A rudimentary treatise on the manufacture of bricks and tiles : containing an outline of the principles of brickmaking, and detailed accounts of the various processes employed in the making of bricks and tiles in different parts of England

Front matter

I

MR. WEALE’S

NEW SERIES OF RUDIMENTARY WORKS

Preface

The preparation of this little work has necessarily ex¬ tended over a considerable period of time, and, although our limits preclude anything like an attempt at a com¬ plete view of the principles and practice of Brick¬ making, it will be found to contain much practical information which has never yet been published, and descriptions of processes which are little known be¬ yond the localities where they are practised. The whole of the illustrations have been drawn expressly for the Work, and the descriptions of tools and pro¬ cesses have been written from personal observation, no dependance having been placed on verbal descrip¬ tion, even by experienced workmen. Working brickmakers are mostly illiterate men, unable to describe correctly their own operations, and still less to explain their meaning. I have therefore considered it necessary to have every process here described carefully watched throughout, either by myself or by some one on whose accuracy of observation I could place dependance.

In the course of last autumn I drew up several papers of questions, embracing a variety of points on which it was found difficult to obtain correct information, but which were distributed amongst those of my friends who were likely to have opportunities of ascertaining what was required.

Many of these papers in course of time were returned, accompanied by valuable details, and I have to express

VI

PREFACE.

my thanks and obligations to many gentlemen per¬ sonally unknown to me, for the assistance thus af¬ forded. Amongst those from whom I have received valuable assistance during the progress of the work, I may especially mention the names of Mr. Arthur Aikin, Mr. John Lees Brown, of Lichfield, Mr. William Booker, of Nottingham, Mr. Richard Prosser, of Birmingham, and Mr. Frederick Ransome, of Ipswich.

Mr. Richard Prosser has kindly contributed a valuable account of the practice of Brickmaking in Stafford¬ shire which will be read with much interest, and it will be worth the reader’s while to compare the processes described in this chapter with those made use of in the neighbourhood of Nottingham, described in Chapter III.

The details given in Appendix I. respecting the manu¬ facture of Suffolk bricks were kindly furnished by Mr. Frederick Ransome, to whom I am also indebted for drawings of a Suffolk kiln, which were intended by him as a contribution to the work, but which un¬ fortunately were committed to the post for transmis¬ sion, and never reached their destination.

In collecting the information requisite for writing the accounts of Brickmaking and Tilemaking as practised in the neighbourhood of London, I am under great obli¬ gations to Mr. Adams and Mr. Randell, of the Maiden- Lane Tileries, and to Mr. Samuel Pocock, of the Cale¬ donian Fields, Islington, for the kindness with which they afforded me facilities for inspecting and sketching their works, and for the liberal manner in which they furnished me with details of prices and quantities.

Although much time and pains have been bestowed upon the work, there is so much difficulty in writing a strictly-accurate account, even of a simple operation, that

PREFACE.

Vll

I cannot hope that it is perfectly free from errors; but I trust that they are only of a trivial nature, and I shall he greatly obliged to any reader who will point out any omissions or mis-statements, that I may be able to cor¬ rect them in a future edition.

There has long been a want of rudimentary treatises on the Materials of Construction, published in a cheap form, and written in a simple and practical style, di¬ vested of scientific technicalities, which render such books nearly useless to those by whom they are most needed. I venture to express a hope that this work may be of service in supplying this deficiency with regard to one very important class of building materials. At the same time it must be observed that the science of Brick¬ making is as yet untrodden ground, comparatively little being known of the manner in which different sub¬ stances mutually act upon each other when exposed to furnace heat, or of the relative proportions of silica, alumina, lime, and other usual ingredients of brick-earths, which are best calculated to produce a sound, well¬ shaped brick, of a pleasing colour. All that I have attempted here, therefore, is to give a clear description of the actual manufacture of bricks and tiles, and to explain the leading differences which exist in the manner of conducting the several operations of Brickmaking in various parts of this country. How far I have suc¬ ceeded in this attempt the reader alone can determine.

EDWARD DOBSON.

CONTENTS OF PART I.

N.B. — The Numbers refer to the Paragraphs and not to the pages.

INTRODUCTION.

I. Early history of the art would not add to our practical know¬ ledge. II. Burnt brick used in the building of the Tower of Babel; in the walls of Babylon ; both burnt and sun-dried bricks used in ancient Egypt. III. Bricks extensively used by the Romans ; the art of brick¬ making lost at the decline of the Roman Empire ; subsequently revived in the middle ages. V. Brickmaking introduced into England by the Romans ; arrived at great perfection at the time of Henry VIII. : only used for large mansions in the time of Queen Elizabeth. VI. Brick generally introduced as a building material in London after the great tire of 1666; many tine specimens of brickwork still extant, executed at the beginning of the 18th century. VII. Enumeration of the duties successively imposed upon bricks and tiles ; abolition of the distinction between common and dressed bricks, by 2nd and 3rd Viet. c. 24. VIII. The new act a great boon to the public. IX. Bricks used for drainage works exempt from duty; difficulty of defining the extent of the ex¬ emption. X. Number of bricks made yearly in Great Britain. XI. Differences in the processes employed in brickmaking in different parts of England.

Chapter I. General Principles Of The Manufacture Of Bricks And Tiles

I. BRICKS.

1. Classification of the various operations of the brickmaker.

preparation of brick-earth.

2. Enumeration of qualities to be aimed at in making bricks. 3. Suc¬ cess depends principally on the selection and preparation of brick-earth. 4. Brick-earths may be divided into three principal classes; viz., pure

Contents

IX clays, marls, and loams; few earths fit for brickmaking without some mixture. 5. Alumina the principal ingredient in brick-earth; cracks in drying, after being moulded, and will not stand firing ; necessary to add sand to strong clays, to diminish (their contraction ; lime and sifted ^ breeze used near London for the same purpose. 6. Composition of fire clay. 7. Table, showing the constituents of several infusible earths.

8. Enumeration of principal localities where fire bricks are made ; rela¬ tive cost of Windsor, Welch, and Stourbridge fire bricks. 9. Bricks made of refractory clav, baked rather than burnt. 10. Composition of fusible earths. 11. London bricks not made of clay, but of loams and marls. 12. Bricks may be divided into two classes, baked and burnt ; difficulties in treating the fusible earths. 13. Cutting bricks made from sandy loams, either natural or artificial. 14. Colour depends not on the natural colour of the clay, but upon its chemical composition. 15. Bricks might be made of various colours by the employment of metallic oxides. 16. Floating bricks. 17- Unsoiling. 18. Clay digging and weatherinq. 19. Stones must be picked out by hand ; injurious effect of limestone in the clay. 20. Grinding. 21. Washing. 22. Cutters made of washed earth mixed with sand. 23. Sufficient attention not generally paid to the preparation of brick-earth.

TEMPERING.

Chapter II

ON THE MANUFACTURE OF BRICKS AND TILES IN HOLLAND, BY HYDE CLARK, C.E.

I. BRICKS.

Bricks extensively used in Holland for a variety of purposes.—Dutch clinkers made at Moor, two miles from Gouda.—Material for making them is the slime of the river Yssel and of the Haarlem Meer._Tlie

sand used is brought from the banks of the river Maes_For Flemish

bricks the sand is brought from the river Scheldt.—The slime and sand are mixed, and kneaded together by treading.—Dimensions of paving bricks and Dutch clinks—House bricks and tiles made at Utrecht from brick-earth found in the neighbourhood.—Dimensions of house-bricks.

II. BRICK-KILNS.

Sometimes made to burn upwards of a million of bricks.—Fire-holes

left in the side-walls.—Doorway made in the breadth of the kiln_Sheds

erected on each side of the kiln to shelter the fires.—Mode of setting the kiln.—Mode of firing. 8

III. TILES.

Varieties of tiles made in Holland.—Clay ground in a pug-mill.— Kneaded by women before moulding—Two moulders, viz., a rough moulder and a finisher.—Tiles dried first in sheds and afterwards in the sun—Moulding of flat paving-tiles—Iron moulds used in Switzerland.

IV. TILE-KILNS.

Tiles burnt in covered kilns with arched furnaces.—Setting Burn-

ing. —Cooling.—Mode of giving a gray colour.—Glazing.—Utrecht the principal seat of the tile manufacture.—Gouda celebrated for pottery and tobacco-pipes. J

CONTENTS.

XI

Chapter III. Brickmaking As Practised At Nottingham

1. Peculiarities in manufacture of bricks near Nottingham. 2. Use of brass moulds not confined to Nottingham. 3. Object of crushing the brick-earth between rollers. 4. Advantages and disadvantages of the use of rollers. 5. Description of brickmaking at Nottingham applies, with slight variations, to the practice of the neighbouring counties. 6. Brick-earth from the marls of the new red sandstone; abounds with layers of skerry and veins of gypsum. 7* Colour of Nottingham bricks. 8. Common bricks made without picking the clay. 9. Prepa¬ ration of clay for making front-bricks. 10. Manufacture of rubbers.

11. Clay at Nottingham not generally suited for making roofing tiles.

12. Size of old and modern bricks.

GENERAL ARRANGEMENT OF A BRICKWORK.

13. Locality of existing yards. 14. Rental and cost of clay. 15. Ar¬ rangement of buildings. 16. Description of clay-mill. 17- Addition of a second set of rollers a great improvement. 18. Reference to engrav¬ ings of clay-mill. 19. Mode of boxing up the machinery. 20. Duty performed. 21. Length of time a clay-mill will remain in working con¬ dition. 22. Description of Wash-mill. 23. The Pug-mill not used at Nottingham. 24. Moulding sand. 25. Moulding table , description of. 2G. Brick mould , description of. 27* Use of copper moulds confined to small articles. 28. Mould placed on the moulding table and not upon a stock-board. 29. Plane, description of. 30. The Flats, how prepared; size of. 31. The Hovel, description of; sometimes provided with flues. 32. Best bricks dried wholly under cover in flued hovels. 33. The Clapper , description of; use of. 34. Dressing bench and dresser. 35. Machi¬ nery for pressing bricks; points to be attained in making. 36. Machine-pressed bricks cheaper than those dressed by hand. 37- Kiln , detailed description of. 38. Different mode of constructing the walls. 39. Com¬ parison of the two methods. 40. Reference to engravings. 41. Steps to the tops of the kilns. 42. Sizes of kilns. 43. Duration of kilns.

PROCESS OF BRICKMAKING.

44. Clay digging. 45. Tempering. 46. Cost of. 47. Moulding , de¬ scription of process. 48. Drying'; laying on flats; hacking. 49. Time that should be allowed for drying. 50. Cost of moulding and drying. 51. Pressed bricks. 52. Polished bricks. 53. Size of brickmoulds. 54. Rate of production. 55. Burning; management of the firing. 56. Cost of fuel. 57. Effect of the fire upon the colour of the bricks. 58. Cost of setting and drawing the kiln. 59. Cost of labour in firing. 60. Enumeration of the varieties of brickware manufactured at Nottingham.

CONTENTS.

xii

COST OF MANUFACTURE.

61. Land and brick-earth; difficulty of estimating rental; cost of clay. 62. Buildings and machinery; difficulty of ascertaining best relative sizes of working floors, hovels, and kilns. 63. Approximate estimate of extent of buildings and plant required for a weekly production of 46.800. 64. Additional buildings required in a yard, where all kinds of brick ware are made. 65. Enumeration of tools required. 66. Labour, how paid for. 67- Summary of cost of production. 68. Relative value of dif¬ ferent qualities of bricks. 69. Reference to illustrations, figs. 1 to 18.

Chapter IV

BRICKMAKING AS PRACTISED IN THE STAFFORDSHIRE POTTERIES, BY R. PROSSER, C.E.

1. Bricks ; enumeration of kinds of brick manufactured. 2. Drab bricks chiefly used for furnace work. 3. Tiles. 4. Clay. 5. Names of strata. 6. 1 wo examples will be given of the process of brick and tile making.

FIRST EXAMPLE—BRICKMAKING.

7 . Buildings and plant. 8. Rates of production. 9. Tempering. 10. Moulding. 11. Drying. 12. Loss of weight whilst drying. \3. Burn¬ ing. 14. Cost of manufacture. 15. Rental.

DESCRIPTION OF ILLUSTRATIONS.

16. Clay-mill. 17-Moulding table. 18. Brick mould. 19. The oven or cupola.

SECOND EXAMPLE—TILE-MAKING.

20. Enumeration of articles made at Basford. 21. Weathering and tempering. 22. Moulding. 23. Drying. 24. The Set. 25. Quarries and Dust Bricks. 26. Drain-tiles. 27. Tile machines. 28. Firing; detailed description of. 29. Selling prices of different articles.

ILLUSTRATIONS.

30. Moulding-bench. 31. Mode of drying tiles. 32. Tile-block and horse. 33. Mode of setting lower part of oven. 34. Mode of setting upper part of oven. 35. Desirability of improving the mode of conductof^lays *&^ rmfaCtU1 ' e ° f bliCkS * 3G, ‘^ x l iense °f carriage. 37. Analysis

BRICKMAKING ON THE SOUTH STAFFORDSHIRE RAILWAY.

38. Bricks made for this line by Mr. George Brown of Walsall Wood. Material not clay but marl. —Description of strata.—Description of processes employed.—Cost of bricks at the kiln.

RUDIMENTS

or THE

ART OF MAKING BRICKS AND TILES.

INTRODUCTION.

I. It would be impossible, in a little volume like the present, to enter at any length upon the early history of the Art of Brickmaking, nor would such an investi¬ gation, however interesting in a historical point of view, add much to our practical knowledge of the subject. It is, however, desirable that we should give a few particulars relative to the progress of the manufacture in this country; and we propose at the same time to give a brief sketch of the legal restrictions which have been imposed from time to time upon the mode of conducting the operations of the brickmaker: in doing which we shall have occasion to point out some anoma¬ lies in the present excise duties, which deserve the attentive consideration of the Legislature.

II. The use of brick as a building material, both burnt and unburnt, dates from a very early period. Burnt brick is recorded in the Bible to have been used in the erection of the tower of Babel; and we have the part i. u

INTRODUCTION.

testimony of Herodotus for the fact, which is confirmed by the investigations of travellers, that burnt bricks, made from the clay thrown out of the trench sur¬ rounding the city, were used in building' the walls of the city of Babylon.

Sun-dried bricks were extensively used in ancient times, especially in Egypt, where their manufacture was considered a degrading employment, and, as such, formed the principal occupation of the Israelites during their bondage in Egypt after the death of Joseph. Very interesting ancient representations of the pro¬ cesses employed are still in existence, and throw much light on various passages of Scripture. Thus, the pas- ] sage in Psalm lxxxi. 6, “ I removed his shoulder from the l burden; his hands were delivered from the {water) pots,” is strikingly illustrated by pictures still preserved to us, in which labourers are carrying the tempered clay on their shoulders to the moulders, whilst others are engaged in carrying vessels of water to temper the clay. The ; Egyptian sun-dried bricks were made with clay mixed with chopped straw, which was furnished to the Israelites by their Egyptian taskmasters before the application of Moses to Pharaoh on their behalf, after which the ob¬ ligation was laid on them to provide their own straw, which appears to have been a grievous addition to their labour. It would appear from the details given, that the Israelites worked in gangs, under the superin¬ tendence of an overseer of their own nation, who was provided with all necessary tools and materials, and who was personally responsible for the labour of the gangs. ;

Burnt bricks were, however, also used in Egypt for river walls and hydraulic works, but, probably, not to any very great extent.

It is recorded in 2 Samuel xii. 31, that David put-

INTRODUCTION.

the children of Ammon under saws, and harrows and axes of iron, and made them pass through the brickkiln: without entering on the question whether the Ammonites were made to labour in the brickfields as the Israelites had themselves previously done during the time of their bondage in Egypt, or whether we are to understand that they were put to death with horrible tortures, as supposed by most commentators, there is a strong presumption that the implements here spoken of in connection with the brickkiln were employed in the preparation of the clay; and if this view be correct, the passage is interesting as evidence of the use of machinery in making bricks at a very early period of history.

III. The Romans used bricks, both burnt and unburnt, in great profusion; all the great existing ruins at Rome being of brick. At the decline of the Roman Empire, the art of brickmaking fell into disuse, but was revived in Italy after the lapse of a few centuries. The me¬ diaeval ecclesiastical and palatial architecture of Italy mental work in terracotta; cornices and other deco¬ rations of great beauty being executed in the latter I material.

IV. In Holland and the Netherlands, the scarcity of stone led, at an early period, to the extensive use of brick, not only for domestic but for ecclesiastical buildings, and these countries abound in fine specimens of brickwork, often in two colours, combined with great j taste, and producing a very rich effect, as in the celebrated j examples at Leeuwarden in Friesland. It is worthy of ; remark, that in the fens of Lincolnshire and Norfolk,

| where we should naturally have expected to have found | the same material made use of, the churches, many of which are exceedingly fine specimens of architecture,

INTRODUCTION.

•are built of small stones, said to have been brought from a great distance on pack-horses.

V. Brickmaking appears to have been introduced into England by the Romans, who used large thin bricks or wall tiles as bond to their rubble constructions; and such wall tiles continued to be used in England until rubble work was superseded by regular masonry, about the time of the Norman Conquest. Brick does not appear to have come into general use as a building material until long afterwards.

In the reign of Henry VIII., however, the art of brickmaking had arrived at great perfection, and the remains of many buildings erected about this time exhibit some of the finest known specimens of orna¬ mental brickwork.

The following is a list of some of the principal brick buildings erected at the period of which we speak:—

NAME.

Gate of the Ryehouse in Hertfordshire Lollards’ Tower, Lambeth Palace Old part of Hampton Court Tattershall Castle, Lincolnshire .

Oxborough Hall, Norfolk .

Hengrave Hall, Suffolk

Gateway, Rectory, Hadleigh, Suffolk .

Manor House, at East Barsham, Norfolk

Thorpland Hall, Norfolk

Parsonage House, Great Snoring, Norfolk

WHEN BUILT.

Early in the reign of Henry VI.

Ditto.

About a.d. 1482.

Finished a.d. 1538.

Close of 15th century.

During the reign of Henry Vll.

Ditto.

During the reign of Henry VIII.

Many of these buildings have been engraved in Pugin’s “ Examples of Gothic Architecture,” to which we would refer the reader. The decorative details of the Manor House at East Barsham and of the Parsonage House at Great Snoring are particularly worthy of notice; the panelled friezes, cornices, and other ornamental work

INTRODUCTION.

being constructed of terracotta moulded to the required form. The use of terracotta for decorative panels and bas-reliefs appears to have been common during the reign of Henry VIII. The gateway of York Place, Whitehall, designed by Holbein, was decorated with four circular panels, which are still preserved at Hatfield Peveril, Hants.

The gateway of the Rectory in Hadleigh churchyard is very similar in character to that at Oxborough Hall, engraved in Pugin’s work, above referred to. It has been lately restored very carefully, the terracotta work for the purpose being made at the Layham Kilns, near ITadleigh, in moulds of somewhat complicated con¬ struction.

In the time of Queen Elizabeth, brick seems only to have been used in large mansions. For common buildings, timber framework, filled in with lath and plaster, was generally used, and this construction was much employed, even when brickwork was in common use, the brickwork, up to a late period, being merely introduced in panels between the wooden framing.

VI. On the rebuilding of London after the great fire of 1666, brick was the material universally adopted for the new erections, and the 19th Car. II. c. 11, regulated the number of bricks in the thickness of the walls of the several rates of dwelling-houses. One of the resolutions of the corporation of the city of London, passed about this time, is interesting; it is as follows;—“And that they (the surveyors) do encourage and give directions to all builders, for ornament sake, that the ornaments and projections of the front buildings be of rubbed bricks; and that all the naked parts of the walls may be done of rough bricks, neatly wrought, or all rubbed,

INTKODTJCTION.

at the direction of the builder, or that the builders may otherwise enrich their fronts as they please.”

Much of the old brickwork still remaining in London, in buildings erected at the end of the 17th and be¬ ginning of the 18th century, is very admirably executed. The most remarkable feature of the brickwork of this period is the introduction of ornaments carved with the chisel. A fine example of this kind of work is shown in the Frontispiece*', which is a sketch of No. 43, St. Martin s Lane, one of a block of houses built by a person of the name of May, who about the same time erected May’s Buildings, to which the date of 1739 is affixed. The house in question is said to have been intended by Mr. May for his own residence. Its deco¬ rations consist of two fluted Doric pilasters, supporting an entablature, the whole executed in fine red brickwork; the mouldings, flutings, and ornaments of the metopes having been carved with the chisel after the erection of the wallsf.

VII. It was not till the close of the last century that bricks were subjected to taxation. The 24 Geo. III. c. 24, imposed a duty of 2s. 6d. per thousand on bricks of all kinds. By the 34 Geo. III. c. 15, the duty was raised to As. per thousand. By the 43 Geo. III. c. 69, bricks were divided into common and dressed bricks,

The author is indebted to the kindness of Mr. Edis for this sketch of one of the most interesting specimens of ornamental brickwork in the me¬ tropolis.

t The author is indebted for this information to Mr. Cannon, Foreign Bookseller, of No. 11, May’s Buildings. This gentleman, who has paid much attention to architecture, took advantage of the opportunities afforded by the erection of scaffolding, at a time when the house was undergoing repair, to make a minute examination of these decorations.

INTRODUCTION.

and separate rates of duty were imposed on each kind. These duties and those on tiles were as follows:—

SCHEDULE (A)—DUTIES.

BRICKS AND TILES.

For every thousand bricks which shall be made in Great Biitain, not exceeding any of the following dimensions, that is to say, ten inches long, three inches thick and five inches

For every thousand of bricks which shall be made in Great Britain exceeding any of the foregoing dimensions .

For every thousand of bricks which shall be made in Great Britain, and which shall be smoothed or polished on one or more side or sides, the same not exceeding the superficial dimensions of ten inches long by five inches wide For every hundred of such last-mentioned bricks, exceeding j The duties or the aforesaid superficial dimensions . . , . J P avm S- tlles -

For every thousand of plain tiles which shall be made in Great Britain ....••••••

For every thousand of pan or ridge tiles which shall be made

in Great Britain . ..

For every hundred of paving tiles which shall be made in Great Britain not exceeding ten inches square .

For every hundred of paving tiles which shall be made in Great

Britain exceeding ten inches square.

For every thousand tiles which shall be made in Great Britain, other than such as are hereinbefore enumerated or described, by whatever name or names such tiles are or may be called

or known, ..

N.B.—The said duties on bricks and tiles to be paid by the maker or makers thereof respectively.

By the 3 William IV. c. 11. (1833), the duties on tiles # were wholly repealed, and two years afterwards the duty

0 5 0

0 10 0

0 12 0

0 4 10

0 12 10

0 2

0 4 10

0 4 10

* By a curious oversight, this Act, which was intended to put roofing tiles on the same footing as slates, also repealed the duties on paving tiles, whilst bricks used for paving remained subject to duty as before. Thus a lump of clay put into a mould 10 in. x5in. x3 pays duty, but the same quantity of clay put into a mould 10 in. square is duty free, because it comes under the denomination of a tile. The manufacturer and not the public reap the advantage thus given.

INTRODUCTION.

on bricks was again raised, making the duty on common bricks 5s. 1(M per thousand.

The brick duties formed the subject of the 18th Report of the Commissioners of Excise Enquiry, 1836; and m 1839, these duties were repealed by the 2 and 3 Viet. c. 24, and a uniform duty of 5s. 10 d. pei thousand imposed on all bricks of which the cubic content does not exceed 150 cubic inches, without any dis¬ tinction as to shape or quality. See Appendix, A and B.

VIII. The new Act is a great boon to the public as well as to the tiade, as, in consequence of the removal of the restrictions on shape, bricks may be made to any lequiied pattern; and moulded bricks for cornices, plinths, string-courses, &c., can be manufactured at a moderate price. Under the old regulations, also, the brickmaker was precluded from correcting any defect which might arise from warping or twisting in the process of drying, without making himself liable to pay the higher rate of duty; this being no longer the case, a very supeiioi article can now be made at a price very little exceeding that of common bricks under the old regulations.

IX. By the new Act*, bricks made and used solely foi the purpose of draining wet and marshy land are exempted from duty, provided they are legibly stamped, in making, with the word u Brain,” and a penalty of fifty pounds is imposed on every person who shall use such bricks “ for any other purpose than in draining wet and marshy lands and in constructing the necessary drains, gouts, culverts, arches and walls of the brickwoik piopei and necessarily required for effecting and maintaining the drainage of such lands.”

* This exemption was originally granted by 7 Geo. IV. c. 49, s. 3.

INTRODUCTION.

The meaning of this clause is not very clear, and it is a question whether the exemption cannot be claimed for all bricks used in the erection of bridges over drains, inasmuch as the drainage of the districts through which they pass could not be maintained without the erection of such bridges. The great number of archways and culverts required in the construction of a railway renders it most desirable that the limits of exemption should be clearly defined. Some information on the point will be found in the Appendix, C, D, and E.

X. The number of bricks annually made in Great Britain is very great, the number annually brought to charge during the last few years being nearly 1,800,000,000, and the annual duty amounting to be¬ tween 500,000/. and 600,000/.

Comparatively few bricks are made in Scotland, on account of the abundance of stone everywhere to be had in that country, the duty paid on bricks in Scotland being only about of the whole amount above named.

It is impossible to ascertain the number of bricks annually made in Ireland, as no duties are paid on bricks manufactured in that country.

Those who are not practically connected with en¬ gineering works may find some difficulty in forming a clear conception of the immense number of bricks annually made for railway purposes; and which may be roughly estimated at from 600 to 800 millions annually. In 1821, before the introduction of the railway system, the number of bricks charged with duty in England and Scotland amounted to 913,231,000. In 1831 the number was 1,153,048,581. In 1840 the number rose to 1,725,628,333.

A common turnpike road bridge over a railway requires for its construction, in round numbers, 300,000

b 3

INTRODUCTION.

bricks; and the lining of a railway tunnel of ordinary dimensions consumes about 8000 for every yard in length, or in round numbers about 14,000,000 per mile.

XI. The processes employed in the manufacture of bricks differ very greatly in various parts of the country. In some districts the clay is ground between rollers, and the pugmill is never used. In others, both rollers and pugmills are employed. In the neighbourhood of London rollers are unknown, and the clay is passed through a wash mill. Equal differences exist in the processes of moulding and drying. Lastly, the form of the kiln varies greatly. In many places the common Dutch kiln is the one employed. In Essex and Suffolk the kilns have arched furnaces beneath their floors; in Staffordshire bricks are fired in circular domed ovens called cupolas; whilst near London kilns are not used, and bricks are burnt in clamps, the fuel required for their vitrification being mixed up with the clay in the process of tempering.