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Plain brick. 

Pressed brick 
showing "frog 

Hollow brick. 

o o o o o 

o o o 
o o o o o 

Perforated brick. 


Arch brick or 

Diamond stretcher. 


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. 


Ventilator or air brick. 









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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. 


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 manufacturers r 
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. 





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


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 


The General Manufacture of Bricks . . 20 

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


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

The Stiff-Plastic Process . 177 

The Semi-Dry or Semi-Plastic Process 219 


The Dry or Dust Process . . . < 240 





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

Vitrified Bricks for Special Work . . . . 36S 


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

Glazed Bricks . . . . , . ... 397 

Perforated, Radial, and Hollow Bricks and Blocks Fireproof Flooring . 412 

Moulded and Ornamental Bricks . . . .... . . 418 

Drying Raw Clay . . . . . . ..'... . 420 

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





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. 



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 u clay 
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 


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 

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. 


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 

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 

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. 


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 

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 : 


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 

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 


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 

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 


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. 


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. 


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 

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 


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- 

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 


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, 


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 

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. 


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 


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 

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 


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 

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. 


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 


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 


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 

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. 




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 


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 

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. 


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 



<?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 

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 


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 

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 


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. 


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 


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 


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 

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 

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 



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 

' 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, 


-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 



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,, 


FIG. 6. Wagon with V-shaped clip. 

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


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 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 

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 




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

FIG. 11. End-tipping wagon. 


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 


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. 


FIG. 12. Overhead or aerial ropeway. 



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- 

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 

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

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


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. 



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 


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. 


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, 


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 


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 

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 K 2 
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 



FIG. 15. Home-made pug-mill. 



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 


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 



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 

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 



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 

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 


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 




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 


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 

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. 


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 


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 


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 

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 



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 


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. 


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. 



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- 



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 



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, 


FIG. 27. German hack. 



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. 



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. 


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. 


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 


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 

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 



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 


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. 


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- 



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 



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. 



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 


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 



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). 





FIG. 35. Eddington's moulding machine. 

FIG. 36. Eddington brick mould. 


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, 


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. 



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, 



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 

(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- 

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. 



(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 



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 



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). 




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 



(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. 



(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 



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 




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 



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 



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 
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 



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 

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 


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 

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 


:iV, ' 



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 



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 


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 


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 



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





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. 


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 




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 



FIG. 57. Light pan mill (Boultoa). 

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


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. 



FIG. 59. Mill with conical runners 

FIG. 60. Mill for limey clays. 



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, 


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. 


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 


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 


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. 



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. 



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 



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). 


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. 




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 

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 

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 



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. 



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. 



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 



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 


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 





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 





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. 



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 



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 



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. 



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 

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 ). 


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- 

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


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 

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 

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


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 


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 

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- 

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. 





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- 



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

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



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 




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 



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 



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. 



FIG. 84. Cutting table with dressing roller. 

FIG. 85. " Simplex '' cutting table. 



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 



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

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. 



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. 


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 

(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 

(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. 



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, 



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 

Repressing. The methods of brickmaking already described are 


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 



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 



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- 



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 



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 

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. 



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). 




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. 



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 

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



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 



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 


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. 



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 



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 



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 

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. 



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 


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 : 


(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- 


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 

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 


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 

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 


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 



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. 


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 







1 1 





















^v I ^^ 





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 



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 



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, 



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 




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 





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 


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. 



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. 



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 


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 


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. 


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 

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, 


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 

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 


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. 


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 


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 


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 


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 



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 



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- 



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 



be cleaned out to prevent iron bolts, etc., remaining in the 

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 



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 


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- 



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 



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. 



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 

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 



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, 



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. 



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 

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 

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 


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 



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 


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 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 



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. 


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 



owing to the necessity of altering its shape so much in the re- 

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) 


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 

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 

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 


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 


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 


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- 



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 



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. 



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 


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 



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 

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, 


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 

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 



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 



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- 



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 



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- 



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. 


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 

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. 


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 

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- 



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. 





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 


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- 



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 



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. 


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- 


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 

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 


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 




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. 


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 

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 







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- 


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 


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, 


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 



bricks to the front, giving ample time for the attendant to remove 


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. t j on j g rea lly 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 


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 


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. 



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 


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 

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 


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 

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. 


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- 


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 


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. 


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 



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 



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 


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 

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 



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- 

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- 

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 



has the disadvantage that a cart cannot be taken into the 

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 

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 



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 



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 



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. 


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 the 1 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 



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 



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). 



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 


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 

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 

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 

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 


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 

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 



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 



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, 



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 


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 (6 3 ) 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 



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 

For an annual output of 1,000,000 or more bricks some form 
of continuous kiln is very desirable, the precise construction 


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 

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 



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, 


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 

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 

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. i i; 

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 

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 



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- 

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 



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 



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 

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). 


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- 




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 



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 


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 

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 

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., 


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 



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 



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 

If the sectional area of the chimney is increased proportion- 
ately, so as to double the cross-section, the draught is doubled. 



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 

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 

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 



FIG. 201. Matthews & Yates fan. 


FIG. 202. Sutcliffe fan. 



Co., Ltd. (fig. 204); James Keith & Blackman Co., Ltd. (fig. 

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 



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 

Fans can be worked without any chimney, but it is better to 



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). 



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 b 1 




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. 



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 




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 


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 

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 



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 

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- 

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 b l e 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- 



"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., 

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 



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 

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 

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 


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- 



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 anc 1 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. 





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 


c'O 7 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. 



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. 


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- 



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, 


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 

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 


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 



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 other way can absolutely continu- 
ous heating without variations due to the removal of ashes be 

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. 


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- 



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 



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 

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 


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 

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- 



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. 


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 



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 


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. 


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 



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 


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 



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 



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 


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 

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. 



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 

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 


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 


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 


shown in fig. 234, he was able to work an unusually delicate 
clay with perfect satisfaction. 


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 

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 



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 


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 



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 






. L 

= -" 


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 



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 



FIG. 239. Trace-holes. 

they may become choked with coal or ash. which would merely 

retard the progress of 

the fire throughout the 


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 



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 

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 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 : 


(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. 



(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 



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 

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. 



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). 


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 



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 

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. 



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 : 




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 


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 

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 

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 


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- 


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 

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 


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 


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 


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 


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 

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 


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 


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 


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 


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 


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 


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 : 



o. 1 chamber 






, 7 

, 8 



, 10 

, 11 

, 12 

, 13 


" Smoking" 


Being fired 

Being emptied] 
Being filled 

15 to 120 C. 

120 to 200 C. 


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. 























or ; 
"Drying". ; 




Bed Hot. 

Red Hot. 


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. 



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 

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 


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. 


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 


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 

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 


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 

In the more modern types of continuous kiln a series of grates 
running from front to back is used. This arrangement, first iritro- 


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 



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 

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," 



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 

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 I960 

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. 



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- 


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 


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. 


" 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- 

" 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 

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 


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 600 n 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 


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. 


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 



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 

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 fuh 1 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 

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. 



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 

(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 

(/) 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 


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 


bricks from which the sample has been taken must be re- 

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. 


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 



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 

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 

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- 


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. 


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. 


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 

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. 


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 

x The 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. 


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 wih 1 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 of 1 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.. 


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 

. 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 


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\ 


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 

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 

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 


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. 


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 


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 

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), 



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 

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. 


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 

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 


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- 

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 (Al 2 O 3 SiO 2 ) 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. 


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 

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 


trying conditions, but they serve a useful purpose in many in- 

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- 

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 


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 


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- 

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 


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. 


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 weh 1 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 


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 J F 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. 


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 

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 

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. 


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 



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- 

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 ah 1 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. 


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- 


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 

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- 


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. 



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- 

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. 


Lead compounds are seldom necessary in hand-fired glazes, 
and their use should be avoided whenever possible for several 

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 : 


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 


of some fire-clays is impracticable on account of the shale-oil they 

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. 


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. 


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. 


The glaze (usually opaque) is applied by dipping in the 
manner already described, it being used direct or preferably on a 

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 



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 


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. 


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 

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- 


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) 


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 


will be firm and the bricks prevented from tipping during the 

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 

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) 


which will show whether the glaze is sufficiently thick and 

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- 

" Scummed bricks " are due to insufficient firing before or after 
adding the salt, and can usually be cured by re-firing at a higher 

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 



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 



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 


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 . 254 a.- 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- 


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 


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 




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 

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. 



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. 



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. 



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 



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 

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 


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. 



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 

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 ". 


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 

The first of these is treacherous because it is strong and sticky 



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 


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 

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 


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 


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 

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. 


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 


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 




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, 

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- 


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 



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 



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, 333 r 

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 


" 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, 

Drying, 56, 154, 213, 238, 239, 339, 342, 

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 


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., 

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, 


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 




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 


83, 84, 94, 179, 183 
Grizzles, 17 

Grog, 18, 375, 380, 383, 389 
size of, 381 
" Groke," 122 
" Guthrie," 267, 268, 300 


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 



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, 


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, 

Lumps, 87, 180 

Machine moulding, 68 
Magnesia, 373, 391, 393 
bricks, 394 



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, 


Mouthpieces, 77, 108, 113, 413 
Muffle, 309 

kilns, 309, 335 
Multiple roller machine, 127 

runner wheel, 191 

" Murray" machine, 125, 126 


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, 

floor, 254 



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, 

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, 


Regeneration, 256, 301, 307, 345 
Regeneratively heated air, 301 
Regenerators, 256, 257, 259, 301, 307, 


" 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 



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 


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, 

" 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 



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, 


" 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, 


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, 


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 



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 


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 


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 



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, 

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 


Zinc oxide, 402 






With 5 Plates and 950 Illustrations. 
500 Pages. Royal 8vo. 


K. H. BIRD, M.A., and W. MOORE BINNS, 

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Scott, Greenwood & Son, 







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as supplied to : 

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Public Works Departments. 

Mining Companies in South Africa. 

Machinery supplied to : East Africa, India, Straits Settle- 
ments, Australia, South Africa and principal Brick- 
works at Home and in the Colonies. 



Established 1860. 


1,300 Workmen. 





MILLS. Buhler's Patent. -Feeders, Pug Mills, 
Revolving Presses, Drain Tile Machines, Cutters, 

DRYING PLANTS, Buhler's Patent. Artificial 
Channel Driers, superior system ; Special Fans. 
Numerous Plants Installed. 

MODERN KILNS, Buhler's Patent. Channel 
Kilns; Circular Kilns and Shaft-Kilns, for burn- 
ing coke, gas and oil ; Special Kilns. 

PLANTS, of any size, for all ceramic products. 


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Special \9ee6nieal J3ooks 





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 

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Fruit Preserving ... .. 30 

Printers' Ready Reckoner 31 

Anti-fouling Paints ... 4 

Fungicides 28 

Printing Inks 3,5 

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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 




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Introductory. Light White Light The Spectrum The Invisible Spectrum Normal 
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CORROSIVE PAINTS. Translated from the German of 
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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- 
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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 
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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, 
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(Varnishes and Drying Oils.) 

Second, greatly enlarged, English Edition, in three Volumes, based on 
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(Oils, Fats, Waxes, Greases, Petroleum.) 

Origin, Preparation, Properties, Uses and Analyses. A Handbook for 
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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. 

By AN EXPERT OIL REFINER. Second Edition. 100 pp. Demy Svo. 
Price 7s. 6d. net. (Post free, 7s. lOd. home ; 8s. abroad.) 

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. 


RICHARD BRUNNER. Translated from the Sixth German Edition by 
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Second Edition Revised and Enlarged. Demy 8vo. 214 pp. 1904. 
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ANIMAL FATS AND OILS: Their Practical Production, 
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perties, Falsification and Examination. Translated from the German 
of Louis EDGAR. ANDES. Sixty-two Illustrations. 240 pp. Second 
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VEGETABLE PATS AND OILS: Their Practical Prepara- 
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Louis EDGAR ANDES. Ninety-four Illustrations. 340 pp. Second 
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EDIBLE FATS AND OILS : Their Composition, Manufacture 
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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. By T. W. KOPPE. Translated from the Second 
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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. 

cated Soaps, Stain-removing Soaps, Metal Polishing Soaps, Soap 
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IRON. Their Uses and Applications as Mordants in Dyeing 
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SHALE OILS AND TARS and their Products. By Dr. W. 

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Chapters I., History of the Shale and Lignite-tar Industry. II., The Bituminous 
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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 
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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- 
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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 
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By K. R. LANGE. Translated from the German. Crown 8vo. 164 pages. 
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INDUSTRIAL ALCOHOL. A Practical Manual on the 
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on the Rational Utilisation, Recovery and Treatment of Waste Pro- 
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from the German of Dr. KARL DIETERICH. Demy 8vo. 340 pages. 
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ETC. By VICTOR SCHWEIZER. Demy 8vo. 185 pages. 
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TIAN. Translated from the German. Crown 8vo. 112 pages. 18 Illus- 
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(Agricultural Chemistry and Manures.) 


HERBERT INGLE, F.I. C.,F.C.S., Late Lecturer on Agricultural Chemistry, 
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and Revised Edition. 400 pp. 16 Illustrations. Demy 8vo. Price 
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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.) 

the French, with numerous Notes. Demy 8vo. 350 pp. 69 Illustra- 
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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- 
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(Industrial Uses of Air, Steam and Water.) 

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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, 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.) 



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.) 

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 ) 


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.) 


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.) 


English Edition, Revised and Enlarged. Based on the French work of 
GEDDES MC!NTOSH. Royal 8vo. 100 Illustrations. 400 pages. Price 
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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 


(Leather Trades.) 

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.) 


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.) 

8vo. 440 pages. 260 Illustrations. Price 12s. 6d. net. (Post free, 
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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 
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Semi = Dry or Semi-Plastic Process. Lamination Drying Troubles Moulds and Arrises. 
The Dry or Dust Process. Lamination. Kilns. Down-draught Kilns Horizontal-draught 
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tinuous Kilns Hoffmann Kilns Hot-air Flues Temporary and Permanent Flues Chamber 
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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. 

by Experts, and Edited by CHAS. F. BINNS. Fourth Edition, Revised 
and Enlarged. DemySvo. 200 pages. (Post free, 
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POTTERY DECORATING. A Description of all the Pro- 
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Manual for Pottery, Tile, and Brick Manufacturers. By EMILE 
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Notes by ALFRED B. SEARLE. Demy 8vo. 308 Illustrations. 460 pp. 
Price 12s. 6d. net. (Post free, 13s. home; 13s. 6d. abroad.) 


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. 
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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.) 

72 pp. 20 Illustrations. Price 3s. 6d. net. (Post free, 3s. 9d. home 
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A Reissue of 


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 

(Originally published in 1837.) 750 pp. Royal 8vo. Price 10s. net. 
(Post free, 10s. 6d. home; 12s. abroad.) 

Demy 8vo. 310 pp. With upwards of Twelve-hundred Illustrations of 
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(Glassware, Glass Staining and Painting.) 

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.) 


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. 


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.) 


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. 


(Paper Making and Testing.) 

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.) 

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 MakingSpecific 
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 

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.) 


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 


(Enamelling on Metal.) 

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.) 


NORMAN BROWN. Second Edition, Revised. Crown 8vo. 60 pp. Price 
3s. 6d. net. (Post free, 3s. 9d. home ; 3s. lOd. abroad.) 

(Textile Subjects.) 

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.) 


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. 


[In the Press. 

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.) 


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. 


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.) 


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-WoollensYarn 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. 

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.) 


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.) 


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.) 

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.) 



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.) 

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.) 

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.) 

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.) 


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.) 


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.) 

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. 


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.) 


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. 

relating to Woollens. From the German of N. REISER. Thirty-four 
Illustrations. Tables. 160 pp. Demy 8vo. 1904. Price 10s. 6d. net. 
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Crown 8vo. About 176 pages. [In the press^ 

M.Sc., and E. MIDGLEY. Demy 8vo. 316 pp. Numerous Tables, 
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Second Edition, Revised and Enlarged. Crown 8vo. 140 pp. 2& 
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MACKIE. Crown 8vo. 76 pp. Price 3s. 6d. net. (Post free, 3s. 9d. 
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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. 


Translated from the German of CARL KRETSCHMAR. Royal 8vo. 123 
Illustrations. 150 pp. Price 10s. 6d. net. (Post free, 10s. lOd. home ; 
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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.) 

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.) 

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. 


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 
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[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.) 


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 

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Coloured Plates and Seventy-two Illustrations. 160 pp. Demy 8vo. 
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Reissue of 

Translated from the French of M. HELLOT, M. MACQUER and M. LE 
PILEUR D'APLIGNY. First Published in English in 1789. Six Plates. 
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GEORGIEVICS. Translated from the Second German Edition. 412 pp. 
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Handbook for the Dyer and Student. By FRANKLIN BEECH, Practical 
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BEECH, Practical Colourist and Chemist. Thirty-three Illustrations. 
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(Silk Manufacture.) 


By HOLLINS RAYNER. Demy 8vo. 170pp. 117 Illus. 
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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. 


(Bleaching and Bleaching Agents.) 


L. TAILFER, Chemical and Mechanical Engineer. Translated from the 
French by JOHN GEDDES MC!NTOSH. Demy 8vo. 303 pp. Twenty 
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By Professor MAX BOTTLER. Translated from the German. Crown 
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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.) 

Spinning Master, Bolton Technical School. 160pp. Eighty-four Illus- 
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COTTON SPINNING (Intermediate, or Second Year). By 
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COTTON SPINNING (Honours, or Third Year). By THOMAS 
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Spinning Master, Technical School. Bolton. Demy 8vo. 117 Illustra- 
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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, 
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The Production, Characteristics, and Regulation of Cotton Waste. The Use of 
Cotton Waste The Making of Waste in Cotton Mills : IntroductionThe 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. 


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. 

8vo. 76 pages. Price 3s. net. (Post free, 3s. 3d. home ; 3s. 6d. abroad.) 

(Flax, Hemp and Jute Spinning.) 

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.) 


(Collieries and Mines.) 

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.) 

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.) 


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.) 

8vo. Thirty-six Illustrations. 200 pp. Price 7s. 6d. net. (Post free, 
7s. lOd. home; 8s. abroad.) 


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 

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.) 


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.) 

Translated from the German of the Third Edition. Crown 8vo. 
120 pp. Price 5s. net. (Post free, 5s. 3d. home ; 5s. 4d. abroad.) 

stitution of Iron Alloys and Slags). Translated from German of 
HANNS FREIHERR v. JUPTNER. 350 pp. Demy 8vo. Eleven Plates 
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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- 
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(The " Broadway " Series of Engineering 

Uniform in Size : Narrow Crown 8vo. (To fit Pocket.) 

EWART S. ANDREWS, B.Sc. Eng. (Lond.). 200 pp. With 57 Illus- 
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Translated and Revised from the German, and adapted to English 
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WORK. By K. SCHINDLER. Translated and Revised from 
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B.Sc. (Lond.). 220 pp. 136 Illustrations. Price 3s. 6d. net. (Post 
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VOLUME V. STEAM TURBINES : Their Theory and Con- 
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and Calculation. By H. WILDA. Translated from the German ; 
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Translated from the German ; revised and adapted to British practice. 
148 pp. 51 Illustrations. Price 3s. 6d. net. (Post free, 3s. 9d. home ; 
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DOMMETT, Wh.Ex., A.M.I.A.E. 2GO pp. 102 Illustrations. Price 
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BLOK, B.Sc. 240 pp. 124 Illustrations and Diagrams and 1 Folding 
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190 pp. With Worked Examples and 89 Illustrations. Price 3s. 6d. 
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VEYING. By M. T. M. ORMSBY, M.I.C.E.I. 244 pp. 
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4 Folding Plates. Price 4s. net. (Post free, 4s. 3d. home ; 4s. 6d. 

MENT. By JOHN BATEY. 232 pp. Price 4s. net. (Post 
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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; 
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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. 

By JOHN BATEY. 220 pp. 18 Diagrams. Price 4s. net. (Post free, 

4s. 3d. home; 4s. 6d. abroad.) [Just published. 

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. 



PORTLAND CEMENT. Its Properties and Manufacture. 
By P. C. H. WEST, F.C.S. 

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. 


(Sanitary Plumbing, Metal Work, etc.) 

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.) 

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. 

W. HART. Demy 8vo. With 208 Illustrations. 250 pp. 1904. Price 
7s. 6d. net. (Post free, 7s. lOd. home; 8s. abroad.) 


JOHN W. HART, R.P.C. With 129 Illustrations. 177 pp. Demy 8vo. 
Price 7s. 6d. net. (Post free, 7s. lOd. home; 8s. abroad.) 

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.) 


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 Enamelling 1 Metals. Enamelling Bed- 
stead Frames and Similar Large Pieces Japanning Tin, such as Tea-trays and Similar Goods 
Enamelling Old Work. Enamelling' and Japanning 1 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. 

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.) 

Demy 8vo. 200 pp. With Two Plates, Ten Tables and Twenty- 
five Illustrations. Price 5s. net. (Post free, 5s. 4d. home; 5s. 6d. 


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; 
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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. 

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.) 

from the German. Seventy-eight Illustrations. 340 pp. Demy Svo. 
Price 10s. 6d. net. (Post free, 11s. home; 11s. 6d. abroad.) 


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.) 


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. 
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.) 


(Wood Products, Timber and Wood Waste.) 


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.) 


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 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.) 

Demy 8vo. 83 Illustrations. 128 pp. Price 5s. net. (Post free, 
5s. 4d. home ; 5s. 6d. abroad.) 


Introduction Chapters I., Workshop II., Plain Work III., Technique IV., Choice of 
Ornaments V., Extended Uses. 


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.) 

Demy 8vo. 380 pp. Price 7s. 6d. net. (Post free, 8s. home; 8s. 6d. 


(Foods, Drugs and Sweetmeats.) 

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. 

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.) 

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 

from the German. Crown 8vo. 125 pp. With 14 Illustrations. Price 
5s. net. (Post free, 5s. 3d. home ; 5s. 4d. abroad.) 

(Dyeing Fancy Goods.) 

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.) 



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. 


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.) 

344 pages. 120 Illustrations. 2 Folding Plates. Copious combined 
Index and Glossary. Price 10s. 6d. net. (Post free, 11s. home; 11s. 3d. 

Crown 8vo. 112 pp. 1904. Price 3s. 6d. net. (Post free, 3s. 9d. home ; 
3s. lOd. abroad.) 


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. 

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.) 


from the German. Crown 8vo. 180 pp. 127 Illustrations. Price 5s. 
net. (Post free, 5s. 4d. home ; 5s. 6d. abroad.) 


(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.) 


from the German of A. HAENIG. Crown 8vo. 45 Illustrations. 110pp. 
Price 5s. net. (Post free, 5s. 3d. home ; 5s. 6d. abroad.) 


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. Grinding 1 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. 


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. 

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.) 



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