to be accomplished, is the expulsion of the carbonic acid gas which enters into its composition.

1849. That lime is generally most esteemed which heats most in slaking, and slakes the If there be among coarse unslakeable lumps quickest, falling into a fine powder. called core, that will not pass through the screen, either the stone has not been sufficiently burnt, or it originally contained extraneous matter; which not only indicates defect in quality, but that it will be, as they more or less abound, more costly in use.

1850. From the experiments of Mr. Smeaton and of Dr. Higgins, it is sufficiently proved that, when chalk or stone lime is equally fresh when used, the cementitious properties of both are nearly, if not quite, equal; but from the circumstance of quicklime absorbing carbonic acid more or less in proportion as its texture is solid or spongy, so it gradually parts with its cementing nature, becoming at length altogether unfit for the purposes of mortar. Thus, though each of the sorts may be equally good, if properly burnt and quite fresh from the kiln, yet from the chalk lime so much more easily and rapidly taking in the carbonic acid than stone lime does, it is not so fit for general use; and, indeed, now the metropolis is so well supplied with the harder chalk and stone limes, there is no excuse for its use, and it should in sound building be altogether banished.

1851. The following table, from Smeaton, contains a list of the limestones he examined on the occasion of building the Eddystone Lighthouse.

Reduction of Weight by burning.

Colour of Brick made of
such Clay.

Sutton, Lancashire

Do.
Brown

1852. In forming mortar from the lime, it must, when slaked, be passed through a sieve leaving only a fine powder, an operation usually performed with a quarter inch wire screen set at a considerable inclination to the horizon, against which the lime is thrown with a shovel after slaking. That which passes through is fit for use; the core falling on that side of the screen against which the lime is thrown, being entirely rejected for the purpose in question, though it is an excellent material for filling in the sides of foundations under wood floors where they would otherwise be next the earth, and the like. The sifted or screened lime is next to be added to the sand, whose quantity will vary as the quality of the lime, of which we shall presently speak. In making mortar, there is no point so important as respects the manufacture itself, as the well tempering and beating up the lime with the sand after the water is added to them. In proportion, too, as this is effectually done, will a The best mode of tempering small proportion of lime suffice to make a good mortar. mortar is by means of a pug-mill with a horse-track similar to the clay-mills used for But if such cannot be had, the mortar should be turned over repeatedly, making bricks. That this process should and beaten with wooden beaters, until it be thoroughly mixed. be carefully performed, will appear of the more importance when it is considered that it thereby admits a greater proportion of sand, which is not only a cheaper material, but the of it renders a less quantity of water necessary, and the mortar will consequently presence set sooner: the work, too, will settle less; for as lime will shrink in drying, while the sand mixed with it continues to occupy the same bulk, it follows that the thickness of the It may be taken, indeed, as an axiom, that no more mortar beds will be less variable. lime is necessary than will surround the particles of sand.

1853. In most of the public works executed in Great Britain of late years, the proportion of lime to sand is as 1 to 3; and when the former is made from good limestone, the sand is by no means too much in proportion. Dr. Higgins, in his experiments, has gone so far as to recommend 7 parts of sand to 1 of lime, which, for mortar, is perhaps carrying the point to the extreme.

1854. Various additions are made to mortar, in order to increase its hardness and

tenacity; such as coal and wood ashes, forge scales, roasted iron ore, puzzuolana, and the like. The cendre de Tournay is used in the low countries. This is an article procured from the lime-kilns bordering the Scheldt. The lime of this district contains a considerable portion of clay mixed with iron; and the pit-coal with which it is burnt contains a large quantity of an argillaceous schist, impregnated with iron. After the lime is taken out of the kilns, there remains the cendre, about one fourth of which consists of burnt lime-dust, and three fourths of coal-ashes. This material is sprinkled with water to slack the lime, and well mixed together, and put into a proper vessel and covered over with wet earth. In this state it is kept for a considerable time; and when taken out, and strongly beaten up for half an hour with an iron pestle in a wooden mortar or trough, it is reduced to a soft pasty consistence; it is then spread out for several days in a shady place, and the operation of beating repeated: the oftener this is done the better, except it should become unmanageable from being too much dried. In a few minutes, this cement, when applied to brick or stone, adheres so firmly that water may be immediately poured over it; and if kept dry twenty-four hours, it afterwards receives no injury even from the most violent action of a flowing stream.

1855. In London, a blue mortar is used for covering parts of buildings much exposed to the weather; and if prepared with similar labour and attention, it might, in a great degree, possess the valuable properties of the mortar of the Scheldt, just mentioned.

1856. Common ashes mortar is made by mixing two bushels of newly slacked lime and three bushels of wood ashes, which, when cold, must be well beaten, in which state it is usually kept for a considerable time, and indeed it improves by keeping if beaten two or three times previous to using it. This mixture is superior to terras mortar in resisting the alternate effects of dryness and moisture, but not comparable with it under water.

1857. Mr. Smeaton discovered, by a course of experiments, that the scales (grey oxide of iron) that fly off under the forge hammer from red hot iron, pulverised, sifted, and mixed with lime, form an admirable cement, equal to puzzuolano. He found, in pursuing his experiments, that roasted iron ore produced an effective water cement, by using a greater proportion of it than either terras or puzzuolano. Equal quantities of iron scales and argillaceous lime, with half the quantity of each of these of sand, produced a cement in every respect equal to terras mortar. If pure carbonate of lime be used, equal parts of each of the ingredients ought to be incorporated. We do not think it necessary here to give any account either of Loriot's cement, nor that proposed by Semple: neither are to be depended on: indeed the first. as a water cement, is of inferior utility, and very little better than common mortar dried before the admission of water upon it.

1858. Sand should by all means, if possible, be procured from a running clear stream, in preference to that obtained from pits. It is cleaner, and not so connected with clayey or muddy particles. About the metropolis it is the practice to use (and an admirable material it is) the sand of the Thames procured from above London Bridge. This sand has acquired a deserved reputation among the architects and builders of the capital. It contains, however, a vast portion of heterogeneous matter, such as calcareous fossil, quartzose, and flint sands, particles of coal alluvium, and much iron. The sharp drift sand of the Thames should therefore, before mixing with the lime, be well screened and washed.

1859. If pit sand only can be procured, it should be repeatedly washed, to free it from the earthy and clayey particles it contains, until it becomes bright in colour, and feels gritty under the fingers. When the architect is obliged to use sea sand, it must be well washed in fresh water until the salt is entirely removed; otherwise the cement for which it is used will never dry.

1860. Grout, or liquid mortar, is nothing more than common mortar mixed with a sufficient quantity of water to make it fluid enough to penetrate the interstices and irregularities of the interior of brick walls, which common mortar will not reach. The mortar whereof it is made will bear 4 of sand to 1 of lime, but it should be thoroughly beat. It may be kept a little longer, whereby its quick setting will be facilitated.

1861. Water. Dr. Higgins recommends the use of lime water for the composition of mortar. This, in practice, would be impossible. The water used, however, for the incorporation of the lime with the sand should be soft and pure. The screened lime and sand

being shovelled together, as little water as possible is added, after which the chafing and beating, or tempering in a pug-mill, takes place.

1862. Under this section, notice must be taken of a compound of ballast or stone chipings and lime mixed together, which has received the name of concrete, from the speedy concretion that takes place between the different particles whereof it is composed. If, however, gallots or small stone chippings are used, sand in a large proportion to the lime must be used. The use of concrete was well known at an early period, and is by no means, therefore, a discovery of modern days. Wherever the soil is soft, and unequal for the reception of the foundations of a building, the introduction of concrete under them is an almost infallible remedy against settlement. The Thames ballast, commonly used for con

crete, is a mixture of sand and small stones. With this, and lime in the proportion of never

less than 4 to 1, and never properly exceeding 9 to 1, of stone lime, or such as is known to set hard in water, a mixture is made. The lime is generally used in powder, and the whole being shovelled together, it is wheeled in barrows to a stage over the spot where it is to be used, and let fall into the trench dug out for the reception of the foundation. The greater the height the concrete is made to fall, the sounder and stronger it becomes. It must always be recollected that no more lime is necessary than with the thinnest coat to surround the particles of the ballast, and that therefore the size of the pebbles or stones should influence the quantity of the lime. As the ground is more or less to be trusted, the thickness of the concrete must be regulated; when used on the best ground, a foot in thickness will be sufficient; while on the worst, as many as four feet or more may be required. The upper surface being levelled, it is usual to lay on it a tier of Yorkshire stone landings, for the reception of the brick-work or mason's work in some cases, after carrying the wall a certain height, a second tier of landings has been introduced. When the soil is watery, no water should be put to the concrete, but the ballast and lime merely mixed and tumbled in. The stones or pebbles forming a portion of the concrete should never exceed the size of a hen's egg.

in use

:

1863. The principal cements used in England are those generally known by the names of Parker's, Atkinson's, and Hamelin's mastic. The first named, also called Roman cement, is manufactured principally from stone found in the Isle of Sheppey, and at Harwich, being septaria from the London clay, and properly classed among the limestones indigenous to this country. It consists of ovate or flattish masses of argillaceous limestone arranged in nearly horizontal layers, chiefly found imbedded in the London clay. The substance being coated with a calcareous spar or sulphate of barytes, forms the basis of the cement. That now we do not think at all equal to the material originally employed. Thirty years ago it was possible to use it in the depth of winter; which, we apprehend, would be a hazardous thing to do with the cement at present made. Whether the inferiority arise from adulteration, bad manufacture, or the material being worse, we cannot pretend to say; we, however, do not believe that it arises from the badness of the raw material. If this cement be of extremely good quality, 2 parts of sand to 1 of the cement may be used. The cement itself is a fine impalpable powder; yet when wetted it becomes coarse, and, unless mixed with great care, it will not take a good surface. When mixed with the sand and water, it sets very rapidly; it is necessary, therefore, to avoid mixing much at a time, or a portion will be lost. The colour of this cement, when finished, is an unpleasant dark brown, and the surface requires frequent colouring. The great value of Parker's cement is its being impervious to water almost the moment it is used; hence it becomes highly serviceable on the backs of arches under streets, for the lining of cisterns, and for carrying up in it, or coating with it, damp walls on basement stories. It will not resist fire so well; and it should therefore never be employed for setting grates, ovens, coppers, or furnaces. 1864. Atkinson's cement is a good material, preferable in colour to the last named, but, as we think, inferior in quality. It takes a much longer time to set than Parker's cement, than which it absorbs more moisture. It answers well enough in dry situations.

1865. Hamelin's mastic cement, which, though patented of late years, is an invention of P. Loriot, a century old, is one in which the medium for mixing is oil instead of water. It is much more difficult to use than the other cements, and requires great experience and care in using. A coat of it should never exceed one quarter of an inch in thickness; hence it is totally unfit for working mouldings in the solid. In the metropolis it is generally used in a very thin coat over a rough coat of Roman cement, in which case it is rarely more than an eighth of an inch thick. Thus used, it not only presents a beautiful surface, but is extremely durable.

1866. The stones whereof the Dutch tarras is made are found in the neighbourhood of Liege, and also, we believe, at Andernach on the Rhine, from the size of a pea to that of a middle-sized turnip. From their being brought down the rivers to Holland the cement has been called Dutch; the only operation they undergo in that country is the reduction of them to a coarse powder by means of mills. They are beaten by iron-headed stampers on an iron bed till they will pass through a sieve whose wires are about one eighth of an inch apart. This cement is sent from Holland in casks.

1867. The Puzzolana, or terra Puteolana of the Romans, which, as well as the last-named cement, has been almost if not quite superseded by the introduction of the Roman cement, is brought from Civita Vecchia. Its name is however derived from Puzzuoli, where it is principally found, though produced in other parts of Italy, in the neighbourhood of extinct volcanoes. It suddenly hardens when mixed with one third of its weight of lime and water, forming a cement more durable under water than any other. Bergman found 100 parts of it to contain 55 to 60 parts of siliceous earth, 20 of argillaceous, 5 or 6 of calcareous, and from 15 to 20 of iron; this last constituent is considered to be the cause of its property of hardening under water. The iron decomposes the water of the mortar, and thus in a very short time a new compound is formed. According to Vitruvius, when used for buildings in the water, 2 parts of Puzzolana were mixed with 1 of mortar.

SECT. XII.

GLASS.

1868. Glass is a combination of silex with fixed alkali, generally soda. The mixture when calcined receives the name of frit, which, after the removal of all its impurities, is conveyed to the furnace and melted in large pots or crucibles till the whole mass becomes beautifully clear, and the dross rises to the top. After being formed into the figures required, it is annealed or tempered by being placed in an appropriate furnace. The fineness depends on the purity and proportion of the ingredients. An extremely fine crystal glass is obtained from 16 parts of quartz, 8 of pure potash, 6 of calcined borax, 3 of flake white, and 1 of nitre. The specific gravity of glass is about 2600; of French plates, 2840; of English flint glass, 3320. Glass is extremely elastic, and less dilatable by heat than metallic substances.

1869. Crown glass is the best sort of window glass, differing from flint glass in its containing no lead nor any metallic oxide except manganese, and sometimes oxide of cobalt, in minute portions, for correcting the colour, and not as a flux. It is compounded of sand, alkali, either potash or soda, the vegetable ashes that contain the alkali, and generally a small portion of lime. To facilitate fusion, a small dose of arsenic is frequently added. Zaffre or oxide of cobalt, in the proportion of 1 ounce for 1000 pounds, is added, to correct the colour; but when the sand, alkali, and lime are very fine, and no other ingredients are used, zaffre is not required. In London were formerly made two sorts of crown glass. The Ratcliffe crown glass, which was the cheapest and best, whereof 24 tables went to the case; each table being 3 feet 6 inches diameter. The Lambeth glass was of a darker and greener colour. From the great disadvantage of manufacturing window glass where fuel is so dear, we have not now left a glass-house in the metropolis. Bristol and Newcastle are now the chief seats of its manufacture.

The

1870. The manufacture of common window glass is conducted differently from that of flint glass articles, the object being to produce a large flat thin plate of glass, which is afterwards by the glazier's diamond cut into the requisite shape. It is blown in circular plates, varying from 3 feet 6 inches to 4 and 5 feet diameter, and the process is as follows: The workman, having a sufficient mass of melted metal on his blow-pipe, rolls it on an iron plate, and then, swinging it backwards and forwards, causes it by its own gravity to lengthen into a cylinder, which is made and brought to the required thinness by blowing with a fan of breath, which persons accustomed to the work know how to manage. hollow cylinder is then opened by holding it to the fire, which, expanding the air confined within it (the hole of the blow-pipe being stopped), bursts it at the weakest part, and while still soft it is opened out into a flat plate by the centrifugal force; and being disengaged from the rod, a thick knob is left in its centre. It is then placed in a certain part of the furnace to undergo the process of annealing. When the table is cut for use, the centre part in which the knob remains is called knob-glass, and is used only for the commonest purposes.

1871. Tables are now made of such a size that squares may be procured 33 inches by 25, and even larger.

1872. The three qualities of glass in common use are called best, second, and third; the last is of a very green hue, and only used for inferior buildings. These are all of them sold by the crate, at the same price, the difference being made up by varying the number of the tables contained in it. Thus a crate of best crown glass contains twelve tables; of seconds, a crate contains fifteen; and of thirds, eighteen tables.

1873. German sheet glass was formerly much in demand here; but the great competition that has lately grown up in the manufacture of English plate glass, which has been much lowered in price, has brought this last into very extended use; and we seem likely to rival, if not surpass, the French in the manufacture of it.

1874. Plate glass is so called from its being cast in large sheets or plates. Its constituent parts are white sand, cleansed with purified pearl-ashes, and borax. If the metal should appear yellow, it is rendered pellucid by the addition, in equal small quantities, of manganese and arsenic. It is cast on a large horizontal table, and all excrescences are pressed out by passing a large roller over the metal. To polish it, it is laid on a large horizontal block of freestone, perfectly smooth, and then a smaller piece of glass, fastened to a plank of wood, is passed over the other till it has received a due degree of polish. For the purpose of facilitating the process, water and sand are used, as in the polishing of marble; and, lastly, Tripoli, smalt, emery, and putty, to give it lustre ; but to give it the finishing polish the powder of smalt is used. Except in the very largest plates, the workmen polish their glass by means of a plank having four wooden handles to move it, and to this plank a plate of glass is cemented.

1875. Pliny gives the following account of the discovery of manufacturing glass, which

was well known in Aristotle's time, 350 B. C. "A merchant vsesel, laden with nitre or fossil alkali, being driven on the coast of Palestine, near the river Belus, the crew accidentally supported the kettles on which they dried their provisions on pieces of the fossil alkali; the sand about it was vitrefied by its union with the alkali, and produced glass." Though, according to Bede, artificers skilled in making glass were brought into England in 674, glass windows were not generally used here till 1180, and were for a considerable time esteemed marks of great magnificence.

SECT. XIII.

ASPHALTE.

a

1876. Asphalte is a calcareous bituminous substance, latterly introduced into this country chiefly for pavements, which (we speak of that of Seyssel) was first discovered at Pyrimont, a mountain on the eastern side of the Jura, and on the right bank of the river Rhone, one league north of the town of Seyssel, and has obtained its name from its intimate combination of asphaltum and other bituminous substances with pure carbonate of lime. The mountain is composed of blocks of stone, which being conveyed to the places where intended to be used, are there reduced to powder, 90 parts whereof are placed in cauldron with 10 parts of mineral pitch, and exposed for a considerable time to a heat of 600 degrees of Fahrenheit. The substance thus obtained is used in a state of fusion, and in a few minutes after being laid down, it becomes so hard that it is, with a temperature of more than 100 degrees of Fahrenheit, susceptible of no impression. It is, however, said, nevertheless, to retain an elasticity, by which it adapts itself to all the action which, for its varied purposes, it is required to undergo. It has long been in use in the south of France, the footway of the Pont Moraud, a much frequented bridge, at Lyons, having been paved with it in 1827, and being, we believe, still in a very sound state. At Fort l'Ecluse, in the vicinity of the mountain, a small building covered with it has withstood the cold of forty Swiss winters, and is said still to continue in a perfect state of repair. For the last fourteen years, it has been occasionally used to cover the roofs of buildings in Paris, a purpose to which, for many reasons, we would not recommend its application in this country, though for a vast number of other objects it seems admirably adapted, such as foot pavements in streets, vaults, kitchens, passages, and all places where it is essential to exclude moisture, for barn floors, piggeries, farm yards, and the like.

1877. It is said (we have had no experience of it) to form with gravel a good concrete, where the soil is doubtful for bearing weight, and that it may be used as a cement for foundations, instead of mortar. It appears, from experience, not to be inflammable, a roof at Bordeaux adjoining a large house that was burnt there not having suffered, though all sorts of ignited materials fell upon it.

1878. In the years 1832, 1833, and 1834, the asphalte appears to have been successfully employed in constructing the fortifications at Vincennes, and also in the military works at Douay, Besançon, Bourbonne les Bains, Grenoble, and Lyons.

1879. Among the arguments used by the proprietors of the asphalte of Seyssel, here, where it is now, we believe, patented, over all the other sorts competing with it, are the following: - that the carbonate of lime and bitumen being combined in it by nature, it is absolutely perfect (these are their words), while in every artificial imitation the calcareous particles are merely enclosed by pitch; that the chalk is, consequently, unamalgamated, and the composition susceptible of the extremes of heat and cold. Another point of advantage whereon they insist is, that the asphalte of Seyssel consists in the large proportion of the calcareous matter to the bitumen, being about 83 to 17; while the combination effected by artificial means has never exceeded 60 of chalk to 40 of bitumen. The quantity, they say, of bitumen to be used should be the smallest that will hold the chalk in combination; and that therefore the manufactured article contains more than it should, and will consequently expand in summer and contract in winter.

1880. Making great allowances for the self-interest which the prospectus of every speculating company exhibits, we are, nevertheless, inclined to think that the asphalte of Seyssel is a valuable and important material for many building purposes, and have no doubt that it will be extensively used in this country. At present the price is high, as well from the cost of the material itself as from the necessity of procuring a solid foundation of concrete, or some other substance, whereon to lay it securely. There are several spots in the metropolis, as at Whitehall, for instance, where it has been used for foot pavements; but for other purposes we must abstain from recommending its application until experience shall justify the architect in its employment.