,transcriber's ,note3 ,in this ,plain ,text version of the e,book1 italic text is indicated by underscores and chemical compounds on pages #gf-gg are shown without subscripts1 e4g41 ,h#b,o4 ,other ,notes will be found at the end of this e,book4 ,,advertisements4 ,,brick ,,dryers #e1jjj ,,to #ajj1jjj ,,daily ,,capacity4 ,illustration3 ,,cross ,,section ,a4 ,b4 ,c4 ,,steam ,,dryer ,,for ,,small ,,producers4 ,,cummer ,,hot ,,air ,,dryer ,,for ,,medium ,,and ,,large ,,producers4 ,,remarkable ,,economy ,,efficiency4 ,large ,dryers at work in ,,england1 ,,france1 ,,germany1 ,,belgium1 ,,denmark1 and ,,america1 ,,fully ,,guaranteed4 ,also ,makers of ,best ,english ,steel ,brick ,cars4 ,all ,styles4 ,prices ,free4 ,,charles ,,erith ,,co41 #gj ,,gracechurch ,,street1 ,,london1 ,e4,c4 ,illustration ,,advertisements4 ,,the ,,cardiff ,,kilns 7,,lee',s ,,patent7 ,,high-,,class ,,building ,,brick1 ,,blue ,,vitrified ,,brick1 ,,front ,,and ,,ornamental ,,brick1 ,,fire ,,brick1 ,,sanitary ,,ware1 ,,salt ,,glazing1 c41 c4 ,,can be burned ,,better and ,,cheaper in these ,,improved ,,regenerative ,,down-,,draught ,kilns than in any other4 ,they are ,,cheap to erect1 ,,durable1 ,,simple in construction1 and ,,completely under control4 ,,easy ,,to ,,burn4 ,,require ,,only ,,small ,,coal1 ,,and ,,allow ,,no ,,waste ,,heat4 ,,give ,,perfect ,,results1 ,,and ,,are ,,the ,,kilns ,,of ,,the ,,day4 ,it has long been admitted that the 8,,down-,,draught0 is the only reliable ,kiln for burning the highest class goods1 and the best for ordinary purposes1 the only drawback to its general adoption for lower grade wares and ,building ,bricks being the heavy consumption of fuel4 ,,this1 the ,,only disadvantage1 is ,,entirely overcome by the patent ,,cardiff ,,kiln1 and the improvements recently devised in their construction1 whereby all the advantages of the ,,hoffmann system are combined with those of ,,down-,,draught system1 while avoiding the defects of the ,hoffmann1 thus rendering these kilns the ,,best1 ,,cheapest1 and ,,most ,,economical of all modern kilns1 producing the ,,best ,,goods at the ,,lowest ,,cost4 ,the system may be applied to existing ,down-draught ,kilns at very moderate cost4 ,,for ,,particulars ,,apply ,,to ,the ,patentee1 ,e4 ,p4 ,,lee1 #bi1 ,the ,parade1 ,,cardiff4 ,,the ,,science ,,of ,,brickmaking ,,the ,,science ,,of ,,brickmaking3 ,,with ,,some ,,account ,,of ,,the ,,structure ,,and ,,physical ,,properties ,,of ,,bricks4 ,,by ,,george ,f4 ,,harris1 ,f4,g4,s41 ,membre de la ,socit ,belge de ,gologie1 ,palontologie et ,hydrologie2 ,lecturer on ,geology1 ,the ,practical ,applications of ,geology1 and ,mineralogy1 in the ,birkbeck ,institution1 ,london2 etc41 etc41 etc4 ,,london3 ,h4 ,,greville ,,montgomery1 #dc1 ,,essex ,,street1 ,,strand4 #ahig4 ,,all ,,rights ,,reserved4 ,,printed ,,at ,,the ,,victoria ,,printing ,,works1 ,,stanstead ,,road ,,forest ,,hill ,s4,e4 ,,preface4 ,the substance of this little work was first published as a series of articles in the ,british ,clayworker1 in #ahie-if1 and ,i am indebted to the courtesy of the ,proprietor of that ,journal for permission to reproduce them4 ,an attempt is here made to furnish some information of an elementary character on a special branch of technical education which has been seriously neglected in this country4 ,but the reader will understand that it is only an elementary treatise4 ,its publication in serial form1 where each article must1 more or less1 be complete in itself1 has to a large extent determined the method of handling the subject1 and ,i am fully cognisant of the drawbacks of the work in that respect4 ,at the same time1 it is hoped that the book will be useful to the more advanced class of brickmakers and clayworkers generally1 many of whom have expressed a desire to see the articles in this form4 ,,geo4 ,f4 ,,harris4 ,birkbeck ,institution1 ,bream's ,buildings1 ,chancery ,lane1 ,e4,c4 #ast ,february1 #ahig4 ,,contents4 ,,chapter4 ,,page4 ,i4 ,,fluviatile ,,brick-,,earths #a ,,ii4 ,,lacustrine ,,and ,,fluviatile ,,brick-,,earths #ag ,,iii4 ,,marine ,,brick-,,earths #bb ,,iv4 ,,the ,,mineral ,,constitution ,,of ,,brick-,,earths #bh ,v4 ,,minerals3 ,,their ,,behaviour ,,in ,,the ,,kiln #ci ,,vi4 ,,minerals3 ,,their ,,behaviour ,,in ,,the ,,kiln 7,contd7 #di ,,vii4 ,,the ,,chemistry ,,of ,,brick-,,earths #eh ,,viii4 ,,the ,,chemistry ,,of ,,brick-,,earths 7,continued7 #ge ,,ix4 ,,drying ,,and ,,burning #id ,x4 ,,the ,,durability ,,of ,,bricks #ajc ,,xi4 ,,the ,,micro-,,structure ,,of ,,bricks #aah ,,xii4 ,,the ,,micro-,,structure ,,of ,,bricks 7,continued7 #abh ,,xiii4 ,,absorption #acb ,,xiv4 ,,strength ,,of ,,bricks #acf ,,xv4 ,,abrasion1 ,,specific ,,gravity #adf ,,the ,,science ,,of ,,brickmaking4 ,,chapter ,i4 ,,fluviatile ,,brick-,,earths4 ,let us go to ,crayford1 near ,erith1 or to ,ilford1 in ,essex1 and take a superficial glance at some of the brickyards found at those places2 in particular1 let us ascertain a little concerning the earths employed4 ,we find in one brickyard a series of stiff brown or bluish clays1 interstratified between sandy clays or 8loams10 with thin brownish partings4 ,in another1 the loam will become very sandy1 and the earth light1 with a slight greenish tinge4 ,a third has thin pebble or gravel beds developed1 or small stones sparingly scattered in the clays and loams on certain horizons4 ,a fourth contains1 in addition to some of the beds above described1 a lime-clay or marl#a with small pellets of chalk4 ,it will be noticed on entering the yards that these various horizons1 or beds1 as they are conveniently termed1 are disposed in regular lines or layers1 more or less horizontal2 in other words1 the beds are 8stratified40 ,on the face of the working being dug into1 it will often be found that these thin beds1 a few inches or feet each in thickness1 vary in depth1 and frequently disappear altogether1 or 8thin out10 whilst1 on the other hand1 a bed only a few inches thick may become as many feet1 and new beds are found to be developed4 ,a pure sand may in like manner become loamy on being dug into1 and1 on being further developed1 pass insensibly into a stiff clay4 ,and many other changes take place into which we will not enquire at the moment4 ,suffice it to say1 that in such brickyards the strata are very locally developed1 though it follows from the circumstance of their existence for so many years1 that what changes have taken place1 to some extent compensate each other1 so that the material is still an earth suitable for making bricks4 ,again1 certain beds of much economic value may be more persistent than others1 both in character and development4 ,having noticed all these things1 we perceive a couple of men digging with care into the brick-earth1 and presently they bring some objects to us which we have no difficulty in recognizing as the remains of the lower jaw of an elephant's skull4 ,returning to the spot where they were exhumed1 the upper jaw and tusks also are uncovered4 ,to the clay workers these things are well known2 in their time they have found many similar skulls of animals in the brick-earth2 but they know next to nothing concerning them1 or how they got there4 ,another expedition to the same localities may yield the remains of rhinoceros1 the musk sheep1 grizzly bear1 hippopotamus1 reindeer1 and many other animals4 ,a fine series of the remains of these1 obtained from the brick-earths of the valley of the ,thames at several points1 is exhibited in the geological department of the ,british ,museum 7,natural ,history71 ,south ,kensington1 and more or less complete skeletons obtained from the same source may be found in other1 and local museums4 ,one of the most interesting points concerning these remains is that so many of the animals represented in the brick-earths are of extinct species--there are no species included in this latter category of precisely similar kinds to animals now living1 ,thus the elephant was different to modern elephants2 we know1 from remains found elsewhere1 that it was clothed with wool4 ,the same also with the rhinoceros4 ,the reindeer no longer lives in this country1 being confined to northerly latitudes2 whilst the musk sheep is a denizen of the ,arctic regions1 and the hippopotamus is restricted to the tropical or sub-tropical climes4 ,but we might continue for a long time expatiating on the character of the very numerous mammalian remains found in our common brick-earths4 ,what a curious assemblage of animals6 ,it is wonderful to contemplate the time when the reindeer and musk sheep lived side by side with the elephant and rhinoceros on the site whereon ,london now stands4 ,that is not all1 however4 ,in the same brick-earths and gravels1 tools 7flint implements71 fashioned by the hands of man1 are also frequently discovered1 and in one place at ,crayford1 the spot whereon flint implements were manufactured has been 'lighted upon4 ,each flake chipped off has been collected and pieced together1 and the shape of the original flint has thus been determined4 ,clearly1 from this evidence1 the earth from which millions of bricks have been made has formed since primval man 7and with him the animals alluded to7 inhabited the valleys of the ,thames and its tributaries4 ,it is interesting1 too1 to reflect on the circumstance that the materials upon which many of these facts of great philosophical significance are based1 have been collected through the instrumentality of the workmen4 ,palontologists are proud to acknowledge that2 their debt of gratitude to the intelligent and persevering men can never be fully repaid4 ,pursuing the matter still further1 we discover a quantity of shells1 blanched and very frail--they seem to be deprived of much of their original substance1 so to speak2 their entombment in the brick-earth has taken all the natural colour out of them4 ,studying these1 we soon ascertain that they belong to land snails and mollusca which inhabit fresh water4 ,living representatives of the same species are1 with few exceptions1 found in ,kent and ,essex4 ,putting all this evidence together1 we come to the conclusion that the brick-earths alluded to accumulated in the channel of a river2 they are found above the present level of the ,thames1 for the simple reason that they have been elevated into that position partly by earth movements and partly by the channel of the river being cut deeper by natural causes1 of which abundant proof will be adduced4 ,the snails were washed down from the land by freshets1 or caught by the river in flood2 the elephant1 rhinoceros1 hippopotamus1 and musk sheep were overcome1 perhaps1 by floods1 drowned1 and subsequently covered up by the mud of the swollen current4 ,we can imagine that the savage hunter1 in his canoe1 attacking the animals swimming in the river1 loses his tomahawk1 or his frail bark may be upset1 and he is striving to gain the shore for dear life4 ,or1 it may be winter time2 the river is frozen over1 and he is cutting a hole in the ice with his flint chisel wherein to fish2 his hands are benumbed1 and he loses his grasp of the tool2 it falls into the water1 to be discovered in the brick-earth by one of our intelligent friends4 ,truly1 the revelations of the brickyard enable us to construct a picture of one of the most interesting phases of the past history of the ,earth4 ,we have given an outline of the evidence upon which certain brick-earths in the ,thames valley are proved to be of fresh-water origin--to have accumulated in quiet reaches of the river1 and at other convenient spots along its course--but we have used that as an illustration only2 phenomena of precisely the same character are manifested in nearly all river valleys in this country1 especially those in which the bottom of the valley has only a slight gradient down to the sea4 ,the brickmaker may ask3 ,what is the practical bearing of these observations8 ,what difference does it make to us whether the earths we use are of fresh-water1 lacustrine1 or marine origin8 ,all the difference in the world1 from the points of view of structure1 composition and suitability of the earths1 and especially of their distribution over the face of the country4 ,how much easier it is to value an extensive brickmaking property when you feel perfectly certain as to whether the face of earth as shown in the pit will die out on being worked into for a few yards1 or whether it will be persistent throughout the whole of the property to be valued4 ,better still1 when your knowledge enables you to state definitely whether the quality of earth now being worked in a pit is likely to continue the same1 or whether it will get better1 or worse4 ,the disposition of the earths1 in some instances1 is so clear that no brickmaker with an eye to business could fail to trace their extent over his property4 ,but this is not often the case1 for the earths being used are for the most part covered by a superficial mantle1 or overburden1 which masks the true character of the beds beneath4 ,a very slight acquaintance with the principles of geology overcomes these difficulties as a rule2 and we are about to lay down the elements of these principles1 so far as they apply to the immediate subject in hand4 ,by seeing why it is the beds of brick-earth vary in structure and composition we shall be in a better position to make forecasts of their general behaviour4 ,in regard to fluviatile deposits1 it goes without saying that every river flows along a general depression more or less pronounced1 called a valley1 and that this valley is bounded physiographically by a ridge1 except in the region of its entrance to the sea or lake1 or1 if a tributary1 of its joining a main stream4 ,the watershed of a river and its tributaries includes and comprises what is technically termed the 8river basin40 ,all valleys are1 in the end1 the result of denudation taking place in them4 ,in other words1 on the birth of a valley a very slight depression or other physical feature determined its general direction for the time being1 but the little rivulet once being formed proceeded1 through the medium of the 8agents of denudation10 to carve out its channel more clearly1 and eventually to eat into the rocks over which it flowed1 until a large valley had been formed4 ,the 8agents of denudation0 in river valleys may be summarised as rain1 snow1 ice1 heat1 and wind1 and their general effect on rocks is called 8weathering40 ,we need not stop to enquire into the precise methods adopted by these agents in accomplishing their work2 it suffices at present to say that the rock destroyed or broken up is removed by the running water constituting the rivulet1 stream1 or river1 as the case may be4 ,some of the material is chemically dissolved in the water1 whilst another and larger proportion is taken away in suspension1 or is said to be dealt with mechanically by the river4 ,the agents of denudation do their work very slowly1 as a rule1 and yet no one who stands on ,london ,bridge and contemplates the swollen stream laden with muddy sediment passing under it after a few days' rain1 could say that they are not doing their duty effectually4 ,to give some idea of the quantity of sand1 gravel1 and mud removed from the land through the medium of rivers1 we may remark that the ,mississippi discharges into the ,gulf of ,mexico annually a mass of earthy matter equal to a prism #bfh feet in height with a base area of one square mile4 ,in regard to denudation by chemical means we may say that the ,thames carries past ,kingston #ai grains of mineral salts in every gallon of water1 or a total of #a1ejb tons every #bd hours1 or #edh1bcj tons every year2 this is not taking into account the muddy sediment1 gravel1 c41 annually sent down to the ,nore1 which must be infinitely greater in quantity4 ,enough has now been said to show that stupendous quantities of mineral matter derived from the destruction of the land are sent down to the sea by natural agencies1 and we may at once state that a very large proportion of this1 which finds a resting-place in and about the mouths of the rivers and their backwaters1 is material suitable for brickmaking at places where it is obtainable4 ,enormous quantities of muddy sediment1 sand and gravel1 however1 never reach as far as the sea with great rivers4 ,this material is arrested at sundry convenient spots1 and1 as a rule1 forms excellent brick-earth4 ,illustration3 ,fig4 #a4--;,formation of ,brick-earth in a river valley4 ,see ,fig4 #a1 which represents part of a river of slow current with three bends1 ,a1 ,b1 ,c4 ,the water is flowing in the direction indicated by the arrows2 and it is part of the mechanics of such a river that in rounding a bend its velocity is greatest 7and its eroding power also7 at the outer portions of the curves approximately indicated by the arrow points4 ,the water 8wheels round0 such portions of the curves1 and 8marks time0 at the points x x x1 and1 indeed1 its progress may be altogether arrested for a time at the latter places4 ,now the transporting power of a river is its velocity1 and1 naturally1 the greater the velocity1 the coarser will be the fragments or particles of rock carried along4 ,it is interesting in this connection to quote the figures calculated by ,mr4 ,david ,stephenson1 giving the power of transport of different velocities of river currents3-- ,ins4 per ,mile per second4 hour4 #c #j4agj will just begin to work on fine clay4 #f #j4cdj will lift fine sand4 #h #j4dede sand as coarse as linseed4 #ab #j4fhai will sweep along fine gravel4 #bd #a4cfch will roll along rounded pebbles #a inch in diameter4 #cf #b4jde will sweep along slippery angular stones of the size of an egg4 ,these figures#b have greater interest for us than in the connection at present used1 as will be noticed hereafter4 ,we have seen that in rounding the bends 7,fig4 #a7 ,a1 ,b1 ,c1 different portions of the stream possess different velocities4 ,we know it is charged with sediment and stones all the time4 ,the tendency1 therefore1 will be for the large stones and coarse detritus to go round the outer side of the bend1 to bombard the banks near the points shown by the arrows1 and to erode the channel deepest in those situations2 whilst a goodly proportion of the fine muddy sediment will find its way to the quiet and shallow parts near x x x1 and in course of time become deposited there1 whilst the main course of the stream is eating its way and shifting its course as indicated by the dotted lines a a4 ,this action proceeds1 it may be1 until the course of the river becomes straighter1 as shown by the dotted lines b b1 when the whole of the loop ,b ,d is abandoned1 its former course there being evidenced by pools of water and irregular heaps of gravel1 sand and mud4 ,the reader will now see that the whole of the land marked x x x has been formed of sediment brought down by the river1 and in the majority of cases such fine silt and sandy mud or clay is specially suitable for brickmaking--many of our largest brickmakers obtain their material from such a source4 ,it should be observed that the valley1 as shown between the lines v v1 may be two or three miles in width1 and it is often much more1 so that the actual amount of land made by the river at x x x may be several thousands of acres in extent4 ,now as to the practical application of the foregoing observations4 ,in the first place1 it will be seen that such deposits of brick-earth as are made in this manner cannot be very thick1 their total thickness perhaps1 resting on the bottom of the valley1 not being more than #bj feet1 and it is frequently much less4 ,the next thing to be noticed is that they must be very variable in character1 a bed changing perhaps every #ajj feet or so horizontally1 and more often every few feet4 ,individual beds must of necessity be very irregularly developed under the circumstances4 ,the velocity of the stream being greater at certain seasons of the year than at others1 we frequently find some such section as the following developed3-- ,illustration3 ,fig4 #b4--,section of ,fluviatile ,brick-earth4 a ,mould and soil1 of no use to the brickmaker4 b ,sandy clay1 with a large proportion of sand2 useful for moulding or incorporating with the 8fat0 clays below for brickmaking4 c ,gravel bed1 lenticularly developed2 suitable for mending roads1 paths1 c4 d ,sandy clay2 similar to b4 e ,thin bed of marl1 with a fair proportion of lime4 f ,sands and small pebbles1 irregularly stratified 7false-bedded74 g ,laminated sandy clay4 h ,stiff clay2 can be mixed with f and passed through the pug mill4 i ,sand2 an irregular bed of very local occurrence4 j ,gravel bed1 with much sand4 ,the above is typical of deposits accumulated in river valleys2 it is different in character to deposits laid down in the sea 7as will presently be described72 the section exhibits very different classes of brick-earth also1 and yields a totally different kind of brick to that obtainable from brick-earths of marine origin4 ,the importance of the question of origin of a brick-earth1 therefore1 is just beginning to dawn upon us4 ,many rivers are noted as having throughout a long period of time wandered from one side of the valley to the other 7by the process depicted in ,fig4 #a7 several times1 in which cases the brick-earth sections relating to them are liable to still greater variation4 ,the reader would perhaps be very much astonished to find how much is known concerning peregrinations of that description in regard to particular localities1 by competent authorities--usually field geologists4 ,we come to another important point in regard to river deposits4 ,the ceaseless flow of the river1 and the abrading action of the large stones rolled along at the bottom of its channel1 tend to cut the latter deeper and deeper1 and we have excellent evidence that most ,english rivers once flowed at a greater elevation in their valleys than they now do4 ,in consequence of this1 the brickmaker may find his pit somewhat higher than the neighbouring river1 which at an earlier stage of its existence made his brick-earths4 ,to a certain extent1 small earth movements1 as previously explained1 are also undoubtedly responsible for many of these brick-earths now being at a considerable elevation above the surface of the river4 ,this phenomenon is illustrated in ,fig4 #c4 ,illustration3 ,fig4 #c4--,section across a river valley1 showing formation of terraces of gravel and brick-earth4 ,this type of disposition of fluviatile deposits is of common occurrence4 ,we will assume that the valley is carved out of clay 7shown by horizontal lines and dots74 ,on both sides of it1 and at the same relative heights1 are two masses 7marked #a and #b7 of brick-earths and gravels running along so as to form two distinct broad terraces4 ,these beds were laid down when the river1 in flood1 though occupying only a small portion of the valley1 was approximately of the height shown by the dotted lines a b4 ,denudation has been hard at work1 however1 since then1 and only vestiges of these beds clinging to the sides of the valley1 as shown1 remain4 ,at a later period1 and coming on towards modern times1 the broad expanse of beds 7comparable in disposition with those depicted in ,fig4 #b7 some miles in width1 marked #c1 were laid down1 and we notice the river channel1 as it now is1 cutting its way through them4 ,thus it comes to pass that brickyards may be situated in terraces one above the other2 and what is much more important1 the brick-earths may vary very widely in quality along these horizons1 those in #a differing from #b and both from #c4 ,the brickyards may be quite close to each other1 and to the unscientific eye the earths are of similar appearance1 but they do not yield the same class of brick1 and no one seems to trouble to enquire the reason why4 ,these differences have resulted primarily from the materials having been derived from other collecting grounds1 other watersheds1 than those comprised within the basin of the river as at present constituted4 ,they are the inevitable accompaniment of the evolution of the river system1 and throw light on successive phases of the past history of the stream and its tributaries4 ,for us1 as we have seen1 they possess considerable practical value of the first importance in selecting the site for a brickyard4 ,apart from differences of the character just described1 serious alterations sometimes take place on these brick-earths being traced higher up the valley1 and indeed an excellent brickmaking material may become absolutely worthless in that respect1 for the reasons about to be explained4 ,the reader will agree that neither stones nor sediment can travel up a valley1 and he will understand that no sediment can be found in the valley earths other than that derived from the destruction of rocks within the watershed of the river system1 to which the valleys belong1 or did belong1 at the time the earths were formed4 ,we desire to put the case in a very simple light1 so as to be clearly comprehended4 ,let us contemplate ,fig4 #d4 ,illustration3 ,fig4 #d4--,map shewing river basin1 with geological formations depicted4 ,here we have represented a river basin1 the limits 7watershed7 of which are indicated by a sinuous dotted line4 ,three geological formations are found therein2 in the upper reaches of the main river is a series of clays marked ,a2 a large tract in the middle1 ,b1 is sandstone2 and the lower part1 ,c1 is occupied by limestone4 ,seeing that nothing but clay crops out in the part ,a1 it follows that the deposits of the river in that region must be principally of an argillaceous character1 to the point a4 ,on flowing over the sandstone ,b1 the main stream1 already charged with clay particles1 will be mixed with sand2 the proportion of sand increases as the first large tributary 7b7 to the east is encountered1 and is considerably augmented as the still more important tributary 7b7 to the west enters it4 ,the superficial deposits in the valleys of the area ,b will likewise be very sandy and perhaps gravelly at b b1 but at c c the sands and gravels will be mixed with much clay4 ,on passing over into the area ,c1 much carbonate of lime is added1 though the larger proportion denuded from the rocks is taken away1 chemically1 in solution4 ,nevertheless1 nodules of 8race0 7lime concretions71 limestone pebbles1 and perhaps chert and flint gravel will come upon the scene at about the point marked e4 ,at d the deposits would principally consist of gravel and impure marls4 ,to sum up1 the clays at a would no doubt be too stiff of themselves to make good bricks2 similarly the beds at b b would be nothing but sand1 though these might be made1 with a little judicious treatment1 into a species of fire-brick2 at c we should find alternating loams and clays suitable for turning out fair bricks2 at c the beds would be more variable in character and more locally developed2 they would consist of thin beds of sand1 clays1 loams and gravels 7principally sandstone fragments71 which as a whole might be made serviceable1 though difficult to deal with2 nothing of much use to us would come from point d1 nor bordering the tributary running over ,c2 there would be too much lime present1 though a trade might be started in basic bricks should there be any demand for them in the neighbourhood2 this1 however1 would only pay under extremely favourable conditions4 ,at e there may be a mixture of all the foregoing deposits1 and providing the beds above were easily weathered and thick beds of loam were thus fairly well developed1 good sites for brick-earth might be found4 ,the point e might possess this advantage over the other sites mentioned1 viz41 that marls would no doubt be present1 and thus no necessity should arise for grinding lime to be incorporated with the brick-earth2 the only danger would be that lumps of limestone might be too numerous--especially if c were a hard limestone4 ,the general character of the deposits might be slightly modified by mineral matter brought up in springs and thrown down at convenient spots4 ,,chapter ,,ii4 ,,lacustrine ,,and ,,fluviatile ,,brick-,,earths4 ,the great variability of brick-earths deposited in river valleys is reflected to some extent in those laid down in lakes1 though the size of the latter is frequently a controlling factor4 ,the chief difference consists in the broader expanse of the sediment laid down--especially in large lakes--and variation in structure is not so noticeable horizontally4 ,let us consider a simple case in which a lake is fed by a large river bringing down abundant sediment4 ,the lake acts as a species of settling tank1 and the method of deposition of the sediment by the river is mainly guided by the velocity of the stream4 ,the tendency under normal conditions is for the river to commence parting with its sediment immediately on entering the lake4 ,the detritus alluded to is only held in suspension by the velocity of the water2 when the latter is checked1 as on entering the lake1 the grosser pieces subside1 and as its rapidity becomes progressively curbed1 medium-sized fragments are compelled to give way1 until at last only very minute particles are left in the water4 ,in due time most of these also are deposited4 ,thus gravel is laid down before grit1 grit before sand1 and sand before clay4 ,if the velocity of the river always remained the same1 we should be presented with thick accumulations of the same character in sharply defined areas4 ,but it is always changing4 ,with every storm and every steady rain the motion of the river becomes greatly accelerated1 with the result that the deposits for the time being are deposited farther out in the lake than in more quiescent periods4 ,in this way we may have a gravel thrown down on sand1 sand on clay1 and so on4 ,from the foregoing observations it will be gleaned that1 in general1 deposits in large lakes are more persistent in character than are river deposits2 indeed1 in very large sheets of water1 as ,lake ,superior1 ,lake ,erie1 c41 they are in this sense more comparable with sediment of marine origin4 ,the practical value of this knowledge hinges on the correct determination of the origin of the deposits1 and it is not always easy to identify a brick-earth of lacustrine origin4 ,in all probability the tyro1 on meeting one1 would be disposed to regard it as a river deposit pure and simple4 ,the valuation of a brick-earth property under such circumstances would thus be greatly in favour of the prospective purchaser2 but it would be disastrous for the seller4 ,a random section1 except in the case of a very large lake1 would show gravels1 sands and clays in much the same manner as the river deposits described in the last article of this series4 ,but1 as previously remarked1 on the whole they would be more continuous and persistent1 and what is quite as important1 the mineral composition of each stratum would be equally homogeneous when traced over wide areas4 ,the geologist distinguishes a lacustrine deposit from one of fluviatile origin more from its mineral constitution and the general disposition of the beds1 as ascertained by mapping1 than from evidence afforded by fossils--these latter for the most part being similar to those found in the deposits left by rivers4 ,the well-known brick-earth called 8,reading mottled clay10 so extensively developed on the outskirts of the ,london basin1 and in the ,isle of ,wight and ,hampshire generally1 furnishes a good example of a lacustrine deposit4 ,many millions of bricks are made from this bed every year1 and in some parts of the districts mentioned the stratum is thick and extensively developed4 ,it is pure enough to be suitable for terra-cotta manufacture here and there4 ,no one who had seen this remarkable deposit could possibly fail to recognise it again4 ,the natural colour of the clay when damp is brilliant red1 scarlet or crimson1 in large blotches and patches mottled tea-green and yellow1 and locally white4 ,we have been intensely amused to note the efforts in recent years to obtain possession of a few acres of this coveted deposit for brickmaking in divers localities4 ,not long since we visited a large brickmaking establishment where these ,reading plastic clays are actively raised and used1 the works being situated four miles from the nearest railway4 ,there were no other brickworks between it and the railway line1 and there was no water accommodation4 ,enquiry revealed the fact that the greater part of the intervening land belonged to the same landowner as the ground where the brickyard stands1 and that no difficulty was apprehended of the owner letting out such intervening land for the same uses and on the same terms if other brickyards were contemplated4 ,the proprietor of the brickyard in question volunteered the information that the reason he started so far from the railway was because the earth at the point selected was the only kind suitable for brickmaking in the neighbourhood4 ,we then questioned him as to his knowledge of the brick-earths in the district1 and eventually elicited the fact that he chanced upon the spot selected1 without any reasoning therefor1 and commenced operations4 ,as a matter of fact1 precisely the same clay extended from his works all the way to the railway line1 and had he known anything whatever of the geology of the district 7even the merest boy's knowledge of the subject71 he would have seen how to save that four miles of road carriage4 ,what prevented him from knowing the fact was a thin mantle of gravel and soil about four feet in thickness1 which covered the plastic clay in the area generally1 except in the immediate vicinity of his brickyard4 ,that was in reference to a lacustrine deposit--the ,reading plastic clay--and shows the value of knowing something of its persistent character2 if it had been a river deposit there would not have been so much room for wonderment4 ,to give some idea of the extent of that particular horizon1 we may say that not only is the plastic clay alluded to found so extensively in the ,london and ,hampshire basins1 it is even more expanded in the north-eastern parts of ,france1 and is there as much utilised as on this side of the ,channel for brickmaking4 ,lacustrine deposits are sometimes of enormous value to the clayworker1 on account of the general purity of the clays4 ,this is more particularly the case when the material deposited is in part or wholly derived from chemical disintegration of granitic rocks1 as in the celebrated ,bovey ,heathfield clays near ,newton ,abbot1 so well described in a small pamphlet by ,mr4 ,s4 ,smith ,harvey4 ,here an experimental boring proved the clays to a depth of #acj feet with no signs of exhaustion4 ,in the divers clay-pits but a small proportion of waste is found1 the different levels vary in composition1 and1 like almost all thick clays1 improve in quality as the depth increases4 ,the strata are very irregular towards the surface1 due perhaps to the action of local freshets in the final periods of the history of the lake4 ,these clays are extensively employed for the manufacture of stoneware pipes1 facing and other bricks1 fire-bricks1 etc4 ,they constitute a somewhat remarkable exception to the class of clays laid down in lakes1 as a rule1 and1 as will have been observed1 are of enormous thickness4 ,we have very little to say in regard to estuarine brick-earths2 as might readily be anticipated1 they are intermediate in character between fluviatile and marine deposits1 and approach the one or the other according to position in the estuary4 ,on the whole1 they are variable in character1 individual beds being thin4 ,the strata frequently contain abundant plant remains 7pieces of wood1 etc471 and1 except in the case of large rivers1 are not noted for yielding very good brick-earths4 ,sometimes1 however1 the quality of the clays is not bad1 as instance the bricks made in ,lincolnshire and ,northamptonshire from ,jurassic ,estuarine clays4 ,,chapter ,,iii4 ,,marine ,,brick-,,earths4 ,turning to brick-earths of marine origin1 we may say that these constitute by far the largest class of deposits from which bricks are made in this country1 and it will be useful to deal with their origin in some detail4 ,if we attentively watch the action of the weather on a friable sea-cliff we notice that large pieces tumble at intervals on to the beach1 and in due time these are washed away by the waves1 thus encouraging more to fall when the time is ripe4 ,this process of denudation each year takes tens of thousands of tons of sandy clays and the like from the beaches around our islands4 ,large pieces of rock1 too1 are detached by the weather1 and eventually succumb to wave action4 ,during storms large stones are hurled against the cliffs1 and the general effect of this bombardment is to wear them away1 and reduce them to powder and sand grains with all possible expedition4 ,no one who has not seen the waves at work at such times can have any idea of their tremendous power of moving blocks of stone many tons in weight4 ,during calm weather the slight movement of the waves on the beach is manufacturing tons and tons of sand4 ,a mass of gravel falls from the cliff2 the finer particles are floated away at the earliest opportunity2 the angular stones have their rough projections knocked off by striking against each other2 and the incessant movement up and down the beach slope reduces the rough stone to a pebble1 all the time the particles thus shaved off are taken out to sea for greater or less distances4 ,if the cliffs are of limestone1 or similar rock1 both chemical and mechanical methods of denudation come into play1 and considerable quantities of lime1 c41 are taken away by the sea water in suspension and solution4 ,large quantities of lime are daily added to the sea through the agency of rivers also4 ,now1 what becomes of these vast quantities of detritus furnished to the sea8 ,that depends on the shore currents at the particular locality4 ,if there is not much of a current1 the larger grains of grit and sand are soon separated from the rest1 and fall to the bottom1 whilst the clays are taken farther out to sea before being laid down4 ,but1 in any case1 the reader will readily perceive that marine deposits must of necessity be on a grander scale1 and of a much more substantial character1 as a rule1 than river1 lacustrine1 or estuarine deposits4 ,by their mode of origin1 too1 they must be more homogeneous1 whilst they are frequently several hundreds of feet in thickness4 ,in their process of deposition they were not influenced by every storm and freshet2 nothing short of great earth-movements in process of time1 or some other equally grand phenomena1 could disturb the even tenour of their existence4 ,how different to the comparatively insignificant strata formed by the other methods alluded to6 ,take samples of brick-earth of fluviatile origin at intervals and analyse them2 no two analyses will be alike1 except by a most remarkable coincidence--more by accident than otherwise4 ,on the other hand1 take a thick marine clay1 and compare its chemical composition as ascertained at the present time with that of it made1 say1 #bj years ago in the same brickyard1 and the analyses will1 in most instances1 be practically identical--at any rate1 so far as they may be of use to the brickmaker4 ,a brickmaker using a marine clay possesses innumerable advantages over another employing brick-earths due to river action4 ,it is no uncommon thing for a marine clay--say1 #cjj feet in thickness--to continue across country for hundreds of miles1 stretching from the ,north of ,england to the ,south1 and over into the ,continent1 save for the slight break occasioned by the scooping out of the ,english ,channel4 ,the composition of the ,oxford ,clay1 from which the well-known bricks at ,peterborough are made1 does not differ in the slightest degree1 so far as suitability for brickmaking is concerned1 from the ,oxford ,clay of ,bourges or ,chateauroux1 in the centre of ,france1 or indeed at almost any other point en route4 ,with marine beds it is possible to deal with the matter on broad lines1 but it is not so with any other class of deposits4 ,if a marine clay in a specified locality is found to be unsuitable for bricks at one point1 by reason of the presence of too much lime1 it would be a phenomenon if clay along the same geological horizon did not present the same unfavourable features at every other point within the district4 ,the homogeneous composition1 both from mineralogical and chemical standpoints1 of thick marine clays renders them of special use to the brickmaker4 ,having by sundry processes1 after infinite labour1 produced a certain class of brick from such an earth1 he does not as a rule have to materially modify those processes as the earth is dug into to continue manufacturing the same brick4 ,he is dealing with an earth which1 comparatively speaking1 is a constant quantity--when the clays are thick1 and no lines of bedding are distinctly visible4 ,we find that a rooted conviction exists in many brickyards that clays of marine origin are no good for brickmaking1 because 7so the opinion runs7 they always contain so much salt4 ,it is wonderful that such ignorance prevails1 when the slightest acquaintance with the subject would teach otherwise4 ,it is perfectly true that such deposits might have contained salt during and for some time after deposition1 but it is absurd to suppose that their marine origin has anything to do with the presence of common salt in the clay at the present time4 ,salt is soluble in water1 and has been removed from such clays by the percolation of underground water in #ii cases out of a hundred4 ,indeed1 as a matter of experience1 we find that salt is most commonly found in beds of lacustrine origin1 or those laid down in enclosed portions of the sea1 for reasons we need not enter into at the present moment4 ,of course1 when material is taken from the sea-shore to make into bricks1 a considerable quantity of salt is manifest1 but that is a totally different thing to the clays deposited--we should not like to say how many thousands of years ago4 ,clays of all kinds1 however1 may be impregnated with salt 7as in parts of ,cheshire71 owing to the proximity of other beds containing that mineral2 also by the percolation of underground water with much salt in solution4 ,to give some idea of the antiquity of the ,oxford ,clay alluded to--and that is quite a 8young clay0 geologically speaking--we may remark that at the time it was laid down not a single species of animal existed like those now living4 ,the only mammals found1 very small and very lowly organised1 were like kangaroo rats2 the birds were more like flying reptiles than anything else2 it was the age of reptiles1 and enormous1 unwieldy brutes swam in the water or floundered about on land2 huge sharks abounded1 and armour-clad fish of kinds very different to those now existing roamed the sea2 even the 8shell-fish0 were not altogether like modern ones2 whilst the plants find their nearest modern analogues in the wilds of ,australasia4 ,no elephants1 tigers1 lions1 bears1 or dogs lived then1 and the face of ,nature wore a totally different aspect to what obtains at the present time in any part of the globe4 ,and this seems a fitting opportunity to the writer to put on record the fact that many of the most wonderful remains found in the ,oxford ,clay and the neighbouring ,kimeridge ,clay are due to the discoveries of brickmakers4 ,without their valuable aid scientists would be quite unable to clearly depict the life of those remote epochs4 ,we have mentioned ,peterborough2 some most interesting remains have been found in the clays near that town during the past few years4 ,to appreciate this let the reader visit the fossil reptile gallery of the ,british ,museum 7,natural ,history71 at ,south ,kensington4 ,one of the most recent acquisitions1 set up a year or two ago1 is the skeleton of a young ,plesiosaurus--without doubt the most perfect specimen in the world of its kind--from ,peterborough4 ,the ,plesiosaurus was a large swimming reptile1 with paddles1 and a long neck4 ,we mention these things not only to instil philosophical interest in such brick-earths1 which may be reflected upon after business hours1 but to impart some idea of the extreme remoteness of the epoch from the human point of view1 and to insist on the immensity of the intervening time throughout which circulating underground waters--even in such an impervious material as stiff clay--may have exerted chemical action4 ,the 8mineralisation0 of the fossils is an eloquent witness of the effect of such changes4 ,the reader will perceive from this that there is scant possibility of soluble salts being present in such marine clays2 and the geological circumstances are fully borne out by the results of hundreds of chemical analyses of thick marine clays4 ,the invertebrate fossils more particularly testify to the marine origin of the clays1 and are thus invested with considerable practical interest4 ,the man whose duty it is to determine the persistence1 or otherwise1 of valuable marine brick-earths has thus a much easier task than when called upon to decide the value of a large tract of land for brickmaking purposes1 of fluviatile origin4 ,finally1 brick-earths do not1 except in extremely rare instances1 vary materially in character when dug into horizontally1 thus every opportunity is afforded to the manufacturer for making an unvariable quality brick1 tile1 or drain pipe4 ,it should be borne in mind1 however1 that these clays often weather a brown colour1 which on being dug into changes to a bluish-black tint1 the latter being the unaltered and best portion as a rule4 ,the only practical advantage the worker of a superficial river deposit possesses over his neighbour using thick marine clay is in the great range of variation in materials disclosed in the former kind of pit4 ,by judiciously mixing the different beds he may be able to live well where the worker of marine clays1 especially where the clay is too stiff1 or contains too much lime1 8comes to grief40 ,a good marine clay is a great boon1 a bad one cannot be remedied other than by the sacrifice of much money4 ,,chapter ,,iv4 ,,the ,,mineral ,,constitution ,,of ,,brick-,,earths4 ,there cannot be any question that the applicability or otherwise1 of an earth for making good bricks1 to a large extent depends on the mineral constitution of that earth4 ,a chemical analysis of a sample of such earth will tell us how much silica1 alumina1 lime1 iron1 etc41 is present therein1 and this information is frequently of great value when given by a scientific chemist2 but it does not tell us the state in which those constituents exist in the earth--an essential desideratum1 if we are to understand the scientific aspects of the question of burning in the kiln4 ,further1 the size of the granules and particles composing the earth is well worth knowing1 as we shall presently see4 ,it is a great mistake to imagine that all clays are essentially chemical deposits4 ,the majority of them have been in part derived from chemical disintegration1 it is true2 but the resulting deposits contain so much also that is purely of mechanical origin1 that the behaviour of the whole is materially modified1 from a metallurgical point of view4 ,take one ingredient1 for example--say1 silica4 ,that may exist in a brick-earth in a variety of ways1 both in a free and combined state2 but its behaviour in the kiln is largely dependent on the particular form assumed1 not only whether it is free or combined1 but as to how it is combined4 ,in a certain sense1 it is very doubtful whether even in the best-burnt brick much of the raw material becomes chemically combined2 a sort of agglutination takes place locally1 as is clearly shown by the microscope2 at such points true fusion undoubtedly takes place1 and there may be actual chemical combination4 ,in the vast majority of cases1 however1 such fusion or possible combination is of an extremely partial and elementary character1 whilst it hardly exists in the average 8rubber40 ,the microscope shows that even in the hardest burnt brick there still remain enormous quantities of what may be termed mineral grains1 that have by no means succumbed to the burning process4 ,the edges of the grains may occasionally be seen merging into the more or less vitreous ground mass in which they are embedded1 but beyond that they appear tolerably fresh1 and their action on polarised light remains unimpaired4 ,we did not intend to say anything yet concerning the microscopic structure of bricks--that will be gone into in a subsequent chapter2 but we thought it useful to state the foregoing elementary facts in order to endeavour to uproot a conviction that seems to be very firmly grounded--viz41 that the chemical composition of a brick-earth imparts an accurate idea of the possible active agents1 on the earth being subjected to the kiln4 ,as a matter of fact1 some of these would-be agents are imprisoned in the mineral grains and particles that have not become involved in the partial melting or agglutination of the mass1 and might as well not be present in the earth for any work they may accomplish either for good or for evil4 ,there is greater probability of the bulk of these grains and particles being of active service when they are ground up exceedingly fine2 but the clayworker's idea of 8fineness10 as demonstrated by what passes through an ordinary clayworking mill1 and 8fineness0 in the sense here intended1 are two totally different things4 ,we mean something that shall render the particles so small as that they shall only be observable on being magnified1 say1 #ej diameters4 ,hardly any clays used in brickmaking are in bulk made of such small particles as this2 there are a few1 of which the best terra-cotta and porcelain are manufactured1 however1 but even these have to be very carefully prepared to exclude grosser foreign particles4 ,from what we have said1 it will be gathered that the terra-cotta and porcelain manufacturer is at the present time in a better position to judge of the work done in the kiln or oven than is the brickmaker4 ,but that is simply a matter of education2 the problems presented to the average brickmaker are rather more complicated than to the terra-cotta manufacturer1 but they may be unravelled on sufficient application1 as we hope to point out4 ,even under the most favourable conditions1 however--when the particles composing the mass require a -inch objective for their elucidation--we find that the best burnt brick is largely made up of them in an unmelted condition4 ,and we should be very sorry to get rid of them2 for if they disappeared1 the stony attributes of the brick would disappear also1 and the general value of the substance would be deteriorated to such an extent that it would be unsaleable as a building material4 ,the brick would nearest resemble a form of slag4 ,all we now insist upon is that in brickmaking a chemical analysis is only useful up to a certain point1 beyond which we must appeal to the microscope to aid us1 and this in conjunction with as perfect a knowledge as possible as to the behaviour of earths of certain mineral composition when under the influence of high temperatures4 ,in many instances1 the value of the brick depends almost entirely on incapacity for fusion on the part of a large proportion of the minerals of which the brick is made4 ,possibly1 a good all-round brick would be where the bulk of its mineral particles were infusible at the temperature employed1 and when the remainder were fusible enough to partially run1 so as to cement or agglutinate the infusible particles firmly together4 ,in order to bring about such conditions artificially1 or to arrive at them even approximately1 we must know at least three things1 viz4--7#a7 the nature of the mineral particles involved in the whole operation2 7#b7 their behaviour under high temperatures2 and 7#c7 a knowledge of certain branches of metallurgical chemistry4 ,now1 obviously1 we cannot undertake to teach even the spirit of what is involved in these three desiderata in a small book like this2 but we can1 and shall1 attempt to do something in that direction1 and we must ask the reader's indulgence to take for granted observations to be occasionally made1 in the inevitable prospect of our not being able to explain them at sufficient length4 ,the following are the principal minerals found in clays used in brickmaking1 together with their more important attributes from our point of view4 ,,kaolin4 ,pure clay is1 theoretically1 composed of this mineral alone1 but pure clay does not exist in ,nature1 except as a mineralogical curiosity4 ,what is generally called pure clay is a white1 or light-grey plastic material1 composed of kaolin with many other substances to a small degree1 from which it frequently has to1 as far as possible1 be separated before being put to its highest uses in porcelain manufacture4 ,chemically1 pure kaolin may be regarded as a hydrous silicate of alumina1 viz4--silica #df4c1 alumina #ci4h1 and water #ac4i4 ,under the microscope1 in reflected light1 it is seen to be made up of extremely minute1 thin1 six-sided plates1 which are said 7doubtfully7 to crystallize in the rhombic system2 though1 when regarded with the naked eye1 one would not suppose that it possessed a crystalline structure1 as it appears to be an earthy1 unctuous substance4 ,it is commonly mixed with grains and small crystals and fragments of quartz1 which mineral will presently be described4 ,being derived from the decomposition of felspars1 the microscope reveals the fact that in addition to the six-sided plates alluded to1 a great deal of opaque matter1 as particles of mud1 occurs in the substance universally known as kaolin4 ,it is very difficult to satisfactorily state what this mud is2 micro-chemically1 its general character may be brought out4 ,there is no doubt1 however1 that in converting the kaolin into china-ware1 these particles are more active than the minute kaolin crystals in uniting with other substances to form a species of flux4 ,the subject has been investigated to a very limited extent1 but from the foregoing observations it will be seen that the proportion of amorphous mud particles to the minute crystals must be an important factor in determining the nature of the fluxing material1 and of the quantity of this latter to be used4 ,correlatively1 the fusing point can be determined in the same manner4 ,for1 in itself1 kaolin is an infusible mineral1 and before it can be made use of for brickmaking1 terra-cotta1 or any kindred purpose1 it must be rendered artificially fusible by the addition of a fluxing substance4 ,when1 therefore1 we learn that kaolin is being used for these purposes1 we know1 if used direct as it comes from the pit1 that it must be impure from a mineralogical standpoint1 or that it is being mixed with other substances4 ,we say that kaolin is infusible 7refractory72 we mean at any temperature used in the industrial arts1 including brickmaking4 ,with the recent improvements in the electric furnace1 the temperature generated is so high that practically any mineral substance may be melted2 it is hard to speak of anything being infusible4 ,but the mineral matter called kaolin in ordinary clays1 such as the brown and blue ,london ,clay1 the ,oxford ,clay1 8brick-earths10 etc41 has very little in common with the more or less pure china-clay4 ,the microscope shows that in the vast majority of such clays scales of true kaolin are few and far between1 that opaque mud particles are more frequent1 and1 above all1 that pieces of highly decomposed felspar 7called 8kaolinised0 matter7 are present4 ,eliminating all other and foreign substances from the clay1 the whole of what would commonly be called kaolin and kaolinised matter1 taken together1 is of very varied chemical composition1 and might1 indeed1 be fusible in the ordinary sense of that term4 ,from this1 the reader will perceive that the term kaolin is very ambiguous and altogether too wide in its meaning4 ,we think it highly desirable1 therefore1 to describe kaolin as a true mineral and not as a rock1 reserving the term for the crystalline plates4 ,the mud particles referred to we may call 8kaolinised particles20 and the highly decomposed felspar 8kaolinised matter40 ,to sum up the relative fusibility of these substances1 per se1 we should say that 7#a7 kaolin crystals are practically infusible2 7#b7 kaolinised particles are either fusible1 partly fusible1 or infusible1 depending on the actual nature of the particles2 and 7#c7 that kaolinised matter may be difficultly fusible or infusible4 ,a mixture of 7#a7 and 7#b7 may not be fusible1 and could not be unless a great proportion of 7#b7 of a fusible character1 so as to form a flux1 were present4 ,the reasons for this will appear in considering the different kinds of felspar1 next to be described4 ,,felspar4 ,this mineral1 a very common constituent of nearly all clays and brick-earths is very variable in character1 but may be separated into a number of mineral species1 each of which possesses a definite structure and a more or less constant chemical composition4 ,to show the range of variation1 the following kinds of felspar1 with their chemical composition1 may be quoted3--#c ,chemical ,composition of ,felspars4 ---------------------------------------- --------------- ,silica4 ,alumina4 ,potash4 ,soda4 ,lime4 ---------------------------------------- -- ,orthoclase #fd4f #ah4e #af4i ,albite #fh4f #ai4e #aa4h ,oligoclase #fc4g #bc4i #a4bj #h4a #b4j ,labradorite #eb4i #cj4c #d4e #ab4c ,anorthite #dc4j #cf4h #bj4a ---------------------------------------- --------------- ,orthoclase felspar1 in addition to the above1 frequently has small proportions of lime1 iron1 magnesia and soda4 ,amongst other things it is an essential constituent of granite1 and on the decomposition of that rock is the first mineral to become affected4 ,when attacked in the open air by rain and the ordinary agents of denudation1 granite ultimately gives way by the dissolution of the felspar1 and on being removed1 the felspathic matter may accumulate in convenient situations to form kaolin4 ,if we now compare the chemical constitution of orthoclase felspar with that of kaolin as previously given1 we notice that the potash has disappeared in the decomposing process2 it has been dissolved and taken away by rivulets1 and the like1 or washed by rain direct into the sea4 ,we also observe that there has been a re-distribution1 so to speak1 of the relative proportions of silica and alumina--following well-known laws4 ,of the remaining felspars the commonest for our purposes is oligoclase1 a mineral found in nearly all ,british 8granites0 in a greater or less degree4 ,that contains a higher percentage of alumina than orthoclase1 and there is a fair proportion of soda and little lime1 but much less potash4 ,the lime-soda felspar1 labradorite1 and its near ally1 anorthite1 are not often met with in a recognisable form in clays4 ,if present1 they are generally as 8kaolinised matter10 too highly decomposed to exhibit their characteristic optical properties4 ,it is pretty generally stated1 and too often assumed by some1 that pure china-clay is derived from the direct decomposition of rocks containing 8orthoclase0 felspar4 ,yet1 this cannot really be so1 if we reflect on the mineral composition of many of the rocks1 which1 obviously1 have yielded the china-clays in question4 ,take the china-clays of ,devon and ,cornwall2 they have undoubtedly been derived from the 8granites0 of those counties4 ,to some extent1 as previously remarked1 the orthoclase is attacked1 and provides the material of which china-clay is made4 ,but in the 8,west of ,england10 we have yet to learn that some of the other felspars are not also involved in the process4 ,if we examine a fresh piece of granite from the flanks of ,dartmoor1 or from the neighbourhood of ,liskeard1 or ,st4 ,austell1 we find no difficulty in recognising a fair proportion of triclinic felspar 7one or more of those mentioned in the table except orthoclase7 in it4 ,there is a difference in the composition 7and therefore the commercial applicability7 of a china-clay derived from a rock containing orthoclase alone1 and one from a rock having orthoclase and one or more triclinic felspars in addition4 ,the latter minerals are more easily decomposed than orthoclase1 especially the lime and lime-soda varieties4 ,we should not have raised this point only that1 by reason of the granites being to some extent mechanically as well as chemically decomposed1 a large proportion of 8kaolinised particles0 and 8kaolinised matter0 is introduced into certain china-clays1 which render them different in their behaviour under intense heat from those china-clays in which orthoclase alone has been principally concerned4 ,in other words1 great practical advantages accrue from an accurate knowledge of the constitution and origin of the china-clays in question4 ,two clays of the same chemical composition often behave in a different manner in the kiln2 the cause of this is frequently to be found in the prevalence of 8mechanical fragments0 of felspar in one of the clays2 and the absence of these1 but the presence of 8kaolinised particles0 of the same chemical composition1 in the other4 ,another point to which we may draw attention is the erroneous supposition that granites which have yielded china-clay have in all instances been reduced to the condition in which we now find them by the action of atmospheric agents of denudation alone4 ,granites1 as a matter of fact1 yield very slowly to the action of the atmosphere1 and taken as a whole no building stone is as durable as they4 ,how comes it1 then1 that they have decomposed to such an extent as to have formed extensive deposits of china-clay in a very short space of time1 geologically8 ,we think the answer is to be sought1 at any rate in some instances1 in the alteration the rock as a whole has undergone in certain situations1 whereby it became more easily decomposable4 ,take the rotten china-stone of the neighbourhood of ,st4 ,austell1 for example4 ,in that material we clearly see a stone from which the 8life0 has been sapped1 and instead of a bright1 sparkling1 porphyritic granite1 as it once was1 we now notice only a ghost of its former self4 ,the large orthoclase felspars may be seen in it as skeletons1 the mica is reduced to mere iron-stains 7when present at all71 whilst the quartz is also slightly affected4 ,this altered and comparatively rotten material 7although sometimes hard enough to be used as building stone7 extends to an enormous depth from the surface2 it has not been bottomed in some parts of the district4 ,such an extensive transformation could not possibly be due to ordinary agents of denudation which do their work at and near the surface of the rock only4 ,it seems to arise from an enormous regional alteration1 acting underground to an unfathomable depth1 and which may not be unconnected with the mineral veins so common in1 and in the immediate vicinity of the workings4#d ,yet another thing to be remembered is that1 under certain conditions1 as near ,st4 ,austell1 china-clay has been formed in situ1 and has therefore not been deposited by the action of running water1 as have the majority of china and other clays4 ,mr4 ,collins remarks that this china-clay is very irregular in its occurrence4 ,it seems to be formed of various granite masses decomposed in place2 it often occupies considerable surface areas1 and extends to a depth unknown4 ,he remarks that at ,beam mine1 and also at ,rocks mine1 both near ,st4 ,austell1 china-clay was found to a depth considerably exceeding #fj fathoms from the surface4 ,this china-clay1 in its natural condition1 is very much the same as china-stone2 but the decomposition has proceeded further1 the felspar being completely changed into clay2 and nothing more is necessary for extracting the clay than the disintegration of the whole mass by a stream of water directed upon it1 when the clay is carried away in suspension and collected at convenient spots4 ,thus there is every gradation between the true crystalline orthoclase and triclinic felspars1 through china-stone into china-clay formed in situ1 so into china-clay deposited from water by natural or artificial means1 and into a pure clay containing a large proportion of kaolin crystals1 8kaolinised particles0 and 8kaolinised matter40 ,but although we can state that much1 a great deal yet remains to be done in connecting mineral structure with chemical composition of the purer clays1 and in defining the various grades scientifically1 in order that full advantage may be derived from them in a commercial sense4 ,,chapter ,v4 ,,minerals3 ,,their ,,behaviour ,,in ,,the ,,kiln4 ,,the ,,silica ,,group4 ,silica1 the oxide of silicon1 is found in brickmaking clays principally in two conditions when not combined with other substances3 in one of these the free silica may be crystalline1 when it is known as quartz2 in the other it may be hard1 but not crystalline1 as flint4 ,we may consider these in order4 ,,quartz4--,when pure this mineral is perfectly white and transparent1 like ordinary window glass4 ,it is exceedingly hard1 and this property is of much service as enabling us by the most elementary examination to distinguish it from certain other minerals1 which it is not unlike at first sight4 ,one of the latter is calcite1 a crystalline form of carbonate of lime1 also white and transparent4 ,quartz and calcite behave in a very different manner in the kiln1 and as we shall see1 they are both rather common constituents of brick-earth4 ,the difference in hardness may easily be ascertained by the point of a good steel knife2 the steel will not scratch the quartz1 but it will1 easily1 the calcite4 ,when it has plenty of room wherein to crystallise1 and is not hemmed in1 as it were1 by other hard crystalline matter1 quartz often forms beautiful six-sided prisms surmounted by a six-sided pyramid1 and1 rarely1 pyramids are found at both ends of a prism4 ,there are no lines1 or 8planes of cleavage10 to interfere with the transparency1 either in the extremely minute forms of the mineral as investigated by the microscope1 or in the gigantic crystals occasionally found4 ,regular crystals of quartz1 although by no means rare in ,nature1 are seldom met with entire in brick-earths4 ,the most common form of the mineral is in irregular aggregates with other minerals1 as in the rock granite1 which is composed essentially1 as previously mentioned1 of quartz1 felspar1 and mica4 ,we have traced the history of the felspar on the decomposition of that rock1 and it may now be said that on complete disintegration of the granite a great part of the quartz present is simply resolved into fragments and dealt with by rain and other transporting agents4 ,for quartz is practically imperishable2 it is almost proof against the deleterious acids in the atmosphere1 which so readily attack many other common minerals4 ,in dealing with it1 all ,nature can do 7at least at the surface of the earth7 is to carry the small quartz grains and pieces about from place to place2 ,she can1 and does1 in this process1 reduce the quartzose fragments by causing them to continually knock against each other and against other mineral fragments and masses until the grains and pieces find a resting place2 ,she may put them in a mill and grind them to powder1 but the quartz is still there4 ,another manner in which quartz occurs in ,nature is as filling cracks in rocks1 but this is comparatively unimportant for our present purposes4 ,the purest quartz is known as rock crystal2 but by far the commonest kinds of the mineral are impure2 they may contain iron1 schorl 7a black needle-like crystal71 and many other minerals4 ,one of the most interesting points about it1 and which undoubtedly in certain cases is of importance to the brick manufacturer as modifying its melting properties1 is the presence of myriads of extremely minute so-called cavities1 generally filled 7or nearly filled7 by liquids of different kinds1 the precise nature of which is not as well-known as it might be1 though in some instances it has been determined with tolerable certainty4 ,in some cases these inclusions are so numerous as to obliterate the transparency of the quartz crystal1 causing it to present a frosted appearance4 ,the fluids in these cavities may have beautiful little crystals of other minerals1 such as salt1 floating about--but it must be remembered that we are referring to something infinitely little4 ,these slight differences in the constitution of minerals1 however1 have their influence in the kiln4 ,for instance1 although the fluid present is usually water1 that often contains carbon dioxide1 which acts as a species of flux to the quartz when present in sufficient quantity4 ,in reference to the second form of silica present in brick-earths1 flint1 that is of precisely the same chemical composition as quartz1 only that it is not crystalline1 nor transparent1 though thin pieces of flint are translucent4 ,flint is by no means as common in ,nature as quartz2 it is very hard1 but brittle1 and breaks with what is termed a conchoidal fracture1 from the fact that the fractured surface frequently resembles the external appearance of the shell of a bivalve mollusc4 ,it occurs in a variety of ways2 7#a7 often as hard lumps or nodules running along in fairly regular layers in limestone rocks such as chalk1 and 7#b7 occasionally filling up cracks or joints in such rocks4 ,it is hard to describe its origin in a few words1 and we shall not attempt it2 all that need be noted is that it is frequently full of the remains of extinct organisms of small size1 which may1 or may not1 constitute an impurity depending on the particular organism and its present condition4 ,when flint contains a fair proportion of iron it is called chert--an extremely common constituent of brick-earths in some localities--though that term refers to other rocks1 such for instance1 as those made up almost exclusively of the siliceous spicules 7hard parts made of silica7 of fossil sponges4 ,a more or less crystalline kind of silica is found1 forming the skeletons of minute aquatic plants1 and these accumulating to some depth1 constitute the basis of such materials as ,kieselguhr and the diatom earth of the ,isle of ,skye1 both of which1 especially the former1 are used for making firebricks4 ,there is very little to be said concerning the behaviour of free silica--quartz and flint--in the kiln4 ,it is infusible except at higher temperatures than are employed by the brickmaker4 ,but1 as we have already remarked1 the impurities often present in the minerals form a species of flux which naturally brings them into the range of fusible substances1 though even then the temperature required is far beyond what is usually attained in the majority of brickyards1 though it might be frequently arrived at in the manufacture of certain fire-bricks4 ,for all ordinary purposes1 therefore1 quartz and flint may be regarded as infusible4 ,in presence of much lime1 iron1 or similar substances1 however1 both of them are readily melted1 and it is part of the science of brickmaking to know exactly how much lime1 c41 to add to yield the best results4 ,many brick-earths contain large quantities of the calcareous and ferruginous substances alluded to1 and are then capable of being made into bricks direct1 without any addition4 ,but although such natural brickmaking earths are frequently employed by the manufacturer1 nearly all of them could be made to yield a better brick by a little artificial mixing4 ,we must keep urging this point2 there is room for great improvement all round4 ,as with the majority of comparatively refractory substances1 the size of the grains and pieces of quartz and flint makes a difference in their readiness to become fusible4 ,the larger the grain the more difficult it is to break down2 fusion commences at the outside of a quartz grain1 the centre of which may at the same time be comparatively unaffected4 ,by arresting the fusing process1 the microscope shows the outside of the grain to have become softened 7so much so as to affect its doubly refracting properties71 whilst the innermost parts still retain their usual optical characters4 ,,mica4 ,the different varieties of mica are important as rock-forming minerals1 but they are not as often met with in brick-earths as is generally supposed1 except in insignificant quantity4 ,some of the purest clays1 however1 contain a great deal of mica1 derived almost directly from the destruction of granite4 ,the two commonest varieties of the mineral are biotite and muscovite4 ,,biotite ,,mica4--,this mineral1 usually known as ferro-magnesian mica1 is composed of silicates of magnesia1 alumina1 iron1 and alkalies in variable proportions4 ,it occurs as six-sided plates or irregular scales1 usually of a bronze-black colour4 ,biotite weathers with comparative facility1 hence the reason why it is not more commonly met with in brown and other impure clays4 ,,muscovite ,,mica4--,this is sometimes called potash- or alumino-alkaline mica1 composed of the silicates of alumina1 alkalies1 iron1 and magnesia2 the proportion of silica ranges from #de to #ej per cent4 ,it may usually be distinguished at sight from biotite by its silvery white or light brown colour4 ,when large enough1 both the micas mentioned may be split up into thin plates1 muscovite yielding large transparent sheets4 ,compared with all other constituents of brick-earth1 the micas are bright and of semi-metallic lustre4 ,muscovite is more durable than biotite1 and is much more frequently met with in brick-earths1 especially in the sandy varieties4 ,the influence of mica in the kiln is not of much importance in ordinary brickmaking2 in general its alkaline character renders it fusible1 though a high temperature is necessary at all times to effect that4 ,in china-clay mica is regarded as a nuisance1 and in breaking down the material it is separated in the washing process by running water1 the mineral collecting in depressions or basins1 called 8micas40 ,when muscovite contains much fluorine1 as it frequently does1 it is very undesirable in clays for high-class purposes4 ,at the best of times the proportion of iron in mica is sufficient to mar the quality of the otherwise most excellent clays4 ,in the kiln1 or porcelain furnace1 the presence of mica 7more particularly biotite7 is apt to create yellow and brown specks1 or a species of mottling4 ,it is highly satisfactory1 therefore1 to note that these little shiny flakes may be easily floated off by a moderate amount of care in washing1 and thus separated from the other constituents of the clay4 ,,iron4 ,except in regard to white kaolin clays1 nearly all earths used in brickmaking contain more or less iron1 which is usually present as protoxide in many mineral constituents4 ,the colouring matter of clays is generally iron in some form1 and blue clays weather into brown by the alteration of that mineral4 ,it is unnecessary for us to consider the various minerals of the iron group2 all we need do is to state the mode of occurrence of iron oxides in clays and earths1 to consider a variety known as iron-pyrite1 and the general effects of ferruginous minerals in the kiln4 ,iron may occur in clays simply as a stain1 when it is usually not in large quantity1 or it may occur combined with some mineral or minerals present--as for instance certain felspars and micas4 ,the brown1 yellow1 or blue appearance of the clay is due to it4 ,in loam it may be found also as a species of ochreous earth1 and in thin bedded loams 7as the upper part of the ,woolwich and ,reading series of the ,london basin7 each layer frequently varies in the proportion of iron present4 ,in the more arenaceous parts of these loamy deposits1 little grains of iron sometimes make their appearance1 as also in certain sands employed in brickmaking2 on careful examination1 however1 many of these grains are found to be other mineral substances coated with iron4 ,certain horizons in what are known as the ,jurassic rocks contain great quantities of ferruginous matter in little pellets4 ,iron1 in large proportion1 acts as a flux to other constituents when the brick-earth is subjected to great heat in the kiln1 and on that account must be carefully watched4 ,but1 to the average brickmaker1 the ferruginous constituent is far more interesting as a colouring medium4 ,at a later stage we shall have something to say concerning the colouring of bricks1 c41 but it may now be remarked that red bricks1 in practically all cases1 owe their colour to the effects of firing on iron4 ,it is a great mistake to imagine1 however1 that a large percentage of iron in a clay will necessarily produce a good red tint4 ,in the first place1 a great deal depends on the way the clay has been mixed or prepared2 and in the second1 the method of burning and the temperature employed1 taken in conjunction with the general composition of the earth1 are all important4 ,this much may be said1 however1 that without the iron 7or some mineral colouring matter possessing similar properties in the kiln7 a red brick would not result4 ,an even colour is the effect of thorough and homogeneous incorporation of the iron with the brick-earth2 that may have been brought about by natural processes1 but it is most frequently obtained in the careful preparation and mixing of the clays4 ,a very essential point is that the earths must be of such a character as to withstand the requisite heat in the kiln without becoming vitreous1 or twisting or warping4 ,it must not be forgotten that a certain proportion of the iron1 under great temperatures1 may be carried away out of the kiln in union with other things1 in the form of vapour4 ,to successfully treat a raw earth1 so that all these points may be taken into account1 and to produce a thoroughly uniform red brick1 that shall not vary in tint from kiln to kiln1 is a matter requiring considerable skill and attention1 though fairly good bricks of that character have been produced by sheer accident in burning natural earths fairly rich in thoroughly disseminated iron oxides4 ,two minerals commonly met with in earths used for brickmaking are pyrite and marcasite1 both of which are of the same chemical composition1 namely1 iron disulphide4 ,we may first consider them separately1 for they are of great importance to the brickmaker4 ,iron pyrite occurs as regular cubic crystals1 or irregular streaks1 or as nodules or lumps2 in clay1 the last-mentioned is its commonest form4 ,it is a good petrifying medium1 so that it is frequently associated with organic remains1 as is exemplified in almost any yard where stiff clay is being worked4 ,the nodules1 on being broken open1 ordinarily exhibit a radiating structure of brassy lustre and extremely beautiful appearance1 though often marred by brown iron stains due to decomposition of the mineral4 ,in the refuse of slates1 now so largely used in several parts of the world for brickmaking1 pyrite is most frequently found as fine cubic crystals of a durable nature4 ,marcasite1 on the other hand1 crystallizes in a different manner 7in the rhombic system of mineralogists71 but is chiefly found in fibrous masses or dirty-brown nodules1 the last-mentioned being common in clays4 ,when bright it is paler in tint than pyrite1 though this is not a constant character4 ,it occurs abundantly in almost all sedimentary rocks diffused as minute particles1 but sometimes in irregular layers4 ,sir ,archibald ,geikie states#e that this form of the sulphide is especially characteristic of stratified rocks1 and more particularly of those of ,secondary and ,tertiary age4 ,that it is not abundant in ,primary rocks is not to be wondered at when we consider its liability to rapid decomposition2 indeed1 for it to be preserved at all it must be well shielded from atmospheric agents by ,nature4 ,exposure even for a short time to the air causes it to become brown1 free sulphuric acid is produced1 which may attack surrounding minerals1 sometimes at once forming sulphates1 at other times decomposing aluminous silicates and dissolving them in considerable quantity4 ,it plays even a larger part than pyrite as a petrifying medium1 at any rate in the younger rocks4 ,both pyrite and marcasite are abundant in many other rocks than those of special interest to the brickmaker2 the former1 in fact1 is almost universal in its occurrence4 ,it will be convenient to consider the behaviour of these two minerals in the kiln together1 as the difference between them from that point of view is practically nil4 ,under the action of the intense heat met with there1 they become partially decomposed2 oxide of iron and basic sulphides of iron remain4 ,when1 at a subsequent period1 bricks containing these substances are exposed to the action of the weather1 oxidation takes place1 sulphate of iron and sometimes of lime are formed1 which on crystallizing expand with considerable force and split or crack the brick4 ,from this it is evident that sulphide of iron in any form is not to be tolerated in brick manufacture1 and if the earth used in the first place contains much1 it must be removed in the preparing process4 ,if permitted to remain1 it is impossible to obtain either a durable1 or a good coloured brick4 ,,chapter ,,vi4 ,,minerals3 ,,their ,,behaviour ,,in ,,the ,,kiln 7continued74 ,,calcite1 ,,aragonite1 c4 ,carbonate of lime may occur in a crystalline form1 or as earthy substances1 and many varieties of it are found in clays used by the brickmaker4 ,the commonest are calcite1 aragonite1 and a white earth4 ,calcite1 known also as calc-spar1 crystallises in the hexagonal system1 though true hexagons are not very common4 ,it occurs principally as rhombohedra and scalenohedra1 with variations therefrom2 also fibrous1 lamellar1 granular1 compact1 nodular1 and stalactitic4 ,when pure1 calcite is colourless and usually transparent1 but when mixed with iron or other mineral colouring matter it commonly assumes yellow and brown tints4 ,aragonite is also a crystalline form of carbonate of lime1 but is by no means as common in ,nature as calcite4 ,it crystallises in the rhombic system1 which assists the mineralogist to distinguish it from the last-mentioned mineral1 from which it differs also in being harder and of higher specific gravity4 ,aragonite may occur as globular masses1 or as incrusting other substances1 or in the stalactitic form4 ,it is sometimes white1 but more often yellowish1 or grey1 and it is not1 commonly1 as transparent as calcite1 whilst it often possesses one to two per cent4 of carbonate of strontia1 or other impurity4 ,it is generally stated that carbonate of lime1 when deposited from cold solutions1 crystallizes in hexagonal 7calcite71 and when from warm solutions1 in rhombic 7aragonite7 forms4 ,no doubt1 on the whole1 that is the case2 but we ought not to forget that many marine organisms make their hard parts of aragonite1 which1 under the circumstances1 is certainly not obtained from warm solutions4 ,these crystalline forms of carbonate of lime are both of them found in fossil shells and the like in clays1 and in not a few instances the calcareous constituent found in the brick-earth is present almost exclusively in the fossils1 which are ground up with the rest in preparing the material for the moulding machine4 ,when present as hard crystalline lumps or pebbles1 they have been derived from the destruction of limestones1 and are then the greatest nuisance imaginable to the brickmaker and the most dangerous constituent at the same time4 ,with proper machinery these hard lumps may be ground down to fine particles1 but they are even then only to be admitted into the earth on sufferance4 ,the best plan1 without doubt1 is to remove them altogether from the raw earth4 ,they are commonly met with in what the geologist calls 8boulder clay0--a deposit owing its origin to glaciers and icebergs4 ,very often the pebbles alluded to are not crystalline1 but of an earthy character1 as is the case when made of chalk4 ,in the semi-dry process of manufacture1 it is next to impossible to incorporate the ground-up particles of carbonate lime sufficiently well to result in the production of such a homogeneous earth as is desirable for making a first-class brick4 ,in sandy clays or loams1 and in a few stiff clays used for brickmaking1 certain remarkable concretions called 8race0 are found1 the deleterious properties whereof are so well known to the average brickmaker that he carefully avoids the particular strata in which they occur4 ,it is fortunate that these concretions have a habit of being confined to narrow limits along definite horizons in the brickyard section1 so that they may be readily discarded in working4 ,but that is not always the case1 and little nodules of 8race0 are usually more or less frequent also in the beds above and below the horizons referred to4 ,they are composed wholly of carbonate of lime1 and their general effect in the kiln1 and afterwards1 will presently be explained4 ,other forms of concretions are known as 8septaria10--tabular or rounded masses of argillaceous limestone found in practically all stiff clays4 ,these are often of enormous size1 and are disposed in regular lines which the field geologist takes to indicate bedding planes in the clay--otherwise often very difficult to make out4 ,in certain stiff clays little pellets of the same substance are found4 ,the larger septaria have commonly been cracked in various directions1 the fissures being subsequently filled with calcite4 ,coprolites are impure varieties of phosphate of lime1 and the term should1 properly speaking1 be restricted to a substance of organic origin1--the fossilised excrement of animals4 ,but the name is now loosely employed to designate phosphatic concretions in general1 such as are commonly found in stiff clays1 in certain 8greensands10 and in other sedimentary deposits4 ,the dark brown phosphate of lime has formed on and often completely envelopes many fossils2 in certain cases it has in fact been utilised as a petrifying medium1 in which form it ordinarily occurs in the thick black clays of ,peterborough1 ,cambridge1 the gault of ,kent1 ,surrey1 etc4 ,summing up the effects of carbonates and other kinds of lime in the kiln1 it may be at once said that when present in any other form than as extremely minute particles1 they are distinctly to be avoided4 ,the small pellets and large pebbles especially are to be avoided1 for the following reasons4 ,carbonate of lime is made up of lime and carbonic acid2 if a lump of this be subjected to great heat and thus calcined1 the carbonic acid is driven off1 escaping by means of flues1 the open chimney1 or kiln4 ,the product is lime pure and simple--ordinary builders' lime4 ,everyone knows that on the addition of water builders' lime becomes 8slacked10 and eventually1 after a fashion1 8sets40 ,precisely the same thing occurs in the brick-kiln4 ,the raw brick is often composed of pieces of chalk or other limestone1 in limestone districts and in areas where boulder clays are largely employed for brickmaking4 ,on being subjected to the heat of the kiln these pieces are promptly reduced to the condition of lime4 ,during the process of conversion considerable expansion takes place1 and subsequently contraction1 leading to the formation of cracks radiating from the fragments of limestone1 the homogeneity of the bricks being at once destroyed4 ,apart from this1 when placed in the open air the lime becomes slacked1 and the quality of the brick is seriously impaired4 ,lime is a highly refractory substance1 strongly basic in character1 and forms fusible compounds with silica and other acid bodies4 ,it is1 therefore1 useful as a flux in many earths used in brickmaking1 being added to them expressly for that purpose1 to the general improvement of the brick4 ,the celebrated ,dinas bricks1 for instance1 are composed of a highly refractory earth containing about #ig per cent4 silica1 the remainder being lime1 oxide of iron1 alumina1 alkali and water4 ,to render this material fusible and so as to make refractory bricks1 from #a to #c per cent4 of lime is added4 ,but what we more particularly desire to draw the reader's attention to at the present stage1 is not the employment of lime in making fire-bricks so much as its mixture with ordinary brick-earth1 as in the manufacture of malm bricks4 ,sometimes the mixture has been effected by ,nature1 as is the case with true marls2 but the brickmaker does not care so much for these1 as without considerable and expensive artificial assistance they do not often make readily saleable bricks4 ,the common practice is1 briefly1 to grind chalk or similar earthy limestone in the wet state1 and then to introduce it to the brick-earth with which it is thoroughly incorporated2 and there are many ways of doing this1 which we shall not attempt to describe now4 ,the object of adding chalk to the brick-earth is twofold2 in the first place it assists in diminishing the contraction of the brick on drying1 i4e41 before burning2 and secondly1 it acts as a flux in the kiln by combining with the free silica1 or the silicates1 in the earth4 ,undoubtedly the second is1 theoretically1 its chief function2 but its beneficial effects in that direction are largely marred by insufficient burning1 whereby a large proportion of the chalk is not actively engaged1 as may be seen on examining the majority of malm bricks with the microscope4 ,indeed1 the eagerness to save fuel1 and to turn out the bricks as rapidly as possible1 often leads to the chalk particles being utterly useless4 ,and1 if we may judge from conversations with several brickmakers1 it would seem that the real reason why the limestone is used at all is unknown to them1 except that it produces bricks of a saleable colour4 ,this question of colour is the all-predominating one with most malm brickmakers4 ,we said just now that the fragments of limestone in the raw brick are reduced to lime on being burnt2 some of the latter1 however1 as may be anticipated from our subsequent remarks1 is engaged in forming a flux wherever possible in the immediate neighbourhood of such fragments3 it is the 8kernel0 that is left which becomes 8slacked10 and weakens the brick4 ,the object of utilising the smallest particles only of the carbonate of lime is thus obvious2 and if it were possible to use ordinary builders' lime instead of carbonate of lime1 the result would be better still4 ,the difficulty in utilising builders' lime is1 of course1 its certainty of slacking during the preparation of the brick-earth with which it would have to be thoroughly incorporated4 ,,selenite4 ,the 8petrified water0 of the brickmaker4 ,it is a crystalline form of gypsum--a hydrous sulphate of lime1 occurring in large quantities in the commonest clays used in brickmaking4 ,large and beautiful crystals1 some of them radiating from a central point1 are found in the ,london ,clay1 ,kimeridge ,clay1 ,oxford ,clay1 c4 ,by expelling the water from selenite1 or gypsum1 plaster of ,paris may be prepared4 ,in the kiln1 therefore1 it is important that this constituent be as finely ground as possible1 so as to localise the effects of the anhydrous sulphate on being moistened subsequently4 ,in hard burnt bricks1 no doubt1 a great deal of it is effectively used as a flux to other constituents of the clay2 but in by far the larger quantity of bricks this sulphate is reduced to fine powdery particles easily picked out as being softer and lighter in tint than the remaining constituents4 ,the weather-resisting qualities of the brick are naturally1 not improved when much baked selenite is present2 and the colour of the whole is apt to become variegated--that is1 in a fairly soft brick4 ,,dolomite4 ,dolomite is1 chemically1 composed of the carbonates of lime and magnesia in about equal proportions4 ,it is found as rhombohedral crystals1 the faces of which are often curved2 also in granular and massive conditions4 ,its prevailing colour is light yellow both in crystals and rock masses1 but1 as with most other minerals1 impurities occasionally make it assume other tints1 principally red and green4 ,carbonate of iron is frequently present1 sometimes to such an extent as to entirely alter the character of the substance4 ,as separate crystals dolomite has very little interest for us1 though rarely it may take the place of calcite or aragonite in the fossils of brick-earths and clays4 ,but in its massive condition1 as magnesian limestone1 it is of increasing importance to the brickmaker4 ,for many years it has been utilised in the manufacture of basic bricks1 though at the present moment the market in these materials is attentively looking at the possibilities of the next mineral to be described4 ,,magnesite4 ,magnesite is pure carbonate of magnesia--that is1 magnesia #dg4f1 and carbonic acid #eb4d per cent4 ,it usually occurs massive or fibrous1 but sometimes granular1 and its fine rhombohedral crystals are well known4 ,like dolomite1 its prevailing tint is yellow or light brown1 but1 when very pure1 is as white as snow4 ,it is usually associated with serpentine rocks4 ,in the kiln it is highly refractory1 and behaves very much in the same way as lime--forming fusible compounds with silica and silicates4 ,for the higher grades of basic bricks it is at this moment largely exploited in the few localities where it occurs in paying quantities4 ,a few years since1 investigation to determine the best basic refractory material was actively prosecuted in ,germany1 and magnesia1 preheated at the highest white heat1 was awarded the palm4 ,magnesite1 when calcined1 yields magnesia1 which1 however1 still contains the impurities that might have been present in the raw material4 ,an average percentage composition of the magnesite of commerce shows it to contain magnesia #de1 carbonic acid #ej1 lime #a4e1 protoxide of iron #a4f1 the remainder being silica1 alumina1 and protoxide of manganese4 ,the presence of silica in magnesite is an objection1 because it is liable to have a fluxing effect at high temperatures4 ,magnesite has been found in paying quantities in ,california1 ,styria1 and recently in ,greece4 ,in ,euba1 in the last-mentioned country1 the mineral occurs in lodes which1 near ,krimasi1 are worked on two levels #cj to #dj feet from the top1 and dipping at an angle of about #gj degrees4 ,the general average of the lode gives #hh per cent4 of carbonate of magnesia1 and the substance is peculiarly suitable for the manufacture of basic bricks4 ,a novelty with the raw material is that the proprietors sell either by guaranteed degree1 or degree of analysis1 the former being #ie per cent4 of pure magnesia1 whilst the latter often gives as much as #ig4h per cent4 ,in inferior grades the principal increase is in the proportion of silica4 ,,salt4 ,chloride of sodium1 or common salt1 is present in many natural clays1 especially 7in ,england7 in that formation known to geologists as the ,trias1 developed largely in ,cheshire4 ,the influence of a salt-bearing bed is1 naturally1 not confined to the immediate vicinity of the formation2 salt being so readily soluble in water1 it comes forth from the rocks in springs1 which1 flowing over loams and other similar absorbent earths1 impart a saline character to them4 ,in this manner otherwise useful earths for brickmaking are rendered absolutely unfit for the purpose4 ,salt is one of the most powerful fluxes known2 when mixed even in very small quantities with clay it becomes impossible to make a good brick of the substance4 ,but we must recur to this matter at a later period in another connection4 ,the fluxing property is sometimes taken advantage of by mixing salt with sand in moulding1 or in employing a sand already saline1 as when dredged from the sea1 or obtained between tide-marks4 ,a species of glaze is produced on the brick by the action of such moulding sand4 ,we may ignore the presence of a number of minerals such as rutile1 augite1 and hornblende in brick-earths1 as they only exist therein in such small proportion1 and have no appreciable effect in the kiln4 ,,chapter ,,vii4 ,,the ,,chemistry ,,of ,,brick-,,earths4 ,introduction3 ,,the ,,blowpipe4 ,it is not our intention to write an elementary treatise on chemistry2 but we know it is the custom for brickmakers to have chemical analyses of their raw earths made1 and we are aware also that the precise meaning to be attached to these analyses is very little understood4 ,our principal aim in introducing this subject1 then1 is to interpret1 in an elementary manner1 certain typical analyses of earths and substances used in brickmaking2 but before doing so we shall explain some easy methods of examining earths by means of the blowpipe1 which will not merely give some insight into their chemical constitution1 but will afford the intelligent brickmaker a means of investigation which he can himself put into practice4 ,the results of a chemical analysis of a compound earth1 as ordinarily used by the brickmaker1 widely differ from those obtained by a mineralogical or petrological examination4 ,the petrologist views the earth as a mineral aggregate1 the constituents of which may be ascertained on appeal to a properly-constructed microscope--that is1 in the majority of instances4 ,by noting the relative proportions of the different minerals1 he is enabled to state1 with approximate accuracy1 what is the ultimate chemical composition of the whole4 ,from this it would appear that a rough chemical analysis could be drawn up by the petrologist without having recourse to the ordinary methods of chemical investigation4 ,and in a limited sense that is true4 ,but we should not lose sight of the fact that there is1 in too many cases1 an amorphous residuum in earths1 the nature whereof the microscope is powerless to reveal4 ,it is upon this remnant that the chemist should direct his most careful attention4 ,the mineralogist also can give a shrewd idea of the chemical composition of a brick-earth by using a blowpipe and accessories4 ,this1 in fact1 may be regarded as a chemical means of investigation2 but it possesses this serious drawback1 viz41 the blowpipe only yields a qualitative1 and not a quantitative analysis4 ,in other words1 it can tell us something concerning chemical compounds present in an earth1 but rarely informs us as to the relative proportions of them4 ,even this1 however1 is of great service in many instances1 though it does not possess the value of a quantitative analysis4 ,for example1 we have stated previously that certain ingredients are very undesirable in a brick-earth1 even in minute quantities2 and that fact becomes of increased value if we extend the field to earths used in terra-cotta1 and china and porcelain manufacture4 ,now1 the blowpipe is a handy instrument2 it may be carried about by the prospector with its usual accessories1 and occupies but little space4 ,suppose he discovers a bed of white earth which he believes to be good china-clay2 he can prove that fact1 or at least obtain a great deal of information to that end1 by the mere use of that useful little instrument4 ,knowing1 for example1 that fluorine is an undesirable constituent in such a clay for many high-class purposes1 he might test first of all for that2 iron1 perhaps1 may come next1 and so in a few minutes he is enabled to arrive at some valuable particulars that would take much longer to obtain by chemistry in the wet way4 ,it will be profitable1 therefore1 for us to briefly describe the blowpipe and the most common of its accessories1 stating results obtained in dealing with substances frequently met with in brick-earths4 ,with but little practice anyone can use the instrument1 though1 as with most other methods of scientific investigation1 it requires expert knowledge to yield really excellent results4 ,the simple minerals and compounds to which we shall direct attention may be detected with the greatest ease4 ,the essential constituents of a blowpipe outfit are as follow3-- #a4 ,blowpipe4 #b4 ,lamp4 #c4 ,platinum-pointed forceps4 #d4 ,platinum wire4 #e4 ,charcoal4 #f4 ,glass tubes4 #g4 ,chemical reagents4 #h4 ,miscellaneous articles4 ,illustration3 ,fig4 #e4--;,blowpipes4 #a4 ,the ,blowpipe4--,common forms of blowpipe are shown in fig4 #e4 ,a may be described as follows4 ,it consists of three separate parts3 a tube a b having a mouthpiece2 an air chamber c to retain moisture caused by the breath of the person blowing2 and a side tube d ending in a platinum-tipped jet4 ,another form of blowpipe1 which1 however1 does not differ essentially from that just alluded to1 is shown in fig4 #e1 ,b4 ,it is not absolutely necessary to have the jet made of or tipped with platinum1 though certain examinations with the instrument are facilitated by the use of such a tip4 ,an essential point is1 that the hole in the jet should be of proper size1 usually about #j4d mm4 ,the trumpet-shaped mouthpiece shown in the diagram may be dispensed with4 ,illustration3 ,fig4 #f4--;,blowpipe ,lamp1 c4 #b4 ,the ,lamp1 or ,candle4--,a convenient form of lamp is a ,bunsen gas-burner furnished with a special jet 7fig4 #f1 ,a74 ,for certain purposes1 however1 this flame cannot be employed1 as when testing a substance for sulphur1 as coal-gas frequently contains sufficient sulphur to vitiate results4 ,moreover1 in country districts and in the field coal-gas is not always procurable4 ,a convenient form of lamp1 though rather too large for transporting purposes1 is known as ,berzelius' blowpipe lamp4 ,this1 as improved by ,plattner1 is shown in fig4 #f ,b4 ,this consists of an oil vessel on a stand provided with two openings closed with screw-caps1 the one opening being used for charging the lamp with oil1 the other being fitted with a burner bearing a flat wick4 ,the lamp may be adjusted to any required height on the stand by means of a screw4 ,olive oil1 or refined rape oil1 is usually burnt4 ,a spirit lamp with a flat wick is sometimes used4 ,in countries where neither coal-gas1 alcohol1 nor oil are readily available1 the prospector may use a small grease lamp4 ,this consists of a cylindrical box of thin metal having a wick-holder soldered on one side1 through which a flattened wick is drawn4 ,the box may then be filled with grease1 solid paraffin1 old candle-ends1 or fat of similar description4 ,professor ,cole describes#f it as follows3--,when brought into use the wick is lighted1 and the flame directed with the blowpipe upon the surface of the solid tallow or fat1 until this is melted to a depth of about a quarter of an inch4 ,the lamp will then become hot enough during use for a continuous supply to be maintained2 but it is still better to hold the lamp with the pliers over a spirit lamp until all the contents become fluid4 ,when about half or three-quarters empty1 it is well to drop in extra lumps of fuel--a single candle-end or so--during use1 and this additional material becomes melted up slowly with the rest4 ,the wick must be freely supplied with fluid fuel1 or it will char and waste away4 ,if the lamp is kept sufficiently hot1 the wick will not require raising during a day's work2 but it can be easily thrust up with a knife point after the flame has been at work a few minutes4 ,a cylindrical cap fits down upon the lamp when put aside4 ,for many ordinary purposes a good carriage-candle may be employed to give a blowpipe flame1 but candles have the disadvantage of not remaining at a constant level--an important point when one is comfortably at work4 #c4 ,platinum-pointed ,forceps4--,at least one pair of forceps is needed1 and it should preferably be made of steel1 nickel-plated to prevent rusting4 ,one end has platinum points self-closing by means of a spring1 so that the piece of mineral to be heated1 placed between them1 may be firmly supported4 ,at the other end are other forceps of ordinary pattern for picking up small fragments2 this end1 however1 should never be placed in the flame4 ,a pair of common self-closing forceps might also be at hand for holding test-tubes1 etc41 in the flame4 #d4 ,platinum ,wire4--,a few inches of thin platinum wire are indispensable1 and lengths of an inch or so may be fixed into suitable handles4 ,a convenient method is to have a small glass rod for a handle1 and by fusing the tip of one end of the rod the glass may readily be made to hold the piece of wire4 ,pieces of platinum foil are useful1 also1 as will presently be seen4 #e4 ,charcoal4--,the outfit should comprise several pieces of charcoal1 and a convenient form for each piece is a circular disc about an inch in diameter1 flat at the top and convex beneath4 ,long prisms of the same material1 square in section1 are occasionally required2 these may be up to #f inches1 or so1 in length4 #f4 ,glass ,tubes4--,these should be of hard glass1 small1 of several diameters1 the bore being large enough to place fragments of minerals or earthy substances within4 ,closed tubes1 such as test-tubes1 are always requisite4 #g4 ,chemical ,reagents4--,these are1 for the most part1 used as fluxes1 and those most commonly employed are borax 7sodium tetraborate71 soda 7sodium carbonate71 and salt of phosphorus or microcosmic salt 7phosphate of soda and ammonia74 ,small quantities of potassium bisulphate 7in a glass bottle71 as also small bottles of hydrochloric1 nitric1 and sulphuric acids1 and a solution of cobalt nitrate1 are also useful in certain cases4 ,it is hardly necessary to remark that the chemicals employed must be of the highest degree of purity4 #h4 ,miscellaneous ,articles4--,strips of test paper1 both turmeric and blue litmus1 a small hammer1 a steel anvil about an inch cube1 a bar magnet1 a pair of cutting pliers1 a three-cornered file1 and a few small watch-glasses are very desirable1 though not absolutely essential4 ,the reader1 on glancing at the foregoing formidable list of articles1 may possibly imagine that some considerable outlay is requisite1 and that they must occupy much space4 ,but that is not the case4 ,an ordinary blowpipe1 a grease lamp1 a small spirit lamp1 and all the articles mentioned in paragraphs #c to #h1 both inclusive1 occupy but a small space4 ,they may be packed in a box specially fitted1 and one in the writer's possession1 containing all of them1 measures only #aj inches by #e inches by #c inches1 and is less than #c lbs4 in weight4 ,now1 as to the use of these various things4 ,first of all1 let us examine the flame1 as produced by a candle1 which is typical of flames obtained by other means described1 except the ,bunsen lamp4 ,a candle flame 7see fig4 #g7 consists of the following parts3-- #a4 ,a dark core 7a71 which contains the gaseous products of decomposition given off by the melted tallow drawn up by the wick4 #b4 ,a highly luminous zone 7b71 in which only partial burning of the combustible gases takes place4 ,in this1 oxygen from the air combines chiefly with the combustible hydrogen1 whilst the carbon is separated in a highly heated state1 which causes the luminosity4 #c4 ,an outer mantle of blue tint 7c71 where the oxygen of the air is always present in excess1 so that the separated carbon is here burnt4 ,the highest temperature is found in this part of the flame4 ,illustration3 ,fig4 #g4--;,candle and ,gas ,flames4 ,technically1 the outermost zone 7c7 is known as the oxidising flame1 and the inner luminous zone 7b7 the reducing flame4 ,the two portions of the candle flame act in different manners on specific mineral substances1 and the blowpipe operator may use either of them at will4 ,the method of doing this is illustrated in the same figure4 ,to obtain the reducing flame1 the blowpipe jet is brought to the edge of the flame a little distance above the burner1 or wick4 ,the operator then produces a gentle blast1 which deflects the latter 7upper figure7 without altogether passing into it1 so that the flame is still charged with glowing carbon4 ,a yellowish luminous flame is the result1 the most active part of which lies at a short distance from the end4 ,on the other hand1 the oxidising flame is utilised by passing the blowpipe jet a little farther into the flame 7lower figure7 and blowing more strongly4 ,a pointed non-luminous flame is the result4 ,this will be seen to possess an inner blue cone1 before the point of which the hottest part is situated4 ,substances to be fused are placed in this part of the flame1 whilst those to be oxidised are placed a little farther away1 in order that they may be exposed to the air at the time they are being highly heated4 ,the 8platinum wire0 is an absolutely indispensable adjunct to a blowpipe outfit1 and is employed as follows3--,a short piece of the wire1 an inch or so in length1 being attached to a handle1 as previously described1 the free end of it is bent into a loop about the size of this ,o4 ,this may be heated in the flame employed1 or1 better still1 in the flame of a spirit lamp1 and1 when hot enough1 it may be dipped into a small quantity of the powdered borax or microcosmic salt1 some of which will be found to adhere to the wire4 ,on further heating the borax it will swell out and form a number of irregular bubbles1 which 7heat still being applied7 will subsequently settle down into a clear1 colourless bead in the loop of the platinum wire4 ,a satisfactory bead having now been made1 a portion of the mineral substance to be analysed 7in the shape of small grains7 is taken up by dipping the heated borax bead therein4 ,the actual operation of determining the nature of the substance then commences4 ,using the blowpipe1 and directing either the reducing flame 7,r4,f471 or the oxidising flame 7,o4,f471 on to the substance on the borax1 according to circumstances presently to be detailed1 the operator notes the change in colour 7if any7 of the flame yielded by the process4 ,at this point a very annoying thing sometimes happens2 for1 in liquefying the borax bead1 it is apt to fall off the wire1 and another bead has then to be made4 ,to avoid this1 great care should be taken not to blow too vigorously at first4 ,with the microcosmic salt especial care and dexterity must be exercised in this connection4 ,if all goes well1 the powdered mineral substance 7if fusible in the borax7 readily melts down1 and becomes incorporated with the borax4 ,on permitting the latter to cool1 which it very rapidly does1 the bead should now be carefully examined1 and any change in tint noted4 ,most beautiful transparent colours1 pregnant with meaning1 are often seen to have formed with the borax as flux4 ,the operator may test his skill by making the following brilliant experiments4 ,take up a few small fragments of the mineral malachite 7a carbonate of copper7 by means of the clear1 colourless1 heated borax bead1 and then introduce them to the oxidising flame4 ,they slowly dissolve in the borax1 and1 whilst doing so1 the tip of the blowpipe flame becomes emerald-green in colour4 ,after applying this flame for a minute or two1 the whole of the mineral will have become incorporated with the borax1 and1 when the bead is still hot1 note that it is also of a rich green tint1 but that1 on cooling1 it turns blue4 ,if too much malachite has been taken up in the first instance1 a very dark green tint is imparted1 which still remains when the bead is cold1 and it appears to be quite black4 ,its true colour1 however1 may be ascertained by flattening the bead out before it is quite cold4 ,it is always well to begin by using a small quantity of the mineral substance at first1 and adding to this as may be required4 ,assuming that a fine rich green bead has been produced1 and that it contains a relatively large amount of copper1 the operator may now hold it in the reducing flame and re-melt the bead2 if the operation has been conducted carefully1 the bead will then show red1 and be practically opaque when cold4 ,the red bead may now be re-heated in the oxidising flame1 when it will be found once more to return to a green colour4 ,the student will find this easy operation excellent practice1 as proving to him1 in the absence of a demonstrator1 that he is really able to recognise and use the oxidising and reducing flames at will4 ,many mineral substances yield a distinctive colour in this way--a useful factor in a qualitative analysis4 ,before using the platinum wire1 be careful to ascertain that it is quite clean2 a borax bead made thereon should be perfectly white and transparent4 ,the 8platinum foil0 is employed as a support during fusions2 pieces about an inch and a half long1 by half an inch in width1 are generally used4 ,a small platinum spoon is sometimes adopted when fusing substances with acid1 potassium1 sulphate1 or nitre4 ,minerals may be tested to see whether1 in the ordinary blowpipe flame1 they are fusible or not4 ,to do this1 a fragment of the substance to be tested is held in the flame by means of the 8platinum-pointed forceps40 ,if the mineral is found to be fusible1 then its 8degree of fusibility0 may be ascertained according to the following table4 ,the 8degrees of fusibility0 are six in number3-- #a4 ,fusible in ordinary gasflame1 even in large fragments4 ,example3 ,stibnite1 or grey antimony4 #b4 ,fusible in fine1 thin pieces1 in the ordinary gasflame1 and in larger fragments in the blowpipe-flame4 ,example3 ,natrolite1 a hydrous silicate of alumina and soda4 #c4 ,if very thin splinters be used1 fusible without difficulty with the blowpipe-flame4 ,example3 ,almandite1 or iron-alumina-garnet4 #d4 ,in thin splinters fusible to a globule4 ,example3 ,actinolite1 a non-aluminous variety of hornblende4 #e4 ,thin edges may be fused and rounded without great difficulty4 ,example3 ,orthoclase felspar--already described4 #f4 ,fusible with great difficulty on the finest edges4 ,example3 ,bronzite1 one of the augite group of minerals4 ,now1 it is highly probable that many of our readers will not understand1 or be able to recognise the six minerals above enumerated2 and we recommend those who may be sufficiently interested1 to purchase them from a mineral dealer--such as ,damon1 of ,weymouth1 or ,russell1 or ,gregory1 or ,henson1 or ,butler1 in ,london4 ,a set1 comprising the six1 should cost from two to three shillings4 ,with these1 as a standard for comparison1 the operator readily grasps the method of assigning a fusible mineral to its proper degree in the scale4 ,another object of examination in the forceps is to see what colour 7if any7 is imparted to the flame by the divers minerals experimented upon4 ,it is a good rule not to permit the specimen1 when being fused1 to touch the forceps in the neighbourhood of the actual part fused4 ,for a mineral containing antimony or arsenic would tend to form a fusible alloy with the platinum points1 and so ruin the forceps4 ,the pieces of 8charcoal0 alluded to in our inventory1 are used for placing the mineral substance upon in certain parts of the blowpipe operation1 which may be briefly described4 ,essentially the charcoal forms a support to the substance during fusion2 but the glowing carbon has also a kind of reducing effect4 ,taking a long prism of charcoal1 such as that described1 page #fc ante1 the mineral to be dealt with should be placed near one end of a flat surface and the prism so held that the flame from the blowpipe1 will sweep down its full length4 ,the object of so doing is to give a chance to any volatile substance 7derived by the operation from the mineral7 to deposit on the comparatively cool surface1 which deposit is often indicative of the chemical nature of the mineral4 ,to carry this point home1 the following experiments may be conducted by the student4 ,taking a piece of stibnite 7sulphide of antimony71 which1 as we have just learnt1 is a most fusible mineral1 we place it on the charcoal in the manner indicated4 ,whilst melting1 and the blowpipe flame be continued to be directed upon it after it has become fused1 it will be noticed that a yellowish-white deposit is taking place on the length of charcoal2 this is called a sublimate4 ,mineral substances may also be assisted in fusing on the charcoal by using the reagents described in our list of chemicals1 c41 included in a blowpipe set4 ,in regard to the use of the 8glass tubes10 it may be remarked that they are used principally for the examination of minerals which yield a volatile substance on being heated therein1 and to detect the presence of water and the like4 ,it is important to make a distinction between the closed and the open tubes4 ,when a mineral fragment is placed in a tube1 closed at one end1 whatever takes place will be in presence of very little air1 or oxygen2 on the other hand1 when the tube is open at both ends1 and is inclined during the experiment1 a constant stream of oxygen passes through the tube1 and the mineral is being dealt with in presence of that4 ,the employment of this oxygen makes a great deal of difference in the results obtained1 as a few elementary experiments will show4 ,if we place a piece of sulphur in a tube1 closed at one end1 and heat it gently1 we notice that a yellow coating takes place inside the tube2 but if we now employ a tube open at both ends and heat it very slowly indeed1 we notice that the sulphur goes off as an invisible gas1 and if the experiment has been properly conducted1 there should hardly be a trace of the sulphur left on the glass4 ,a number of experiments of a similar nature might be quoted1 but enough has been said for the present to show the utility of the tubes4 ,the 8chemical reagents0 alluded to have already been sufficiently described to render any further discussion on them unnecessary for our immediate purpose4 ,in regard to the 8miscellaneous articles0 mentioned1 it may be remarked that the test papers are employed in the detection of certain acids and bases2 whilst a strip of brazil-wood paper is for the detection of fluorine4 ,the hammer and anvil are for breaking the substance to be tested into small fragments2 the magnet for withdrawing particles of iron from the pulverised material2 the three-cornered file for assisting in determining the relative hardness of minerals1 c41 c4 ,in examining substances before the blowpipe1 it is highly desirable that the various operations should be carried out in some definite order4 ,the following has been found convenient3-- a4 ,in a glass tube closed at one end4 b4 ,in an open tube4 c4 ,on charcoal4 d4 ,with borax and microcosmic salt4 e4 ,as to flame colouration4 f4 ,with other reagents4 ,the size of the fragment to be dealt with in an examination1 depends on circumstances1 but for ordinary purposes a piece of the size of a small rabbit-shot will be found sufficient4 ,it is convenient in this place to describe a few chemical reactions without the use of the blowpipe2 that will render the effects on certain minerals1 presently to be mentioned1 clearer to the reader4 ,in the first place it may be ascertained whether the mineral is soluble in water1 and if so1 to what extent4 ,then as to whether it becomes soluble in certain acids1 such as hydrochloric or nitric acid4 ,the former acid is generally used1 except for metallic sulphides1 and those minerals containing heavy metals1 such as lead1 silver1 c42 the latter is employed for the exceptions named4 ,several minerals1 even when in a powdered state1 are hardly1 if at all1 affected by acids4 ,the results to be noted during the test with acids1 commonly fall into the following three groups4#g ,a4 ,the mineral may dissolve quietly with or without colouring the solution2 this holds good1 for example1 with hematite 7a variety of iron71 also of many of the sulphates and phosphates4 ,b4 ,there may be a bubbling off or effervescence of a gas1 which gas is usually carbon dioxide2 but may be hydrogen sulphide4 ,chlorine may be liberated1 or reddish fumes of nitrogen4 ,c4 ,there may be separation of some insoluble substance as sulphur1 silica1 c4 ,we will close this chapter by stating the behaviour under blowpipe examination of various minerals1 given in preceding pages1 as being common in clays and earths used in brickmaking3-- ,quartz4--,this is infusible1 and remains undissolved1 even in a microcosmic salt bead2 but it fuses readily with soda1 on charcoal4 ,in the flame it splinters into fragments1 which fly off with great rapidity4 ,it is soluble in hydrofluoric acid4 ,flint1 when pure1 behaves in a similar manner4 ,orthoclase ,felspar4--,fusibility1 #e2 flame colouration brilliant yellow1 when much sodium is present2 not decomposed by hydrochloric acid4 ,it may be distinguished from other common felspars by its high degree of fusibility4 ,oligoclase ,felspar4--,gives a sodium yellow flame2 fusibility1 #c4e2 not decomposed by hydrochloric acid4 ,biotite ,mica4--,with fluxes gives a strong iron reaction of yellowish red colour2 decomposed in concentrated sulphuric acid1 leaving a residue of siliceous matter4 ,muscovite ,mica4--,when heated in a tube closed at one end1 yields water which often gives fluorine reaction with brazil-wood test paper by colouring it straw-yellow2 it is not decomposed by acids1 and whitens and fuses only on thin edges4 ,kaolin4--,is infusible2 gives off water when heated in a closed tube2 and with cobalt nitrate on charcoal1 a fine alumina reaction is obtained4 ,aluminium4--,on charcoal1 this becomes blue with cobalt nitrate1 though if the surface is fused the reaction is not so clear4 ,prof4 ,cole advises that the soda-residue be dissolved in dilute hydrochloric acid1 then evaporated to dryness1 re-dissolved in that acid water1 filter off any silica1 and neutralise with ammonia2 alumina is precipitated together with any iron present4 ,the precipitate1 if white1 or nearly so1 may be tested with cobalt nitrate1 and the result is a fine blue colour4 ,limonite ,iron4--,fusibility about #e2 yellow and reddish beads2 water given off in closed tube2 in reducing flame magnetic residue on charcoal2 soluble in hydrochloric acid after a short time4 ,iron ,pyrites4--,fusibility about #b2 yellow and red beads2 in closed tube yellow precipitate due to sulphur2 magnetic after reduction on charcoal2 insoluble in hydrochloric acid4 ,rock ,salt4--,intense yellow sodium flame2 fusibility about #a2 microcosmic salt with copper oxide shows strong chlorine reaction--a fine blue flame surrounding the bead when re-introduced into the flame4 ,it is soluble in water4 ,selenite 7,gypsum74--,fusibility about #b4e2 brilliant flame2 in closed tube it becomes white and opaque and much water is given off2 with soda1 on charcoal1 sulphur reactions are obtained2 soluble in hydrochloric acid4 ,calcite 7,carbonate of ,lime74--,flame glows very strongly2 infusible2 effervesces freely in cold hydrochloric acid4 ,dolomite4--,flame1 with hydrochloric acid1 like calcite2 infusible2 effervesces in hot hydrochloric acid4 ,magnesite4--,infusible2 with cobalt nitrate a fair magnesia reaction on charcoal1 i4e41 turns into a dull pink2 effervesces in hot hydrochloric acid4 ,manganese4--,with borax in oxidising flame a red-violet bead is obtained1 but with the reducing flame it is colourless4 ,the above are commonly met with in brick-earths2 for other minerals and substances also found1 the reader may be referred to special works dealing with blowpipe analysis4 ,,chapter ,,viii4 ,,the ,,chemistry ,,of ,,brick-,,earths 7,continued74 ,in this chapter we shall fulfil our promise 7ante p4 #eh7 to explain in an elementary manner the precise meaning of ordinary commercial chemical analyses of some typical earths used in brickmaking1 etc4 ,we may commence by explaining a few terms used by the chemist4 ,an atom is the smallest imaginable portion of matter1 and all matter is said to consist of atoms4 ,a molecule is the smallest conceivable combination of atoms1 and every compound substance is ultimately built up of molecules4 ,an element is a substance that has hitherto defied the efforts of the chemist to subdivide or split up4 ,over seventy of these elementary substances are at present known1 and their number is being constantly added to4 ,again1 by improvement in analytical methods1 a so-called element may be subdivided1 and thus removed from the list4 ,the elements are classified into metals and non-metals2 and it is convenient to give each of them a symbol to save trouble in writing1 and to render clearer to the reader the chemical nature of a compound body4 ,thus1 the symbol for the element aluminium is ,al2 for silicon ,si2 for carbon ,c2 for calcium ,ca2 for oxygen ,o2 for iron ,fe2 for hydrogen ,h2 for chlorine ,cl2 and so on4 ,we are taught by chemistry that elements are capable of combining only in definite proportions1 and that each substance possesses a definite proportion peculiar to itself4 ,that proportion is called the atomic weight of the element2 or1 it is the relative weight of the atom of each substance compared with that of the lightest substance known1 hydrogen4 ,thus1 the atomic weight of hydrogen being taken as #a1 it is found that an atom of chlorine is #ce4e times as heavy as that1 so that the atomic weight of chlorine is said to be #ce4e4 ,now1 in spite of the enormous difference between the weight of the two elements just mentioned1 they combine in the same proportions by volume2 and the union is known as hydrochloric acid1 or ,h,cl4 ,but in certain cases elements do not combine in equal proportions2 for instance1 an atom of oxygen will not combine with less than two of hydrogen4 ,further1 with this we find that the three volumes are condensed into the space of two volumes--a very common phenomenon in the chemical combination of gases4 ,the union of hydrogen and oxygen alluded to forms water1 the chemical symbol of which is1 consequently1 ,h#b,o4 ,chemical affinity1 or chemical attraction1 is the force which is exerted between molecules not of the same kind4 ,thus1 in water1 which1 as we have seen1 is composed of hydrogen and oxygen1 it is affinity which unites these elements1 but it is cohesion which binds together two molecules of water4 ,in compound bodies1 cohesion and affinity operate simultaneously2 whilst in simple bodies1 or elements1 cohesion alone has to be considered4 ,to affinity are due all the phenomena of combustion and of chemical combination and decomposition4 ,certain gases1 such as chlorine and nitrogen1 and such substances as sulphur1 carbon1 and silicon1 with many others1 form acids in conjunction with hydrogen1 or hydrogen and oxygen4 ,these combine with greater or less facility with other elements which do not form acids1 and are termed bases4 ,a combination of an acid and a base is known as a salt4 ,salts the names of which end in -ide1 such as chloride1 sulphide1 etc41 are combinations of a metal with a non-metal4 ,monoxide means an oxide containing one atom of oxygen2 dioxide one containing two atoms2 protoxide means the first oxide1 because it is the first or lowest of the oxides of the given metal in amount of oxygen present2 the highest oxide is often known as peroxide4 ,the terminations -ous and -ic are frequently used for the lower and higher oxides respectively4 ,examples3-- ,fe,o1 iron protoxide1 or ferrous oxide4 ,fe#b,o#c1 iron sesquioxide1 or ferric oxide4 ,fe,s#b1 iron disulphide4 ,sb#b,s#c1 antimony trisulphide4 ,the following symbols may be indicated as referring to compounds especially met with in brick-earths3-- ,ca,o1 lime1 instead of calcium oxide4 ,al#b,o#c1 alumina1 instead of aluminium trioxide4 ,si,o#b1 silica1 instead of silicon dioxide4 ,na#b,o1 soda1 instead of sodium oxide4 ,k#b,o1 potash1 instead of potassium oxide4 ,mg,o1 magnesia1 instead of magnesium oxide4 ,in analysing a body1 the first step consists in determining the nature of the elementary substances contained therein4 ,that may be accomplished in the dry way by means of the blowpipe and accessories1 as explained in the last chapter4 ,such an examination1 as previously remarked1 is known as a qualitative analysis4 ,or1 it may be accomplished in the wet way by ordinary chemical examination4 ,the next step is to determine the amount of the constituents present1 and that is known as a quantitative analysis4 ,in making a qualitative analysis1 the chemist is assisted by the knowledge that certain basic substances and certain acids produce peculiar phenomena in the presence of known substances or preparations termed reagents4 ,there is a great difference between a chemical compound and a simple mixture of elements2 and it is not always easy 7e4g41 some alloys7 to say whether a substance is in the one state or the other4 ,this distinction is well exemplified by the air we breathe4 ,the chemist finds by analysis that the air is nearly constant in composition1 containing essentially in #ajj parts #gf4h by weight of nitrogen 7including about #a per cent4 of the recently-discovered element1 argon71 and #bc4b of oxygen4 ,small proportions of water vapour1 carbon dioxide1 etc41 may be ignored for our present purposes4 ,in view of this comparatively uniform composition1 the question at first arises as to whether the air is1 or is not1 a chemical compound8 ,the answer is in the negative1 for1 amongst other things1 it can be shown that the ratio of #gf4h to #bc4b is not that of the atomic weights of the two elements present1 viz41 #ad 3 #af1 nor of any simple multiples of these4 ,we will now quote a few analyses of well-known earths1 and explain each in turn3 ,chemical ,composition of ,china-clays4#h ---------------------------------------- -------- ,kaolin4 ,kaolin average4,sandy ,kaolin4 ------------------------------------- ,silica #df4cb #dd4fj #ff4fh ,alumina #ci4gd #dd4cj #bf4jh ,iron oxide 4#bg 4#bj #a4bf ,lime 4#cf #a4fj 4#hd ,magnesia 4#dd trace ,water #ab4fg #h4gd #e4ad ---------------------------------------- -------- ,the kaolin alluded to in the first column is a remarkably pure material1 perfectly white1 and contains an enormous quantity of water4 ,it refers to one of the finest washed china-clays in the market1 and is extensively used in porcelain manufacture4 ,it is quoted here principally to give an idea of what a really pure clay is like chemically4 ,we notice that1 in spite of its relative purity1 it contains 4#bg per cent4 of iron oxide4 ,this could have been well done without1 from the manufacturer's standpoint1 but is of course a very minute proportion4 ,small as it is1 it must exert a slight amount of colouring influence4 ,the lime and magnesia are present in slightly larger proportions1 and a little more of either would be advantageous rather than otherwise1 as assisting to flux the material4 ,this is an earth with which practically anything may be done by judicious blending and careful preparation4 ,with reference to the second column1 the figures do not refer to any particular clay1 but they have been compiled to show the average composition of kaolins as used in the market4 ,it will be observed that the silica and alumina are present in approximately equal proportions1 which is a characteristic of fairly good china-clays4 ,the iron oxide remains as before1 but there is a larger proportion of lime and magnesia--as much as can be permitted except in a second-rate clay4 ,the evidence of the third column shows that the sand in the china-clay is to a large extent quartzose1 and this is at the expense of the alumina4 ,such a material would be suitable for making a species of white fire-brick1 and it might do for the commoner kinds of china-ware4 ,the earth is really of the nature of a loam--a sandy clay4 ,there is too much iron in it for the production of perfectly white goods4 ,the proportion of lime might be increased to advantage4 ,chemical ,composition of ,fire-clays from ,newcastle-on-,tyne4#i ---------------------------------------- ---------------------- #a #b #c #d #e #f #g ---------------------------------------- ---------- ,silica #ea4aj #dg4ee #dh4ee #ea4aa #ga4bh #hc4bi #fi4be ,alumina #ca4ce #bi4ej #cj4be #cj4dj #ag4ge #h4aj #ag4ij ,iron oxide #d4fc #i4ac #d4jf #d4ia #b4dc #a4hh #b4ig ,lime #a4df #a4cd #a4ff #a4gf #a4cj ,magnesia #a4ed 4#ga #a4ia trace #b4cj #b4ii ,water1 etc4 #aj4dg #ab4ja #aj4fg #ab4bi #f4id #c4fd #g4eh ---------------------------------------- ---------------------- ,the reader will see at a glance that the range of variation permissible in fire-clays is very wide4 ,these earths are all found close together1 and are utilised for similar purposes1 though often blended to produce desired results4 ,it will be noticed that one of them 7,no4 #f7 contains as much as #hc4bi of silica1 whilst another has no more than #dg4ee per cent4 ,the range with reference to alumina is very wide also1 from #h4aj percent4 7,no4 #f7 to #ca4ce4 ,the refractory character of any sample of fire-clay is determined by the proportions in which the silica and alumina are contained1 and by the absence of lime1 iron1 and other easily fluxible substances4 ,the proportion of iron discovered in sample ,no4 #b is certainly much in excess of the requirements of the material1 as a fire-clay1 and this no doubt is tempered by admixture1 unless utilised for inferior goods4 ,the iron oxide in the other samples is about sufficient for general purposes4 ,the amount of lime present in all the samples constitutes a good feature2 much lime cannot on any account be allowed in earths for fire-clay goods4 ,with so much iron present1 and the fair proportions of magnesia 7except in sample ,no4 #d7 these clays may be regarded as typical1 with the exception of ,no4 #f4 ,they have been utilised for many years in the manufacture of fire-bricks and the like4 ,chemical ,composition of ,fire-clays1 from ,welsh localities4 --------------------------------- #a #b #c --------------------- ,silica #ej4ce #ef4ij #ed4hj ,alumina #bc4ej #bd4ij #bg4fj ,iron oxide #aj4dj #b4hc #b4ef ,soda #a4ee #c4jj #b4jj ,magnesia #a4de #a4jg #a4jj ,water1 etc4 #aa4he #aa4fj #aa4hj --------------------------------- ,the first thing that will strike the reader on looking at these results on ,welsh materials1 is their uniform composition as compared with the clays from ,newcastle4 ,yet there is as much as #aj4dj per cent4 of iron in sample ,no4 #a1 which cannot be a first-rate clay4 ,its proportion of silica to alumina is1 however1 excellent1 and1 as in sample ,no4 #c1 the amount of soda and magnesia is not excessive4 ,the soda in sample ,no4 #b 7which acts somewhat like lime in the kiln7 taken together with the magnesia and iron in the same material1 is too much for a first-class clay1 and would have to be suitably modified before good results could be obtained4 ,on the whole1 it is possible that sample ,no4 #c would yield the best results from the chemical standpoint4 ,we should not forget that remarkable substance of which the well-known ,dinas bricks are made4 ,the proportion of silica present ranges from about #if to #ii per cent41 the remainder consisting principally of alumina1 though traces of iron1 lime1 and magnesia frequently occur4 ,there is not1 of course1 sufficient natural flux for this 8clay10 so a small proportion 7#b4e to #c per cent47 of lime is added1 which produces the desired effect4 ,in other words1 if we can obtain a pure siliceous sand1 with hardly any lime1 iron or magnesia in it1 we have the material of which the better kinds of fire-bricks are made4 ,such sandy earths are not uncommon in the ,south of ,england1 but strange to relate1 they are not used for the purpose indicated4 ,the earths from which the superior ,stourbridge bricks are made1 are approximately of the following chemical composition3--,silica1 #fd4aj2 alumina1 #bc4ae2 iron oxide1 #a4he2 magnesia1 4#ie2 water and loss1 #aj4jj per cent4 ,it will be observed that the proportion of iron and magnesia here is very small1 whilst lime is altogether absent4 ,it is a most excellent earth for the purposes for which it is used1 and the chemical results may be taken as a standard for that class of material4 ,another ,stourbridge earth yields as much as #d4ad per cent4 of iron1 however1 whilst its proportion of silica is lower1 #ea4hj1 and alumina higher1 #cj4dj1 which serves to remind us of the variability of even good earths used in the manufacture of fire-clay goods4 ,let us now turn to the consideration of pottery clays1 of which the following results may be taken as typical3-- ,chemical ,composition of ,pottery ,clays4 ---------------------------------- #a #b #c ---------------------- ,silica #df4ch #di4dd #eh4jg ,alumina #ch4jd #cd4bf #bg4ch ,iron oxide #a4jd #g4gd #c4cj ,lime #a4bj #a4dh 4#ej ,magnesia trace #a4id trace ,water #ac4eg #e4ad #aj4cj ---------------------------------- ,some of the chief qualifications1 from a chemical point of view1 of earths suitable for making pottery1 is the proportion and potentiality of the colouring matters present4 ,where the pottery is to be glazed1 that is not so important2 but with ordinary unglazed ware1 colour and uniformity are two highly essential desiderata4 ,we know that the temperature employed will modify the tint1 but under similar conditions the clays alluded to in the above table will give1 approximately1 the following results4 ,sample ,no4 #a is typical of an excellent blue pottery clay1 which burns white4 ,it contains more alumina than is commonly met with in such materials1 in which respect it differs markedly also from the fire-clays just described4 ,the proportion of oxide of iron is very small1 not sufficient to perceptibly colour the finished product1 though1 no doubt1 on careful examination it would be seen not to be perfectly white4 ,the latitude of the term 8white0 is pretty considerable with clayworkers1 as the reader is probably aware4 ,the pottery clay 7also used for bricks7 referred to in the middle column1 is brown in colour2 it is an ordinary kind1 used primarily for black and common red ware4 ,the proportion of iron is high1 and considerable quantities of both lime and magnesia exist4 ,as might naturally be expected of such material1 it will not bear exposure to great heat1 though that might be regarded as a qualification in some brick and pottery yards4 ,the proportion of silica is high in sample ,no4 #c1 which appertains to a common yellow clay1 with1 possibly1 some siliceous sand in it4 ,the amount of alumina is correspondingly low1 but the iron oxide is not excessive--for a common pottery clay4 ,it is used for the manufacture of coarse ware1 and burns yellow4 ,the chemical composition of earths used for terra-cotta and bricks of that substance is so variable1 that without going into each case specifically it would be impossible to convey an adequate idea4 ,it may be stated generally that it is not one whit less important to consider the composition of the raw earths for ordinary brickmaking1 than in respect of that for high-class bricks and pottery4 ,an excellent earth1 from the neighbourhood of ,ruabon1 is of the following composition3-- ,chemical ,composition of ,ruabon ,clay4 ,silica #fc4jj ,alumina #bj4aj ,sesquioxide of iron #d4hd ,protoxide of iron #a4ea ,potash #b4cg ,soda #c4aj ,combined water #c4ed ,moisture #a4ed ,the proportion of silica in this is higher than in many clays used for brick- or terra-cotta making1 but the alkalis1 potash and soda1 are in strong force1 so that any refractoriness on the part of the silica is soon subdued in the kiln4 ,the iron1 also1 is in abundance4 ,the principal colouring ingredient is the sesquioxide1 and we can quite understand the manufacturer when he informs us that1 in spite of the rich tint of the goods produced1 nothing is artificially mixed with this clay to produce such a result4 ,we may call attention to the method of expressing the chemical analysis in this case1 which might be copied to advantage4 ,in the first place1 the combined and the uncombined iron are separately shown1 or rather the degree of combination is indicated2 and secondly1 the proportion of water chemically combined is differentiated from that which has simply soaked into the clay1 though expelled1 following a well-known practice of chemists1 prior to commencing the analysis proper4 ,it is of very little use giving the amount of water1 unless the proportions are divided in this manner4 ,in the result given above we learn that there is very little chance of the clay shrinking1 as it only contains moisture to the extent of #a4ed per cent42 but if that had been added to the water combined1 we should have had a result of #e4jh per cent41 which is not nearly so clear in its meaning4 ,we may add that the ,ruabon earth referred to is utilised also in the manufacture of tesselated and encaustic tiles4 ,in regard to the composition of earths employed in the manufacture of the commoner kinds of bricks1 we may give the following examples3-- ,chemical ,composition of ,common ,brick-earths4 ---------------------------------------- ------------------------ ,alumina ,water ,silica4 and ,lime4,magnesia4,manganese4 and ,iron4 ,loss4 ---------------------------------------- ----- ,reddish-brown brick clay #eb4f #cj4h #c4d #b4h #a4d #i4j ,red-brick clay #ej4d #bd4j #b4g #a4c --- #ba4f ,common brick-earth #cc4j #aa4b #ci4h #f4j --- #aj4j ,sandy-clay 7loam7 #fj4b #bd4j #b4d #a4f --- #aa4h ---------------------------------------- ------------------------ ,reviewing these results1 it will be noted that the brown colouring imparted to the brick in the first-mentioned example is due1 to a large extent1 to the presence of manganese1 a rather uncommon feature in brick-earths1 except where these have resulted from the denudation of iron-producing rocks rich in manganese4 ,it will be noticed also that the proportion of water is not high for a common earth1 and it must be a fairly easy material to deal with4 ,there seem to be some possibilities in it that might1 in competent hands1 lead to higher things4 ,the amount of lime and magnesia is1 however1 a rather serious one for a first-class clay4 ,in regard to the 8red-brick0 clay1 an essential feature is the comparative absence of lime1 and it would1 no doubt1 make 8rubbers0 of an ordinary kind4 ,unfortunately1 in the results given1 the iron is not separated from the alumina1 but clearly the latter is very small in amount1 and the results refer to a sandy material4 ,the proportion of water is disastrous for the employment of this earth by unskilful hands4 ,in drying1 the greatest care would have to be exercised to prevent undue shrinking1 and1 in any case1 the earth would have to be very thoroughly incorporated to make a really serviceable brick4 ,it is with earths of this character that the majority of brickmakers in embryo come to grief2 they know not how to handle them successfully1 and twisting1 warping1 cracking1 and 8bursting0 follow as a natural consequence4 ,it is a common and treacherous material1 that could only be made to succeed by perseverance and wide experience4 ,the 8common brick-earth10 as will be seen1 contains an abnormal quantity of lime1 and doubtless refers to a marl1 though not much alumina is shown4 ,malm bricks could be made from it1 and the product would have to be burned at a low temperature4 ,for bricks useful to the 8jerry-builder0 this earth could be strongly recommended4 ,it was1 no doubt1 mainly derived from limestone rocks2 and1 judging from the high proportion of magnesia1 probably from within a watershed composed to some extent of magnesian limestone4 ,the 8sandy-clay0 or loam is of a very common type1 and produces light-red bricks4 ,there is much in common between this and the 8red-brick clay0 previously referred to4 ,the practice resorted to in various parts of the world of making bricks from slate dbris1 although not hitherto adopted to any large extent in this country1 merits some description in this place4 ,slates may be regarded as a highly compressed clay1 the original structure of which has been materially modified by the great pressure exerted during their manufacture in ,nature's laboratory4 ,to all intents and purposes they are silicates of alumina1 plus iron1 lime1 magnesia1 and so on1 and have1 practically1 the same range of variation as have ordinary clays4 ,but during their manufacture1 and subsequently1 certain adventitious mineral matter has been frequently introduced1 as may be gathered from the following results3-- ,chemical ,composition of ,slates4 ---------------------------------------- ------------- #a #b #c #d ---------------------------- ,silica #fj4ej #fj4ae #dh4jj #ej4hh ,alumina #ai4gj #bd4bj #bf4jj #ad4ab ,iron 7protoxide7 #g4hc #e4hc --- #i4if 7sesquioxide7 --- #a4hb --- --- --- --- #ad4jj --- ,lime #a4ab --- #d4jj #h4gb ,magnesia #b4bj --- #h4jj #h4fg ,potash #c4ah --- --- 4#hh ,soda #b4bj --- --- --- ,alkalis 7not determined7 --- #d4bh --- --- ,carbon dioxide --- --- --- #f4dg ,water1 c4 #c4cj #c4gb --- --- ---------------------------------------- ------------- ,analysis ,no4 #a refers to a blue ,welsh roofing slate of ,cambrian age4 ,it is quite certain that the large proportion of alkalis present would render this material unsuitable for brickmaking1 except for the commonest kinds of bricks4 ,the iron1 again1 is very large in quantity1 whilst the amount of alumina is low4 ,we could not recommend this slate for good bricks under any consideration4 ,analysis ,no4 #b is of a dark-blue slate from ,llangynog1 in ,north ,wales4 ,the amount of iron present is high1 but from the low content of alkalis this material1 under proper treatment1 should make fairly good bricks4 ,the ferruginous constituent is too powerful1 however1 for fire-bricks to be made of this slate4 ,analysis ,no4 #c1 of a purple slate from ,nantlle1 shows a remarkable diminution in silica and a corresponding increase in iron4 ,lime and magnesia being present to such an enormous extent1 taken in conjunction with the iron1 would render this slate absolutely useless for brickmaking4 ,there is not a redeeming feature about it4 ,analysis ,no4 #d1 which refers to a green ,westmorland slate1 has a low percentage of alumina and very large quantities of iron1 lime1 and magnesia4 ,only bricks of an exceedingly inferior quality could result from such material4 ,summing up the general characteristics of these slates from the chemical aspect1 one would say that none of them are very suitable for high-class bricks4 ,no4 #b is the best4 ,several minor differences will be observed between the results quoted and those referring to ordinary brick-earths--in particular1 the distribution of the alkalis4 ,a general impression is abroad that any purple slate will do for brickmaking1 and manufacturers do not yet seem to have realised that the chemical nature of slates is as variable as of brick-earths4 ,that may account for the difficulties experienced in many cases in turning out a satisfactory material4 ,the microscope is of much use in this connexion1 however1 and the practical effects of chemical analyses are not always as bad as they seem at first sight4 ,the remainder of this chapter will be devoted to the consideration of rarer kinds of brick-earth and other raw earths used principally in the manufacture of bricks for special purposes1 or as pointing to certain anomalies4 ,as an example of what some manufacturers can do1 we may quote the chemical composition of a peculiar brick-earth employed in ,zurich1 in ,switzerland3-- ,chemical ,composition of ,brick-earth1 ,zurich4 ---------------------------------------- ------ ,yellow ,blue ,clay4 ,clay4 ------------ ,carbonate of ,lime #bc4fh #bg4hj ,magnesia -- #e4g ,other carbon dioxide #b4he #a4ee ,silica #db4ci #ch4be ,alumina #ah4af #ab4dd ,iron oxide #c4ff 4#gc ,lime 7as silicate7 -- #a4he ,magnesia -- 4#ae ,potash #b4ad #a4ed ,soda #a4bg #c4je ,moisture 7at #ajj ,c47 #a4bg #a4cg ,water1 c41 chemically combined #c4he #d4gb ---------------------------------------- ----- ,here we have two clays with the carbonates of lime and magnesia present1 in one case of over #ce per cent41 and in the other of over #bf per cent4 ,professor ,lunge1 of ,zurich1 states that the bricks made from them1 if burned at the ordinary heat1 say a moderate red heat1 are red1 and do not keep in the air1 but crumble away very soon1 as the quicklime slackens on combining with the moisture4 ,when burned at a bright red heat1 about #bjj ,c4 above the former1 however1 they become nearly white4 ,the lime is then present as a ferri-alumina-calcic silicate1 which causes the red colour of the iron oxide to disappear1 and1 at the same time1 entirely prevents any action of the moisture1 quicklime being no longer present4 ,we have no hesitation whatever in saying that most ,british makers would look down upon raw earths such as these from ,zurich1 and yet many millions of really good bricks have been made from them during the past twenty years1 and they are especially noted for their durability4 ,the crux of the case is the temperature at which the earths are burned1 as the reader has perceived4 ,under the heading of 8magnesia10 we have said a few words regarding basic bricks4 ,in this country they have been made primarily from magnesian limestone1 the chemical composition of which is shown in the following results of analyses3-- ,chemical ,composition of ,magnesian ,limestones4 ---------------------------------------- -------- #a #b #c #d ---------------------------------------- -------- ,silica #c4f #b4ec 4#h -- ,carbonate of lime #ea4a #ed4ai #eg4e #ee4g magnesia #dj4b #da4cg #ci4d #da4f ,iron1 alumina #a4h 4#cj 4#g 4#d ,water1 c4 #c4c #a4fa #a4f #b4c ---------------------------------------- -------- ,analysis ,no4 #a refers to the well-known magnesian limestone of ,bolsover4 ,analysis ,no4 #b to that from ,huddlestone4 ,analysis ,no4 #c to that from ,roach ,abbey4 ,analysis ,no4 #d to that from ,park ,nook4 ,these results were obtained by ,professors ,daniell and ,wheatstone in connexion with an enquiry many years ago as to the kind of stone suitable for the erection of the ,houses of ,parliament4 ,regarding them generally1 it may be said that they are remarkable as not containing much acid1 practically the whole substance of the rocks 7except ,no4 #a7 being made of the carbonates of lime and magnesia4 ,in manufacturing bricks of such materials as these1 it will be seen that the ordinary methods of brickmaking would not suffice4 ,on heating magnesian limestone1 the carbonic acid is driven off1 leaving the base behind2 it is estimated that the loss of the acid1 plus moisture dried out1 leads to its reduction in weight of from #dj to #de per cent41 and the shrinkage is from #be to #ce per cent4 ,if water were mixed with this material1 after calcination1 strong chemical reactions would result1 and of such a nature as to render a coherent mass of the kind required for making bricks impossible4 ,seeing that water cannot be employed1 crude petroleum oil1 coal oil1 resin oil1 c41 have been employed1 all of them with more or less satisfactory results4 ,the petroleum1 c41 is mixed with the lime1 and when the whole is burned the oil passes off1 leaving bricks of solid lime4 ,in manufacture it is highly essential to see that the lime is well burned1 and it must be fresh1 and not have been exposed to a damp atmosphere4 ,an improvement has been effected by mixing from #e to #g per cent4 of burned clay1 which makes the lime harder after burning4 ,an admixture of from #c to #e per cent4 of iron oxide also consolidates the lime1 though it increases shrinkage4 ,the bricks are commonly made1 in the first instance1 under hydraulic pressure4 ,the diatomaceous earth known as ,kieselguhr1 which is used in the manufacture of fire-bricks for chemical works and the like1 and which1 for the most part1 is of ,german origin1 has the following chemical composition3-- ,chemical ,composition of ,kieselguhr4 ,silica #hc4h ,lime 4#h ,magnesia 4#g ,alumina #a4j ,oxide of ,iron #b4a ,organic matter #d4e ,water1 c4 #g4a ,the reader will perceive that this earth is composed very largely of silica1 though there is enough iron1 c41 to flux it1 at any rate1 without material addition4 ,the product is extremely light1 and when properly made1 ,kieselguhr bricks are the lightest known4 ,they are usually of a light yellow tint1 with iron spots4 ,the silica is not in a crystalline form1 the bulk of the material being composed of the hard parts of microscopic plants known as diatoms2 it is more like flint4 ,an earth of a similar character is found in the ,isle of ,skye1 as previously mentioned1 though that burns into a redder colour4 ,an infusorial earth from ,tuscany is composed of silica #ee1 magnesia #ae1 water #ad1 alumina #ab1 lime #c1 and iron #a per cent4 ,that also is made into very light bricks4 ,the general principle underlying the method of utilising those earths of organic origin is similar to that of the ,dinas bricks1 though they do not always require artificial fluxing4 ,at ,saarbrcken1 in the ,rhenish ,province of ,germany1 a material known as 8iron brick0 is manufactured4 ,it is made by mixing equal proportions of finely-ground red clay-slate with fine clay1 and adding #e per cent4 of iron ore4 ,this mixture is then treated with a #be per cent4 solution of sulphate of iron1 together with a certain quantity of finely divided iron ore4 ,it is then moulded and baked in a special manner4 ,we do not intend to describe the chemical composition of the various volcanic ashes1 trass1 and other volcanic ejectamenta used for brickmaking on the ,continent in several localities4 ,the materials of which glass-sand bricks1 slag-bricks1 c41 are made have no special interest in connexion with our present subject1 their composition naturally varying according to the particular kinds of 8refuse0 employed4 ,,chapter ,,ix4 ,,drying ,,and ,,burning4 ,of the merely mechanical aspects of the operations of drying and burning bricks1 we shall say little or nothing4 ,but there are just a few points of a more or less scientific nature that offer themselves at this juncture to which we desire to allude4 ,the brickmaker hardly needs to be told that if he places his bricks in the sun to dry1 they1 or a large percentage of them1 will crack1 and become practically worthless from a commercial standpoint4 ,to dry a brick properly in the open air is a lengthy operation--too lengthy for many manufacturers1 who1 in consequence1 have had recourse to artificial drying4 ,many a brickyard has had to be abandoned from the inability of the worker to produce bricks that did not crack at some period of the operation1 either in the drying1 or burning1 or both4 ,and several manufacturers have their particular methods of 8doctoring0 the raw earths to prevent cracking4 ,these are invariably 8trade secrets20 though usually of a very open and transparent character1 however1 to the student of the subject4 ,it is most curious to learn the different reasons for adding this or that ingredient to the earths to prevent the brick from cracking4 ,one who in a district has found that the addition of a little sand is beneficial1 imparts that information by degrees1 either personally or through his workmen1 and in time it is laid down as a general axiom that 8sand will prevent cracking40 ,another has discovered that clay should be mixed in small quantity to produce the desired result1 so he and his neighbours do that1 and pity the ignorance of the 8sand mixers40 ,a third feels quite certain that crushed brick1 or brick dust1 is a good thing2 while a fourth will add a little lime4 ,now1 each of these ingredients is useful in its way2 everything depends upon the class of brick-earth to be dealt with4 ,it may happen that what will1 in a measure1 prevent cracking1 will be a bad thing in the burning1 and the art of the brickmaker is to know what to do under the varied conditions4 ,as a general rule1 where care is exercised in the drying1 the cracks arise from the brick-earth being too wet or plastic in the first place1 and it cannot be too well understood that1 cteris paribus1 the wetter the earth the more liable it is to crack during drying4 ,the contraction1 even when the unburnt brick is shielded1 and in the open air1 often proves too much for the material4 ,then we have that class of brick-earth composed of too much clay1 and that would be improved by the addition of sand--just how much depends on the particular earth2 and there is no better method of ascertaining the quantity required than by subjecting the materials to direct practical experiment in the kiln4 ,where no sand is available1 it frequently happens that brick-dust will answer the purpose1 though this may be at the expense of homogeneity in the long run4 ,in the semi-dry process of manufacture the initial causes of cracking are not present1 the block having to contract so little that it may be taken from the press and stacked in the kiln for burning4 ,unless the brick-earth be carefully prepared1 however1 the surfaces of the hard blocks produced by that process are liable to develop minute cracks4 ,and here it may be stated that unless the clay1 with brick dust or other foreign substance1 be thoroughly incorporated prior to being sent under the press1 and the whole ground very fine1 it is impossible to prevent cracking during some part of the process4 ,apart from the fierce and variable drying action of the open air1 we have a fruitful source of cracks in the indentations made by stamping the makers' name or trade-mark upon the blocks4 ,with bricks burnt very hard this does not so much matter1 but on the commoner kind of materials one may often perceive minute1 hair-like cracks radiating from the indentations4 ,we presume that in this age of advertising it is impossible to convince many makers of that fact1 yet if full justice is to be done to the material1 it will be better not to make any sharp or deep marks on the brick4 ,the commoner kinds of brick-earth1 as we have seen1 mostly possess gross particles1 grit1 pebbles1 c42 these act as so many centres from which cracks radiate either during the drying or burning1 and apart from their influence in a chemical sense1 they are apt to seriously weaken the brick4 ,it is truly marvellous to see how little attention many large makers pay to the initial drying2 often the long rows of drying blocks are left unprotected except for a rude kind of roof placed over them4 ,the passing shower of rain drives in underneath1 and wets the exposed surfaces1 causing the clay to swell4 ,these surfaces1 being moister than the remaining portions of the brick1 contract at a different rate1 the centre occasionally being drier than the outside4 ,the unequal contraction produces minute cracks even in most excellent earths4 ,turning to a smaller matter1 the hand-barrow coming from the drying stacks to the kiln is unprotected1 which often means that a good brick is spoilt4 ,of course1 we are not alluding1 in this connexion1 to what takes place during clamp stacking2 the brick produced by such a process must take its chance4 ,the method of stacking in the kiln or clamp is very often responsible for damage to the bricks4 ,a common method is to build them sloping outwards1 and all sorts of strains and stresses are thus set up1 which have their effect in producing lines of weakness1 if not of actual visible cracks4 ,the 8,london stock10 if not a thing of beauty1 is usually strong1 and that in spite of the 8breeze0 which forms so many points from whence cracks radiate4 ,we must not forget1 however1 that a really good ,london stock is1 above all things1 thoroughly burnt1 and that is a set-off against the numerous and often wide cracks4 ,we will assume that the brick has been either naturally or artificially dried1 that no cracks have made their appearance1 and that it is properly stacked in the kiln ready for burning4 ,now comes a most important part of the process4 ,it is possible that any microscopic cracks will be closed by fusion or agglutination2 but it more frequently happens that in unskilled hands the kiln is responsible for many cracked and 8starred0 bricks4 ,to know exactly how to introduce the heat so gradually that the bricks shall not be impaired1 is an art begotten only of considerable experience4 ,even when dealing with one particular kind of brick-earth1 the maker must be careful to notice the relative moistness of his charge1 and vary the mode of procedure accordingly4 ,suppose the brick to be as 8dry as a bone0 before being put in the kiln1 we shall notice a considerable amount of moisture coming out of it as soon as the fires are alight2 and if the heat is applied too suddenly1 the bricks are not improved--they contract unevenly and too quickly1 and warp4 ,when well alight1 care should be taken to keep the temperature as uniform as possible1 and when sufficiently burnt it must be lowered by almost imperceptible degrees4 ,above all things1 there should not be too great a disparity between the temperature in the kiln and the outside air when unloading4 ,except to those who had minutely studied this matter1 such a precaution might seem superfluous2 it may be that no damage caused will be visible to the naked eye1 but the microscope frequently shows flaws due apparently to this cause4 ,the manufacturer may test this for himself by heating a good1 sound medium burnt brick to the temperature usually found in his kiln when unloading1 and suddenly plunging it in snow4 ,it is not1 perhaps1 that any one of these things is especially dangerous to the brick1 but it is the combined effect of all of them trending in the same direction4 ,we desire to be clearly understood on this point4 ,the cracks produced may not seriously impair the strength of the brick2 they may be merely superficial1 and they mostly are4 ,but they materially assist the agents of denudation in 8scaling0 the brick1 and weathering it unevenly4 ,to this we shall return later on4 ,let us now say something concerning the superficial changes produced in bricks by burning4 ,the most important of all is the change of colour1 upon which the sale of the brick depends in ninety-nine cases out of a hundred4 ,we said a few words on this subject when dealing with the behaviour of individual minerals in the kiln4 ,the production of an uniform tint is the main point aimed at2 and it may be at once remarked that unless the brick-earth employed is very homogeneous1 or has been most carefully prepared and thoroughly incorporated1 the production of an uniform colour is impossible4 ,in regard to the tint to be produced1 it should be remembered that the temperature employed in burning is a most potent factor4 ,it is frequently laid down that such and such a temperature will form a red brick1 and another and higher temperature1 a blue one4 ,that is a most absurd notion4 ,in a general sense the principle could be correctly applied to a limited district1 and with one class of brick-earth2 but it cannot be made to apply all round4 ,there is nothing like experience in regard to a point like this4 ,in a general way1 of course1 a pink1 red1 or blue tint may be produced from one brick-earth depending upon the temperature employed2 but the bulk of brick-earths would melt and the whole kiln-full be ruined in any attempt to attain such a temperature as is used in burning a sound 8,staffordshire blue40 ,quite a large number of bricks made in the ,southern half of ,england1 may be described as having been dried in the kiln only--they cannot be said to be burnt1 except that the heat employed was enough to turn them red1 or to make them piebald2 the particles are not agglutinated by fusion1 and1 indeed1 there is often no trace of the constituents having been melted4 ,on the other hand1 we have red bricks in which the constituents are distinctly agglutinated by fusion1 and the whole burnt thoroughly4 ,the brick-earth of which these latter are made1 would barely turn tint--would certainly not become red--at so low a temperature as that employed in producing the red in the non-agglutinated bricks alluded to4 ,it is not always an easy matter in burning a red brick to obtain two kilns full of the same tint1 even in the same yard4 ,when the employment of pyrometers becomes more general1 that will be considerably simplified2 but it is a difficult matter to get a reliable instrument1 none of the forms hitherto invented being altogether suitable4 ,that by ,professor ,roberts-,austen is as good as any4 ,many manufacturers1 we are sorry to say1 place colour before everything else2 they even sacrifice durability to attain a certain tint4 ,and there is much excuse for them so long as they find a ready sale for the material4 ,when colours are made from artificially introduced mineral matter 7which is not so often the case as some appear to think7 the mineral introduced is1 most commonly1 iron2 though it will be understood1 from what we have previously said1 that it must be used very sparingly4 ,the ultimate tint assumed by the brick cannot always be judged beforehand from the colour of the brick-earth4 ,in brickmakers' language1 a red clay is one that produces a red brick1 a blue clay a blue brick1 and so on4 ,for the most part1 colour depends on the proportion of hydrated oxide of iron in the clay2 if iron is present in an earth that contains no lime1 or similar mineral substance1 the colour produced in the brick at a moderate red heat will be red1 and at the same temperature1 with the same brick-earth1 the more iron present the deeper the tint4 ,in an ordinary brick-earth1 when more than #aj per cent4 of iron is present1 the clay is apt to burn bluish1 however1 and1 in certain cases1 almost black4 ,with a smaller proportion of iron1 and the application of intense heat1 the same tint may result1 and the brick become vitrified4 ,a brown colour may frequently be obtained when the brick-earth has from #b4ge to #d per cent4 of magnesia1 or a similar proportion may be artificially added to the earth4 ,to obtain a white brick1 so that it shall also be of excellent quality1 the pure white clays of ,devon and ,cornwall are the best1 though the so-called 8white0 is1 in the majority of cases1 a light cream colour1 unless1 of course1 the brick is glazed4 ,in the neighbourhood of ,london1 a whitish brick results from a mixture of chalk 7carbonate of lime7 with clay or loam1 and is known as a 8malm40 ,in parts of ,yorkshire1 white pressed bricks are manufactured from common red clay mixed with magnesian lime 7made from magnesian limestone7 in a slacked condition4 ,the latter ingredient1 on introduction1 immediately absorbs about #dj per cent4 of the moisture present in the clay4 ,yellow bricks can easily be manufactured from the more impure kaolins2 also from certain clays in ,cambridgeshire1 ,huntingdonshire1 ,kent1 c4 7gault bricks72 8malms0 are mostly yellow1 though called white4 ,laboratory experiments1 many years old1 show that with white clay as a basis the following tints may be obtained4 ,phosphates of lime of various kinds very light blue bricks4 ,the phosphates1 mixed with a quarter by weight of alum brighter blue bricks4 ,a mixture of white vitriol 7sulphate of lime7 three-quarters1 with borax one-quarter light dirty green4 ,sulphur and tin oxide in equal proportions yellow4 ,these experiments are interesting1 but the ingredients would1 as a rule1 be too expensive for ordinary brick manufacture4 ,they are more applicable for the production of ornamental tiles4 ,a time-honoured method of producing black bricks is to make any ordinary bricks red-hot and to dip them in a cauldron of boiling coal-tar for a few seconds4 ,it is essential that the brick should be very hot1 or the black staining will rub off4 ,a good test that the operation has been successful is1 that the surface shall be dull black1 not shining4 ,and there are many other ways of obtaining different tints1 the description of which would be beyond the scope of the present work4 ,unless a brick is extremely well burnt it is not uniform in colour throughout4 ,a considerable proportion of a 8draw0 is often ruined in regard to tint by the adoption of an unsuitable form of kiln4 ,where the brick is actually burned 7as distinguished from being baked71 the contact of the flame from the fires is almost sure to lead to uncertainty in that respect along the flues4 ,impurities in the coal1 such as iron pyrite1 are the chief delinquents1 and there is sure to be a certain amount of 8flash40 ,in that1 as well as in the baking method1 bricks are liable to be discoloured by the bringing out of impurities which they themselves contain4 ,,chapter ,x4 ,,the ,,durability ,,of ,,bricks4 ,this is one of the most important parts of our subject1 and it may be approached from several points of view4 ,when a brick decays1 its structure1 for the most part1 is responsible therefor4 ,a great deal depends on whether the ingredients forming the brick are merely baked in the process of manufacture1 or whether they are wholly or in part agglutinated by igneous fusion4 ,a rough and ready plan of determining this point1 in the absence of experience1 is by ascertaining the porosity of the brick4 ,other things being equal1 the absorption test is undoubtedly the best all-round method of gauging the weathering qualities of a brick4 ,but there are certain kinds of bricks which defy that method2 an imperfectly burnt one with a vitreous exterior is especially treacherous in that respect1 and1 indeed all 8vitrified0 bricks are difficult to deal with by the 8absorption process40 ,again1 a brick cracked all over1 not with superficial cracks only1 but with those which go far into the interior1 will not yield its quality by mere immersion in water4 ,the water1 it is true1 finds its way right into the brick1 but1 as often as not1 the sides of the cracks are perfectly vitrified and almost damp proof1 so that on lifting the brick out of the water the latter rolls off as though it were on 8a duck's back40 ,yet such a brick1 yielding but the merest fraction as a result of the immersion1 may be utterly worthless when put into a building1 because it would not be strong enough4 ,then we have those bricks which are seriously affected chemically1 but which seem fairly good in other respects4 ,they also1 in many cases1 defy the efforts of the experimenter in regard to absorption2 though they are nevertheless easily detected as being of bad quality1 by other methods4 ,such bricks often resist great 8crushing weights10 and generally bear a good character1 their subsequent behaviour when put in the building to the contrary notwithstanding4 ,in determining the weather-resisting qualities of a brick we have the following things to consider3-- #a4 ,the chemical composition of the brick4 #b4 ,its absorptive capacity4 #c4 ,its minute structure4 #d4 ,its specific gravity4 #e4 ,its strength4 ,the last-mentioned property can often be inferred from a knowledge of the three preceding ones1 and need not1 therefore1 form the subject of direct experiment4 ,in spite of that1 however1 we find that the 8crushing strength0 is much more popular than the others4 ,the reason1 so far as brick manufacturers are concerned1 is not far to seek4 ,architects demand that especial quality4 8,what is the #8crushing strength' of your bricks80 enquires the architect4 ,and if the maker does not know1 he stands a good chance of losing the order4 ,figures are demanded1 and if the maker cannot produce a higher figure than his neighbour1 woe betide him4 ,but statistics are ever deceptive1 and as applied to bricks in regard to their strength especially so4 ,in general1 we have to consider whether the brick is strong enough for the purpose to which it is to be applied2 and that depends much more on the manner in which it is built up1 than on the strength of the individual brick4 ,for ordinary building purposes almost any kind of brick is1 per se1 strong enough1 and a mere inspection of the specimen suffices to carry conviction as to its suitability or otherwise in that respect4 ,for certain structures1 such as buildings to carry heavy weights--especially moving weight--for engineering purposes1 and the like1 we ought1 it is true1 to know a little more4 ,yet the engineer would be a very poor one who could not tell at sight whether a brick submitted to him was fit or not for the purpose he has in view1 from the point of view of its weight-carrying properties4 ,in any case1 however1 fashion demands the 8crushing weight0 in figures1 and although such figures are in general of but little practical value1 they must be given4 ,the principal difficulty the architect and engineer have to contend with is not lack of strength1 but the setting in of decay1 and that even in bricks sometimes of the strongest description4 ,unless the strength is going to be maintained1 it is of no use whatever1 in a scientific sense1 to give it in the first instance4 ,after these few preliminary observations1 it will be well to treat the subject more systematically4 ,,the ,,effect ,,of ,,the ,,atmosphere ,,on ,,bricks4 ,air is a mixture of gases2 dry air consists of at least four of them1 namely1 nitrogen1 oxygen1 carbonic acid1 and argon4 ,of these1 by far the most abundant is nitrogen1 present to the extent of about #gh per cent41 then oxygen1 #bj4if per cent41 argon about #a per cent41 and carbonic acid #j4jd per cent4 ,extremely minute quantities of ammonia and ozone1 though practically always present1 have been omitted from the preceding results of analysis of air4 ,we have been speaking of pure dry air2 but the atmosphere is hardly ever of precisely the same chemical composition in two different places4 ,by the seaside it has more ozone1 and chloride of sodium is found in particular abundance4 ,in cities1 especially where large factories exist1 nitric acid and sulphuric acid appear most conspicuously1 and the proportion of ammonia becomes larger4 ,in the air of streets and houses1 the proportion of oxygen diminishes1 whilst that of carbonic acid increases4 ,dr4 ,angus ,smith has shown that very pure air should contain not less than #bj4ii per cent4 of oxygen1 with #j4jcj of carbonic acid2 but he found impure air in ,manchester to have only #bj4ba of oxygen1 whilst the proportion of carbonic acid in that city during fogs was ascertained to rise sometimes to #j4jfgi1 and in the pit of a theatre to the very large amount of #j4bgcd4 ,although these may seem to be very small percentages1 yet the total amount of carbonic acid in the atmosphere is enormous1 and plays a conspicuous part in the decay of certain kinds of bricks4 ,sulphuric acid is found in the air of large cities principally as a product of combustion1 and is1 of course1 a distinct impurity4 ,a portion of this acid is free1 and a larger quantity is combined4 ,free sulphuric acid is very destructive to clay goods in the open2 and it should be remembered that the relative abundance of this impurity depends on the precise locale in the city4 ,a great deal has been said and written about the decomposition of the stone of which the ,houses of ,parliament are built4 ,the air in the immediate vicinity must be highly charged with both sulphuric and nitric acid from the proximity of the busy factories on the opposite banks of the ,thames in ,lambeth4 ,had the ,houses of ,parliament been erected1 say1 in ,kensington1 where but few factories exist1 it is conceivable that the stone would have behaved much better4 ,air in itself1 however1 has no power to destroy bricks--the various gases1 acids1 chlorides1 salts1 solid carbon1 inorganic and organic dust can do nothing by themselves4 ,but the air is always laden with vapour1 the most important of which is water vapour1 which condenses into rain1 hail1 snow1 and dew4 ,when rain is formed1 the drops of water take up minute quantities of air with its proportion of carbonic acid1 sulphuric acid1 or what not1 and it is these acids1 applied to the surface of bricks through the medium of rain and moisture generally1 that are liable to do the damage if the nature and composition of the brick are favourable4 ,let us assume that we have a brick composed of a goodly percentage of carbonate of lime4 ,the carbonic acid in the rain reduces this to a bi-carbonate1 which is soluble in water1 and hence the surface of the brick decays1 the rain water washing it away4 ,other things being equal1 it follows that the same brick will decay most rapidly in a district where the rainfall is very great and where there is the largest proportion of these deleterious acids in the air4 ,whilst speaking of the various acids which attack and destroy bricks1 we must not forget those formed by the decomposition of organic matter on the surface of bricks which 8vegetate40 ,the lichens1 mosses1 and so forth1 growing from cracks in the wall1 or spread over on to the brick from the mortar1 yield1 on decomposition1 some of the most powerful acids in existence4 ,a brick with a 8crumbly0 surface affords good foothold for these plants1 and when they die they give rise to the so-called humus acids--crenic and apocrenic acid--which undoubtedly do an immense amount of damage4 ,by keeping the surface of the brick moist1 the plants permit the ordinary acids in rain to do more execution than they otherwise would4 ,taking two bricks1 one which 8vegetates0 and one that does not1 and exposing them in the same situation1 it will be found that after a smart shower of rain the surface of the former has become thoroughly soaked1 and the vegetation keeps it so1 completely rotting it in time2 whereas the surface of the latter1 exposed to the same shower1 may be quite dry within an hour or two after the rain has fallen4 ,returning to the subject of rainfall1 which exercises such material influence on the durability of bricks1 we may give a few particulars concerning the distribution of rain in this country4 ,speaking generally1 the east coast of ,england is the driest part of the country1 the west coast having the greatest rainfall4 ,the annual quantity at sea-level ranges from #fj to #hj inches on the west coasts of ,ireland and ,scotland1 to about #bj inches on the east coast of ,england4#aj ,in some localities1 however1 the fall is much greater1 amounting to #aed inches on the average of six years at ,seathwaite1 in ,borrowdale1 at the height of #dbb feet above the sea4 ,the quantities which fall in particular showers are often very great1 and this aspect of rainfall also has its interest for us4 ,about ,london a fall exceeding an inch in #bd hours is comparatively rare1 although on ,august #a1 #ahdf1 #c4ab inches were collected in ,st4 ,paul's ,churchyard in two hours and seventeen minutes4#aa ,on our west coasts this amount is often exceeded4 ,on ,october #bd1 #ahdi1 #d4cg inches were collected at ,wastdale ,head2 ,june #cj1 #ahha1 #d4hj inches at ,seathwaite2 on ,april #ac1 #ahgh1 #d4f inches fell at ,haverstock ,hill1 ,london2 and a fall of #e4cf inches was recorded from ,monmouthshire on the #adth ,july1 #ahge4 ,taking averages of districts1 we may give the following statistics1 referring1 of course1 to annual rainfall3-- ,less than #be inches ,essex1 ,suffolk1 ,norfolk1 ,cambridgeshire1 ,huntingdonshire1 ,rutland1 ,middlesex1 and parts of ,surrey1 ,oxfordshire1 ,buckinghamshire1 ,bedfordshire1 ,northamptonshire1 ,leicestershire1 ,nottinghamshire1 ,lincolnshire1 ,yorkshire1 and ,durham4 ,in other words1 with the exception of parts of the ,north and ,east ,ridings of ,yorkshire and parts of ,herts4 and ,bucks41 which have a rainfall of from #be to #cj inches1 the eastern half of ,england1 to the east of a line drawn from ,sunderland to ,reading1 and then eastwards to the mouth of the ,thames1 has only a rainfall of #be inches1 or slightly less1 per annum4 ,between #cj and #dj inches ,practically the whole of the south coast from ,kent to ,devonshire1 the whole of ,somerset1 ,wilts41 and the west of ,england generally1 with the exceptions about to be noticed4 ,between #dj and #ej inches ,a great part of ,devon and ,cornwall1 the western half of ,wales1 with the exceptions presently to be given1 a great part of ,lancs41 and ,cumberland4 ,between #ej and #ge inches ,a small patch in the centre of ,devon1 a large strip in ,west ,wales1 and an enormous tract of country in ,cumberland1 ,westmorland1 with ,lancs4 and north-west ,yorks4 ,above #ge inches ,the wettest parts of the country4 ,a small part of ,dartmoor1 a region in ,wales in the vicinity and to the south-east of ,snowdon1 and the ,lake ,district4 ,with reference to statistics concerning rainfall1 it should be borne in mind that those relating to special districts1 especially to hilly parts of the country1 are often very deceptive1 and require careful local study4 ,a slight difference in the physical features of a locality is often sufficient to lead to considerable variation--the proximity of a conical hill rising from the plain1 the sudden convergence of the two sides of a valley1 or1 conversely1 the widening of a valley into a flat stretch of land1 all materially affect the local distribution of rain4 ,a clump of trees situated in proximity to a house will frequently be the means of a downpour that would otherwise have passed over4 ,with winding valleys great latitude must be allowed4 ,then1 again1 the geological structure of the locality is an important factor in determining the amount of moisture delivered at a given spot4 ,where we find a thick clay cropping out in the bottom of a valley1 with more or less porous rocks rising on either side of it1 we soon ascertain that the houses on the clay receive more moisture 7or the latter is distributed over a longer period7 than those edifices on the hill sides in the same district4 ,our readers could no doubt give us plenty of instances where in a circumscribed area their bricks have behaved very erratically--the bricks of a house in one part of the district weathering well1 and in another badly4 ,that may often be due1 not only to the actual distribution of the rain1 but to the manner in which the rain or dew has fallen4 ,if an inch of rain falls in the neighbourhood in one day1 that would not tend to weather the bricks so vigorously as though the fall had been spread over1 say1 a week4 ,a very important aspect of the subject is that which deals with the 8efflorescence0 on bricks4 ,this appears to be greatly misunderstood1 being commonly assumed to be due to one set of circumstances rather than to the conspiracy of several4 ,there are many kinds of efflorescence1 and an explanation of one of them obviously will not apply to all4 ,the 8scum0 that appears on the surface of bricks is1 however1 to some extent bound up in the composition of the rain in the particular locality where it occurs4 ,examined attentively1 the commoner kinds of efflorescence are seen to be minute white and yellowish-white crystals4 ,the substance of which these are formed has been drawn out of the brick1 or the mortar1 or both1 and rain has been the principal agent in accomplishing this work1 though its power in that respect must necessarily vary according to the chemical composition and structure of the brick or mortar1 as compared with the nature of impurities in the rain4 ,if some substance were present in the rain that could readily form an alliance with an ingredient of the brick1 and the union was capable of crystallising out1 the surface of the brick would naturally form a convenient spot for the crystallisation to take place4 ,to prevent it1 we ought to know the composition of the air at the spot where the house is to be erected1 and also the chemical and physical structure of the brick to be employed4 ,that is rather too much to expect from the manufacturer and architect2 but there is a method--we will not say an infallible one--which may be adopted to get rid of that particular kind of scum4 ,that method could not always be adopted1 as will be seen4 ,the bricks must be burned more thoroughly1 and at a high temperature2 that would lead in most cases to the active employment of practically all the ingredients of which the bricks are composed1 and the impurities in the rain would1 in consequence1 stand less chance of successfully inducing some of them to break their allegiance4 ,in practice1 however1 we believe it would be found that the high temperature requisite to bring about the result just stated would either tend to spoil the colour of the brick or partially melt it4 ,the latter could be prevented with due care1 but we are afraid the former could not be so easily dealt with1 with the majority of brick-earths4 ,and if the brick is to be permanently discoloured to prevent efflorescence1 it is better to permit the latter to manifest itself4 ,the life of the 8scum0 is very variable2 sometimes1 after having once appeared and disappeared1 it will never come again4 ,the passing shower may wash it off 7though it is not always so easily removed71 and it may come again and again for years4 ,it behaves very erratically4 ,the amount of the efflorescence may be such as1 in course of time1 to lead to the surface of the brick 8bursting0 and peeling off1 or1 on the other hand1 it may be a mere film4 ,there is one thing in connexion with efflorescence which cannot be overlooked in regarding its practical effects in the building4 ,in ever so many cases we find that the scum1 or the major part of it1 is only to be found in the neighbourhood of the mortar joints4 ,that is a matter of direct observation1 and we have taken some considerable trouble to verify it1 as it has always been regarded as a point whereon to hinge a debate4 ,we do not say that in all cases the efflorescence appears only in the position on the brick just indicated2 but it unquestionably does so in too many instances to enable us to regard its occurrence as mere accident4 ,taking a large surface of brickwork just commencing to show efflorescence1 we find that the vicinity of the mortar joints are the first places1 in very many instances1 where the nuisance begins to manifest itself4 ,from thence it spreads over the surface of the brick until the whole is more or less discoloured4 ,it seems impossible to deny that the mortar is guilty1 to some extent1 in such cases4 ,at the same time1 we must confess that we have never seen the efflorescence spreading over the mortar4 ,it would appear that something in the mortar enters into chemical alliance with certain ingredients of the brick1 and that neither without the other could produce the phenomenon alluded to4 ,the remedy suggesting itself most readily is to chemically analyse the efflorescence1 the brick1 and the mortar2 supplementing the experiments with a micro-examination to see how far it is possible to locate the deleterious substances found to exist1 so that they may be removed in the manufacture of the materials1 if that is possible4 ,but information on that head is of the scantiest description1 and much more will have to be done before the question is definitely settled4 ,another kind of 8efflorescence0 that often appears on bricks in damp situations is mere vegetable growth1 which bears a superficial resemblance to the crystalline 8scum0 just described1 though it can1 of course1 be easily differentiated on examination with a lens4 ,the damp atmosphere is no doubt largely responsible for this1 though ineffectual damp-courses are contributors4 ,the remedy lies in having a less absorbent brick--one that will not afford ready foothold to the vegetation4 ,the influence of rain on the weathering of bricks may be considered from yet another standpoint4 ,where the brick is fairly porous1 its durability is liable to be materially influenced through the agency of successive frosts4 ,the water finds its way a short distance into the brick and saturates it4 ,during frost the water is turned into ice at and near the surface of the brick4 ,in forming1 the ice exerts considerable expansive force1 which forces asunder the particles 7sand-grains and the like7 of which the brick is composed--that is to say1 near the surface of the brick4 ,the accumulated effects of successive frosts in this way tends to weather the brick by breaking up its exposed surfaces4 ,to be materially affected1 however1 the brick would have to be of very poor quality1 and it will be seen that the presence of cracks would much facilitate the operation4 ,the style of a building1 the manner of its construction1 and especially the class of metals used for exterior decoration1 all assist rain in its work4 ,a projecting course will have its upper surface washed clean1 whilst the underside remains very dirty--in cities1 becoming quite black4 ,the limit of this dark discolouration is often frayed out by the irregular action of the rain dripping from the projecting ledge1 assisted by the wind4 ,where the projection is so designed that the rain is induced to drain to one point1 and then to fall over on to the wall1 an unsightly streak down the latter is the result4 ,the free use of metal ornaments1 railings1 for supporting signs1 for down-pipes1 c41 is unfortunate in not a few instances4 ,at the point of junction between the metallic substance and the brick into which it is inserted1 or in the immediate neighbourhood above which it is fastened1 the brickwork is sure to be discoloured4 ,this may arise from the dripping of rain-water from the metal1 or it may be from the decomposition of the latter1 or from both4 ,iron rust leads to brown streaks1 zinc-compo4 to dirty red1 and so on4 ,the action of the wind as affecting the durability of bricks is sufficiently important to warrant passing allusion4 ,it drives rain and its deleterious acids farther into the brick than the moisture would soak in the ordinary way4 ,it leads to wet walls interiorly1 unless the latter are so constructed as to overcome the effects4 ,on the other hand1 a gentle breeze dries moisture on the face of the brickwork4 ,in cities1 wind indirectly assists rain and its impurities by blowing organic matter from the streets into niches and corners1 where it lodges1 and1 decomposing1 provides powerful acids capable of doing much work4 ,discolouration is the chief effect produced on the average brick through this medium4 ,in certain countries1 wind1 by driving dust1 sand1 c41 acts as a species of sand blast4 ,considerable diurnal variations in temperature are known to be peculiarly destructive to certain kinds of brick and terra-cotta work4 ,very porous bricks are not much affected1 but the more compact kinds1 and especially terra-cotta blocks1 often suffer4 ,these observations do not so much apply to our own country as to warmer climates2 though we are not altogether without experience here4 ,on being heated these materials expand2 when made loosely1 as in rubbers and the like1 the effect of the expansion is not very manifest1 because the motion is absorbed1 so to speak1 by the brick itself4 ,on the other hand1 increased compactness of the particles leads to a perceptible increase in the size of the bricks1 and when the sun has gone down contraction takes place as the bricks are cooling4 ,it often happens in hot climates that the brick or terra-cotta block is unable to part with its heat as rapidly as the surrounding air becomes cooler1 although it tries hard to do so1 and this leads to corners of the brick being broken off1 the physical forces exerted during the struggle doing the damage4 ,a highly interesting case of the effects of temperature on terra-cotta was detailed by ,mr4 ,t4 ,mellard ,reade1 ,c4,e41 ,f4,g4,s41 a few years ago4#ab ,he shews that the cumulative effect of small1 but repeated changes of temperature is very striking1 and describes the lengthening of a terra-cotta coping in that connexion4 ,the coping in question1 which was freely exposed to the direct rays of the sun1 consisted of two courses of red ,ruabon terra-cotta bricks set in cement upon a fence wall1 built with common bricks in mortar1 a brick and a half in thickness4 ,the courses were level1 but1 in consequence of the inclination of the road1 the coping stepped down at intervals1 so that the undercourse of bricks of one length was just gripped and held in position by the top course of the next length of coping4 ,it will be observed that that form of construction constituted1 by liability to lifting1 a more delicate test than ordinarily of any increase of length1 that might take place in the coping4 ,on subsequent examination of the coping1 the end position of one length1 abutting against the next length at the drop in the level1 was found to be thrown up into an arch-shape bend of about #f feet span2 the coping bricks being lifted in the highest part one inch from their bed4 ,there was a fracture at the crown of the arch1 and another at the foot or springing1 but for a distance of #cj feet the coping was practically one solid continuous bar4 ,a careful examination shewed that the coping had 8grown0 about a quarter of an inch longer than when it was first set1 and that this lengthening1 as shewn by movement on the corbel bricks which occur at intervals1 was evenly distributed along a length of #cj feet4 ,mr4 ,mellard ,reade tells us that this is by no means an isolated case4 ,in the neighbourhood of ,blundellsands inspection of brick copings shewed that it was quite a common feature1 and he has noted several instances in which the end brickwork and piers have been badly fractured by the force of expansion4 ,in a case where the coping was of blue ,staffordshire bricks1 the top course in cement and the under course in mortar1 a change in length was clearly shewn by the coping being lifted off the wall at each of the two ramps which exist in its length1 and the movement was readily measured on the corbel bricks as in the case previously detailed4 ,in this case the lengthening was also a quarter of an inch1 and was evenly distributed over a considerable length of coping4 ,whilst speaking of changes of temperature in their effect on bricks1 we may allude to the behaviour of the material in severe conflagrations4 ,a general rule cannot be laid down1 because it is customary now-a-days to use fire-bricks for ordinary building purposes which will withstand practically any heat to which they may be subjected4 ,leaving them out of the question1 and referring to ordinary bricks1 it may be said that those of an inferior class frequently become cracked all over during a fire1 or1 it may be1 by the sudden cooling after the fire has been put out1 or by the sudden lowering of the temperature in them by the continuous action of the fireman's hose4 ,all the same1 the average brick withstands heat far better than any kind of granite1 or similar igneous holo-crystalline rock2 loosely compacted sandstones and limestones crumble up on the surface1 or flake1 or may be utterly destroyed when subjected to a conflagration that would not have the slightest effect on bricks4 ,,chapter ,,xi4 ,,the ,,micro-,,structure ,,of ,,bricks4 ,the reader may be tempted to enquire1 ,what is the use of knowing the micro-structure of a brick8 ,we have anticipated the question to some extent in dealing with the structure of brick-earths1 but it may be well to enlarge upon it here4 ,in the first place1 the study of the minute structure enables the manufacturer to ascertain whether the brick is thoroughly and homogeneously burnt4 ,it tells him whether the materials mixed together in the earlier stages of manufacture were thoroughly incorporated or not1 whereby1 if need be1 he can improve that part of the process4 ,in carefully examining what the average manufacturer would call a well-burnt brick1 the microscope assists us in perceiving that it is often anything but well burnt1 small local patches--8tears0--of semi-vitrified matter being observed1 which should not exist1 of course1 in a perfectly homogeneous brick4 ,and if the brick is not homogeneous1 it suffers in respect of its strength as a whole1 and in the majority of cases its colour is not uniform4 ,to arrive at the cause of this lack of uniformity is to indicate the manner in which the manufacture of the brick may be improved1 and the microscope often enables us to arrive at a satisfactory solution of the problem4 ,from a chemical standpoint we know that a high percentage of iron in the average brick-earth is not conducive to the production of a good brick4 ,in the same manner by 8rule of thumb0 we learn that a high percentage of lime prevents the manufacture of the raw material into a fire-brick1 unless1 indeed1 we are making basic bricks4 ,the chemist tells us also of the respective values of potash and soda4 ,too much iron will cause the brick to 8run02 salt has a similar effect2 but beyond this the chemist cannot go1 except that in the broad sense he explains what unions take place to produce such results4 ,the microscope1 on the other hand1 enables one to see exactly what has taken place2 the deleterious constituents are detected at their work1 and careful chemical investigation teaches us what to add to the brick-earth to neutralise the effects observed2 for it is only from its effects that the artificial constitution of the brick-earth can be properly regulated4 ,the same instrument is extremely useful in all questions concerning the relations subsisting between a brick and the glaze upon it1 the cause and prevention of the cracking of the latter1 and its general quality from a physical aspect4 ,and1 speaking of cracks1 we may again draw attention to the influence these have on the strength and durability of the brick3 many of these minute fissures cannot be seen by the naked eye4 ,in a similar way can the microscope be made use of in the manufacture of terra-cotta and faence4 ,the cracking of glazes is one of the most troublesome features the high-class brick and tile manufacturer has to deal with4 ,if the character of the surface of the brick is not suitable for 8taking0 the glaze1 the maker knows in a moment2 the trouble is where the glaze takes readily and then1 some time after the operation is finished1 it becomes covered with 8spider-web0 cracks1 unsightly and considerably detracting from the value of the brick4 ,the cause of the cracking is commonly attributed to the composition of the glaze1 and the manner in which the latter is allowed to cool1 and no doubt a great deal is due on both those heads4 ,at the same time1 we know of many instances where the same glaze being used under similar conditions on two different surfaces of bricks made from one and the same brick-earth1 the glaze cracks in the one case1 and hardly ever in the other4 ,the direction of the cracks points to their origin1 and the character of the surface is brought in guilty4 ,and yet the average manufacturer would not detect any difference in the quality of the surface--he could not1 without a good lens or low power objective1 perceive the slightest discrepancy4 ,the ordinary glaze behaves very much like ,canada balsam with reference to surfaces on which it is laid1 and something akin to what petrologists call 8perlitic0 cracks is produced in the glaze4 ,we can make these cracks1 and imitate the structure artificially1 by suitably distributing the ,canada balsam over the surface of a piece of ground glass1 and in other ways4 ,that direct relationship exists between the cracks and the grain of the surface on which the preparation is laid1 is certain1 for we may vary the distribution of the cracks by varying the grain of the surface4 ,an intelligent appreciation of the disposition of cracks in glazes should be the means of preventing them altogether1 and not only with bricks1 but with faence and vitrified work generally1 the study may be best carried on by aid of the microscope4 ,the microscope1 also1 may be made use of in identifying bricks in case of dispute1 though its applications in this respect are not so important as in dealing with building stones4 ,questions of durability may frequently be decided on appeal to that instrument4 ,take a case in which a brick is known to contain a rather high percentage of lime3 if the lime were in a combined state1 the quality of the brick would not be materially affected2 but assuming it were not so employed1 it is possible that in a short space of time the brick would be thoroughly decomposed by atmospheric agencies4 ,the microscope tells us at a glance the state in which that and other ingredients exist1 in a well-burnt brick4 ,we draw the line at bricks intended for the 8jerry0 builder2 they may well be left to take care of themselves2 we allude only to high-class productions in which science may be some aid to the manufacturer4 ,and now as to the microscope--for we do not use an ordinary one in such investigations4 ,the best kinds of microscope are those used by petrologists in the study of the minute structure of rocks and minerals4 ,the reader will find these fully described in works specially devoted to the subject1#ac but we may say a few words thereon4 ,a common form of 8,student's0 petrological microscope1 as manufactured by ,swift of ,london1 may be described as follows3-- ,eye ,pieces and ,objectives4--,these need not be expensive1 clear definition being the principal object to aim at2 the objectives should be of low power1 #b-;inch1 #a-;inch and -inch objectives being plenty for the purpose4 ,unless the reader desires to follow the subject from a purely petrological point of view1 to study the development of trichites1 globulites1 skeleton crystals1 etc41 in vitrified bricks1 in such places as these latter have cooled from igneous fusion1 there is no occasion to resort to higher powers4 ,we are far from saying that the brickmaker of the present day would not derive any advantage from studying this subject in its higher aspects1 for the origin of crystallization appeals strongly to the imaginative mind1 and is one of the most remarkable problems that ,nature offers for our investigation4 ,but in an elementary treatise of this kind we cannot go into the matter2 and1 as previously remarked1 low power objectives are sufficient for our present purpose4 ,the eye-pieces should be fitted with cross-wires1 the use of which will presently be explained4 ,the ,stage4--,in the instrument we are now describing this is circular with a hole in the middle1 and is so arranged as to revolve horizontally on a collar about an axis1 the centre of which comes exactly underneath the centre of the objective4 ,in other words1 a straight line drawn through the eye-piece down the centre of the barrel of the microscope1 and passing through the objective passes through that axis4 ,to assist in more accurately centreing than is otherwise possible 7depending on the lenses7 with this cheap form of instrument1 a collar with adjustable screws is ordinarily affixed to the lower part of the barrel of the microscope4 ,the stage1 with suitable clips to hold the object to be examined1 is graduated so that on its being revolved it is easy to ascertain the number of degrees1 at any period of the revolution1 through which it has been turned4 ,thus1 it will be observed that the object revolves with the stage4 ,a pointer is placed in a suitable position on the frame of the microscope to facilitate the observation4 ,the ,polariscope4--,this is an indispensable adjunct1 for determinative purposes it is often necessary to observe the object in polarised light4 ,briefly1 the polariscope consists of two parts--the analyser1 placed in the barrel of the microscope above the objective1 and the polariser1 arranged underneath the revolving stage4 ,the analyser is so fitted that it may be shot in and out of the barrel in order that the polariser alone may be used1 or the latter may be removed1 leaving only the analyser in position1 or both may be removed to enable the object to be examined in ordinary light1 either reflected or transmitted4 ,the lower nicol#ad is made to revolve1 and the collar in which it is fixed is broadly graduated and furnished with a pointer4 ,reflector4--,an ordinary reversible and adjustable reflector is arranged beneath all4 ,accessories4--,for the more accurate determination of minerals1 a quartz wedge1 a quartz plate1 etc41 are used by the petrologist1 but the description of these is beyond the scope of the present work4 ,for examination in reflected light it is highly desirable to have a 8bull's-eye0 condenser4 ,an ordinary microscope with a revolving stage may be readily converted to petrological purposes1 though it is better to have a special instrument4 99 99 99 99 99 ,the object to be examined may be in the form of 7a7 a fragment of the brick1 or 7b7 a very thin slice of the same4 ,the fragment may be securely clipped and held in position on the stage1 the 8bull's-eye0 condenser being brought into use to throw a strong light on the part immediately under the objective4 ,the polarising apparatus is no use for this1 and may be thrown out of gear4 ,a very low power should be employed4 ,the observation may be directed towards ascertaining how far the fragments composing the brick are agglutinated1 and their size may be noted4 ,anything like a discolouration should be specially observed1 and a minute description jotted down4 ,in bricks that have not been burnt very hard1 and in those that have merely been baked1 we shall often be able to detect particles of mineral matter which further investigation1 after the manner presently to be described1 shows are opaque4 ,different forms of iron1 iron pyrite1 fragments of clay that have merely been dried in the process of baking1 and minute pieces of chalk 7now converted into lime7 are amongst the most prominent opaque substances met with in common bricks4 ,these may generally be differentiated and determined at sight1 and bricks thus composed are never of good quality1 though the ingredients have been ground very fine1 and there may be nothing superficially to find fault with4 ,their bad qualities are usually brought out in the weathering4 ,a great deal may1 therefore1 be learned from a careful examination of fragments in this manner4 ,in regard to the examination of very thin slices1 that is in the majority of instances the most instructive1 and1 if we may say so1 the most interesting method of investigation1 though it must always go hand in hand with the other4 ,the slice of the brick is so thin that the bulk of the constituents is rendered transparent1 or semi-transparent4 ,the preparation of such slices#ae is not difficult1 but demands some experience2 those who have neither the time nor patience to make them will find it convenient to send the fragments of brick to ,damon1 of ,weymouth1 or some other first-class dealer in geological and mineralogical specimens4 ,the price charged1 per slide1 is usually #as4 #f;d4 ,at the same time1 the student will find it eminently to his advantage to prepare the slices himself4 ,in the process he will learn much that escapes attention when the work is done by another4 ,the thin slice mounted on a slip of glass is placed on the stage of the microscope and firmly clipped1 as with the fragment4 ,the reflector is brought into position1 and a beam of light thrown through the slice--the thin section is now being examined in transmitted light4 ,at first it will be convenient to study it with the polariser and analyser thrown out of position4 ,a certain proportion of the constituents is found to be opaque1 and should be examined in reflected light1 as above described4 ,the remainder are more or less transparent1 and some of the grains will1 possibly1 be coloured4 ,we notice the way in which the whole of the fragments are bound together--say1 by some opaque mineral such as iron--or whether they seem to be partially or wholly fused together4 ,in the case of a vitrified brick1 the latter phenomenon is most usual1 and we shall find that although crystalline fragments have been melted1 or partially fused1 there is commonly a centre or nucleus of each fragment in its original condition remaining1 which passes through insensible gradations from the crystalline to the non-crystalline1 or amorphous state4 ,this latter circumstance may be ascertained by using the polariscope4 ,ignoring the opaque matter adverted to1 we shall then see that what was transparent in ordinary light appears1 for the most part1 to be opaque in polarised light4 ,those portions which still let the light through are truly crystalline1 and by revolving the stage we notice that they frequently change tint1 becoming alternately light and dark4 ,in that brick where the particles are agglutinated by igneous fusion1 we shall observe the light decreasing in intensity from the crystalline portion 7forming the nucleus1 as it were1 of each particle7 outwards1 and where the crystal fragment has been melted1 so as to become fused to its neighbour1 the periphery1 or rather what was originally the boundary of the fragment1 is quite dark4 ,polarised light cannot pass through non-crystalline matter1 and in being melted that portion of the crystal fragment had passed from the crystalline to the non-crystalline stage4 ,it is very easy1 therefore1 to determine how far the fragments composing a vitrified brick have been melted down and fused together2 but to observe the phenomena under the most favourable conditions1 the brick must be thoroughly well-burnt1 and the section taken1 by preference1 from near the outside surface of the brick4 ,in some instances1 partial fusion is so well exemplified 7especially in bricks from fairly pure china clay71 and the brick1 after being burnt1 has been permitted to cool so slowly1 that devitrification has set in1 when we are presented with aggregates of crystallites closely resembling the 8felspathic matter0 of petrologists4 ,that is a circumstance which the maker should note well1 for he has burnt the brick to the best advantage1 and it is not then so brittle as it might have been had more 8glass0 made its appearance in the section4 ,prolonged heat1 just above the agglutinating point1 has accomplished this1 and the microscope here clearly shows the advantage of allowing the kiln to cool slowly1 and to permit the lapse of several days in the operation4 ,,chapter ,,xii4 ,,the ,,micro-,,structure ,,of ,,bricks 7,continued74 ,turning now to the actual appearance of minerals commonly found in bricks as they are examined under the microscope1 we may remind the reader1 that the physical aspect of the majority of them has already been described in those chapters dealing with the 8,mineral ,constitution of ,brick ,earths0 and 8,minerals3 their behaviour in the ,kiln10 and the particulars that follow may be read in conjunction with what was there said4 ,it will be convenient now to describe the appearance of certain well-known minerals1 as they are seen 7,a7 in reflected light and 7,b7 in thin sections in transmitted light1 whilst the latter will be subdivided into #a denoting the phenomena observed in ordinary light1 and #b in polarised light4 ,to save repetition1 the letters and figures will be used to denote the methods of examination as indicated4 ,,quartz4--,present in nearly all rubber-bricks1 and in the vast majority of common stocks1 as well as in vitrified goods and fire-bricks4 ,in the last mentioned1 the grains are usually partially agglutinated1 and are extremely minute4 ,a4 ,as more or less rounded1 or sub-angular fragments1 white and crystalline1 like clear window glass4 ,b4 #a--;,clear white1 often broken up by thin hair-like lines running in various directions1 and rows and patches of minute specks1 which1 as previously remarked1 have been shown to contain fluid1 c4 #b--,on revolving the stage of the microscope1 the crystals are usually seen to present beautiful1 clear transparent colours1 which in characteristic sections are very vivid--red1 blue1 yellow1 c4 ,,flint4--,found in the same class of bricks as quartz4 ,a4 ,bluish horn colour2 irregular fragments and splinters4 ,b4 #a--,translucent2 often melted more thoroughly than quartz in hard burnt bricks2 colourless4 #b--,opaque unless in some such form as chalcedony1 when an extremely minute granular aspect results1 becoming slightly transparent4 ,melted portions always opaque4 ,,felspar4--,the alteration which the different kinds of felspar have undergone in a hard burnt brick1 when present1 render it almost impossible to recognise them specifically4 ,a4 ,milk white1 or more rarely light pink2 the mineral1 even when red in the raw earths1 becomes white on the application of moderate heat1 as in the burning of common bricks4 ,it is often closely fractured1 and but rarely powdered4 ,b4 ,the characteristic parallel lines of the triclinic varieties may often be observed1 especially in rubber bricks2 but great heat1 such as leads to partial peripheral fusion1 frequently obliterates them to a large extent1 and in a well-burnt brick it is quite impossible in the majority of cases to determine whether the felspars present are triclinic or monoclinic4 ,more particularly is this the case when the mineral has been more or less decomposed prior to its having been burnt4 ,the bulk of the fragments of the mineral can only be alluded to in the general term 8felspars10 and in ordinary light these are opaque or 8fleecy10 whilst in polarised light minute portions may be found to be slightly birefringent4 ,in a decomposed state it forms a prominent constituent of brick-earths in the first place1 and that is precisely the material which most readily agglutinates in presence of a suitable flux4 ,crystallites are not uncommon in the melted peripheries1 as may be seen in a hard-burnt brick in ordinary light4 ,,mica4--,in minute flakes1 shining1 or glistening1 and commonly black1 silvery or bronze-coloured4 ,a4 ,detected at once by its thin shining scales1 which frequently have not suffered much in the kiln except near the outside of the brick4 ,b4 #a--,the darker micas are usually citron coloured or light brown1 and unless cut parallel to the cleavage of the mineral1 exhibit a number of closely-set parallel lines1 the fragments being much 8frayed out0 and 8ragged0 at the edges4 #b--,using one nicol only1 the mineral changes from dark to light on the revolution of the stage1 and is said 7in common with other minerals exhibiting a similar property7 to be dichroic4 ,with both nicols in position but little further difference is noted1 except that in changing tint the whole is darker4 ,vivid colours are not observed except in yellows and browns4 ,muscovite mica is often quite white and transparent4 ,,iron4--,common except in white bricks made from the purest china-clays4 ,a4 ,brown or reddish-brown specks2 sometimes as blue black films in fire-bricks2 dull and frequently powdery in common bricks4 ,surrounding1 film-like1 grains of mineral matter of which the brick is composed4 ,a grain of quartz1 for instance1 is frequently seen enveloped by a film of red iron4 ,other metallic iron is more lustrous and whiter than magnetite when seen in reflected light1 but such unaltered particles of the mineral could only occur in a brick that had not been subjected to great heat4 ,b4 ,opaque either in #a or #b4 ,,iron ,,pyrite only occurs as such in bricks that have not been thoroughly burnt1 or in common 8baked0 bricks4 ,higher temperatures lead to the separation of the iron from the sulphur and the general incorporation of both in the agglutination of the brick during partial fusion4 ,a4 ,brassy yellow particles4 ,b4 ,opaque both in #a and #b4 ,,calcite4--,not found in burnt bricks1 nor indeed in any except those that have been sun-dried1 or have been subjected to very little heat4 ,small pellets of lime are of common occurrence in poorly-burnt bricks4 ,in reflected light such pellets are generally of a dirty white tint2 opaque in transmitted light4 ,,dolomite4--,practically the same observations apply as to calcite1 crystals of dolomite not being found except in sun-dried bricks and the like4 ,under the action of much heat the mineral1 like calcite1 is reduced to lime4 ,,selenite4--,this is not rare in the commoner class of bricks1 though the application of much heat reduces it to the state of powder4 ,in reflected light it is found to be present as extremely minute specks or 8tears0 of whitish powdery plaster4 ,opaque1 of course1 in transmitted light4 ,the description of the micro-appearance of many other minerals which occur but rarely in bricks does not fall within the scope of the present elementary treatise2 for practical purposes they may be ignored4 ,,chapter ,,xiii4 ,,absorption4 ,the advantage of knowing the relative absorptive capacity of bricks has been stated in these pages in divers connexions4 ,the means of arriving at the total capacity for absorption of water1 as generally practised by experimenters1 are very incomplete and founded on an erroneous principle4 ,it is admitted by all that absorption is one of the very best tests as to the quality of a brick1 but such tests are meaningless unless they imitate one or other or several of the influences to which the brick would be subjected on being used in the building1 or other structure4 ,a common method is to weigh the brick when dry and then to immerse it in water for periods varying from one to three days1 subsequently re-weighing it1 the difference in weight between the dry and wet states being termed the brick's 8absorptive capacity40 ,mr4 ,heinrich ,ries remarks#af that the absorption is determined by weighing the thoroughly dry samples1 immersing in clean water from #dh to #gb hours1 then wiping dry and weighing again4 ,vitrified bricks should not show a gain in weight of over #b per cent4 ,there are cases where bricks of apparently good quality shew a greater absorption than this1 but they have great toughness and refractory qualities4 ,bricks made from fire-clays which will not vitrify so easily will1 naturally1 show higher absorption4 ,again1 ,mr4 ,e4 ,s4 ,fickes1 of ,steubenville1 ,ohio1 has recently made#ag a large series of valuable tests of both paving and building bricks1 in which he shews the connexion between the power of absorption and the strength of the materials experimented with4 ,mr4 ,fickes' more important conclusions are3-- #a4 ,the strength of the building brick1 both transverse and crushing1 varies in tolerably close inverse ratio with the quantity of water absorbed in twenty-four hours4 ,the strongest bricks absorb the least water4 #b4 ,good building bricks absorb from #f to #ab per cent4 in #bd hours1 and with no greater absorption than #ab per cent4 will ordinarily show from #g1jjj to #aj1jjj or more pounds per square inch of ultimate crushing strength4 #c4 ,poor building bricks will absorb one-seventh to one-fourth of their weight of water in #bd hours1 and average a little more than one-half the transverse and crushing strength of good bricks4 #d4 ,an immersed brick is nearly saturated in the first hour of immersion1 and in the remaining #bc hours the absorption is only five-tenths to eight-tenths of #a per cent4 of its weight1 as a rule4 ,these experiments are of much interest and are probably approximately correct2 but we venture to think that if the absorption experiments had been carried out in a different manner1 the results would have been still more valuable4 ,long before the publication of the results of the last mentioned series of experiments1 the present writer had discovered the close connexion which subsists between the relative absorptive capacity of bricks and their strength2 a slight correction must be applied for specific gravity4 ,we are not prepared to enter into this subject at any length1 but it may be observed that we should not have arrived at such close results had we experimented in the same way as the ,american authors just quoted 7or others1 for the matter of that74 ,when you completely immerse a brick in water you prevent the escape of air to a very large extent from the pores in the interior of the brick4 ,an old-fashioned way of overcoming this difficulty1 was to place the brick in the receiver of an air-pump and exhaust the air1 subsequently immersing the brick4 ,this latter method certainly possessed the merit of enabling the experimenter to arrive at total absorption very rapidly1 but it did not imitate natural processes any more than does the thorough immersion of the brick in water4 ,a writer in the ,builder of ,may #beth1 #ahie1 p4 #cig1 experimented as follows3--,the bricks were placed in water in a large vessel1 on edge1 supported where necessary by flat blocks1 to bring the uppermost face of each brick about -inch above the surface of the water4 ,experience had shewn that by completely immersing a brick1 the air did not get an opportunity of escaping from its pores with the same facility as when one surface was left out of water4 ,this disability1 it was found1 materially impaired the results of the rate of absorption 7rate1 as well as total tests1 being carried out74 ,by arranging the experiments in the manner described1 there can be no doubt that each brick absorbed the maximum quantity of water possible2 at any rate1 there was no water-pressure from above to retard the expulsion of the air4 ,the tests in the last-mentioned case extended over one week1 the relative absorption being taken at intervals of #a second1 #a minute1 #cj minutes1 #a day1 and at the end of the week4 ,it was found that ,english vitrified bricks absorbed from #a4af to about #a4he per cent4 in one week2 white glazed and good red and blue facing bricks from #e4ca to #aj4cd per cent4 in one week2 wire cut facers and rubbers1 with white gaults1 imbibed as much as from #ab4ic to #bj4ej per cent4 of their dry weight in one week4 ,the rate of percolation suggested many interesting problems1 not the least important being the effect of chemical decomposition in prolonged immersions1 whereby after being quiescent for a few days 7after taking in the water for a few hours71 absorption 8burst out0 again and continued to the end of the week4 ,one thing is very apparent from this1 namely1 that for the lower grade brick even an immersion for one week is not sufficient for practical purposes4 ,the writer remarks1 8some of the red bricks from ,bracknell1 being placed in the vicinity of the white gault bricks 7in the water71 discoloured the latter to such an extent as to disfigure them4 ,it was not merely a surface colouration2 it extended to at least -in4 into the interior4 ,the red colouring matter was iron1 but there was not enough of it by weight dissolved to materially interfere with the experiments4 ,this very clearly shews1 however1 the folly of erecting a building coursed with white and red bricks1 when both are very absorbent and the red has so little hold of the iron of which it is partly composed--unsightly stains are bound to appear40 ,this question of the solubility of certain ingredients of bricks1 has not received the attention it deserves2 and closely connected with that is gradual decomposition1 whereby the brick becomes more and more porous--a potent factor in its ultimate destruction4 ,,chapter ,,xiv4 ,,strength ,,of ,,bricks4 ,a very great deal is known concerning the strength of bricks4 ,in addition to the innumerable experiments carried out by public bodies1 we have the results of painstaking investigation by professors in universities and colleges1 and the results carried out for and published by brickmakers themselves4 ,yet another large series of results have been published from time to time by professional journals1 and it is1 indeed1 to these that we must look 7at any rate in ,britain7 for anything like detailed work4 ,the 8,minutes of ,proceedings of the ,institution of ,civil ,engineers10 the 8,transactions of the ,royal ,institute of ,british ,architects10 the 8,proceedings0 of several allied provincial architectural societies1 the 8,builder10 the 8,british ,clayworker10 builders' 8,price ,books10 and several engineering 8,handbooks10 have all contributed to our knowledge in regard to the strength of bricks4 ,of works consecrated entirely to the subject there are none--applied to ,british materials2 but we have that excellent text-book by ,professor ,unwin1 ,f4,r4,s41 8,the ,testing of ,materials of ,construction10 and the important work by ,mr4 ,david ,kirkaldy1 both of the greatest possible value as being the results1 largely1 of original work4 ,the experiments of recent years have been made almost exclusively by ,mr4 ,david ,kirkaldy at his works in ,southwark2 by ,professor ,w4 ,c4 ,unwin at the ,central ,institution of the ,city and ,guilds of ,london ,institute2 and by the ,yorkshire ,college1 ,leeds4 ,with such a wealth of information a whole treatise might profitably be written1 but it will be understood that in a small work like the present we can only give a comparatively few results1 prefaced by observations to impart a general idea4 ,with the strength of brickwork1 it is different1 and it would seem rather remarkable1 at first sight1 that architects and engineers1 who are every day using thousands of bricks1 should have been at little pains to ascertain the 8safe load0 which this or that brick pier or wall would carry4 ,experience is1 of course1 of great value in all work of that description2 but there is always the lurking suspicion that the engineer is making his piers too big1 and that the architect is by no means running the thing close4 ,the real reason why so little has been done to test the strength of brickwork is the difficulty in getting machines of such capacity as would crush sufficiently large masses4 ,small piers have been built from time to time1 and bricks embedded in putty for mortar have served their purpose1 but practically nothing of a really serious nature was carried out in ,britain until a few months ago4 ,the science committee of the ,institute of ,architects1 well knowing the advantage of information as to the strength of brickwork1 have partially carried out a most elaborate series of experiments1 the first fruits of which have already been published1 but it would be out of place to allude to them here4 ,when the remaining brickwork shall have been built long enough at the experimental station1 the final experiments will be made1 and the results will1 we have no doubt1 be the most important contribution to our knowledge concerning the strength of brickwork that has ever been published in the kingdom4 ,but we must give our attention solely to the strength of bricks4 ,to begin with1 we must deprecate the idea that experiments as at present carried out give anything like the actual strength of bricks--the results are generally either too high or too low4 ,neither are the results comparative1 except to a limited extent4 ,one kind of brick has a 8frog0 on one side1 another is recessed on both sides1 a third is stamped with the maker's name1 or some device by way of trade mark1 a fourth is as flat on all sides as may be1 a fifth is pressed1 a sixth is hand made1 and a seventh wire-cut1 and there are many other varieties of make4 ,with such different kinds it is next to impossible to arrive at comparative data that shall be of much use for working purposes4 ,again1 the whole brick may be subject to the experiment1 or only the half-brick4 ,the faces placed between the dies of the crushing machine may not be flat1 and they are most frequently irregular4 ,if the dies are applied to such bricks it is evident that corners will be broken off before the brick has really suffered much1 and that to get the best result the faces must either be made perfectly true and parallel to each other1 or some other method adopted to put matters right4 ,that commonly employed is to place some yielding substance between the faces and the surface of the dies4 ,sometimes thin sheets of lead or pine wood are inserted4 ,professor ,unwin has the faces of the brick made smooth and parallel by means of plaster of ,paris1 and the brick is then crushed between two pieces of millboard or between the iron pressure-plates1 one plate having an arrangement to allow for any slight want of parallelism between the two surfaces of the brick applied to the plates4 ,now it will be obvious1 what with the difference in the shape and the various modes of experimenting1 that the results are by no means comparative unless the precise facts are given2 and when they are1 it is but rarely that you can find more than half-a-dozen or so kinds of bricks of each category that offer all the elements necessary for comparison4 ,so that1 with all the wealth of information1 we are by no means laden with much that is of actual comparative value1 and if the experiments and their results are not comparative1 of what use are they8 ,so long as experimenters are each allowed a different method of research1 and so long as makers will have partial or whole 8frogs10 will stamp their names or initials1 or will produce plain bricks only1 so long will it be impossible to arrive at the best results that are really attainable4 ,what we want is a government testing station as they have in ,germany2 or1 at least1 the mode of experimenting should be under some central control4 ,the experimenter1 further1 should select the samples to be crushed1 and should be at liberty to publish all results obtained4 ,at present1 if the brickmaker does not like the results arrived at1 he1 of course1 does not publish them4 ,and1 if he has had a number of experiments carried out from time to time1 he will1 usually1 quote only the highest results on his bricks4 ,that is perfectly natural1 and would be understood as 8business40 ,all brickmakers may not do that1 and a few may publish every or average results 7we do not mean of one set of experiments1 on say six bricks7 of different experiments1 but we fancy they are very rare4 ,therefore1 in a matter so important to the architect and the engineer1 and indeed to the general public1 from the point of view of safety1 we maintain that the whole thing should be carried out under some central control1 as on the continent4 ,and now to proceed with the description of results on a few typical bricks4 ,glancing at table ,i1 we may say that the strength of bricks as a whole is often quoted as here given1 and has done duty for many years as the average strength of bricks4 ,these bricks were crushed in a ,clayton machine1 and all were bedded upon a thickness of felt and laid upon an iron faced plate1 and the experiments were conducted by the ,metropolitan ,board of ,works4 ,,strength ,,of ,,bricks4--,i4 ---------------------------------------- --------- ,description4 ,pressure in tons to ------------------- ,crack4 ,crush4 ---------------------------------------- ------- ,four white bricks1 each #af4be #da4jj ,three #ag4je #da4je ,red bricks1 ordinary #ac4jj #bf4be ,red bricks1 not well burned #ac4ge #be4je ,best ,paviours #ad4jj #bc4jj ,grey ,stocks1 ,london #ab4jj #ad4jj ---------------------------------------- ------- ,turning to the second table1 compiled for the most part from brickmakers' circulars1 and from the original results obtained for the late ,building ,exhibition1 at the ,agricultural ,hall1 all the experiments1 we believe1 having been carried out by ,mr4 ,david ,kirkaldy1 it will be noted that great variation in strength is apparent1 following the different kinds of bricks4 ,the highest result1 #ajfd4b tons per square foot1 was obtained on a blue ,staffordshire brick1 though that is very closely run by bricks made from slate dbris 7#ajef4b tons7 from ,south ,wales4 ,the lowest result1 #aci4e tons per square foot1 was from a ,worcester brick4 ,,strength ,,of ,,bricks4--,,ii4 ---------------------------------------- --------------------------------- ,mean stress of ,dimensions1 six samples in ,locality4 ,description4 ,inches4 tons per square ft ----------------- ,cracked ,crushed ---------------------------------------- -------------------------------- ,west ,bromwich ,blue #b4gd1 #i4jc #d4cf #edh4f #ajfd4b ,blue 7another #b4hj1 #h4ge #d4ab #bfj4g #fea4j make7 ,white glazed1 8,terra ,metallic10 #c4aj1 #h4hj #d4bb #bbe4j #bgc4g recessed #c4af1 #h4gj #d4cd both sides ,blue vitrified #b4ee1 #i4jc #d4cj #bde4a #fed4i 8,pressed10 ,worcester recessed top #c4bj1 #i4ad #d4ej #fe4j #aci4e and bottom 8,builders40 recessed top #c4bj1 #i4cj #d4ej #ef4a #aee4e and bottom ,saltley1 ,red1 recessed #c4bj1 #h4ij #d4ce #ach4g #ahj4e ,birmingham one side #c4be1 #h4ie #d4dj ,rowley ,regis1 ,blue vitrified #b4he1 #h4ge #d4bj #che4f #gbb4g ,staffs4 no recess ,leicester ,red1 recessed #b4fe1 #h4ij #d4be #aje4i #aej4f both sides #b4ge1 #i4aj #d4cf ,napton-on-the-,hill1 ,light brown1 #b4he1 #h4ib #d4bj #aca4f #cjc4i ,rugby wire cut #b4ij1 #i4aj #d4be ,ruabon ,red1 no #c4aj1 #h4ge #d4bh #dci4b #fgf4h recess #c4ae1 #h4gc #d4bi ,blue1 no #c4jb1 #h4ii #d4cg #ceh4i #efa4b recess #c4ja1 #h4ie #d4cf ,glogue1 ,whitland1 ,slate dbris #b4cc1 #h4gj #d4be #eef4d #ajef4b ,s4 ,wales ,ravenhead1 ,st4 ,red1 brown #b4ij1 #i4jj #d4bj #bae4h #ced4g ,helens1 ,lancs4 wire cut #b4ij1 #h4ij #d4bg ,earith1 ,st4 ,ives1 ,yellow1 wire #b4ej1 #h4gj #d4aj #ace4i #agh4h ,hunts4 cut #b4ej1 #h4hj #d4bj ,gillingham1 ,dorset ,red1 wire cut #b4fj1 #h4ij #d4cj #aei4e #bfa4g #b4fj1 #h4ij #d4be ,newton ,abbot1 ,vitrified #b4hj1 #h4ij #d4ce -- #dde4b ,devon 8granite0 #b4hj1 #i4aj #d4ee ---------------------------------------- -------------------------------- ,table ,,iii4 is by ,professor ,unwin1#ah and records the strength of several well-known bricks4 ,professor ,unwin's mode of experimenting we have already alluded to4 ,,strength ,,of ,,bricks4--,,iii4 ---------------------------------------- -------------------------------- ,cracked1 at,crushed at ,description4 ,dimensions4 tons per tons per ,colour4 ,remarks4 ,inches4 sq4 ft4 sq4 ft4 ---------------------------------------- -------------------------------- ,london stock #d4f #d4a #b4d #abh #agg ,yellow ,half brick #d4f #d4j #b4de #acc #aha #i4b #d4a #b4h -- #abi #h4i #d4b #b4c -- #aac #h4i #d4be #b4e -- #ajc ,aylesford1 #h4i #d4d #b4g #dh #ahc ,pink common #h4i #d4d #b4g #aaa #bbh pressed#i4a #d4c #b4g #ga #ada ,red ,deep frog ,rugby1 common #i4e #d4b #b4i #aeh #aij ,between #i4j #d4b #c4j -- #abj pine bds4 ,lodge ,colliery1 ,notts #i4j #d4b #c4d #abg #aei #i4j #d4b #c4be #ee #abb ,digby ,colliery1 ,notts #i4c #d4a #c4be #bdh #cec ,not crushed #d4f #d4b #c4b #dad #dad ,half brick ,ruabon1 pressed#h4h #d4c #b4g #cfa #cfa ,not crushed ,grantham1 wire #i4b #d4d #c4b -- #hc cut ,leicester1 #d4d #d4a #b4f #bea #ccg ,pale red,half brick #d4c #d4a #b4f #aji #cjh #i4jf #d4b #b4h #aae #bbi ,cranleigh1 #d4g #d4f #b4e #adi #aha ,half brick pressed frog4 #d4f #d4f #b4e #afe #bcg ,candy1 pressed #h4h #d4c #b4h #hj #cha -- ,gault1 wire cut#h4g #d4a #c4j #aaa #agc ,white #d4d #d4b #b4e #aai #ade ,half brick #h4g #d4a #b4i -- #afi ,staffordshire blue1 common #d4e #d4c #c4j #baf #dfd ,blue #d4c #d4b #c4j #aeb #chf #h4i #d4c #c4a #bdj #cec ,not crushed ,staffordshire blue1 pressed#i4j #d4c #c4a -- #bge ,glazed brick #h4h #d4d #c4c #fi #aff -- ,frog4 #h4i #d4d #b4i #aff #agd -- ---------------------------------------- -------------------------------- ,table ,no4 ,,iii4 is specially instructive as indicating the relative strength of several well-known bricks1 the experiments being carried out solely for scientific purposes4 ,yet the figures must not be taken too seriously4 ,glancing at those relating to 8,london ,stocks10 we find the strength varied from #ajc tons per square foot to #aha tons4 ,but more recent experiments made by ,professor ,unwin#ai on some ,london ,stocks from ,sittingbourne1 in ,kent1 shewed that with four samples one crushed at #fj4gf tons per square foot and another gave out #id4f tons1 the mean strength of the four yielding #hd4bg tons per square foot4 ,with such heterogeneous materials as ,london ,stocks1 we ought not to be surprised at these results1 but they form a striking commentary on the value of general statements concerning the strength of bricks of varied character going by the same name in the market4 ,when we consider the strength of homogeneous bricks1 and especially where these latter are made of thick marine clays1 or where the relative proportions of earths employed are carefully attended to in the raw material1 the results appear to be more generally applicable--as far as they go4 ,with ordinary ,gault bricks we find a range in strength from #ade tons to #agc tons per square foot2 but ,professor ,unwin1#bj in his more recent experiments1 finds that of four ,gault bricks1 one reached as high as #aig4f tons per square foot1 and he gives #ahb4b tons as the average strength4 ,to shew the absurdity of alluding to the strength of 8blue ,staffordshire0 bricks1 without also giving the precise locale of the samples dealt with1 the reader is requested to refer to ,table ,,iii41 where the figures indicate a range from #bge tons to #dfd tons per square foot1 and to compare them with the results on ,staffordshire bricks as stated in ,table ,,ii41 where we find a range from #fea tons to #a1jfd4b tons per square foot4 ,of what value can a single formula be which gives the strength of ,staffordshire bricks as a whole as based on such widely divergent figures as these8 ,professor ,unwin1 in his recent series of experiments alluded to1 finds that with four ,staffordshire blue bricks1 the weakest gave a result of #efd4h tons per square foot1 and the strongest #ghh tons2 the mean of the four being #gja4a tons per square foot4 ,the results on the ,leicester 8reds0 are no more encouraging2 the figures in the foregoing tables are #aej4f tons1 #bbi tons1 #cjh tons1 and #ccg tons per square foot4 ,similarly1 ,professor ,unwin has more recently found that the ,leicester 8reds0 from ,elliston1 near ,leicester1 bear a crushing strain varying from #caa4d tons to #eia4d tons per square foot in four samples4 ,from the foregoing it will appear to the reader that average results are of very little value to the architect or engineer1 unless--7#a7 the brickyard is mentioned from which the bricks experimented with came2 7#b7 the particular class of brick from that yard2 7#c7 the method of experimenting1 as to whether any substance was placed between the dies of the press and the brick to be crushed1 and if so1 what2 7#d7 if recessed or initialled2 7#e7 whether machine or hand made1 and 7#f7 as to whether the surfaces of the bricks were concave1 convex1 or flat4 ,results on bricks not localised are not of much value1 and it is absolutely useless for working purposes to give in one figure the strength of 8,london ,stocks10 8,staffordshire blues10 8,leicestershire reds10 and the like4 ,in a general way1 of course1 it will be admitted that the 8,staffordshire blue0 is a stronger brick than the 8,london ,stock10 and so forth2 but that is as much as can be permitted--it is of no practical use to give relative figures in general terms4 ,it frequently happens that the capacity of the machine used for testing the strength of bricks is not enough for those bricks having a very high resistance to crushing4 ,in the recent experiments by ,professor ,unwin1 more than once alluded to in this article1 it was found necessary to experiment with half-bricks only1 and he ascertained that bricks tested as half-bricks shew about #be per cent4 less resistance per square foot than when tested as whole bricks4 ,further observations on strength are made under the next heading in connexion with other forms of testing the value and physical properties of bricks4 ,,chapter ,,xv4 ,,abrasion1 ,,specific ,,gravity4 ,abrasion4--,in this country it is not customary to test bricks and stone by means of the abrasion process1 though many ,english materials have been dealt with in this manner on the continent4 ,abrasion tests are of special value in regard to paving bricks1 and this mode of experiment is largely carried out in the ,united ,states4 ,as ,mr4 ,h4 ,ries remarks1#ba the abrasion test approximates closely the conditions under which the paving brick is used1 and is1 therefore1 an important one4 ,the usual method of conducting this test is to put the bricks in an ordinary 8foundry rattler10 filling it about one-third full4 ,it is then rotated at the rate of about #cj revolutions per minute1 and about #a1jjj turns are sufficient4 ,the bricks are weighed before and after to determine loss by abrasion4 ,a more recent modification is to line the 8rattler0 with the bricks to be tested and then put in loose scrap iron4 ,this is claimed to give more accurate results1 and avoids loss by chipping due to the bricks knocking against each other1 as in the previous method1 although that has been somewhat obviated by ,professor ,orton1 jun41 by the introduction of a few billets of wood into the rattler4 ,the abrasion test may also be made by putting the weighed bricks on a grinding table covered with sand and water1 and noting the weight before and after grinding4 ,this last method seems to us to be decidedly the best1 provided the bricks be weighted1 that the weight is constant1 that the feed of sand and water is uniform1 and that the bricks to be tested are placed equidistant from the centre of the turning table4 ,if this last point be not attended to1 it will be obvious that in course of the revolutions the sand will tend to accumulate towards the centre of the table1 and the bricks placed in that vicinity would receive more than their fair share of abrasion1 as compared with those bricks situated near the edge of the table4 ,conversely1 those bricks near the periphery would be subjected to greater grinding action1 from the circumstance that the table would move faster underneath them than under those bricks nearer the centre of the table4 ,the bricks should certainly be weighted in such abrasion tests1 and it seems desirable that the weights should be so adjusted that the weight of the brick is also taken into account4 ,it is obvious that the abrading action of1 say1 street traffic1 will be the same on a brick1 no matter what the latter weighs1 depending on the area of surface exposed to traffic4 ,and if we experiment with one brick1 weighing say #g lbs41 and another weighing #ad lbs41 the greater weight of the latter1 will 7cteris paribus71 by the abrasion tests as usually adopted1 give a much higher result than would the lighter brick4 ,on the other hand1 if the #g lbs4 brick be weighted another #g lbs41 then the results would be strictly comparable1 provided always that the area exposed to abrasion in each case be the same1 and that the other conditions we have laid down are strictly observed4 ,knowing as we do that the rough and ready method of 8rattling0 cannot possibly give truly comparative results1 we do not intend to enlarge much on the results of the ,american tests2 but the following are suggestive as shewing the connexion between the tests for absorption1 rattling1 and strength combined4 ,some valuable and interesting tests were recently made by the ,ohio ,geological ,survey1 to determine the relative merits of fire-clays and shales for the manufacture of paving bricks1 as well as the influence1 if any1 of the method of manufacture adopted4 ,twenty-two varieties of shale bricks1 or bricks the largest constituent of which is shale1 were grouped together3 fifteen varieties of fire-clay brick2 four varieties composed of shale and fire-clay mixed in equal proportion2 and three varieties made from ,ohio ,river sedimentary clays4 ,the averages of these four classes of results were as follow3-- ---------------------------------------- ---------- ,,tests ,,of ,,fire-,,clay ,,and ,,shales4--,,paving ,,bricks4 ---------------------------------------- ------- ,absorption4,rattling4 ,crushing4 ------------------------------------ ,square ,cubic ,inches4 ,inches4 ---------------- ,shales #a4ag #ag4fa #g1cjg #a1gfd ,fire-clay #a4fb #ag4cb #f1hgf #a1fgh ,mixture #a4dd #ah4gb #e1ghh #a1djj ,river ,clay #a4cf #ai4jb #d1fje #a1agf ---------------------------------------- ------ ,from a series of tests recently made by ,mr4 ,fickes1#bb the following factors were educed3-- #a4 ,a brick which stands the 8rattling0 test well1 has ample crushing strength and rarely chips under less than #e1jjj lbs4 per square inch1 or crushes under less than #aj1jjj lbs4 ,the crushing strength tends to vary with the resistance to abrasion1 however1 but more slowly and irregularly4 #b4 ,the transverse strength also tends to vary with the resistance to abrasion1 but more slowly and irregularly4 #c4 ,the toughest bricks usually absorb the least water4 ,specific ,gravity4--,the practical value of knowing the specific gravity of a brick has1 perhaps1 been a little over-rated by writers on the subject4 ,at the same time we do not deny that there is some use in ascertaining this property4 ,foremost1 we have to mention its value in conjunction with absorption in arriving at a rough and ready means of gauging the strength of a brick1 without having actual recourse to the crushing machine4 ,it appears to us1 however1 that the specific gravity of bricks is rarely quoted in a proper manner1 and until there is one uniform method1 the results will always be at a discount4 ,we allude to the fact that some experimenters take the specific gravity of a porous brick1 without stating whether the amount of water absorbed1 during the process1 was taken into account in arriving at the specific gravity or not4 ,theoretically1 of course1 the substance to be dealt with is non-porous1 and experimenters1 worthy the name1 either render the brick waterproof1 or1 ascertaining the amount of water the brick has absorbed1 take that into consideration in calculating results4 ,the writer is in the habit of quoting the specific gravity in two ways1 viz43 7a7 the true specific gravity1 and 7b7 the specific gravity of the particles4 ,in an elementary treatise like the present1 however1 it is not desirable to enlarge on this subject4 ,,the ,,end4 ,,footnotes #a ,this1 and all other technical terms used1 will be explained in an alphabetical glossary at the end of the book4 #b 8,canal and ,river ,engineering10 p4 #cae4 #c ,see1 ,geikie's 8,text ,book of ,geology10 #ahhb1 p4 #gb4 #d ,information on this subject will be found in ,mr4 ,j4 ,h4 ,collins' work1 8,the ,hensbarrow ,granite ,district40 ,truro1 #ahgh4 #e 8,text ,book of ,geology10 #ahhb1 p4 #he4 #f 8,aids in ,practical ,geology10 #ahic1 page #cf4 #g ,see ,e4 ,s4 ,dana1 8,minerals and ,how to ,study ,them10 #ahie1 p4 #aed4 #h ,consult 8,applications of ,geology10 etc41 by ,prof4 ,ansted1 #ahfe1 p4 #aaf1 et seq4 #i 8,industrial ,resources of the ,tyne1 ,wear and ,tees10 #ahfd1 p4 #bjd4 #aj ,r4 ,h4 ,scott1 8,elementary ,meteorology10 #ahhc1 p4 #acg4 #aa ,report of ,british ,association for #ahdf1 ,part ,,ii41 p4 #ag4 #ab ,geological ,magazine1 ,n4,s41 ,dec4 ,,iii41 ,vol4 ,v1 #ahhh1 pp4 #bf et seq4 #ac ,such as 8,the ,study of ,rocks10 by ,f4 ,rutley3 8,aids in ,practical ,geology10 by ,prof4 ,grenville ,cole2 8,tables for the ,determination of the ,rock-forming ,minerals10 by ,prof4 ,lwinson ,lessing2 8,petrology for ,students10 by ,a4 ,harker2 and especially 8,microscopic ,physiography of the ,rockmaking ,minerals10 by ,rosenbusch 7transl4 ,iddings74 #ad ,consult the works on petrology previously mentioned4 #ae ,the mode of preparation of thin rock sections for examination by the microscope is described in much detail in the works of ,mr4 ,rutley and ,professor ,cole previously alluded to2 also in 8,outlines of ,field ,geology10 by ,sir ,archibald ,geikie1 #ahhb1 p4 #bjb et seq4 #af #afth ,ann4 ,rep4 ,u4 ,s4 ,geol4 ,surv4 7#ahid-ie71 pt4 ,,iv41 p4 #ecb4 #ag #afth ,ann4 ,rep4 ,u4 ,s4 ,geol4 ,surv4 7#ahid-ie71 pt4 ,,iv41 p4 #eci4 #ah 8,testing of ,materials of ,construction10 #ahhh1 p4 #dch4 #ai ,british ,clayworker1 ,april1 #ahif1 ,supplement1 p4 iv4 #bj ,op4 cit4 p4 iv4 #ba #afth ,ann4 ,rep4 ,u4,s4 ,geol4 ,surv4 ,pt4 ,,iv41 #ahie1 p4 #ecb4 #bb ,engineering ,news 7,u4,s471 ,dec4 #acth1 #ahid4 ,,index1 c4 ,abrasion tests1 #adf ,absorption of bricks1 #acb ,acids defined1 #gf ,actinolite1 #fi ,air1 chemical composition of1 #aje ,albite felspar1 chemical composition1 #cd ,almandite1 #fh ,aluminium1 under blowpipe1 #gc ,anorthite felspar1 chemical composition1 #cd ,aragonite1 #di ,bases defined1 #gf ,basic bricks1 #ij dolomite for1 #ee magnesite for1 #ef ,biotite mica1 #dc under blowpipe1 #gc ,black bricks1 #aja ,blowpipe1 #eh ,blue bricks1 #aja ,bluish-black brick-earths1 #bg ,boulder clay1 #ej ,bourges1 ,oxford clay of1 #bd ,bovey ,heathfield clays1 #bj ,bracknell bricks1 #ace ,brick earths1 artificial mixing1 #db artificial mixtures1 #id1 #ie bluish-black1 #bg boulder clay1 #ej brown1 #bg chalk pebbles in1 #ej changes in character on being dug into1 #b1 #e1 #aj chemical composition of1 #bc1 #eb1 #hc1 #hd1 #he chemistry of1 #eh1 #ge chert in1 #da1 #db coprolites found in1 #ea ,cornwall1 #ce ,crayford1 #a ,devon1 #ce ,erith1 #a estuarine1 #ba fluviatile--,chapter ,i41 #a-af fossil shells in1 #ej ,ilford1 #a ,kimeridge clay1 #bf lacustrine--,chapter ,,ii41 #ag-ba ,lincolnshire1 #ba ,london clay1 #cc marine1 #bb mineral constitution1 #bh minerals found in 7see ,kaolin1 ,felspar1 ,quartz1 ,flint1 ,mica1 ,iron1 ,calcite1 ,aragonite1 ,selenite1 ,dolomite1 ,salt1 etc474 ,northamptonshire1 #ba ,north-,eastern ,france1 #bj ,oxford clay1 #cc ,reading mottled clay1 #ai of river terraces1 #ab salt in1 #be sea-shore1 #be section of fluviatile brick-earths1 #aj several kinds of fluviatile1 discussed1 #ad1 #ae ,switzerland1 #hi ,thames ,valley1 #a1 #b1 #c1 #d1 #e value of chemical analyses of1 #bh1 #bi ,brickmaking3 earths suitable for 7see ,brick-earths7 ,bricks1 abrasion tests1 #adf absorption of1 #acb basic1 #ij ,bracknell1 #ace colour of1 #ajj ,dinas1 #ha discolouration of1 #aad durability of1 #ajc effect of conflagrations on1 #aag efflorescence on1 #aaj ,london stock1 #ig micro-structure of1 #bi1 #aah1 #abh rubber1 #bi specific gravity1 #adf1 #adi ,staffordshire blue1 #ii ,stourbridge1 #hb strength of1 #acf vegetable growth on1 #aac weathering of1 #aje1 #aac ,british ,museum1 fossils in1 from brick-earths1 #c1 #bf ,bronzite1 #fi ,brown brick-earths1 #bg ,burning bricks1 #id changes produced by1 #ih temperature1 #hi ,calc spar1 #di ,calcite1 #ci1 #di behaviour in kiln1 #ci micro-structure of1 #aca under blow-pipe1 #gd ,californian magnesite1 #ef ,carbon dioxide in quartz1 #da ,carbonate of lime 7see ,calcite1 ,aragonite7 ,chalk in brick-earths1 #a mixed with brick-earths1 #ec pebbles in brick-earths1 #ej ,chateauroux1 ,oxford clay of1 #bd ,chemical affinity1 #gf analyses of brick-earths1 #bh analysis1 #gg composition of air1 #ajf composition of brick-earths1 ,dinas1 #eb composition1 china clays1 #gh composition of fire-clays1 #hj composition of ,kieselguhr1 #ib composition of magnesian limestones1 #ij composition1 pottery clays1 #hb composition of slates1 #hg disintegration of rocks1 #bj re-agents1 #fj1 #fc1 #ga ,chemistry of brick-earths1 #eh1 #ge ,chert1 #da ,cheshire1 salt in clays in1 #be ,china-clays1 behaviour in the kiln1 #cf chemical composition1 #gh ,cornwall1 #ce1 #cf1 #cg ,devon1 #ce ,china-clay 7see ,kaolin and ,felspar7 thickness of1 #ch ,china-stone1 decomposed1 #cg ,colour in the kiln1 #ih1 #ii ,colouring matter of bricks1 #de of bricks1 #ec ,colour of bricks 7see ,blue1 ,black1 etc474 ,coprolites3 impure varieties of phosphate of lime found in brick-earths1 #ea ,cornish granite1 #ce ,cornwall1 china-clays1 #ce1 #cf1 #cg ,cracks formed in bricks1 #eb ,crayford1 brick-earth at1 #a ,dartmoor granite1 #ee ,denudation1 agents of1 described1 #f1 #g of sea-cliffs1 #bb ,devon1 china-clays1 #ce ,diatomaceous earth1 #db1 #ia ,dinas bricks1 #eb1 #ha ,discolouration of bricks1 #aad1 #ace ,dolomite in brick-earths1 #ee micro-structure of1 #aca under blow-pipe1 #gd ,drying bricks1 #id ,durability of bricks1 #ajc ,efflorescence on bricks1 #aaj ,electric furnace1 #cc ,elephants' remains1 found in brick-earth1 #b1 #c ,erith1 brick-earth at1 #a ,estuarine brick-earths1 #ba ,expansion of bricks and variations of temperature1 #aae ,felspar1 #cd chemical composition of1 #cd micro-structure of1 #abi under blow-pipe1 #gc ,ferruginous matter 7see ,iron7 ,fire-bricks1 ,dinas1 #eb earths suitable for making1 #ba effect of lime in1 #ec ,kieselguhr for1 #db1 #ia strength of1 #acf ,fire-clays1 chemical composition of1 #hj1 #ha ,newcastle-on-,tyne1 #hj tests1 #adh ,welsh localities1 #ha ,fishes1 fossil1 #be ,flint1 #ci1 #da behaviour of in the kiln1 #db1 #dc implement3 an implement1 or tool1 made of flint--in the sense indicated in this work an implement made by pre-historic man4 implements1 found in brick-earths1 #c1 #e micro-structure of1 #abi origin of1 #da ,fluid inclusions in quartz1 #da ,fluorine in clays1 #ei ,fluviatile brick-earths3 brick-earths that have been deposited in rivers ,fossil shells1 carbonate of lime in1 #ej shells found in brick-earths1 #d sponges1 in flint1 #db ,fusion of brick-earths in the kiln1 #bi1 #ca ,gault clay1 #ea ,glaze1 micro-structure of1 #aai1 #abj ,glazing1 salt1 #eg ,granite1 ,cornish1 #ce ,dartmoor1 #ce ,granites1 weathering of1 #cf ,greece1 magnesite in1 #ef ,green bricks1 #aja ,grizzly bear's remains found in brick-earth1 #b ,gypsum in brick-earths1 #ed under blow-pipe1 #gd ,heat1 bricks affected by1 #aag ,hippopotamus remains found in brick-earth1 #b ,ilford1 brick-earth at1 #a ,infusorial earth1 ,tuscany1 #ib ,iron1 #dd a constituent of brick-earths1 #dd behaviour in the kiln1 #de bricks1 ,saarbrcken1 #ib micro-structure of1 #acj mode of occurrence in brick-earths1 #de under blow-pipe1 #gc1 #gd vapour in the kiln1 #df pyrites1 #df1 #aca pyrites1 behaviour in the kiln1 #dh pyrites1 under blow-pipe1 #gd pyrites1 weathering of in bricks1 #dh ,jurassic estuarine clays1 #ba ,kangaroo rats1 fossil1 #be ,kaolin3 a hydrous silicate of alumina1 derived chiefly from the decomposition of felspars ,kaolin1 #ca behaviour in the kiln1 #cb1 #cc chemical composition of1 #gh micro-structure1 #cb1 #cc under blow-pipe1 #gc 8,kaolinised0 matter1 #cc ,kilns1 temperature in1 #ih ,kieselguhr3 a diatomaceous earth ,kieselguhr1 #ia chemical composition of1 #ib of the ,isle of ,skye1 #db ,kimeridge clay brick-earth1 #bf ,labradorite felspar1 chemical composition1 #cd ,lacustrine brick-earth3 that laid down or deposited in lakes brick-earths--,chapter ,,ii41 #ag-ba brick-earths1 formation of1 #ag1 #ah ,lime1 builder's1 #eb in bricks1 #eb in manufacture of fire-bricks1 #ec ,limestone1 a flux1 #ed ,limonite1 under blow-pipe1 #gc ,lincolnshire brick-earths1 #ba ,loam3 sandy clay ,london stock bricks1 #ig1 #adj ,magnesian limestones1 chemical composition of1 #ij limestone 7see ,dolomite7 ,magnesite1 #ee behaviour in the kiln1 #ef ,californian1 #ef in ,greece1 #ef ,styrian1 #ef under blow-pipe1 #gd ,malachite1 #fg ,malm bricks1 #ec1 #hf ,manganese1 under blow-pipe1 #gd ,marcasite1 #df1 #dg behaviour in the kiln1 #dh weathering of1 #dg1 #dh ,marine brick-earths3 those laid down or deposited on the sea-floor ,marine brick-earths1 not so variable in character as river1 lacustrine1 or estuarine1 #bc brick-earths--,chapter ,,iii41 #bb-bg brick-earths1 origin of1 #bc ,marl3 clay containing much lime4 ,mica1 #dc behaviour in the kiln1 #dd micro-structure of1 #acj under blow-pipe1 #gc ,microscopes1 #aba ,microscopes1 use of1 #ei useful in analysing earths1 #cj ,micro structure as a means of determining fusibility of minerals and brick-earths1 #dc of bricks1 #aah1 #abh ,minerals1 their behaviour in the kiln 7see ,kaolin1 ,felspar1 ,quartz1 ,flint1 ,mica1 ,iron1 ,calcite1 ,aragonite1 ,selenite1 ,dolomite1 ,salt1 etc474 behaviour under the blow-pipe 7see ,quartz1 ,felspar1 ,mica1 ,calcite1 etc474 ,mississippi1 sediments of the ,delta of1 #g ,mortar and ,scum1 #aab ,muscovite mica1 #dc mica1 under blow-pipe1 #gc ,musk-sheep remains1 found in brick-earth1 #b1 #c ,natrolite1 #fh ,newcastle-on-,tyne fire-clays1 #hj ,newton ,abbot1 clays near1 #bj ,northamptonshire brick-earths1 #ba ,oligoclase felspar1 chemical composition1 #cd felspar1 under blow-pipe1 #gc ,origin of fluviatile brick-earths--,chapter ,i41 #a-af ,orthoclase1 #fi felspar1 chemical composition1 #cd felspar1 under blow-pipe1 #gc ,overburden3 the material for the most part useless1 overlying the good brick-earth1 sand1 limestone1 or other rock for which the pit or quarry was exploited1 and which1 in the majority of cases1 has to be removed to obtain the material sought for4 ,oxford clay1 #bd1 #be1 #cc ,oxidising flame1 #fe ,paving bricks1 tests1 #adh ,peterborough bricks1 #bd clays1 #ea ,plants1 fossil1 #ba1 #bf ,platinum wire1 #fj1 #fc1 #ff ,plesiosaurus1 fossil reptile1 #bf ,porcelain earths1 #cj ,pottery clays1 chemical composition1 #hb ,power of transport of sediment by rivers1 #h ,pumice for brickmaking1 #ic ,pyrite1 #df behaviour in the kiln1 #dh under blow-pipe1 #gd ,pyrometers1 #ii1 #ajj ,quartz1 behaviour in the kiln1 #ci1 #db1 #dc cavities in1 #dj1 #da characters of1 #ci imperishable1 #dj micro-structure of1 #abh occurrence in brick-earths1 #dj under blowpipe1 #gb vein1 #dj ,race3 concretions of carbonate of lime1 commonly found in brick-earths in brick-earths1 #ej ,rainfall and the durability of bricks1 #ajh 8,rattling0 tests1 #adh ,reading mottled clay1 #ah ,red brick1 #ajj ,red brick clay1 #hf ,red bricks1 colouring matter of1 #de ,reducing flame1 #fe ,refractory minerals 7see ,calcite1 ,dolomite1 ,magnesite1 ,quartz1 etc474 ,reindeer remains1 found in brick-earth1 #b1 #c ,reptiles1 fossil1 #be ,rhinoceros' remains1 found in brick-earth1 #b1 #c ,river deposits1 typical section1 #aj1 #aa ,river terraces1 brick-earths of1 #ab1 #ac ,rock crystal1 #dj ,rock salt1 under blow-pipe1 #gd ,ruabon bricks and terra-cotta1 #hd terra-cotta1 #aaf ,rubbers1 #bi1 #hf ,saarbrcken 8iron bricks10 #ib ,salt1 a powerful flux1 #eg behaviour in the kiln1 #eg glazing1 #eg in brick-earths1 #be1 #bg1 #ef in quartz crystals1 #da under blow-pipe1 #gd ,schorl1 #dj ,scum1 #aaj ,sea-shore1 brick-earths from the1 #be ,selenite1 #ed1 #aca under blow-pipe1 #gd ,septaria3 tabular or rounded concretions of argillaceous limestone1 commonly found in clays ,septaria1 #ea ,shrinkage of brick-earth in the kiln1 #he ,silica1 behaviour in the kiln1 #bh group of minerals1 #ci ,slates1 chemical composition of1 #hg dbris for brickmaking1 #hg refuse1 #dg used in brickmaking1 #dg ,snails1 found in brick-earth1 #d ,specific gravity of bricks1 #adf1 #adi ,stacking in the kiln1 #ig ,staffordshire blue bricks1 #ii ,stibnite1 #fh1 #gj ,stocks1 ,london1 #adj ,stoneware1 earths for making1 #ba ,stourbridge bricks1 #hb ,strength of bricks1 #acf ,styrian magnesite1 #ef ,swiss brick-earths1 #hi ,temperature and weathering of bricks1 #aae in kilns1 #ih ,terra-cotta earths1 #ai1 #cj earth1 chemical composition of1 #hd expansion of in weathering1 #aae ,ruabon1 #aaf ,tests for bricks 7see strength1 absorption1 specific gravity1 chemical composition1 micro-structure1 etc474 ,thames1 mineral salts in solution in the1 #g ,thames ,valley brick-earths1 #a1 #b1 #c1 #d1 #e ,tuscany1 infusorial earth1 #ib ,variable character of brick-earths1 #aj ,variability in character of marine brick-earths1 #bc1 #bd of estuarine brick-earths1 #ba of lacustrine brick-earths1 #ag ,vegetable growth on bricks1 #aac ,vein quartz1 #dj ,volcanic ejectamenta for brickmaking1 #ic ,wales1 fire-clays of1 #ha ,warping1 #ih 8,weathering0 agents which affect bricks1 #f ,weathering of brick-earths1 #bg ,white bricks1 #ajj ,yellow bricks1 #aja ,illustration ,transcriber's ,notes ,as ,footnote #a states1 technical terms are explained in the ,index at the end of the book4 ,punctuation and spelling were made consistent when a predominant preference was found in the original book2 otherwise they were not changed4 ,inconsistent hyphenation was not changed4 ,simple typographical errors were corrected2 unbalanced quotation marks were remedied when the change was obvious1 and otherwise left unbalanced4 ,figures #a and #d were repositioned slightly in the paragraphs that reference them1 thereby splitting those paragraphs4 ,the uncaptioned illustration above the second advertisement is an image of that advertisement4 ,the uncaptioned illustration at the end of the book is decorative4 ,in this ,plain ,text version of the e,book1 the chemical formulas on pages #gf-gg are shown unsubscripted1 e4g41 ,h#b,o4 ,the original book used middle-dots to represent decimal points2 this e,book uses baseline periods4 ,the index was not checked for proper alphabetization or correct page references4