — Hydrated Soaps, Smooth and Marbled — Pasting or Saponification —
Graining Out — Boiling on Strength — Fitting — Curd Soaps — Curd Mottled — Blue and Grey
Mottled Soaps — Milling Base — Yellow Household Soaps — Resting of Pans and Settling of
Soap — Utilisation of Nigres — Transparent Soaps — Saponifying Mineral Oil — Electrical Pro-
duction of Soap. Treatment of Settled Soap. — Cleansing — Crutching — Liquoring of Soaps
— Filling — Neutralising, Colouring and Perfuming — Disinfectant Soaps — Framing — Slabbing
— Barring — Open and Close Piling — Drying — Stamping — Cooling. Toilet, Textile and
Miscellaneous Soaps.— Toilet Soaps— Cold Process Soaps— Settled Boiled Soaps— Remelted
Soaps— Milled Soaps — Drying, Milling and Incorporating Colour, Perfumes, or Medicaments
— Perfumes — Colouring Matter — Neutralising and Super-fatting Material — Compressing —
Cutting — Textile Soaps — Soaps for Woollen, Cotton and Silk Industries — Patent Textile
Soaps — Stamping — Medicated Soaps — Ether Soap — Floating Soaps — Shaving Soaps —
Miscellaneous Soaps. Soap Perfumes. — Essential Oils — Source and Preparation — Properties
—Artificial and Synthetic Perfumes. Glycerine Manufacture and Purification.— Treat-
ment of Lyes — Evaporation — Crude Glycerine — Distillation — Distilled and Dynamite
Glycerine — Chemically Pure Glycerine — Animal Charcoal for Decolorisation — Glycerine
resultant from other methods of Saponification — Yield of Glycerine from Fats and Oils.
Analysis of Raw Materials, Soap and Glycerine.— Fats and Oils— Alkalies and Alkali
Salts — Essential Oils — Soap — Lyes — Crude Glycerine. Statistics of the Soap Industry.
Appendix A. — Comparison of Degrees Twaddell, Beaume and Actual Densities.
Appendix B. — Comparison of Different Thermometric Scales. Appendix C. — Table of
the Specific Gravities of Solutions of Caustic Soda. Appendix D.— Table of Strength
of Caustic Potash Solutions at 60° F. Index.

MANUAL OF TOILET SOAPMAKING, including Medi-
cated Soaps, Stain-removing Soaps, Metal Polishing Soaps, Soap
Powders and Detergents. Translated from the German of Dr. C.
DEITE. Demy 4to. 150 pages. 79 Illustrations. Price 12s. 6d. net.
(Post free, 13?. home; 13s. 6d. abroad.)

8

(Cosmetical Preparations.)

COSMETICS : MANUFACTURE, EMPLOYMENT
AND TESTING OP ALL COSMETIC MATERIALS
AND COSMETIC SPECIALITIES. Translated
from the German of Dr. THEODOR ROLLER. Crown 8vo. 262 pp.
Price 5s. net. (Post free, 5s. 4d. home ; 5s. 6d. abroad.)

(Glue, Bone Products and Manures.)

GLUE AND GLUE TESTING. By SAMUEL RIDEAL, D.Sc.
(Lond.). Second Edition, Revised and Enlarged. Demy 8vo. 196 pp.
14 Illustrations. Price 10s. 6d. net. (Post free, 10s. lOd. home; 11s.
abroad.)

BONE PRODUCTS AND MANtJRES : An Account of the
most recent Improvements in the Manufacture of Fat, Glue, Animal
Charcoal, Size, Gelatine and Manures. By THOMAS LAMBERT. Second
Revised Edition. Demy Svo. 172 pp. 17 Illustrations. Price 7s. 6d.
net. (Post free, -7s. lOd. home ; 8s. abroad.)

(See also Chemical Manures, p. 10.)

(Chemicals, Waste Products, etc.)

REISSUE OF CHEMICAL ESSAYS OF C. W.
SCHEELE. First Published in English in 1786. Trans-
lated from the Academy of Sciences at Stockholm, with Additions. 300
pp. Demy Svo. Price 5s. net. (Post free, 5s. 6d. home ; 5s. 9d. abroad.)
Contents.

Memoir : C. W. Scheele and his work (written for this edition by J. G. Mclntosh) — On
Fluor Mineral and its Acid — On Fluor Mineral — Chemical Investigation of Fluor Acid,
with a View to the Earth which it Yields, by Mr. Wiegler — Additional Information
Concerning Fluor Minerals — On Manganese, Magnesium, or Magnesia Vitrariorum — On
Arsenic and its Acid — Remarks upon Salts of Benzoin — On Silex, Clay and Alum — Analysis
of the Calculus Vesical — Method of Preparing Mercurius Dulcis Via Humida — Cheaper and
more Convenient Method of Preparing Pulvis Algarothi — Experiments upon Molybdaena
— Experiments on Plumbago — Method of Preparing a New Green Colour— Of the De-
composition of Neutral Salts by Unslaked Lime and Iron — On the Quantity of Pure Air which
is Daily Present in our Atmosphere — On Milk and its Acid — On the Acid of Saccharum Lactis
—On the Constituent Parts of Lapis Ponderosus or Tungsten— Experiments and Observations
on Ether — Index.

THE MANUFACTURE OF ALUM AND THE SUL-
PHATES AND OTHER SALTS OF ALUMINA AND
IRON. Their Uses and Applications as Mordants in Dyeing
and Calico Printing, and their other Applications in the Arts, Manufac-
tures, Sanitary Engineering, Agriculture and Horticulture. Translated
from the French of LUCIEN GESCHWIND. 195 Illustrations. 400 pp.
Royal Svo. Price 12s. 6d. net. (Post free, 13s. home; 13s. 6d. abroad.)

AMMONIA AND ITS COMPOUNDS : Their Manufacture
and Uses. By CAMILLE VINCENT, Professor at the Central School of
Arts and Manufactures, Paris. Translated from the French by M. J.
SALTER. Royal Svo. 114 pp. Thirty-two Illustrations. Price 5s. net.
(Post free, 5s. 4d. home ; 5s. 6d. abroad.)

CHEMICAL WORKS : Their Design, Erection, and Equip-
ment. By S. S. DYSON and S. S. CLARKSON. Royal Svo. 220 pp.
With 9 Folding Plates and 80 Illustrations. Price 21s. net. (Post
free, 21s. 6d. home; 22s. abroad.)

MANUAL OP CHEMICAL ANALYSIS, as applied to the

Assay of Fuels, Ores, Metals, Alloys, Salts and other Mineral Products.
By E. PROST, D.Sc. Translated by J. CRUICKSHANK SMITH, B.Sc.
Royal 8vo. 300 pages. 44 Illustrations. Price 12s. 6d. net. (Post
free, 13s. home ; 13s. 6d. abroad.)

TESTING OF CHEMICAL REAGENTS FOR PURITY.

Translated from the German of Dr. C. KRAUCH. Royal 8vo. 350 pages.
Price 12s. 6d. net. (Post free, 13s. home ; 13s. 6d. abroad.)

SHALE OILS AND TARS and their Products. By Dr. W.

SCHEITHAUER. Translated from the German. Demy 8vo. 190 pp.

70 Illustrations and 4 Diagrams. Price 8s. 6d. net. (Post free, 8s. lOd.

home; 9s. abroad.)

Contents.

Chapters I., History of the Shale and Lignite-tar Industry. II., The Bituminous
Raw Materials. — Occurrence — Origin — Properties and Composition — Working — Utilization.
III., The Production of Distillation Tar.— The Dry-distillation Process— The Winning of
Lignite Tar — The Messel Tar Industry — The Recovery of Shale Tar in Scotland. IV., The
Distillation Products.— The Tar— The Tar Water (Ammonia Liquor)— Gas— The Distillation
Residues. V., The Distillation of the Tar and Tar Oils.— The Distillation Process— Tar
Distilling in the Saxon-Thuringian Industry— The Messel Distillation Process— The Distilla-
tion Process in the Scottish Industry. VI., I. Chemical Treatment of the Tar and its
Distillates. — The Refining Process — The Refining Process in the Saxon-Thuringian Industry
— Refining Process in the Messel Industry — Refining Process in the Scottish Industry.
II. The Utilization of the Refinery Waste.— Uses and Treatment. VII., The Manu-
facture of Paraffin. — The Manufacture of Paraffin in the Saxon-Thuringian Industry —
Manufacture of Paraffin in the Messel Industry — Paraffin Manufacture in the Scottish
Industry. VIII., Products Furnished by Shale Oil and Lignite=Tar. IX., Candle-
making.— The Raw Materials— The Candle Material— The Wick— The Colouring Matters.
The Manufacture — The Moulding Process — Finishing — Packing the Candles — Working up
Candle Waste. X., Chemical Composition of the Tars and their Distillates.— Lignite
Tar— Shale Tar. XL, The Laboratory Work.— Testing the Raw Materials— Testing the
Tars and other Distillation Products— Testing the Tar Oils— Testing the Reagents used for
Refining the Oils and Paraffin— Testing the Paraffin— Tests Applied in Candle Works— Test-
ing the By-Products of Tar Distillation. XII., Statistics. Index.

THE BY-PRODUCTS OF COAL-GAS MANUFACTURE.

By K. R. LANGE. Translated from the German. Crown 8vo. 164 pages.
13 Illustrations. Price 5s. net. (Post free, 5s. 4d. home ; 5s. 6d. abroad.)

[Just published.

INDUSTRIAL ALCOHOL. A Practical Manual on the
Production and Use of Alcohol for Industrial Purposes and for Use as
a Heating Agent, as an Illuminant and as a Source of Motive Power.
By J. G. MclNTOSH. Demy 8vo. 1907. 250 pp. With 75 Illustra-
tions and 25 Tables. Price 7s. 6d. net. (Post free, 7s. lOd. home;
8s. 3d. abroad.)

THE UTILISATION OF WASTE PRODUCTS. A Treatise
on the Rational Utilisation, Recovery and Treatment of Waste Pro-
ducts of all kinds. By Dr. THEODOR ROLLER. Translated from the
Second Revised German Edition. Second English Revised Edition.
Demy 8vo. 336 pages. 22 Illustrations. Price 7s. 6d. net. (Post free,
8s. home; 8s. 6d. abroad.) [Just published.

ANALYSIS OF RESINS AND BALSAMS. Translated
from the German of Dr. KARL DIETERICH. Demy 8vo. 340 pages.
Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. 3d. abroad.)

DISTILLATION OF RESINS, RESINATE LAKES AND
PIGMENTS, CARBON PIGMENTS AND PIGMENTS
FOR TYPEWRITING MACHINES, MANIFOLDERS,
ETC. By VICTOR SCHWEIZER. Demy 8vo. 185 pages.
68 Illustrations. Price 7s. 6d. net. (Post free, 8s. home ; 8s. 3d. abroad.)

DISINFECTION AND DISINFECTANTS. By M. CHRIS-
TIAN. Translated from the German. Crown 8vo. 112 pages. 18 Illus-
trations. Price 5s. net. (Post free, 5s. 3d. home ; 5s. 6d. abroad.)

10

(Agricultural Chemistry and Manures.)

MANUAL OF AGRICULTURAL CHEMISTRY. By

HERBERT INGLE, F.I. C.,F.C.S., Late Lecturer on Agricultural Chemistry,
the Leeds University ; Lecturer in the Victoria University. Third
and Revised Edition. 400 pp. 16 Illustrations. Demy 8vo. Price
7s. 6d. net. (Post free, 8s. home ; 8s. 6d. abroad.)
Contents.

The Atmosphere — The Soil — The Reactions occurring in Soils — The Analysis and Com-
position of Soils— Manuring and General Manures — Special Manures — Application of Manures
— The Analysis and Valuation of Manures — The Chemical Constituents of Plants — The Plant
—Crops— The Animal— Foods and Feeding— Milk and Milk Products— The Analysis of Milk
and Milk Products — Miscellaneous Products used in Agriculture — Appendix — Index.

(For Insecticides, Fungicides and Weed Killers, see p. 28.)

CHEMICAL MANURES. By J. FRITSCH. Translated from
the French, with numerous Notes. Demy 8vo. 350 pp. 69 Illustra-
tions and 108 Tables. Price 10s. 6d. net. (Post free, 11s. home;
11s. 6d. abroad.)

Contents.

History — Origin and Distribution of Phosphoric Acid in Nature — Properties of Phos-
phorus— Principal Phosphate Deposits — Drying and Enrichment of Phosphates — Historical
Review of Superphosphate Manufacture — Theory of Manufacture of Soluble Phosphates —
Manufacture of Superphosphate — Crushing, Sifting, Drying, and Storing of Superphosphate
— Retrogradatton — Compound Manures — The Manufacture of Phosphoric Acid, Double
Superphosphates, and Various Products — The Manufacture of Phosphorus in the Electric
Furnace — Manufacture of Bone Dust and of Bone Superphosphate (Vitriolized Bones) —
Manufacture of Basic Slag — Nitrogenous Manures — Manufacture of Manure from Animal
Waste — Recovery of Nitrogen from Distillery By-Products — Manufacture of Cyanamide and
of Nitrate of Lime — Nitrogenized Phosphatic Manures — Potassic Manures — Transference
and Handling of Raw Materials and Finished Products.

(See also Bone Products and Manures, p. 8.)

(Writing Inks and Sealing Waxes.)

INK MANUFACTURE : Including Writing, Copying, Litho-
graphic, Marking, Stamping, and Laundry Inks. By SIGMUND LEHNER.
Translated from the German of the Fifth Edition. Second Revised and
Enlarged English Edition. Crown 8vo. 180 pages. 3 Illustrations.
Price 5s. net. (Post free, 5s. 3d. home; 5s. 6d. abroad.)

SEALING-WAXES, WAFERS AND OTHER ADHES-
IVES FOR THE HOUSEHOLD, OFFICE, WORK-
SHOP AND FACTORY. By H. C. STANDAGE. Crown
8vo. 96 pages. Price 5s. net. (Post free, 5s. 3d. home ; 5s. 4d. abroad.)

(Lead Ores and Lead Compounds.)

LEAD AND ITS COMPOUNDS. By THOS. LAMBERT,
Technical and Consulting Chemist. Demy 8vo. 226 pp. Forty Illus-
trations. Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. 3d. abroad.)

NOTES ON LEAD ORES : Their Distribution and Properties.
By JAS. FAIRIE, F.G.S. Crown 8vo. 64 pages. Price Is. net. (Post
free, Is. 3d. home; Is. 4d. abroad.)

(White Lead and Zinc White Paints, see p. 4.)

11
(Industrial Hygiene.)

THE RISKS AND DANGERS TO HEALTH OP VARI-
OUS OCCUPATIONS AND THEIR PREVENTION.

By LEONARD A. PARRY, M.D., B.Sc. (Lond.). 196 pp. Demy 8vo.
Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. abroad.)

(Industrial Uses of Air, Steam and Water.)

DRYING BY MEANS OF AIR AND STEAM. Explana-
tions, Formulae, and Tables for Use in Practice. Translated from the
German of E. HAUSBRAND. Second Revised English Edition. Crown
8vo. 80 pp. Two folding Diagrams and Thirteen Tables. Price 5s. net.
(Post free, 5s. 3d. home ; 5s. 6d. abroad.)

Contents.

The Metric and British Systems Compared — Comparison between Fahrenheit and Centi-
grade Thermometers. Chapters I. Introduction and Lists of Symbols — II. Calculations of
the Maximum Weight of Saturated Aqueous Vapour which can be contained in 1 kilo, of Air
at different Pressures and Temperatures — III. Calculation of the necessary Weight and
Volume of Air, and of the least Expenditure of Heat, for Drying Apparatus with Heated Air, at
Atmospheric Pressure — (a) With the assumption that the Air is completely saturated
with Vapour both before entry and at its exit from the Apparatus — (b) When the Atmos-
pheric Air is completely saturated before entry, but at its exit is only f, ^ or J saturated
with moisture — (c) When the Atmospheric Air is not saturated with Water Vapour before
entering the Drying Apparatus. IV. Drying Apparatus in which, in the Drying Chamber, a
Pressure, higher or lower than that of the Atmosphere, is Artificially Maintained — V.
Drying by means of Superheated Steam svithout Air — VI. Heating Surface, Velocity of the
Air Current, Dimensions of the Drying Room, Surface of the Drying Material, Losses of
Heat — Index.

List of Tables.

I. Pressures and weights of 1 cubic metre of saturated water vapour and of dry air —
The weight of water in 1 kilo, of air at the absolute (barometric) pressures of 250, 500, 740,
760, 780 and 1,140 mm., and at temperatures from- 20° to + 100° C., when the air is completely
saturated with vapour. II. Weight and volume of air, outlet temperature of air and
expenditure of heat required to evaporate 100 kilos, of water when the external tempera-
ature is - 20° to+ 30° C., the maximum temperature is 30° to 130° C., the barometric pressure
is 760 mm. The external air and the air at its exit are both completely saturated with water
vapour. III. Pressures and weights of 1 cubic metre off, i and J saturated water vapour and
of the accompanying dry air — The weights of f , \ and \ saturated vapour contained in 1
kilo, of air, with the barometer at 760 mm., and at temperatures from - 20° to + 100° C.
IV., V. and VI. Weight and volume of air, temperature of exit and expenditure of heat
required to evaporate 100 kilos, of water when the external temperature is - 20° to 4- 30° C.,
the maximum te'mperature is 35°, 50°, 70°, 100° and 130° C., the external air is completely
saturated and the emergent air is only f , J and \ saturated with water vapour — Also expendi-
ture of heat when the external air is | saturated. VII. Temperatures at which the air would
be completely saturated with water if it is only f , J or J saturated by the same quantity of
water at certain higher temperatures. VIII., IX. and X. The weight and volume of air, tem-
perature of exit and expenditure of heat required to evaporate lOO kilos, of water when the
external temperature is - 20°, 0° and + 30° C., the maximum temperature is 35°, 50°, 70°, 100°
and 130° C., and both external and emergent air are completely saturated with water
vapour. VIII. The absolute pressure is 1,140 mm. (H atmos.) 50. IX. The absolute pressure
is 500 mm. (H atmos.) 51. X. The absolute pressure is 250 mm. (1£ atmos.) 52. XI. The
weights of steam and their volumes, before and after heating required to evaporate 100
kilos, of water in the circuit drying apparatus, without air, at absolute pressures of 148
to 2,660 mm., and with maximum temperature of 65° to 200° C. XII. The quantities of
heat given up by 1 square metre of the source of heat in 1 hour when the external air is
at - 20° to + 30° C., the source of heat is at 100° to 140° C., the heated air is at 35° to 130°
C., and the air current passes over the heating surface with a velocity of 1 to 6 metres per
second. XIII. Losses of heat, in calories, by drying apparatus in one hour from 1 square
metre of masonry, wooden wall or simple window at temperature differences between
interior and exterior of 5° to 100° C.

(See also " Evaporating, Condensing and Cooling Apparatus," p. 25.)

PURE AIR, OZONE AND WATER. A Practical Treatise
of their Utilisation and Value in Oil, Grease, Soap, Paint, Glue and
other Industries. By W. B. COWELL. Twelve Illustrations. Crown
8vo. 85 pp. Price 5s. net. (Post free, 5s. 3d. home ; 5s. 6d. abroad.)

12

THE INDUSTRIAL USES OF WATER. COMPOSI-
TION — EFFECTS— TROUBLES — REMEDIES— RE-
SIDUARY WATERS— PURIFICATION— ANALYSIS.

By H. DE LA Coux. Royal 8vo. Translated from the French and
Revised by ARTHUR MORRIS. 364 pp. 135 Illustrations. Price 10s. 6d.
net. (Post free, lls. home; 11s. 6d. abroad.)
Contents.

Chemical Action of Water in Nature and in Industrial Use — Composition of Waters —
Solubility of Certain Salts in Water Considered from the Industrial Point of View — Effects on
the Boiling of Water — Effects of Water in the Industries — Difficulties with Water — Feed
Water for Boilers — Water in Dyeworks, Print Works, and Bleach Works — Water in the
Textile Industries and in Conditioning — Water in Soap Works — Water in Laundries and
Washhouses — Water in Tanning — Water in Preparing Tannin and Dyewood Extracts — Water
in Papermaking — Water in Photography — Water in Sugar Refining — Water in Making Ices
and Beverages — Water in Cider Making — Water in Brewing — Water in Distilling — Preliminary
Treatment and Apparatus — Substances Used for Preliminary Chemical Purification — Com-
mercial Specialities and their Employment — Precipitation of Matters in Suspension in Water
— Apparatus for the Preliminary Chemical Purification of Water — Industrial Filters — Indus-
trial Sterilisation of Water — Residuary Waters and their Purification — Soil Filtration —
Purification by Chemical Processes— Analyses— Index.

(See Books on Smoke Prevention, Engineering and Metallurgy, p. 24, etc )

(X-Rays.)

PRACTICAL X RAY WORK. By FRANK T. ADDYMAN,
B.Sc. (Lond.), F.I.C., Member of the Roentgen Society of London;
Radiographer to St. George's Hospital ; Demonstrator of Physics and
Chemistry, and Teacher of Radiography in St. George's Hospital
Medical School. Demy 8vo. Twelve Plates from Photographs of X Ray
Work. Fifty-two Illustrations. 200 pp. Price 10s. 6d. net. (Post free,
10s. lOd. home ; lls. 3d. abroad.)

Contents.

Historical — Work leading up to the Discovery of the X Rays — The Discovery — Appara-
tus and its Management — Electrical Terms — Sources of Electricity — Induction Coils —
Electrostatic Machines — Tubes — Air Pumps — Tube Holders and Stereoscopic Apparatus —
Fluorescent Screens— Practical X Ray Work— Installations— Radioscopy— Radiography—
X Rays in Dentistry — X Rays in Chemistry — X Rays in War — Index.

List of Plates.

Frontispiece — Congenital Dislocation of Hip-Joint. — I., Needle in Finger. — II., Needle in
Foot.— III., Revolver Bullet in Calf and Leg.— IV., A Method of Localisation.— V., Stellate
Fracture of Patella showing shadow of "Strapping". — VI., Sarcoma. — VII., Six-weeks-old
Injury to Elbow showing new Growth of Bone. — VIII., Old Fracture of Tibia and Fibula
badly set.— IX., Heart Shadow.— X., Fractured Femur showing Grain of Splint.— XI.. Bar-
rell's Method of Localisation.

(India=Rubber and Qutta Percha.)

INDIA-RUBBER AND GUTTA PERCHA. Second

English Edition, Revised and Enlarged. Based on the French work of
T. SEELIGMANN, G. LAMY TORRILHON and H. FALCONNET, by JOHN
GEDDES MC!NTOSH. Royal 8vo. 100 Illustrations. 400 pages. Price
12s. 6d. net. (Post free, 13s. home ; 13s. 6d. abroad.)
Contents.

India- Rubber.— Indiarubber, Latex— Definitions— Laticiferous Vessels— Botanical Origin
— Habitats — Methods of obtaining the Latex — Methods of Preparing Raw or Crude India-
rubber — Rubber Cultivation in Various Countries — Climatology — Soil — Rational Culture and
Acclimatisation of the Different Species of Indiarubber Plants — Classification of the Com-
mercial Species of Raw Rubber— Physical and Chemical Properties of the Latex and of
Indiarubber — General Considerations — Mechanical Transformation of Natural Rubber into
Washed or Normal Rubber (Purification)— Softening, Cutting, Washing, Drying, Storage-
Mechanical Transformation of Normal Rubber into Masticated Rubber — Vulcanisation of
Normal Rubber— Chemical and Physical Properties of Vulcanised Rubber— Hardened Rubber
or Ebonite— Considerations on Mineralisation and Other Mixtures — Coloration and Dyeing —
Analysis of Natural or Normal Rubber and Vulcanised Rubber — Rubber Substitutes —
Imitation Rubber — Analysis of Indiarubber.

Qutta Percha. — Definition of Gutta Percha — Botanical Origin — Habitat — Climatology —
Soil— Rational Culture— Methods of Collection— Felling and Ringing versus Tapping— Extrac-
tion of Gutta Percha from Leaves by Toluene, etc. — Classification of the Different Species of
Commercial Gutta Percha— Physical and Chemical Properties of Gutta Percha— Mechanical
Treatment of Gutta Percha — Methods of Analysing utta Percha — Gutta Percha Substitute

13

(Leather Trades.)

THE LEATHER WORKER'S MANUAL. Being a Com-
pendium of Practical Recipes and Working Formulae for Curriers,
Bootmakers, Leather Dressers, Blacking Manufacturers, Saddlers,
Fancy Leather Workers. By H. C. STANDAGE. Demy 8vo. 165 pp.
Price 7s. 6d. net. (Post free, 7s. lOd. home; 8s. abroad.)

Contents.

Blackings, Polishes, Glosses, Dressings, Renovators, etc., for Boot and Shoe Leather-
Harness Blackings, Dressings, Greases, Compositions, Soaps, and Boot-top Powders and
Liquids, etc., etc. — Leather Grinders' Sundries — Currier's Seasonings, Blacking Compounds,
Dressings, Finishes, Glosses, etc. — Dyes and Stains for Leather — Miscellaneous Information
— Chrome Tannage — Index.

(See also Manufacture of Shoe Polishes, Leather Dressings, etc., p. 5.)

(Pottery, Bricks, Tiles, Glass, etc.)

MODERN BRICKMAKING. By ALFRED B. SEARLE. Royal
8vo. 440 pages. 260 Illustrations. Price 12s. 6d. net. (Post free,
13s. home ; 13s. 6d. abroad.)

Contents.

Nature and Selection of Clays. — Lake and River Deposited Clays— Rock Clays— Shale
—Fire-clay. The Colour of Bricks.— Marls— White, Yellow, and Red Bricks— Terra-cotta—
Blue Bricks. General Characteristics of Bricks.— Fletton, Bath, and Accrington Bricks
—London Stocks— Plastic Bricks— Sand-faced Bricks— Glazed Bricks— Fire Bricks— Qualities
of Bricks. Sand, Breeze, and other Materials. — Chalk-water — General Manufacture of
Bricks— Clay-washing— Haulage— rland-Brickmaking— Preparation of the Paste— Pugging
— Slop-moulding — Sand-moulding — Drying — Shrinking — Pressing — Clamp Kilns — Firing a
Clamp. Plastic Moulding by Machinery.— Wire-cut Bricks— Brick Machines and Plant-
Crushing Rolls— Grinding Mills— Wet Pans. Mixers and Feeders.— Pug-mills, Mouthpiece
Presses, and Auger Machines — Expression Roller Machines — Cutting Tables — Repressing —
Screw Presses— Eccentric Represses— Die- Boxes. Drying. —Transport. Stiff -plastic
Process. — Mill Feeding Machines — Grinding Mills — Elevating — Screens — Sieves — Revolving
Screens — Stiff-plastic Brickmaking Machines— Repressing— Carrying-off— Drying— Kilns.
Semi = Dry or Semi-Plastic Process.— Lamination— Drying Troubles— Moulds and Arrises.
The Dry or Dust Process.— Lamination. Kilns.— Down-draught Kilns— Horizontal-draught
Kilns— Continuous Kilns— Up-draught Kilns— Newcastle Kiln— Gas-fired Kilns— Semi-con-
tinuous Kilns — Hoffmann Kilns — Hot-air Flues — Temporary and Permanent Flues — Chamber
Kilns— Steam— Draught— Mechanical Draught— Gas-fired Continuous Kilns— Muffle Kilns-
Kiln Construction.— Choice of Bricks— Foundations— Construction of Arches and Crowns-
Fire Boxes— Feed-holes— Chimneys— Selecting a Kiln. Setting and Burning.— Up-draught
and Down-draught Kilns— Horizontal-draught or Continuous Kiln— Glazed Bricks. Firing.—
Drying or Steaming — Volatilization — Full Fire — Smoking — Seger Cones — Draught Gauge —
Cooling. Vitrified Bricks for Special Work.— Clinkers and Paving Bricks— Acid-proof
Bricks. Fire-Bricks and Blocks.— Materials— Grog— Grindipg— Blocks— Drying— Dipped
Fire-bricks— Firing — Silica Bricks— Canister Bricks— Bauxite and Magnesia Bricks —
Neutral Fire-bricks. Glazed Bricks.— Pressing— Dipping— Glazes— Coloured Glazes— Ma-
jolica Glazes— Firing— Salt-glazed Bricks. Perforated, Radial, and Hollow Bricks.—
Fireproof Flooring. Moulded and Ornamental Bricks— Drying Raw Clay— Sources of
Difficulty and Loss.— Improper Materials or Site— Unsuitable Methods of Working— Lack
of Capital — Defective Accounting. — Index.

THE MANUAL OF PRACTICAL POTTING. Compiled
by Experts, and Edited by CHAS. F. BINNS. Fourth Edition, Revised
and Enlarged. DemySvo. 200 pages. Pricel7s.6d.net. (Post free,
17s. lOd. home; 18s. 3d. abroad.)

14

POTTERY DECORATING. A Description of all the Pro-
cesses for Decorating Pottery and Porcelain. By R. HAINBACH.
Translated from the German. Crown 8vo. 250 pp. Twenty-two
Illustrations. Price 7s. 6d. net. (Post free, 7s. lOd. home; 8s. abroad.)

A TREATISE ON CERAMIC INDUSTRIES. A Complete

Manual for Pottery, Tile, and Brick Manufacturers. By EMILE
BOURRY. A Revised Translation from the French, with some Critical
Notes by ALFRED B. SEARLE. Demy 8vo. 308 Illustrations. 460 pp.
Price 12s. 6d. net. (Post free, 13s. home; 13s. 6d. abroad.)

Contents.

Preface. Definition and Classification of Ceramic Ware. Brief History of Ceramics.
Raw Materials of Bodies. Plastic Bodies — Properties and Composition — Preparation — Puri-
fication. Processes of Formation : Thowing, Expression, Moulding, Pressing, Casting, Slip-
ping. Drying — Evaporation —Aeration — Heat — Absorption. Glazes: Manufacture and
Application. Firing: Properties of Bodies and Glazes during Firing — Kilns. Decoration:
Materials and Methods. Terra Cottas — Bricks — Hollow Blocks — Roofing Tiles — Paving
Bricks — Pipes— Architectural and Decorative Terra-Cotta — Common Pottery — Tobacco Pipes
— Lustre Ware — Tests. Fireclay Goods : Varieties, Methods of Manufacture and Tests.
Faiences: Classification, Composition, Methods of Manufacture and Decoration. Stoneware
— Paving Tiles — Sanitary Ware — For Domestic Purposes — For Chemical Purposes — Decora-
tive Objects. Porcelain : Classification — Composition — Manufacture — Decoration.

ARCHITECTURAL POTTERY. Bricks, Tiles, Pipes, Ena-
melled Terra-cottas, Ordinary and Incrusted Quarries, Stoneware
Mosaics, Faiences and Architectural Stoneware. By LEON LEFEVRE.
Translated from the French by K. H. BIRD, M.A., and W. MOORE
BINNS. With Five Plates. 950 Illustrations in the Text, and numerous
estimates. 500 pp. Royal 8vo. Price 15s. net. (Post free, 15s. 6d.
home; 16s. 6d. abroad.)

THE ART OP RIVETING GLASS, CHINA AND
EARTHENWARE. By J. HOWORTH. Second Edition.
Paper Cover. Price Is. net. (By post, home or abroad, Is. Id.)

NOTES ON POTTERY CLAYS. The Distribution, Pro-
perties, Uses and Analyses of Ball Clays, China Clays and China
Stone. By JAS. FAIRIE, F.G.S. 132 pp. Crown 8vo. Price 3s. 6d.
net. (Post free, 3s. 9d. home ; 3s. lOd. abroad.)

HOW TO ANALYSE CLAY. By H. M. ASHBY. Demy 8vo.
72 pp. 20 Illustrations. Price 3s. 6d. net. (Post free, 3s. 9d. home
3s. lOd. abroad.)

15

A Reissue of

THE HISTORY OF THE STAFFORDSHIRE POTTER-
IES ; AND THE RISE AND PROGRESS OF THE
MANUFACTURE OF POTTERY AND PORCELAIN.

• With References to Genuine Specimens, and Notices of Eminent Pot-
ters. By SIMEON SHAW. (Originally published in 1829.) 265 pp.
Demy 8vo. Price 5s. net. (Post free, 5s. 4d. home; 5s. 9d. abroad.)

A Reissue of

THE CHEMISTRY OF THE SEVERAL NATURAL
AND ARTIFICIAL HETEROGENEOUS COM-
POUNDS USED IN MANUFACTURING POR-
CELAIN, GLASS AND POTTERY. By SIMEON SHAW.
(Originally published in 1837.) 750 pp. Royal 8vo. Price 10s. net.
(Post free, 10s. 6d. home; 12s. abroad.)

BRITISH POTTERY MARKS. By G. WOOLLISCROFT RHEAD.
Demy 8vo. 310 pp. With upwards of Twelve-hundred Illustrations of
Marks in the Text. Price 7s. 6d. net. (Post free, 8s. home; 8s. 3d.
abroad.)

(Glassware, Glass Staining and Painting.)

^RECIPES FOR FLINT GLASS MAKING. By a British
Glass Master and Mixer. Sixty Recipes. Being Leaves from the
Mixing Book of several experts in the Flint Glass, Trade, containing
up-to-date recipes and valuable information as to Crystal, Demi-crystal
and Coloured Glass in its many varieties. It contains the recipes for
cheap metal suited to pressing, blowing, etc., as well as the most costly
crystal and ruby. Second Edition. Crown 8vo. Price 10s. 6d. net.
(Post free, 10s. 9d. home; 10s. lOd. abroad.)

Contents.

Ruby — Ruby from Copper — Flint for using with the Ruby for Coating — A German Metal--
Cornelian, or Alabaster — Sapphire Blue — Crysophis — Opal — Turquoise Blue — Gold Colour —
Dark Green— Green (common) — Green for Malacnite — Blue for Malachite — Black for Mala-
chite— Black — Common Canary Batch — Canary — White Opaque Glass — Sealing-wax Red-
Flint— Flint Glass (Crystal and Demi)— Achromatic Glass— Paste Glass— White Enamel-
Firestone — Dead White (for moons) — White Agate — Canary — Canary Enamel — Index.

A TREATISE ON THE ART OF GLASS PAINTING.

Prefaced with a Review of Ancient Glass. By ERNEST R. SUPPLING.
With One Coloured Plate and Thirty-seven Illustrations. Demy 8vo.
140 pp. Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. abroad.)

Contents.

A Short History of Stained Glass — Designing Scale Drawings — Cartoons and the Cut Line
— Various Kinds of Glass Cutting for Windows — The Colours and Brushes used in Glass
Painting — Painting on Glass Dispersed Patterns — Diapered Patterns — Aciding — Firing —
Fret Lead Glazing— Index.

16

(Paper Making and Testing.)

THE PAPER MILL CHEMIST. By HENRY P. STEVENS,
M.A., Ph.D., F.I.C. Royal 12mo. 60 Illustrations. 300 pp. Price
7s. 6d. net. (Post free, 7s. 9d. home; 7s. lOd. abroad.)
Contents.

Introduction. — Dealing with the Apparatus required in Chemical Work and General
Chemical Manipulation, introducing the subject of Qualitative and Quantitative Analysis.
Fuels. — Analysis of Coal, Coke and other Fuels — Sampling and Testing for Moisture, Ash,
Calorific Value, etc. — Comparative Heating Value of different Fuels and Relative Efficiency.
Water. — Analysis for Steam Raising and for Paper Making Purposes generally — Water
Softening and Purification — A List of the more important Water Softening Plant, giving
Power required, Weight, Space Occupied, Out-put and Approximate Cost. Raw Materials
and Detection of Adulterants. — Analysis and Valuation of the more important Chemicals
used in Paper Making, including Lime, Caustic Soda, Sodium Carbonate, Mineral Acids,
Bleach Antichlor, Alum, Rosin and Rosin Size, Glue Gelatin and Casein, Starch, China Clay,
Blanc Fixe, Satin White and other Loading Materials, Mineral Colours and Aniline Dyes.
Manufacturing Operations. — Rags and the Chemical Control of Rag Boiling — Esparto
Boiling — Wood Boiling — Testing Spent Liquors and Recovered Ash — Experimental Tests
with Raw Fibrous Materials — Boiling in Autoclaves — Bleaching and making up Hand Sheets
— Examination of Sulphite Liquors — Estimation of Moisture in Pulp and Half-stuff — Recom-
mendations of the British Wood Pulp Association. Finished Products. — Paper Testing,
including Physical, Chemical and Microscopical Tests, Area, Weight, Thickness, Apparent
Specific Gravity, Bulk or Air Space. Determination of Machine Direction, Thickness,
Strength, Stretch, Resistance to Crumpling and Friction, Transparency, Absorbency and
other qualities of Blotting Papers — Determination of the Permeability of Filtering Papers —
Detection and Estimation of Animal and Vegetable Size in Paper — Sizing Qualities of
Paper — Fibrous Constituents — Microscopical Examination of Fibres — The Effect of Beating
on Fibres— Staining Fibres -Mineral Matter— Ash— Qualitative and Quantitative Examina-
tion of Mineral Matter — Examination of Coated Papers and Colouring Matters in Paper.
Tables. — English and Metrical Weights and Measures with Equivalents — Conversion of
Grams to Grains and vice versa — Equivalent Costs per lb., cwt.,and ton — Decimal Equivalents
of IDS., qrs., and cwts. — Thermometric and Barometric Scales — Atomic Weights and Molecular
Weights — Factors for Calculating the Percentage of Substance Sought from the Weight of
Substance Found— Table of Solubilities of Substances Treated of in Paper Making—Specific
Gravity Tables of such substances as are used in Paper Making, including Sulphuric Acid,
Hydrochloric Acid, Bleach, Milk of Lime, Caustic Soda, Carbonate of Soda, etc., giving
Percentage Strength with Specific Gravity and Degrees Tw. — Hardness Table for Soap
Tests— Dew Point— Wet and Dry Bulb Tables— Properties of Saturated Steam, giving
Temperature, Pressure and Volume — List of Different Machines used in the Paper Making
Industry, giving Size, Weight, Space Occupied, Power to Drive, Out-put and Approximate
Cost — Calculation of Moisture in Pulp — Rag-Boiling Tables, giving Percentages of Lime, '
Soda and Time required — Loss in Weight in Rags and other Raw Materials during Boiling
and Bleaching — Conditions of Buying and Selling as laid down by the Paper Makers' Associa-
tion— Table of Names and Sizes of Papers — Table for ascertaining the Weight per Ream from
the Weight per Sheet— Calculations of Areas and Volumes— Logarithms— Blank pages for
Notes.

THE TREATMENT OP PAPER FOR SPECIAL
PURPOSES, By L. E. ANDES. Translated from the
German. Crown 8vo. 48 Illustrations. 250 pp. Price 6s. net. (Post
free, 6s. 4d. home ; 6s. 6d. abroad.)

Contents.

I., Parchment Paper, Vegetable Parchment.— The Parchment Paper Machine-
Opaque Supple Parchment Paper — Thick Parchment — Krugler's Parchment Paper and Parch-
ment Slates — Double and Triple Osmotic Parchment — Utilising Waste Parchment Paper —
Parchmented Linen and Cotton — Parchment Millboard — Imitation Horn and Ivory from
Parchment Paper — Imitation Parchment Paper — Artificial Parchment — Testing the Sulphuric
Acid. II., Papers for Transfer Pictures. III., Papers for Preservative and Packing
Purposes. — Butter Paper — Wax Paper — Paraffin Paper — Wrapping Paper for Silverware —
Waterproof Paper — Anticorrosive Paper. IV., Grained Transfer Papers. V., Fireproof and
Antifalsification Papers. VI., Paper Articles.— Vulcanised Paper Mache— Paper Bottles-
Plastic Articles of Paper— Waterproof Coverings for Walls and Ceilings— Paper Wheels,
Roofing and Boats — Parer Barrels — Paper Boxes — Paper Horseshoes. VII., Gummed Paper.
VIII., Hectograph Papers. IX., Insecticide Papers.— Fly Papers— Moth Papers. X.,
Chalk and Leather Papers.— Glace Chalk Paper— Leather Paper— Imitation Leather.
XL, Luminous Papers— Blue-Print Papers— Blotting Papers. XII., Metal Papers— Medi-
cated Papers. XIII., Marbled Papers. XIV., Tracing and Copying Papers — Iridiscent or
Mother of Pearl Papers. XV., Photographic Papers— Shellac Paper— Fumigating Papers-
Test Papers. XVI., Papers for Cleaning and Polishing Purposes— Glass Paper—
Pumic Paper — Emery Paper. XVII., Lithographic Transfer Papers. XIX., Sundry
Special Papers— Satin Paper— Enamel Paper— Cork Paper— Split Paper— Electric Paper-
Paper Matches— Magic Pictures— Laundry Blue Papers— Blue Paper for Bleachers. XX.,
Waterproof Papers— Washable Drawing Papers— Washable Card— Washable Coloured Paper
—Waterproof Millboard— Sugar Paper. XXL, The Characteristics of Paper— Paper Testing

17

(Enamelling on Metal.)

ENAMELS AND ENAMELLING. For Enamel Makers,
Workers in Gold and Silver, and Manufacturers of Objects of Art.
By PAUL RANDAU. Translated from the German. Second and Revised
Edition. With Sixteen Illustrations. Demy 8vo. 200 pp. Price
10s. 6d. net. (Post free, 10s. lOd. home; 11s. abroad.)

THE ART OF ENAMELLING ON METAL. By W.

NORMAN BROWN. Second Edition, Revised. Crown 8vo. 60 pp. Price
3s. 6d. net. (Post free, 3s. 9d. home ; 3s. lOd. abroad.)

(Textile Subjects.)

THE FINISHING OF TEXTILE FABRICS (Woollen,
Worsted, Union and other Cloths). By ROBERTS BEAUMONT, M.Sc.
With 150 Illustrations of Fibres, Yarns and Fabrics, also Sectional
and other Drawings of Finishing Machinery. Demy 8vo. 260 pp.
Price 10s. 6d. net. (Post free, 10s. lOd. home; 11s. 3d. abroad.)

Contents.

Woollen, Worsted and Union Fabrics— Processes of Finishing and their Effects— The
Process of Scouring : Scouring Machines — Theory of Felting: Fabric Structure — Compound
Fabrics— Fulling and Milling Machinery. The Theory of Raising— Raising Machinery and
the Raising Process — Cutting, Cropping or Shearing — Lustring Processes and Machinery —
Methods of Finishing— Index.

STANDARD CLOTHS. By ROBERTS BEAUMONT.

[In the Press.

FIBRES USED IN TEXTILE AND ALLIED INDUS-
TRIES. By C. AINSWORTH MITCHELL, B.A. (Oxon.), F.I.C.,
and R. M. PRIDEAUX, F.I.C. With 66 Illustrations specially drawn
direct from the Fibres. Demy 8vo. 200 pp. Price 7s. 6d. net.
(Post free, 7s. lOd. home ; 8s. abroad.)

Contents.

Classification of Fibres. — General Characteristics of Fibres — Microscopical Examination
of Fibres — Stegmata— Chemical Examination — Ultimate Fibres — Methyl Value — Moisture in
Fibres. Wool. — Nature of Wool — Commercial Varieties — Characteristics of Good Wool —
Merino — Microscopical Appearance — Mould in Wool — Felting Property — Curl of Wool —
Chemical Composition — Action of Reagents on Wool — Chlorinised Wool — Detection of Dyed
Fibres in Wool— Conditioning of Wool. Vicuna — Camel Hair — Alpaca — Llama Hair —
Mohair— Cashmere— Goats' Hair— Cow Hair— Horse Hair— Deer Hair— Reindeer Hair
—Rabbits' Hair— Cats' Hair— Dogs' Hair— Kangaroo's Hair— Human Hair. Silk.—
Origin of Silk— Reeling— Waste Silk— History— Commercial Varieties of Thread— Size of
Yarns — Wild Silks — Microscopical Characteristics — Colour of Silk — Size of Fibres — Strength
and Elasticity — Specific Gravity — Chemical Composition — Fibroin — Sericin— Hydrolysis of
Silk Proteins — Action of Chemical Agents — Absorption of Tannin — Weighting — Differentiation
and Separation from other Fibres. Cotton.— History — Commercial Varieties — Structure of
the Fibre — Cell Walls — Dimensions of Fibre — Chemical Composition — Cellulose — Action of
Reagents — Nitrated Cotton — Examination of Bleached Fabrics — Absorption of Tannin —
Absorption of Gases — Absorption of Dyestuffs — " Animalizing " of Cotton — Sized Cotton —
Polished Cotton — Mould in Cotton — Waterproofed Cotton. Mercerised Cotton. — History —
Structural Alteration of Fibres — Affinity for Dyestuffs — Chemical Changes in Mercerisation — '•
Effect upon Strength of Fibre — Measurement of Shrinkage — Reactions and Tests for Mercer-
ised Cotton— Dyestuff Tests. Artificial Silks. Linen and Ramie.— Linen : Source-
Varieties of Commercial Flax — Retting of Flax — Lustrous Linen — Use of Linen as a Textile
— Characteristics of the Fibre — Structure — Action of Reagents — Physical Properties — Com-
position— Flax Wax. Ramie : Source — Preparation — History — Properties — Composition.
Jute and other Fibres. Brush Fibres. Vegetable Downs and Upholstery Fibres.—
Bombax Cottons — Kapok — Ochroma Down — Kumbi or Galgal — Vegetable Silk — Asclepias
Cotton — Calotropis Down — Beaumantia Down — Other Vegetable Silks — Vegetable Wool —
Tillandsia Fibre— Vegetable Horsehair. Index.

16

DRESSINGS AND FINISHINGS FOR TEXTILE
FABRICS AND THEIR APPLICATION. Description
of all the Materials used in Dressing Textiles : Their Special Pro-
perties, the Preparation of Dressings and their Employment in
Finishing Linen, Cotton, Woollen and Silk Fabrics. Fireproof and
Waterproof Dressings, together with the principal machinery employed.
Translated from the Third German Edition of FRIEDRICH POLLEYN.
Demy 8vo. 280 pp. Sixty Illustrations. Price 7s. 6d. net. (Post
free, 7s. lOd. home ; 8s. abroad.)

Contents.

The Dressing Process and Materials for Same -Stiffening and Glazes— Wheaten
Starch — Maize Starch — Rice Starch — Buckwheat Starch — Arrowroot — Tapioca— Sago —
Artichoke Starch — Differentiating and Examining Starches — The Gelatinization Temperature
of Starches — Flour — Protamol for Dressings and Sizes — Adhesive Dressings— Gluten—
Protein Glue — Vegetable Glue — Arbol Gum — Apparatine — Vegetable Glue Dressing — Pus-
cher's Vegetable Glue — Vegetable Glue Containing Fat — Dextrin (British Gum) — Preparation,
of Dextrin — Gum, Gum Arabic — Feronia Gum — Cherry Gum, Plum Tree Gum — Testing Gum
Arabic — Tragacanth— Vegetable Mucilage — Carragheen Moss — Iceland Moss— Hai-Thao
Fleawort Seed— Linseed — Peru Gum — Ceylon Moss — Canary Grass Seed — Albumin— Casein
— Caseo Gum— Glutin — Glue — Gelatine — Starch Syrup — Potato Syrup— Colophony (Rosin) —
Materials for Soft Dressings— Glycerine— Wax— Paraffin Wax— Stearine— Fats and Fatty
Oils — Soaps — Softenings— Dressings for Filling and Loading — Alum — Barium Chloride —
Barium Sulphate — Barium Carbonate — Bleaching Powder — Lead Sulphate — Gypsum — Cal-
cium Chloride — Magnesium Chloride — Sodium Sulphate — Glauber Salt — Magnesium Sulphate
(Epsom Salt) — Magnesium Carbonate — Magnesia White— Magnesium Silicate — China Clay
(Aluminium Silicate)— Zinc Chloride— Alkali Silicates— Water-Glass— Antiseptic Dressing
Ingredients— Dyeing and Blueing Agents— Ultramarine Blue— Paris Blue— Soluble Pans
Blue — Indigpcarmine — Various Dressings — Endosmin— Eau de Crystall — Crystallfixe —
Lukon — Algin — Paramentine — Cream Softening — Norgine — Dressing Soaps — Gum Tragasol —
Senegalin — Monopol Soap— Liquid Size for Dressing Bleached and Coloured Fabrics —
Vegetable Gum Dressing— Gum Substitute— S. Size— Puntschart's Vegetable Glue— Vegetable
Glue and P. Size— The Preparations of Dressings— Various Adjuncts to Dressing Pre-
parations— Fatty Adjuncts — Potato Starch and Rosin Adjunct — Dressing Composition — Ha'i-
Thap Dressing— Appliances for the Preparations of Dressings— Rushton's Size Boiler-
Sifting Machine— Recipes for Dressings— Dressings for Linens— For Medium Finish— For
Heavy Finish — For Very Heavy Finish — Damask Dressings — For Crash Linens — For Very
Glossy Linens — Dressings for Black Cottons — Black Glace Dressings — Black Dressing for
Half-Woollens—Yarn Dressings— Laundry Glazes— Yarn Sizing— Finishing Woollen
Goods — Silk Finish for Wool — Looke's Dressing for Worsteds — Dressing for Flannels and
Woollens— Dressing for Heavy Trouserings — Dressing for Inferior Woollens — Protamol
Dressing for Wool— Dressing for Worsteds, Cheviots, and Half- Woollens — Back Dressing for
Worsteds— Finishing Woollens by the Electric Current— Finishing Silk Fabrics— Single
Dressing for Silk— Full Dressing for Silk— Amber Dressing— Finishing Half-Silk Satins-
Waterproof Dressings — Alexanderson's Recipe — Recipe of Arieny-Flouy, Baypl and Laurens
— Balard's Recipe — Che'

Recipe — Chevallot and Girres' Recipe — Felton's Recipe — Kappelin's Recipe —
Sorel's Recipe — Waterproof Dressing lor Linens and Cottons — Half-Woollens — Jacquelin's
Process of Waterproofing Linens, Cottons, Woollens and Silks — Baswitz's Recipe — Doering's
Recipe— Various Waterproofing Recipes— Fireproof Dressings— Special Finishing Pro-
cesses— Imparting a Silky Appearance to Vegetable Fibres— Silvering and Gilding Silk-
Flexible Mother-of-Pearl Design on Various Fabrics — Metal Lustre Finishes— Applying
Spangles to Fabrics — Colour Photography on Woven Fabrics — Gold and Silver Designs —
Applied by Heat — Imitating Embroidery and Lace — Silvering and Gilding Silks — Velvet Effect
— Embossed Metal or Colour Designs on Velvet — Metallizing Clothing Materials — Bouillone
Finish— The Application of Dressing Preparations— Testing Dressings.

THE CHEMICAL TECHNOLOGY OF TEXTILE
FIBRES : Their Origin, Structure, Preparation, Washing,
Bleaching, Dyeing, Printing and Dressing. By Dr. GEORG VON
GEORGIEVICS. Translated from the German by CHARLES SALTER.
320 pp. Forty-seven Illustrations. Royal 8vo. Price 10s. 6d. net.
(Post free, lls. home ; 11s. 3d. abroad.)

POWER-LOOM WEAVING AND YARN NUMBERING,

According to Various Systems, with Conversion Tables. Translated
from the German of ANTHON GRUNER. With Twenty-Six Diagrams
in Colours. 150 pp. Crown 8vo. Price 7s. 6d. net. (Post free>
7s. 9d. home ; 8s. abroad.)

19

TEXTILE RAW MATERIALS AND THEIR CON-
VERSION INTO YARNS. (The Study of the Raw

Materials and the Technology of the Spinning Process.) By JULIUS
ZIPSER. Translated from German by CHARLES SALTER. 302 Illus-
trations. 500 pp. Demy 8vo. Price 10s. 6d. net. (Post free, 11s.
home; 11s. 6d. abroad.)

GRAMMAR OP TEXTILE DESIGN. By H. NISBET,
Weaving and Designing Master, Bolton Municipal Technical School.
Demy 8vo. 280 pp. 490 Illustrations and Diagrams. Price 6s. net.
(Post free, 6s. 4d. home ; 6s. 6d. abroad.)
Contents.

THE PLAIN WEAVE AND ITS MODIFICATIONS. TWILL AND KINDRED WEAVES. — Classifi-
cation of Twill Weaves. DIAMOND AND KINDRED WEAVES. BEDFORD CORDS. BACKED
FABRICS. FUSTIANS. TERRY PILE FABRICS. GAUZE AND LENO FABRICS. TISSUE, LAPPET,
AND SWIVEL FIGURING ; ALSO ONDULK EFFECTS, AND LOOPED FABRICS.

ART NEEDLEWORK AND DESIGN, POINT LACE. A

Manual of Applied Art for Secondary Schools and Continuation Classes.
By M. E. WILKINSON. Oblong quarto. With 22 Plates. Bound in
Art Linen. Price 3s. 6d. net. (Post free, 3s. lOd. home; 4s. abroad.)
Contents.

Sampler of Lace Stitches — Directions for working Point Lace, tracing Patterns, etc. —
List of Materials and Implements required for working. Plates I., Simple Lines, Straight and
Slanting, and Designs formed from them. II., Patterns formed from Lines in previous
Lesson. III., Patterns formed from Lines in previous Lesson. IV., Simple Curves, and
Designs formed from them. V., Simple Leaf form, and Designs formed from it. VI., Ele-
mentary Geometrical forms, with Definitions. VII., Exercises on previous Lessons. VIII.,
Filling of a Square, Oblong and Circle with Lace Stitches. IX., Design for Tie End, based
on simple Leaf form. X., Lace Buttertties (Freehand). XI.. Twenty simple Designs evolved
from Honiton Braid Leaf. XII., Design for Lace Handkerchief, based on previous Lesson.
XIII., Design for Tea-cosy. XIV., Freehand Lace Collar. XV., Freehand Lace Cuff (to
match). XVI., Application of Spray from Lesson XI. XVII., Adaptation of Curves within
a Square, for Lace Cushion Centre. XVIII., Conventional Spray for corner of Tea-cloth.
XIX., Geometrical form for Rosebowl D'Oyley, to be originally filled in. XX., Geometrical
form for Flower-vase D'Oyley, to be originally filled in. Each Lesson contains Instructions
for Working, and application of new Stitches from Sampler.

HOME LACE-MAKING. A Handbook for Teachers and
Pupils. By M. E. W. MILROY. Crown 8vo. 64 pp. With 3 Plates and
9 Diagrams. Price Is. net. (Post free, Is. 3d. home ; Is. 4d. abroad.)

THE CHEMISTRY OF HAT MANUFACTURING. Lec-
tures delivered before the Hat Manufacturers' Association. By WAT-
SON SMITH, F.C.S., F.I.C. Revised and Edited by ALBERT SHONK.
Crown 8vo. 132 pp. 16 Illustrations. Price 7s. 6d. net. (Post free,
7s. 9d. home; 7s. lOd. abroad.)

THE TECHNICAL TESTING OF YARNS AND TEX-
TILE FABRICS. With Reference to Official Specifica-
tions. Translated from the German of Dr. J. HERZFELD. Second
Edition. Sixty-nine Illustrations. 200 pp. Demy 8vo. Price 10s. 6d.
net. (Post free, 10s. lOd. home; 11s. abroad.)

DECORATIVE AND FANCY TEXTILE FABRICS.

By R. T. LORD. For Manufacturers and Designers of Carpets, Damask,
Dress and all Textile Fabrics. 200 pp. Demy 8vo. 132 Designs and
Illustrations. Price-7s. 6d. net. (Post free, 7s. lOd. home; 8s. abroad.)

THEORY AND PRACTICE OF DAMASK WEAVING.

By H. KINZER and K. WALTER. Royal 8vo. Eighteen Folding Plates.
Six Illustrations. Translated from the German. 110pp. Price 8s. 6d.
net. (Post free, 9s. home ; 9s. 6d. abroad.)
Contents.

The Various Sorts of Damask Fabrics— Drill (Ticking, Handloom-made)— Whole
Damask for Tablecloths — Damask with Ground- and Connecting-warp Threads — Furniture
Damask— Lampas or Hangings— Church Damasks— The Manufacture of Whole Damask
— Damask Arrangement with and without Cross-Shedding — The Altered Cone-arrangement —
The Principle of the Corner Lifting Cord — The Roller Principle — The Combination of the
Jacquard with the so-called Damask Machine— The Special Damask Machine— The Combina-
tion of Two Tyings.

20

FAULTS IN THE MANUFACTURE OF WOOLLEN
GOODS AND THEIR PREVENTION. By NICOLAS
REISER. Translated from the Second German Edition. Crown 8vo.
Sixty-three Illustrations. 170 pp. Price 5s. net. (Post free, 5s. 4d.
home ; 5s. 6d. abroad.)

Contents.

Improperly Chosen Raw Material or Improper Mixtures — Wrong Treatment of the
Material in Washing, Carbonisation, Drying, Dyeing and Spinning — Improper Spacing of the
Goods in the Loom— Wrong Placing of Colours— Wrong Weight or Width of the Goods
—Breaking of Warp and Weft Threads— Presence of Doubles, Singles, Thick, Loose,
and too Hard Twisted Threads as well as Tangles, Thick Knots and the Like — Errors in
Cross-weaving — Inequalities, i.e., Bands and Stripes — Dirty Borders — Defective Selvedges —
Holes and Buttons — Rubbed Places — Creases — Spots — Loose and Bad Colours — Badly Dyed
Selvedges — Hard Goods — Brittle Goods — Uneven Goods — Removal of Bands, Stripes,
Creases and Spots.

SPINNING AND WEAVING CALCULATIONS, especially
relating to Woollens. From the German of N. REISER. Thirty-four
Illustrations. Tables. 160 pp. Demy 8vo. 1904. Price 10s. 6d. net.
(Post free, 10s. lOd. home; 11s. abroad.)

WORSTED SPINNERS' HANDBOOK. By H. TURNER,

Crown 8vo. About 176 pages. [In the press^

ANALYSIS OF WOVEN FABRICS. By A. F. BARKER,
M.Sc., and E. MIDGLEY. Demy 8vo. 316 pp. Numerous Tables,
Examples and 82 Illustrations. Price 7s. 6d. net. (Post free, 7s. 10d*
home ; 8s. abroad.)

WATERPROOFING OF FABRICS. By Dr. S. MIERZINSKI.
Second Edition, Revised and Enlarged. Crown 8vo. 140 pp. 2&
Illustrations. Price 5s. net. (Post free, 5s. 4d. home ; 5s. 6d. abroad.)

HOW TO MAKE A WOOLLEN MILL PAY. By JOHN
MACKIE. Crown 8vo. 76 pp. Price 3s. 6d. net. (Post free, 3s. 9d.
home; 3s. lOd. abroad.)

Contents.

Blends, Piles, or Mixtures of Clean Scoured Wools— Dyed Wool Book— The Order Book
— Pattern Duplicate Books — Management and Oversight — Constant Inspection of Mill De-
partments— Importance of Delivering Goods to Time, Shade, Strength, etc. — Plums.

YARN AND WARP SIZING IN ALL ITS BRANCHES.

Translated from the German of CARL KRETSCHMAR. Royal 8vo. 123
Illustrations. 150 pp. Price 10s. 6d. net. (Post free, 10s. lOd. home ;
11s. abroad.)

Contents.

The Materials to be Sized — Linen or Flax— Ramie and Jute — Wool — The Materials used
in Sizing — The Sized Material — The Sizing Process; (a) Appliances for, and Method of, pre-
paring the size ; (b) Sizing the Yarn in Hanks or Warps by hand ; (c) Machine Sizing — Sizing
Recipes for Different Effects — Combined Dyeing and Sizing — The Purchase and Testing of
Sizing Ingredients.

(For " Textile Soaps and Oils," see p. 7.)

(Dyeing, Colour Printing, Matching and
Dye = stuffs.)

THE COLOUR PRINTING OF CARPET YARNS. Manual
for Colour Chemists and Textile Printers. By DAVID PATERSON,
F.C.S. Seventeen Illustrations. 136 pp. Demy 8vo. Price 7s. 6d.
net. (Post free, 7s. lOd. home ; 8s. abroad.)
Contents.

Structure and Constitution of Wool Fibre — Yarn Scouring — Scouring Materials — Water for
Scouring — Bleaching Carpet Yarns — Colour Making for Yarn Printing — Colour Printing
Pastes — Colour Recipes for Yarn Printing — Science of Colour Mixing — Matching of Colours
— " Hank " Printing — Printing Tapestry Carpet Yarns — Yarn Printing — Steaming Printed
Yarns— Washing of Steamed Yarns— Aniline Colours Suitable for Yarn Printing— Glossary of
Dyes and Dye-wares used in Wood Yarn Printing — Appendix.

21

TEXTILE COLOUR MIXING. A Manual intended for
the use of Dyers, Calico Printers and Colour Chemists. By DAVID
PATERSON, F.R.S.E., F.C.S. Formerly published under title of " Science
of Colour Mixing". Second Revised Edition. Demy 8vo. 140pp. 41
Illustrations with 5 Coloured Plates and 4 Plates showing Dyed Speci-
mens. Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. abroad.)

[Just published.

DYERS' MATERIALS : An Introduction to the Examination,
Evaluation and Application of the most important Substances used in
Dyeing, Printing, Bleaching and Finishing. By PAUL HEERMAN, Ph.D.
Translated from the German by A. C. WRIGHT, M.A. (Oxon.), B.Sc.
(Lond.). Twenty-four Illustrations. Crown 8vo. 150 pp. Price 5s.
net. (Post free, 5s. 4d. home ; 5s. 6d. abroad.)

COLOUR MATCHING ON TEXTILES. A Manual in-

tended for the use of Students of Colour Chemistry, Dyeing and

Textile Printing. By DAVID PATERSON, F.C.S. Coloured Frontis-

. piece. Twenty-nine Illustrations and Fourteen Specimens Of Dyed

Fabrics. Demy 8vo. 132 pp. Price 7s. 6d. net. (Post free, 7s. lOd.
home; 8s. abroad.)

COLOUR: A HANDBOOK OF THE THEORY OF
COLOUR. By GEORGE H. HURST, F.C.S. With Ten
Coloured Plates and Seventy-two Illustrations. 160 pp. Demy 8vo.
Price 7s. 6d. net. (Post free, 7s. lOd. home; 8s. abroad.)

Reissue of
THE ART OF DYEING WOOL, SILK AND COTTON.

Translated from the French of M. HELLOT, M. MACQUER and M. LE
PILEUR D'APLIGNY. First Published in English in 1789. Six Plates.
Demy 8vo. 446 pp. Price 5s. net. (Post free, 5s. 6d. home ; 6s.
abroad.)

THE CHEMISTRY OF DYE-STUFFS. By Dr. GEORG VON
GEORGIEVICS. Translated from the Second German Edition. 412 pp.
Demy 8vo. Price 10s. 6d. net. (Post free, lls. home ; 11s. 6d. abroad.)

THE DYEING OF COTTON FABRICS: A Practical
Handbook for the Dyer and Student. By FRANKLIN BEECH, Practical
Colourist and Chemist. 272 pp. Forty-four Illustrations of Bleaching
and Dyeing Machinery. Demy 8vo. Price 7s. 6d. net. (Post free,
7s. lOd. home ; 8s. abroad.)

THE DYEING OF WOOLLEN FABRICS. By FRANKLIN

BEECH, Practical Colourist and Chemist. Thirty-three Illustrations.
Demy 8vo. 228 pp. Price 7s. 6d. net. (Post free, 7s. lOd. home;
8s. abroad.)

(Silk Manufacture.)

SILK THROWING AND WASTE SILK SPINNING.

•By HOLLINS RAYNER. Demy 8vo. 170pp. 117 Illus. Price5s.net.
(Post free, 5s. 4d. home ; 5s. 6d. abroad.)

The Silkworm— Cocoon Reeling and Qualities of Silk— Silk Throwing— Silk Wastes— The
Preparation of Silk Waste for Degumming— Silk Waste Degumming, Schapping and Dis-
charging— The Opening and Dressing of Wastes — Silk Waste "Drawing" or "Preparing"
Machinery— Long Spinning— Short Spinning— Spinning and Finishing Processes— Utilisation
of Waste Products — Noil Spinning — Exhaust Noil Spinning.

22

(Bleaching and Bleaching Agents.)

A PRACTICAL TREATISE ON THE BLEACHING OF
LINEN AND COTTON YARN AND FABRICS. By

L. TAILFER, Chemical and Mechanical Engineer. Translated from the
French by JOHN GEDDES MC!NTOSH. Demy 8vo. 303 pp. Twenty
Illus. Pricel2s.6d.net. (Post free, 13s. home ; 13s. 6d. abroad.)

MODERN BLEACHING AGENTS AND DETERGENTS.

By Professor MAX BOTTLER. Translated from the German. Crown
8vo. 16 Illustrations. 160 pages. Price 5s. net. (Post free, 5s. 3d.
home ; 5s. 6d. abroad.)

Contents.

Bleaching Agents — Old and New Bleaching Methods and Bleaching Agents — Sodium
Peroxide — Perborates — Ozone — Sodium Bisulphite and Hydrosulphurous Acid — Discharging
Colour from Textile Fabrics with Hydrosulphurous Acid — Permanganate — Hydrogen Per-
oxide— Bleaching Fats, Oils, Wax and Paraffin — Solid, Stable Calcium Hypochlorite and
Bleaching Soda — Electric Bleaching — Detergents — Benzine Soaps — Extractive Detergents
and Detergent Mixtures — Carbon Tetrachloride — Aceto-Oxalic Acid as a Detergent ; Special
Methods of Removing Stains — Bleaching Processes Used in Chemical Cleaning — Hydrogen
Peroxide as a Detergent — Oxygen as a Detergent — Sodium Peroxide as a Detergent — Sundry
New Detergents and Cleansing Agents.

(Cotton Spinning, Cotton Waste and
Cotton Combing.)

COTTON SPINNING (First Year). By THOMAS THORNLEY,
Spinning Master, Bolton Technical School. 160pp. Eighty-four Illus-
trations. Crown 8vo. Second Impression. Price 3s. net. (Post free,
3s. 4d. home ; 3s". 6d. abroad.)

COTTON SPINNING (Intermediate, or Second Year). By
THOMAS THORNLEY. Second Impression. 180 pp. Seventy Illustra-
tions. Crown 8vo. Price 5s. net. (Post free, 5s. 4d. home ; 5s. 6d.
abroad.)

COTTON SPINNING (Honours, or Third Year). By THOMAS
THORNLEY. 216 pp. Seventy-four Illustrations. Crown 8vo. Second
Edition. Price 5s. net. (Post tree, 5s. 4d. home; 5s. 6d. abroad.)

COTTON COMBING MACHINES. By THOS. THORNLEY,
Spinning Master, Technical School. Bolton. Demy 8vo. 117 Illustra-
tions. 300pp. Price 7s. 6d. net. (Post free, 8s. home ; 8s. 6d. abroad.)

COTTON WASTE : Its Production, Characteristics, Regula-
tion, Opening, Carding, Spinning and Weaving. By THOS. THORNLEY.
Demy 8vo. 286 pp. 60 Illustrations. Price 7s. 6d. net. (Post free,
7s. lOd. home ; 8s. abroad.)

Contents.

The Production, Characteristics, and Regulation of Cotton Waste.— The Use of
Cotton Waste— The Making of Waste in Cotton Mills : Introduction—The Blowing-room—
Various Kinds of Waste Droppings — Waste from Crighton Opener with Hopper Feeder —
Scutcher Droppings — The Leaf Bars— Licker-in Fly — The Beater Bars of Openers and
Scutchers — The Schaelibaum Bars — Testing for Waste — Calculations on Waste per cent. —
Summary of Wastes— Carding Engine Waste— Card Strips— Long Fibre in Flat Strips— The
Stripping of Flat Cards — Removal of Stripping Dust — Claims for Vacuum System of Stripping
Cylinders and Doffers of Cards— Dust Extraction and the Wire Clothing of a Card— Vacuum
System of Stripping — The Front Plate of the Carding Engine — Communications on the Front
Plate Question sent to the Author— Holland's Web Conductor for Carding Engines— Hand
Cards — Undercasings — Comber Waste — The Disposal of the Comber Waste — Lecture — De-
fects in Rovings : Their Causes and Remedies — The Work on Self-acting Mules — Spinning
Waste, Middle Iron Roller Laps, Fluker Rods, and Crows for Mule Bottom Rollers— Banding
— A Manager's Letter on Waste in Cotton Mills — The Waste Question — Waste and Stop-
motions for Doubling Frames — Extra Waste from Inferior Cotton — Fuller Details of Waste in
Indian Mills— Double Yarn on Ring-Frames. [Continued on next page.

23

CONTENTS OF COTTON WASTE— (continued).
Treatment of Best Cotton Wastes in Cotton ^spinning Mills, with Other Notes.—

Treatment of Roving Waste — Roving Waste Opening — Modern Roving Waste Openers — •
Delivery of Waste — Blending of the Waste from Roving Opener— Excessive Use of Waste —
The Cylinder Lags -of Roving Waste Opener — The Gearing — Another Make of Roving Waste
Opener — Thread Extractor — Automatic Feed — Process of Recovering Good Cotton from Card-
ing tngine Strips — Letter on Cotton Mill Waste.

The Opening- and Cleaning of Cotton Waste. — Summary of Machines more or less
used in the Treatment of Cotton Waste — Possible Systems of Machinery in using Cotton
Waste — Mixings — Soaping Apparatus — Opening and Cleaning of Cotton Waste : General
Remarks — Productions — The Willow — Central Feature : Strong Spikes — A Make of Willow —
General Appearance of Willow — Spiked Cylinders — Weighting of Feed Rollers — Preparation
System — Cop-bottom Machine — Blow-room Fires — Heavy Driving — The Soaper — Systems of
Machines— The Scutcher— Extra Beaters— Cop-bottom Breaking Machine— Single-Beater
Lap-fornrng Scutching Machine with Hopper Feeder — The Scutcher Bars and Lap-licking —
Hard Ends— The Crighton.

The Carding of Cotton Waste. — Rollers and Clearers — Action of Roller and Clearer —
Specification of Cotton Waste Card— The Cylinder— The Wire Covering— Methods of Feeding
the Breaker Card — Double Lap Method — Single, breaking Carding Engine — Methods of Feed-
ing the Finisher Card — The Lap Drum — The Scotch Feed — Tin Rollers — The Derby Doubler —
Derby Doubler for Cotton Waste — Improved Lattice Feed — The "Fancy" and " Humbug "
Rollers — The Fancy Roller — Single-finishing Carding Engine — Breaker and Finisher Cards
Combined with Scotch Feed— Methods of Delivering Cotton Waste from Finisher Cards—
The Preparation System — The Ring Doffer System — Rubbers — The Tape Condenser — The
Rubbers— Patent " Leather Tape " Condenser— Waste Carding, Side Slivers— Patent for Per-
fecting Side Ends in Carding Engines — Remarks on Cotton Waste Carding — Patent Automatic
Feeding Machine for Breaking Carding Engines — Single Finishing Carding Engine with Patent
Quadruple Coiling and Can Motion — Adjustment of Rollers and Clearers — Flat Card — The
"Humbug," "Fancy," and "Dirt" Rollers: General Remarks — The Universal Carding
Principle— Universal Cotton Waste Set, 72 in. wide— Tape Condensers— Double Doffing
Arrangement for Cotton Waste Cards — Other Double Doffer Condensers — Condenser Bobbins
—The Waste Card Condenser— Feed Rollers of Card— Special Rollers— Preparation System-
Waste Carding Engines : Double Cards — Condenser — Combined Driving for Cards — Improved
Waste Stubbing Frame for Preparatory System.

Final Spinning Machines for Cotton Waste.— Peculiar Spinning Machines— The Can
Spinning Frame — The Spindle and Cop— Cup-Spinning Machine— Spinning Frame — THE SELF-
ACTOR MULE. — Draughting of Cotton Waste on the Waste Mule — The Headstocks — Spindles
and Productions — Cotton Waste Mule with Cotton Headstock — Driving for Variable Spindle
Speeds — Three Speeds of Spindle — Stop Motions — Remarks on Three-speed Driving and Waste
Mules — Round of Movements in Cotton Waste Mule — The Slubbing Motion — Wheel Stubbing
Motion — Self-acting Mule — Slubbing Motion — Draw-back Motion — Spindle Stop Motion — The
" Draw-back " Motion — Winding Click Motion — Details — Special Motions — Guage and Speed
— Ring Frame for Cotton Waste.

The Use of Cotton Waste Yarns in Weaving.— The Weaving of Cotton Waste Yarns
— Woven Goods in which Yarns spun from Cotton Waste may be used — Raising Process —
Cleaning Cloths— Double Cloth Weave from Waste Cotton Weft— Waste in Weaving Sheds-
Cop Skewering — Improved Tubular Winding Machine.

Various Notes. — The Counts of Cotton Waste Yarns — Approximate Prices of Cotton
Waste — Approximate Prices of Condenser Yarns — Cotton Seed Products — The Condenser
Rubbers — Stripping — Banding — Overlooking and Kinds of Waste — Hard Ends — Workmen —
Fine Counts from Waste — Cone-drum Driving for Mules — Use of Stores — Woollen and
Worsted Machines, Summary — Carding and Spinning Machinery — Coal — City Guilds Examina-
tion Question, 1909 — Vigogne Yarns — Extracts from Recent Consular Reports — Wastes in the
Woollen Trade — Absorbent Cotton — Waste in Doubling — Waste in Wiping up Oil — Loose
Cotton Bleaching— Waste in American Mills— Artificial Silk— Baine's Loss Table, 1833— New
Patent Machine— Fire Risk with Cotton Waste— Danger of Flannelette— Candlewick— Carpet
Cops — Condensed Yarn — Objectionable Wastes — Woollen Mill Wastes — Indian Raw Cotton —
Copious Index.

THE RING SPINNING FRAME : GUIDE FOR OVER-
LOOKERS AND STUDENTS. By N. BOOTH. Crown
8vo. 76 pages. Price 3s. net. (Post free, 3s. 3d. home ; 3s. 6d. abroad.)

(Flax, Hemp and Jute Spinning.)

MODERN FLAX, HEMP AND JUTE SPINNING AND
TWISTING. A Practical Handbook for the use of Flax,
Hemp and Jute Spinners, Thread, Twine and Rope Makers. By
HERBERT R. CARTER, Mill Manager, Textile Expert and Engineer,
Examiner in Flax Spinning to the City and Guilds of London
Institute. Demy 8vo. 1907. With 92 Illustrations. 200 pp. Price
7s. 6d. net. (Post free, 7s. 9d. home ; 8s. abroad.)

24

(Collieries and Mines.)

RECOVERY WORK AFTER PIT FIRES. By ROBERT
LAMPRECHT, Mining Engineer and Manager. Translated from the
German. Illustrated by Six large Plates, containing Seventy-six
Illustrations. 175 pp. Demy 8vo. Price 10s. 6d. net. (Post free,
10s. lOd. home; 11s. abroad.)

VENTILATION IN MINES. By ROBERT WABNER, Mining
Engineer. Translated from the German. Royal 8vo. Thirty Plates
and Twenty-two Illustrations. 240 pp. Price 10s. 6d. net. (Post free,
11s. home; 11s. 3d. abroad.)

THE ELECTRICAL EQUIPMENT OF COLLIERIES. By

W. GALLOWAY DUNCAN, Electrical and Mechanical Engineer, Member
of the Institution of Mining Engineers, Head of the Government School
of Engineering, Dacca, India ; and DAVID PENMAN, Certificated Colliery
Manager, Lecturer in Mining to Fife County Committee. Demy 8vo.
310 pp. 155 Illustrations and Diagrams. Price 10s. 6d. net. (Post
free, lls. home; 11s. 3d. abroad.)

(Dental Metallurgy.)

DENTAL METALLURGY : MANUAL FOR STUDENTS
AND DENTISTS. By A. B. GRIFFITHS, Ph.D. Demy
8vo. Thirty-six Illustrations. 200 pp. Price 7s. 6d. net. (Post free,
7s. lOd. home; 8s. abroad.)

Contents.

Introduction — Physical Properties of the Metals — Action of Certain Agents on Metals —
Alloys — Action of Oral Bacteria on Alloys — Theory and Varieties of Blowpipes — Fluxes —
Furnaces and Appliances — Heat and Temperature — Gold — Mercury — Silver — Iron — Copper —
Zinc — Magnesium — Cadmium — Tin — Lead — Aluminium — Antimony — Bismuth — Palladium —
Platinum — Iridium — Nickel — Practical Work — Weights and Measures.

(Engineering, Smoke Prevention and
Metallurgy.)

THE PREVENTION OF SMOKE. Combined with the

Economical Combustion of Fuel. By W. C. POPPLEWELL, M.Sc.,

A.M.Inst., C.E., Consulting Engineer. Forty-six Illustrations. 190pp.

Demy 8vo. Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. 3d. abroad.)

Contents.

Fuel and Combustion — Hand Firing in Boiler Furnaces — Stoking by Mechanical Means —
Powdered Fuel— Gaseous Fuel— Efficiency and Smoke Tests of Boilers— Some Standard
Smoke Trials — The Legal Aspect of the Smoke Question — The Best Means to be adopted for
the Prevention of Smoke — Index.

GAS AND COAL DUST FIRING. A Critical Review of
the Various Appliances Patented in Germany for this purpose since
1885. By ALBERT PUTSCH. 130 pp. Demy 8vo. Translated from the
German. With 103 Illustrations. Price 5s. net. (Post free, 5s. 4d.
home ; 5s. 6d. abroad.)

THE HARDENING AND TEMPERING OF STEEL
IN THEORY AND PRACTICE. By FRIDOLIN REISER.
Translated from the German of the Third Edition. Crown 8vo.
120 pp. Price 5s. net. (Post free, 5s. 3d. home ; 5s. 4d. abroad.)

SIDEROLOGY: THE SCIENCE OF IRON (The Con-
stitution of Iron Alloys and Slags). Translated from German of
HANNS FREIHERR v. JUPTNER. 350 pp. Demy 8vo. Eleven Plates
and Ten Illustrations. Price 10s. 6d. net. (Post free, lls. home;
lls. 6d. abroad.)

25

EVAPORATING, CONDENSING AND COOLING
APPARATUS. Explanations, Formulae and Tables for Use
in Practice. By E. HAUSBRAND, Engineer. Translated by A. C.
WRIGHT, M.A. (Oxon.), B.Sc. (Lond.). With Twenty-one Illustra-
tions and Seventy-six Tables. 400 pp. Demy 8vo. Price 10s. 6d. net.
(Post free, 11s. home; 11s. 6d. abroad.)

(The " Broadway " Series of Engineering
Handbooks.)

Uniform in Size : Narrow Crown 8vo. (To fit Pocket.)
VOLUME I.— ELEMENTARY PRINCIPLES OF RE-
INFORCED CONCRETE CONSTRUCTION. By

EWART S. ANDREWS, B.Sc. Eng. (Lond.). 200 pp. With 57 Illus-
trations, Numerous Tables and Worked Examples. Price 3s. net.
(Post free, 3s. 3d. home; 3s. 6d. abroad.)

VOLUME II.— GAS AND OIL ENGINES. By A. KIRSCHKE.
Translated and Revised from the German, and adapted to English
practice. 160 pp. 55 Illustrations. Price 3s. net. (Post free,
3s. 3d. home ; 3s. 6d. abroad.)

VOLUME III.— IRON AND STEEL CONSTRUCTIONAL

WORK. By K. SCHINDLER. Translated and Revised from
the German, and adapted to English practice. 140 pp. 115 Illus-
trations. Price 3s. 6d. net. (Post free, 3s. 9d. home ; 4s. abroad.)

VOLUME IV.— TOOTHED GEARING. By G. T. WHITE,
B.Sc. (Lond.). 220 pp. 136 Illustrations. Price 3s. 6d. net. (Post
free, 3s. 9d. home ; 4s. abroad.)

VOLUME V.— STEAM TURBINES : Their Theory and Con-
struction. By H. WILDA. Translated and Revised from the
German, and adapted to English practice. 200 pp. 104 Illus-
trations. Price 3s. 6d. net. (Post free, 3s. 9d. home ; 4s. abroad.)

VOLUME VI. — CRANES AND HOISTS. Their Construction
and Calculation. By H. WILDA. Translated from the German ;
revised and adapted to British practice. 168 pp. 399 Illustrations.
Price 3s. 6d. net. (Post free, 3s. 9d. home ; 4s. abroad.)

VOLUME VII.— FOUNDRY MACHINERY. By E. TREIBER.
Translated from the German ; revised and adapted to British practice.
148 pp. 51 Illustrations. Price 3s. 6d. net. (Post free, 3s. 9d. home ;
4s. abroad.)

VOLUME VIII.— MOTOR CAR MECHANISM. By W. E.
DOMMETT, Wh.Ex., A.M.I.A.E. 2GO pp. 102 Illustrations. Price
3s. 6d. net. (Post free, 3s. 9d. home ; 4s. abroad.)

VOLUME IX.— ELEMENTARY PRINCIPLES OF ILLUM-
INATION AND ARTIFICIAL LIGHTING. By A.

BLOK, B.Sc. 240 pp. 124 Illustrations and Diagrams and 1 Folding
Plate. Price 3s. 6d. net. (Post free, 3s. 9d. home ; 4s. abroad.)

VOLUME X.— HYDRAULICS. By E. H. SPRAGUE, A.M.I.C.E.
190 pp. With Worked Examples and 89 Illustrations. Price 3s. 6d.
net. (Post free, 3s. 9d. home ; 4s. abroad.)

26

VOLUME XI.— ELEMENTARY PRINCIPLES OF SUR-
VEYING. By M. T. M. ORMSBY, M.I.C.E.I. 244 pp.
With Worked Examples and 135 Illustrations and Diagrams, including
4 Folding Plates. Price 4s. net. (Post free, 4s. 3d. home ; 4s. 6d.
abroad.)

VOLUME XII.— THE SCIENCE OF WORKS MANAGE-
MENT. By JOHN BATEY. 232 pp. Price 4s. net. (Post
free, 4s. 3d. home ; 4s. 6d. abroad.)

VOLUME XIII.— THE CALCULUS FOR ENGINEERS.

By EWART S. ANDREWS, B.Sc. Eng. (Lond.), and H. BRYON HEYWOOD,
D.Sc. (Paris), B.Sc. (Lond.). 284 pp. 102 Illustrations. With Tables
and Worked Examples. Price 4s. net. (Post free, 4s. 3d. home;
4s. 6d. abroad.)

VOLUME XIV. — LATHES: Their Construction and Operation.

By G. W. BURLEY, Wh.Ex., A.M.I.M.E. 244 pp. 200 Illustrations.

Price 3s. 6d. net. (Post free, 3s. 9d. home ; 4s. abroad.)

[Just published.
VOLUME XV.— STEAM BOILERS AND COMBUSTION.

By JOHN BATEY. 220 pp. 18 Diagrams. Price 4s. net. (Post free,

4s. 3d. home; 4s. 6d. abroad.) [Just published.

VOLUME XVI.— REINFORCED CONCRETE IN PRAC-
TICE. By A. ALBAN H. SCOTT, M.S.A., M.C.I. 190 pp.
130 Illustrations and Diagrams and 2 Folding Plates. Price 4s. net.
(Post free, 4s. 3d. home ; 4s. 6d. abroad.) [Just published.

[IN PREPARATION.]

STABILITY OF MASONRY. E(y E. H. SPRAGUE, A.M.I.C.E.
BRIDGE FOUNDATIONS. By W. BURNSIDE, M.I.C.E.

PORTLAND CEMENT. Its Properties and Manufacture.
By P. C. H. WEST, F.C.S.

TESTING OF MACHINE TOOLS. By G. W. BURLEY,
Wh.Ex., A.M.I.M.E.

CALCULATIONS FOR A STEEL FRAME BUILDING.

By W. C. COCKING, M.C.I.

GEAR CUTTING. By G. W. BURLEY, Wh.Ex., A.M.I.M.E.
MOVING LOADS BY INFLUENCE LINES AND

OTHER METHODS. By E. H. SPRAGUE, A.M.I.C.E.

THE STABILITY OF ARCHES. By E. H. SPRAGUE,

A.M.I.C.E.
DRAWING OFFICE PRACTICE. By W. CLEGG.

ESTIMATING STEELWORK FOR BUILDINGS. By

B. P. F. GLEED and S. BYLANDER, M.C.I.
THE THEORY OF CENTRIFUGAL AND TURBO

PUMP. By J. WELLS.
STRENGTH OF SHIPS. By JAMES BERTRAM THOMAS.

MACHINE SHOP PRACTICE. By G. W. BURLEY, Wh.Ex.,
A.M.I.M.E.

Prospectus giving full Contents of any of the above volumes in preparation will
be sent, when ready, to anyone sending their address to the Publishers.

27

(Sanitary Plumbing, Metal Work, etc.)

EXTERNAL PLUMBING WORK. A Treatise on Lead
Work for Roofs. By JOHN W. HART, R.P.C. 180 Illustrations. 272
pp. Demy 8vo. Second Edition Revised. Price 7s. 6d. net. (Post
free, 7s. lOd. home ; 8s. abroad.)

HINTS TO PLUMBERS ON JOINT WIPING, PIPE
BENDING AND LEAD BURNING. Third Edition,
Revised and Corrected. By JOHN W. HART, R.P.C. 184 Illustrations.
313 pp. Demy 8vo. Price 7s. 6d. net. (Post free, 8s. home; 8s. 6d.
abroad.)

SANITARY PLUMBING AND DRAINAGE. By JOHN
W. HART. Demy 8vo. With 208 Illustrations. 250 pp. 1904. Price
7s. 6d. net. (Post free, 7s. lOd. home; 8s. abroad.)

THE PRINCIPLES OF HOT WATER SUPPLY. By

JOHN W. HART, R.P.C. With 129 Illustrations. 177 pp. Demy 8vo.
Price 7s. 6d. net. (Post free, 7s. lOd. home; 8s. abroad.)

THE PRINCIPLES AND PRACTICE OF DIPPING,
BURNISHING, LACQUERING AND BRONZING
BRASS WARE. By W. NORMAN BROWN. Revised and
Enlarged Edition. Crown 8vo. 48 pp. Price 3s. net. (Post free,
3s. 3d. home and abroad.)

A HANDBOOK ON JAPANNING. For Ironware, Tinware,
and Wood, etc. By WILLIAM NORMAN BROWN. Second Edition.
Crown 8vo. 70 pp. 13 Illustrations. Price 3s. 6d. net. (Post free,
3s. 9d. home ; 4s. abroad.)

Contents.

Introduction. — Priming or Preparing the Surface to be Japanned — The First Stage in
the Japanning of Wood or of Leather without a Priming. Japan Grounds. — White Japan
Grounds — Blue Japan Grounds — Scarlet Japan Ground — Red Japan Ground — Bright Pale
Yellow Grounds — Green Japan Grounds — Orange-Coloured Grounds — Purple Grounds — Black
Grounds — Common Black Japan Grounds on Metal — Tortoise-shell Ground — Painting Japan
Work — Varnishing Japan Work. Japanning or Enamelling1 Metals. — Enamelling Bed-
stead Frames and Similar Large Pieces — Japanning Tin, such as Tea-trays and Similar Goods
— Enamelling Old Work. Enamelling' and Japanning1 Stoves. — Apparatus used in
Japanning and Enamelling— Modern Japanning and Enamelling Stoves— Stoves Heated
by Direct Fire — Stoves Heated by Hot-water Pipes — Pigments suitable for Japanning
with Natural Lacquer — White Pigments — Red Pigments — Blue Pigments — Yellow Pig-
ments— Green Pigments — Black Pigments — Methods of Application — Modern Methods of
Japanning and Enamelling with Natural Japanese Lacquer. Colours for Polished
Brass — Miscellaneous. — Painting on Zinc or on Galvanized Iron — Bronzing Compositions —
Golden Varnish for Metal— Carriage Varnish— Metal Polishes— Black Paints— Black Stains
for Iron — Varnishes for Iron Work. Processes for Tin=Plating. — Amalgam Process —
Immersion Process — Battery Process — Weigler's Process — Hern's Process. Galvanizing.
Index.

SHEET METAL WORKING. Cutting, Punching, Bending,
Folding, Pressing, Drawing and Embossing Metals, with Machinery for
same. By F. GEORGI and A. SCHUBERT. Translated from the German.
Demy 8vo. 160 pages. 125 Drawings and Illustrations. 2 Folding
Plates. Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. abroad.)

[Just published.

(Electric Wiring, etc.)

THE DEVELOPMENT OF THE INCANDESCENT
ELECTRIC LAMP. By G. BASIL BARHAM, A.M.I.E.E.
Demy 8vo. 200 pp. With Two Plates, Ten Tables and Twenty-
five Illustrations. Price 5s. net. (Post free, 5s. 4d. home; 5s. 6d.
abroad.)

28

WIRING CALCULATIONS FOR ELECTRIC LIGHT
AND POWER INSTALLATIONS. A Practical Hand-
book containing Wiring Tables, Rules, and Formulae for the Use of
Architects, Engineers, Mining Engineers, and Electricians, Wiring
Contractors and Wiremen, etc. By G. W. LUMMIS PATERSON. Crown
8vo. 96 pp. 35 Tables. Price 5s. net. (Post free, 5s. 3d. home;
5s. 6d. abroad.)

Contents.

Systems of Electrical Distribution— Direct Current Wiring Calculations — Data Relating to
Direct Current Motors — Data Relating to Direct Current Dynamos — Alternating Current
Wiring Calculations — Alternating Current Motor Wiring Calculations — Calculation of Alter-
nating Current Exposed Wiring Circuits — Data Relating to Alternating Current Motors —
Insulation Resistance — Minimum Insulation Resistance of Electric Light Installation — 1 Lamp
to 150 Lamps — Particulars of Electrical Conductors — Approximate Wiring Capacity of Metal
Conduits — Carrying Capacity of Conductors in 16 Candle Power Lamps at Various Voltages
and Efficiencies — Current Density in Conductors 1000 Amperes per square inch.

ELECTRIC WIRING AND FITTING. By SYDNEY F.
WALKER, R.N., M.I.E.E., M.I.Min.E., A.M.Inst.C.E., etc., etc. Crown
8vo. 150 pp. • With Illustrations and Tables. Price 5s. net. (Post
free, 5s. 3d. home; 5s. 6d. abroad.)

(Brewing and Botanical.)

HOPS IN THEIR BOTANICAL, AGRICULTURAL
AND TECHNICAL ASPECT, AND AS AN ARTICLE
OF COMMERCE. By EMMANUEL GROSS. Translated
from the German. Seventy-eight Illustrations. 340 pp. Demy Svo.
Price 10s. 6d. net. (Post free, 11s. home; 11s. 6d. abroad.)

INSECTICIDES, FUNGICIDES, AND WEED KILLERS.

By E. BOURCART, D.Sc. Translated from the French. Revised and
Adapted to British Standards and Practice. Demy Svo. 450 pp. 83
Tables and 12 Illustrations. Price 12s. 6d. net. (Post free, 13s. home ;
13s. 6d. abroad.)

Contents.

Introduction. — Relative and Absolute Diseases — Etiology — Symbiosis — Therapeutics —
Surgical Treatment — Chemical Treatment — Curative Treatment — Indispensable Properties of
the Chemical Agents — Methods of Using Chemical Products in Treating the Diseases of Plants
— Use of Chemical Agents in the Form of Powder — Use of Chemical Agents in the Liquid
Form — Prophylaxy — Preventive Surgical Treatments — Preventive Treatment by Means of
Chemical Agents — Growth Stimulants — Nutrition — Exhaustion of the Soil — Choice of Species
— Meteorological Influences — United Efforts to Exterminate Injurious Insects, Fungi, and
Weeds. Water, Hot and Cold — Submersion of Field, Forest, and Vineyard — Scalding.
CHEMICAL AGENTS AND PRODUCTS EMPLOYED— Derivatives of Carbon (Carbon
Compounds)—!. Products derived from the Fatty Series: Petroleum (Burning Oil)—
Petroleum Sprays — Petroleum Oil and Soap Emulsions-Petroleum Spirit- Vaseline-Acetylene
— Chloroform — Carbonic Oxide— Methyl Alcohol — Ethyl Alcohol — Amylic Alcohol — Glycerine
(Tri-Hydric Alcohol)— Ether— Mercaptan— Formic Aldehyde — Acetic Acid— Oxalic Acid—
—Oils and Fats— Soaps— Hard Soap— Soft Soap— Whale Oil Soap— Fish Oil Soap— 2.
Products of the Aromatic Series: Benzol— Coal Tar— Wood Tar — Naphthalene— Ter-
penes — Oleo Resins — Galipot — Turpentine — Rosins — Rosin Soaps— Rosin Emulsions — Metallic
Rosinates — Copper Rosinate — Camphor — Nitrobenzene — Carbolic Acid — Picric Acid — Cresol
— " Sapocarbol " — Creosote — " Creolines " — " Lysol " — Potassium Dinitro-Cresylate — Thymol
— /3-Naphthol— Methyl Violet— Tobacco (Nicotine Tobacco Juice) — Quassia — Hellebore—
Pyrethra — Delphinium (Larkspur) — Strychnine — Nux Vomica — Walnut Leaves — Glue— Cutch
—Aloes— Glossary of the Principal Diseases of Plants and the Parasites which occa-
sion them— Copious Index, including the Names of Cultivated Plants and Diseases
from which each Plant may suffer.

(For Agricultural Chemistry, see p. 10.)

29

(Wood Products, Timber and Wood Waste.)

WOOD PRODUCTS : DISTILLATES AND EXTRACTS.

By P. DUMESNY, Chemical Engineer, Expert before the Lyons Com-
mercial Tribunal, Member of the International Association of Leather
Chemists; and J. NOYER. Translated from the French by DONALD
GRANT. Royal 8vo. 320 pp. 103 Illustrations and Numerous Tables.
Price 10s. 6d. net. (Post free, 11s. home ; 11s. 6d. abroad.)

TIMBER : A Comprehensive Study of Wood in all its Aspects
(Commercial and Botanical), showing the Different Applications and
Uses of Timber in Various Trades, etc. Translated from the French
of PAUL CHARPENTIER. Royal 8vo. 437 pp. 178 Illustrations. Price
12s. 6d. net. (Post free, 13s. home ; 14s. abroad.)

Contents.

Physical and Chemical Properties of Timber— Composition of the Vegetable Bodies
— Chief Elements — M. Fremy's Researches — Elementary Organs of Plants and especially of
Forests — Different Parts of Wood Anatomically and Chemically Considered — General Pro-
perties of Wood— Description of the Different Kinds of Wood— Principal Essences with
Caducous Leaves — Coniferous Resinous Trees — Division of the Useful Varieties of Timber
in the Different Countries of the Globe— European Timber— African Timber— Asiatic
Timber — American Timber — Timber of Oceania — Forests — General Notes as to Forests ; their
Influence — Opinions as to Sylviculture — Improvement of Forests — Unwooding and Rewooding
— Preservation of Forests — Exploitation of Forests— Damage caused to Forests — Different
Alterations— The Preservation of Timber— Generalities— Causes and Progress of De-
terioration— History of Different Proposed Processes — Dessication — Superficial Carbonisation
of Timber — Processes by Immersion — Generalities as to Antiseptics Employed — Injection
Processes in Closed Vessels — The Boucherie System, Based upon the Displacement of the
Sap — Processes for Making Timber Uninflammable — Applications of Timber — Generalities
— Working Timber — Paving — Timber for Mines — Railway Traverses — Accessory Products —
Gums — Works of M. Fremy — Resins — Barks — Tan — Application of Cork — The Application of
Wood to Art and Dyeing — Different Applications of Wood — Hard Wood — Distillation of
Wood — Pyroligneous Acid — Oil of Wood — Distillation of Resins — Index.

THE UTILISATION OF WOOD WASTE. Translated from
the German of ERNST HUBBARD. Crown 8vo. 192 pp. Fifty Illustra-
tions. Price 5s. net. (Post free, 5s. 4d. home ; 5s. 6d. abroad.)
(See also Utilisation of Waste Products, p. 9.)

(Building and Architecture.)

ORNAMENTAL CEMENT WORK. By OLIVER WHEATLEY.
Demy 8vo. 83 Illustrations. 128 pp. Price 5s. net. (Post free,
5s. 4d. home ; 5s. 6d. abroad.)

Contents.

Introduction— Chapters I., Workshop— II., Plain Work— III., Technique— IV., Choice of
Ornaments — V., Extended Uses.

THE PREVENTION OF DAMPNESS IN BUILDINGS;

with Remarks on the Causes, Nature and Effects of Saline, Efflores-
cences and Dry-rot, for Architects, Builders, Overseers, Plasterers,
Painters and House Owners. By ADOLF WILHELM KEIM. Translated
from the German of the Second Revised Edition by M. J. SALTER, F.I.C.,
F.C.S. Eight Coloured Plates and Thirteen Illustrations. Crown 8vo.
115 pp. Price 5s. net. (Post free, 5s. 3d. home ; 5s. 4d. abroad.)

HANDBOOK OF TECHNICAL TERMS USED IN ARCHI-
TECTURE AND BUILDING, AND THEIR ALLIED
TRADES AND SUBJECTS. By AUGUSTINE C. PASSMORE.
Demy 8vo. 380 pp. Price 7s. 6d. net. (Post free, 8s. home; 8s. 6d.
abroad.)

30

(Foods, Drugs and Sweetmeats.)

FOOD AND DRUGS. By E. J. PARRY, B.Sc, F.I.C., F.C.S.
Volume I. The Analysis of Food and Drugs (Chemical and Micro-
scopical). Royal 8vo. 724 pp. Price 21s. net. (Post free, 21s. 6d.
home; 22s. 6d. British Colonies; 23s. 3d. other Foreign Countries.)
Volume II. The Sale of Food and Drugs Acts, 1875-1907. Royal 8vo.
184 pp. Price 7s. 6d. net. (Post free, 7s. lOd. home; 8s. abroad.)
Contents of Volume I.

Tea, Cocoa and Chocolate, Coffee— Milk, Cheese, Butter, Lard, Suet, Olive Oil— The Car-
bohydrate Foods — The Starches and Starchy Foods — -Spices, Flavouring Essences, etc. — •
Alcoholic Beverages — Flesh Foods — Microscopical Analysis — Drugs containing Alkaloids, etc.
—Drugs (generally)— The Essential Oils of the British Pharmacopoeia— Fatty Oils, Waxes, and
Soaps of the British Pharmacopoeia — The Chemicals of the British Pharmacopoeia.

Contents of Volume II.

The Sale of Food and Drugs Act. 1875 — Description of Offences— Appointment and Duties
of Analysts, and Proceedings to obtain Analysis — Proceedings against Offenders — Expenses of
executing the Act — The Sale of Food and Drugs Amendment Act, 1879 — The Sale of Food
and Drugs Acts, 1899— The Margarine Act, 1887— The Butter and Margarine Act, 1907.

THE MANUFACTURE OF PRESERVED FOODS AND
SWEETMEATS. By A. HAUSNER. With Twenty-eight
Illustrations. Translated from the German of the third enlarged
Edition. Second English Edition. Crown 8vo. 225 pp. Price 7s. 6d.
net. (Post free, 7s. 9d. home ; 7s. lOd. abroad.)
Contents.

The Manufacture of Conserves — Introduction — The Causes of the Putrefaction of Food
— The Chemical Composition of Foods — The Products of Decomposition — The Causes of Fer-
mentation and Putrefaction — Preservative Bodies — The Various Methods of Preserving Food
— The Preservation of Animal Food — Preserving Meat by Means of Ice — The Preservation
of Meat by Charcoal — Preservation of Meat by Drying — The Preservation of Meat by the
Exclusion of Air— The Appert Method— Preserving Flesh by Smoking— Quick Smoking— Pre-
serving Meat with Salt — Quick Salting by Air Pressure — Quick Salting by Liquid Pressure —
Gamgee's Method of Preserving Meat — The Preservation of Eggs — Preservation of White
and Yolk of Egg — Milk Preservation — Condensed Milk — The Preservation of Fat — Manu-
facture of Soup Tablets— Meat Biscuits— Extract of Beef— The Preservation of Vegetable
Foods in General — Compressing Vegetables — Preservation of Vegetables by Appert's Method
— The Preservation of Fruit — Preservation of Fruit by Storage — The Preservation of Fruit
by Drying — Drying Fruit by Artificial Heat — Roasting Fruit — The Preservation of Fruit with
Sugar — Boiled Preserved Fruit — The Preservation of Fruit in Spirit, Acetic Acid or Glycerine
—Preservation of Fruit without Boiling — Jam Manufacture — The Manufacture of Fruit
Jellies— The Making of Gelatine Jellies— The Manufacture of " Sulzen "—The Preservation of
Fermented Beverages — The Manufacture of Candies — Introduction — The Manufacture of
Candied Fruit — The Manufacture of Boiled Sugar and Caramel — The Candying of Fruit —
Caramelised Fruit — The Manufacture of Sugar Sticks, or Barley Sugar — Bonbon Making —
Fruit Drops — The Manufacture of Dragees — The Machinery and Appliances used in Candy
Manufacture — Dyeing Candies and Bonbons — Essential Oils used in Candy Making — Fruit
Essences — The Manufacture of Filled Bonbons, Liqueur Bonbons and Stamped Lozenges —
Recipes for Jams and Jellies — Recipes for Bonbon Making — Dragdes — Appendix — Index

RECIPES FOR THE PRESERVING OF FRUIT, VEGE-
TABLES AND MEAT. By E. WAGNER. Translated
from the German. Crown 8vo. 125 pp. With 14 Illustrations. Price
5s. net. (Post free, 5s. 3d. home ; 5s. 4d. abroad.)

(Dyeing Fancy Goods.)

THE ART OF DYEING AND STAINING MARBLE,
ARTIFICIAL STONE, BONE, HORN, IVORY AND
WOOD, AND OF IMITATING ALL SORTS OF
WOOD. A Practical Handbook for the Use of Joiners,
Turners, Manufacturers of Fancy Goods, Stick and Umbrella Makers,
Comb Makers, etc. Translated from the German of D. H. SOXHLET,
Technical Chemist. Crown 8vo. 168 pp. Price 5s. net. (Post free,
5s. 3d. home; 5s. 4d. abroad.)

31

(Celluloid.)

CELLULOID : Its Raw Material, Manufacture, Properties and
Uses. A Handbook for Manufacturers of Celluloid and Celluloid
Articles, and all Industries using Celluloid ; also for Dentists and
Teeth Specialists. By Dr. Fr. BOCKMANN, Technical Chemist. Trans-
lated from the Third Revised German Edition. Crown 8vo. 120pp.
With 49 Illustrations. Price 5s. net. (Post free, 5s. 3d. home ; 5s. 4d.
abroad.)

Contents.

Chapters I., Raw Materials for the Manufacture of Celluloid : Cellulose and Pyroxylin
— Gun-cotton — Properties of Gun-cotton — Special Gun-cottons for Celluloid Manufacture —
Nitrating Centrifugalisers— Collodion Wool — Methods of Preparing Collodion Wool — Cam-
phor — Japanese (Formosa) Camphor, Ordinary Camphor — Borneo Camphor (Borneol),
Sumatra Camphor, Camphol, Baros Camphor) — -Properties of Camphor — Artificial Camphor
— Camphor Substitutes. II,, The Manufacture of Celluloid; Manufacturing Camphor by
the Aid of Heat and Pressure — Manufacture of Celluloid by Dissolving Gun-cotton in an
Alcoholic Solution of Camphor— Preparing Celluloid by the Cold Process — Preparation with
an Ethereal Solution of Camphor — Preparation with a Solution of Camphor and Wood
Spirit. III., The Employment of Pyroxylin for Artificial Silk : Denitrating
and Colouring Pyroxylin — Uninflammable Celluloid — Celluloid and Cork Composition —
Incombustible Celluloid Substitute — Xylonite or Fibrolithoid. IV., Properties of
Celluloid. V., Testing Celluloid. VI., Application and Treatment of Celluloid:
Caoutchouc Industry — Making Celluloid Ornaments — Working by the Cold Process —
Working by the Warm Process — Celluloid Combs — Celluloid as a Basis for Artificial
Teeth — Stained Celluloid Sheets as a Substitute for Glass — Celluloid Printing Blocks
and Stamps— Collapsible Seamless Vessels of Celluloid— Making Celluloid Balls— Celluloid
Posters— Pressing Hollow Celluloid Articles— Casting Celluloid Articles— Method for Pro-
ducing Designs on Plates or Sheets of Celluloid, Xylonite, etc. — Imitation Tortoiseshell —
Metallic Incrustations — Imitation Florentine Mosaic — Celluloid Collars and Cuffs — Phono-
graph Cylinder Composition — Making Umbrella and Stick Handles of Celluloid — Celluloid
Dolls— Celluloid for Ships' Bottoms— Celluloid Pens— Colouring Finished Celluloid Articles-
Printing on Celluloid — Employment of Celluloid (and Pyroxylin) in Lacquer Varnishes — Index.

(Lithography, Printing and Engraving.)

ART OF LITHOGRAPHY. By H. J. RHODES. Demy 8vo.
344 pages. 120 Illustrations. 2 Folding Plates. Copious combined
Index and Glossary. Price 10s. 6d. net. (Post free, 11s. home; 11s. 3d.
abroad.)

PRINTERS' AND STATIONERS' READY RECKONER
AND COMPENDIUM. Compiled by VICTOR GRAHAM.
Crown 8vo. 112 pp. 1904. Price 3s. 6d. net. (Post free, 3s. 9d. home ;
3s. lOd. abroad.)

Contents.

Price of Paper per Sheet, Quire, Ream and Lb.— Cost of 100 to 1000 Sheets at various
Sizes and Prices per Ream— Cost of Cards— Quantity Table— Sizes and Weights of Paper,
Cards, etc. — Notes on Account Books — Discount Tables — Sizes of spaces — Leads to a Ib. —
Dictionary — Measure for Bookwork — Correcting Proofs, etc.

ENGRAVING FOR ILLUSTRATION. HISTORICAL
AND PRACTICAL NOTES. By J. KIRKBRIDE. 72 pp.
Two Plates and 6 Illustrations. Crown 8vo. Price 2s. 6d. net. (Post
free, 2s. 9d. home ; 2s. lOd. abroad.)

(For Printing Inks, see p. 3.)

(Bookbinding.)

PRACTICAL BOOKBINDING. By PAUL ADAM. Translated
from the German. Crown 8vo. 180 pp. 127 Illustrations. Price 5s.
net. (Post free, 5s. 4d. home ; 5s. 6d. abroad.)

32

(Sugar Refining.)

THE TECHNOLOGY OF SUGAR : Practical Treatise on
the Modern Methods of Manufacture of Sugar from the Sugar Cane and
Sugar Beet. By JOHN GEDDES MC!NTOSH. Third Revised and
Enlarged Edition. Demy 8vo. Fully Illustrated.

[New Edition in the press.

(See "Evaporating, Condensing, etc., Apparatus," p. 25.)

(Emery.)

EMERY AND THE EMERY INDUSTRY. Translated
from the German of A. HAENIG. Crown 8vo. 45 Illustrations. 110pp.
Price 5s. net. (Post free, 5s. 3d. home ; 5s. 6d. abroad.)

Contents.

Abrasive Materials. — Natural Abrasive Materials — Emery — Corundum — The Artificial
Abrasives : Carborundum, Acheron's Carborundum Furnace Equipment and Operation of
Carborundum Works, Purification and Properties of Carborundum, Output of Carborundum
—Artificial Corundum— Crushed Steel— Electrite. Emery and Grinding Discs.— The Pre-
paration of Discs and Emery Wheels — The Binding Medium — Hardness and Grain — Peri-
pheral Velocity — Hardness of the Abrasive Material — The Manufacture of Emery Discs, etc.
— Varieties and Shapes of Emery Discs — Wheels and Cylinders — Experiments on the Stability
and Capacity of Emery Wheels — Points on the Use of Grinding Discs — The Further Treat-
ment of Grinding Discs — Mounting the Discs — Guards — Results of Bursting Tests — Dust
Exhauster — Roughing and Trueing the Grinding Discs. Grinding1 Machines. — Introductory
— Principal Types of Grinding Machines — Tool-Grinding Machines — Knife-Grinding Machines
— Saw- Sharpen ing Machines — Machines for Grinding Flat Surfaces — Special Types of Grind-
ing Machines— Circular Grinding— Universal Tool Grinding Machines— Working Results
Obtained in Practical Grinding.

(Bibliography.)

CLASSIFIED GUIDE TO TECHNICAL AND COM-
MERCIAL BOOKS. Compiled by EDGAR GREENWOOD.
Demy 8vo. 224 pp. 1904. Being a Subject-list of the Principal
British and American Books in print ; giving Title, Author, Size, Date,
Publisher and Price. Price 5s. net. (Post free, 5s. 4d. home ; 5s. 6d.
abroad.)

HANDBOOK TO THE TECHNICAL AND ART
SCHOOLS AND COLLEGES OF THE UNITED
KINGDOM. Containing particulars of nearly 1,000 Techni-
cal, Commercial and Art Schools throughout the United Kingdom.
With full particulars of the courses of instruction, names of principals,
secretaries, etc. Demy 8vo. 150 pp. Price 3s. 6d. net. (Post free,
3s. lOd. home; 4s. abroad.)

SCOTT, GREENWOOD & SON,

TECHNICAL BOOK AND TRADE JOURNAL PUBLISHERS,
8 BROADWAY, LUDGATE, LONDON, E.C., ENGLAND.

Telegraphic Address, "Printeries, Cent., London". July, 1915.

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