sufficient sand to fill up the interstices between the stones; one-third of the entire bulk, or one-half of the shingle, is required for the sand-a point not so often attended to as it should be. Plenty of water is advocated for the mixing; and for making a good face against a wood shutter it is essential that the concrete should be wet.

1864h. Concrete constructions are described under BRICKLAYING.

18641. STRENGTH OF LINTELS of various compositions, each 6 inches deep, 4 inches wide, and 3 feet 6 inches long, 28 days after manufacture; 3 feet clear space, and loaded gradually in the middle (see par. 1903x):

Brown Portland stone

These three were composed of 1 of cement, 4 of core, 1 piece of hoop iron 1 inches by thick in middle.

1864. A natural cement deposit, of very large extent, has been worked at Barrington, Cambridgeshire, where it is found from 13 feet to 21 feet in thickness, immediately under the surface. It is considered as giving the material for the best quality of cement aud lime, and it can be manufactured at about half the cost of the usual system (1887).

1865. Hamelin's mastic cement, though patented of late years, is an invention of P. Loriot, a century old; the medium for mixing the pounded brick-dust, limestone, and sand, is oil instead of water. It is much more difficult to use than the other cements, and requires great experience and care. 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 presents a beautiful surface, is durable, but it requires to be painted as often as do the other

cements.

1866. Keene's cement is obtained by soaking plaster in alum water after a first calcination; it is then kiln-burnt a second time and ground. It is in reality only a plaster, and is capable of being worked to a very hard and beautiful surface. Martin's patent

fireproof and ornamental cement is a plaster of somewhat similar make. and equally goodlooking. It is manufactured in three qualities, coarse, fine, and superfine. It is said to be used with greater facility by workmen than any other cement yet produced, requiring only about an hour to set, which is less by one-half the time of other cements. It appears to be chiefly prepared at Derby. Parian cement (K ating's patent) is also composed of gypsum, but mixed with borax (borate of soda) in powder, and the mixture calcined and ground. A fine quality produces a hard scagliola imitation of marble. When applied to old brick or plastered work, as in repairs, these cements may be papered or painted upon in about 18 or 24 hours after execution. But on new work time must be given for any efflorescer ce, or damp, to disengage itself

1866a. John's patent permanent stucco wash, stucco cement, and stucco paint, were introduced about 1843. As a paint it is cheap, durable, agreeable in colour, and finishes without a gloss. It gives out no deleterious exhalations or odour in drying, and it is stated that as the oil cannot evaporate (?), but is held in intimate and indissoluble union with the other materials, there can be no decay, an objection to which oil mastic is so liable. It requires no driers or turpentine, and is applicable both for outside and inside work. The cement, which is stated not to deteriorate with age, is packed in casks, and requires to be mixed with 3 parts of good, sharp, clean sand to make a stucco, its application for which is the same as for any other stucco. It adheres well to glass, iron, slate and tiles in roofing, wood, old plaster, or Roman cement. When set it is hard, and impervious to wet and damp. One coat of its own paint, which it will take after twenty-four hours, is sufficient. Mouldings may be run in it, and castings made.

in use.

18666. A cement which will withstand a moist climate, is stated to be composed of one bushel of lime with 15 gallons of water and half a bushel of fine gravel sand, mixed with 3 lbs. of copperas dissolved in hot water, and kept stirred while being incorporated and Sufficient should be made for the day during which it is to be used, as the colour is not eas ly matched. The Bristol Purimachos cement is new, and is stated to be an effectual fire-resisting material, uniting readily with a metal, brick, stone, or like surface, and forming a permanent joint, impervious to air, gas, smoke, &c. It renews burnt-out parts of fire-brick without any taking down and rebuilding. It repairs cracked and holed iron boilers, ovens. stoves, pipes, &c. Used as a wash, it imparts a smooth glazed surface to the interior of retorts of gas works. It may for many purposes be used instead of white or red lead in making joints subject to the action of fire. Other similar materials will be noticed s. v. PLASTERER.

1866c. GYPSUM, better known as Plaster of Paris, 1s a sulphate of lime. It is found at Alston, in Cumberland; at Shotover Hill, Oxfordshire; at Orston, near Grantham; in Nottinghamshire, in Derbyshire, and in Cheshire; in France, in the neighbourhood of Pa-is, chiefly at Montmartre ; and in the departments of the Saone, Loire, of the Rhone and of many others; and in Tuscany, Savoy, Spain and Switzerland; in some parts of the British Colonies of North America, wherefrom it is exported principally to the United States. The stone is broken into small blocks, and burnt in a walled space with openings in the tiled roof to let out the steam. After its water of crystallization is driven off, it becomes pulverulent and like flour. On fresh water being added, it combines with the normal quantity of water, and reassumes the form of a hydrate, recovering its original density and strength to a very great degree. A heat of about 200° centigrade is sufficient. The London manufacturers adopt a kind of oven for burning the stone, which prevents the smoke from injuring the plaster. In France it has been proposed to throw a jet of steam heated above 400° Fahr. over the stone, which is broken very much smaller than usual: this jet takes up all the water present, and leaves the plaster in the state of a pure anhydrous sulphate of lime. The plaster obtained from Paris is considered the best of all in quality, probably arising from the fact that the stone is the hardest. Gypsum swells in setting in contradistinction to the cements, which generally shrink. The specific gravity of pure gypsum may be taken at 2-3-2; and its constituent parts to be sulphuric acid 46, lime 32, and water 21. (See GLOSSARY, s. v.)

1867. The best bituminous cements are obtained from the natural asphalte, which is found in large quantities on the shores of the Dead Sea; in Albania; in Trinidad; at Lobsann, and Bekelbronn, in the department of the Bas Rhin; in the department of the Puy de Dome; at Gaugeac in that of the Landes, &c. The asphalte which is found in inexhaustible quantities at Pyrimont Seyssel, in the Jura Mountains, in the department of the Aire in France, was introduced into England about 1838, under Claridge's patent. The principal ingredient in its composition is a bituminous limestone, of a rich brown colour. After it has been reduced to a fine powder, a certain portion of grit is mixed with it; it is then placed in cauldrons heated by strong fires with a sufficient quantity of mine al tar to prevent the asphalte from calcining. The whole mass is thoroughly incorporated and reduced to a mastic, in which state it is run into moulds to form blocks, each 1 foot 6 inches square, 6 inches in depth, and weighing 125 lbs.

1867a. The mastic is of three qualities, fine, gritted, and coarse gritted. The first, being without any admixture of grit, is used for magazine floors, and as a cement for making, in special cases, very close joints in brickwork. II. The fine gritted is used for covering terraces, roofs and arches, lining of tanks, and as a cement for brickwork, and for running the joints of stones. III. The coarse gritted is used for paving and flooring, and where great strength of work is desirable, such as gun-shed floors, tun-room floors, and margins of stable floors; while in gateways for heavy carriage traffic, small pieces of granite chippings are introduced. These mastics, and more particularly the first two, being ductile and readily yielding to any change that may take place on the surfaces upon which they are laid, require a proper foundation to be prepared.

18676. When required for use, an iron cauldron having been prepared, 2 lbs. of mineral tar are put in, and then 56 lbs. of asphalte broken into pieces of not more than 1 lb. in weight. These are mixed together until the asphalte becomes soft. After a quarter of an hour the stirring is repeated, and another 56 lbs. of asphalte added, and so on until a proportion of 112 lbs. of asphalte to each 1 lb. of tar, under ordinary circumstances, fills the cauldron and the whole is thoroughly melted. When fit for use the asphalte will emit jets of light smoke, and freely drop from the stirrer.

1867c. It will be well to note that it is stated asphalte never flames, but merely passes into a state of fusion. At the fire at Hamburg in 1842, it was remarked that when asphalted roofs fell in, "the asphalte, in which a sort of rubble is mixed up, was found to have resisted the effects of the heat, and, like a mass of dirt, served rather to smother the flames than to give them increased vitality." A like result is recorded of a fire that took place at the Bazaar Bordelais, at Bordeaux, in 1835; of another in Stangate, London, in 1855; and experiments were made by order of the authorities of the British Museum before this material was allowed to be applied to the snow gutters of the dome of the new Reading Room and other roofs, with a satisfactory result. Notice is not generally taken of the fact that if in works, asphalte or tar be used in places where it may be affected by heat, a smell arises which is very prejudicial to the comfort of the occupiers of the building.

1867d. The term asphalte has also been given to several compositions formed by the admixture of chalk, lime, gas tar, and other substances for cheapness. The coal tars, and vegetable pitch, although not so good as the bitumens, are fairly good substitutes in many cases, as in coating vaults, or walls exposed to the dampness of earth. The proportions in which to mix powdered calcareous stone must be regulated by practice, as also the heat, that the stone be not converted into quicklime, perhaps from 6 to 7 of the pitch in volume to 1 of limestone will suffice; and it is recommended to use these in greater thickness than the asphalte, being about half an inch for the latter material.

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.

1868a. Four pieces of the common sort of glass being cut from one strip, each piece was 5 inches wide, 6 inches long, and 4 inches thick. In the trial of strength they were calcu lated out at a standard size, and gave 17,208 lbs., 15,435 lbs., 14,931 lbs., and 11,385 lbs. ; the mean being 14,931 lbs. This great difference is the more singular from the circumstance of all the pieces being cut from the same plate. The weight of the glass at a size of 90 x 4.5 x 3, all in inches, would be 11.12 lbs. Sheet glass is stated to be stronger than plate or crown glass, but less flexible. The compressive strength of glass is about 121 tons per square inch. The resistance of glass to a crushing force is about 12 times its resistance to extension.

1869. Pliny gives the following account of the discovery of manufacturing glass, which was well known in Aristotle's time, 350 B. c. "A merchant vessel, 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 vitrified 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.

1870. The manufacture of window glass during the last thirty years has undergone entire alteration, especially since the abolition of the excise duty in 1845. There are now three special kinds of glass used for glazing purposes, and several varieties of them:

1870a. I. Crown glass, which is blown into large globes and opened out into circular flat tables. II. Sheet glass, which is blown into long cylinders or muffs; then split down and flattened. III. Plate glass, which is either cast on iron tables for large purpose, and polished; or for smaller squares, blown into a cylinder and polished.

1871. Crown glass, the commonest window glass, differs from flint glass in its containing no lead or 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. Its manufacture is conducted differently from that of flintglass articles, the object being to produce a large flat thin plate, 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: the process is as follows:-The workman, having a sufficient mass of melted metal on his blowpipe, rolls it on an iron plate, and then, swinging it backwards and forwards, causes it by its own gravity to form into a globe, 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. The hollow globe is then opened by holding it to the fire, which expanding the air confined within it (the hole of the blowpipe being stopped), bursts it at the weakest part, and while still soft it is opened out into a flat plate by centrifugal force; and being disengaged from the rod, a thick knob is left in its centre. It is then placed in a furnace, or 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 very commonest purposes. Tables are now made of such a size that squares may be procured 38 inches by 24 inches as extra sizes.

1871a. The qualities of crown glass in common use are called best, seconds, thirds, and fourths or coarse; with two still coarser. The last is of a very green hue, and only used for inferior buildings. They were 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 contained twelve tables; of seconds, a crate contained fifteen; and of thirds, eighteen tables. They are now sold (by Messrs. Hartley) in crates of eighteen tables of the usual NN

thickness averaging 53 inches; and in crates of twelve tables of extra thick..ess averaging 52 inches. Flattened slabs of the same qualities are sold in crates of thirty-six slabs of the usual thickness, and in crates of twenty-four slabs of extra thickness, each averaging 24 inches, 22 inches, and 21 inches. The flattened slab is also made as obscured' glass. The sizes of both qualities vary from 'quarries'; under 9 by 7; up to, above 4 feet, and 1ot above 5 feet superficial. Taking the usual thickness of

99

43 and 40

150

135

110

85

CC and CCC 63 and 50 (Adcock). 1872. Sheet glass has been manufactured in England with great improvements since 1832 to 1838 by Messrs. Chance and Hartley, with the co-operation of M. Bontemps, of Paris. Though inferior in colour, this glass is in other points generally superior to that of the foreign manufacture. It is composed of the same or similar materials to the above, in well ascertained proportions, and with sulphate of soda to give whiteness. In the manufacture of sheet glass a sufficient quantity of the metal is collected at the extremity of a blowpipe, and then lengthened by swinging and blowing, till it acquires the form of a hollow cylinder, which is then detached, the neck being cut off with a thread of hot glass; and one side of the cylinder is cut down lengthwise with a heated iron or diamond. It is then taken to the flattening kiln, where the heat causes it gradually to open nearly flat on a bed called largre, where it is rubbed down by means of a block of wood called a polissoir, and then becomes flattened sheet. After this operation it is placed in the annealing oven to cool gradually. This operation is referred to by the monk Theophilus, who wrote about the end of the twelfth century or later, as in use in his time. The method was also employed by the Venetians especially for coloured glass, as it secured uniformity. But on the cessation for its demand, the employment of the cylinders was entirely superseded in France, England, and the North of Germany, for the rotary principle.

1872a. The great advantage of sheet glass is that of affording plates of larger dimensions, and not only of avoiding the waste arising from the circular form of the crown tables, but also from the knob or bull's eye in the centre. The surface, however, is much less brilliant than that of crown glass, and is more wavy and undulated. Messrs. Chance, in 1838, introduced a thicker quality of sheet glass, which was at the same time of a better surface, and since then its use has become general.

18726. In 1840 the same firm introduced a new variety of window glass under the name of patent plate, which they obtained from a thick sheet glass by a new process of grinding and polishing. They made plates of several degrees of thickness, and of sizes containing from 8 to 12 feet superficial. The surface of the glass obtained by this process, though not perfectly true, is very nearly so; and in brilliancy it is unsurpassed even by cast plate. For glazing sashes it has nearly superseded crown and sheet glass. But for squares of somewhat large dimensions, it may be calculated whether plate glass will not be as cheap or cheaper.

1872c. As will be perceived by the above short account of the mode of manufacture of sheet glass, its size is almost only limited by the strength of the workman. It is chiefly sold in crates as manufactured, in sheets of not less in width than 28 inches, and not less than 9 feet superficial area; with a limit of width not exceeding 45 inches, and a limit of length not exceeding 75 inches; but these extremes of width and length cannot be combined in the same sheet. Thus in glass of 15 ounces to the foot, the dimensions 55 by 36 inches, or 12 feet in area, is the largest plate. In 21 ounce glass, 75 by 45 inches, or 18 feet area: in 26 ounce glass, 75 by 45 inches, or 17 feet area: in 32 ounce glass, 65 by 44 inches, or 15 feet area in 36 ounce glass, 60 by 42 inches, or 12 feet area and in 42 ounce glass, 55 by 38 inches, or 11 feet area. The four first weights are made in qualities of best, seconds, thirds, and fourths; and the two first have two qualities A and B for pieThere is no fourth quality to the two last named weights. All these sorts are cut into squares for glazing.

tures.

1872d. Fluted sheet glass of 15 ounce and 21 ounce is usually supplied in crates not above 43 inches long; but it is made up to 50 inches in length. Obscured sheet glass is supplied in all substances.

1873. Patent plate glass, already described (par. 1872b.) is made in three qualities, B or best, C or second, and CC or third, quality. Each of these are of four kinds, known as No. 1, which is of an average thickness of th of an inch, and is of an average weight of 13 ounces to the foot; No. 2 is th thick, and 17 ounces; No. 3 is th, and 21 ounces; and No. 4 is th, or 24 ounces to the foot. No. 4 B is thus the very best quality made; the prices for the size required vary but about one or two pennies per foot in each kind; and from threepence to sevenpence in each quality. They are manufactured in sizes from 4 to 13 feet in area, not above 50 inches long, or 36 inches wide.

1874. German sheet, or Belgian sheet glass, as it is sometimes called, was formerly in much demand in England; and is still used for cheapness. Its appearance is more wavy

547

and speckled than the English manufacture. Crystal white sheet glass, for glazing pictures and prints, is imported from Florence in cases of 100, 200 and 300 feet, in first, second and third qualities, and appears superior to other glass in whiteness, but it has the defect of 'sweating.' Similar named glass for such purposes made by Messrs. Chance, appears to us to be very green, and therefore detrimental to prints and pictures; but on the other hand it does not sweat.

1875. 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 smalier 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 afford 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.

1876. For the unsilvered polished plate glass for mirrors there are two qualities, second and best, The Paris factory supplied in 1865 two looking glasses for the Mayor's room in the Town Hall at Liverpool, each 15 feet by 10 feet. Polished plate glass is manufactured for general glazing purposes up to about 80 feet superficial, of two qualities, usual and best. The usual thickness is a quarter of an inch: higher prices are charged for glass selected to be cut aboveths., ths.. and ths. thick; while for above ths, thick, special prices are charged. The best quality is declared to be of the very purest colour, free from specks, and not subject to dampness or sweating.

1877. Rough plate glass, cast, is used for roofing, in skylights, windows, &c., in plates from not above 20 inches long, to above 120 inches long, in thicknesses of }, }, {, †, inch, 14, and 1inch; but these thicknesses have certain limited lengths. The widths are the same as for plate glass. This glass is not ground or polished, but rough from the table, and showing the table marks on its underside.

1878. The patent rough plate glass, which is also cast, must not be confounded with the above. It is extensively used for ridge and furrow roofs, conservatories, manufactories, skylights, workshops, and other places where "obscured" glass is required to intercept the vision without diminishing the light. Blinds are unnecessary, and when it is used in greenhouses, no scorching of the plants occurs. The quality known as th. of an inch thick, weighing about 2 lbs., or 32 ounces to the foot, is usually provided for these purposes, and is no more, weight for weight, than common crown glass. When greater strength is required, ths, and 4 inch thick is said to be cheaper and of a finer quality than the common rough plate; but we demur to this statement, as of late years the manufacture appears to have decreased in strength from the greater use of sand for cheapness; in moveable window. frames in warehouses, a lamentable quantity of broken squares is to be seen almost before the floors are occupied.

1878a. This glass is made of two kinds; I. Plain, which is merely marked by the fine grain of the casting table, and is that above noticed; and II. Fluted, of two sorts, No. 1, large pattern, having 3 flutes to the inch; and No. 2, small pattern, having 12 flutes to the inch. Both the plain and the fluted kinds are made th.ths., ths. and 1⁄2 inch in thickness. The width is about 3 feet, and the length usually not above 70 inches; but 75, 90, and 100 inches long, are also made. When a clear glass and much non-transparency are required, No. 2 fluted is the best.

1879. Quarry glass is also made in this material; No. 1 being 6 inches by 4th inches from point to point; No 2 being 3 inches by 2 inch. A stained ornamented patent quarry rough plate is made for churches, chapels, schools, &c. A patent diamond rough plate glass is also manufactured. A patent rough plate, and sheet, perforated glass, polished or unpolished, for ventilation, can be obtained in sizes, which require consideration in arranging, on account of the length of the slits or perforations. It is usually made in columns 1 inches wide, and 2 inches apart; the space between each slit vertically being 1 inches. Larger sizes, or the columns wider apart, can be obtained from various manufacturers, or

to order.

1880. Many other applications of glass will be noticed in the ensuing chapter. We must here state that the details given in this section are founded upon the price list issued by Messrs. Hartley, of Sunderland, and would state our regret that the manu facturers have not deemed it advisable for their own interests, to provide some place in London, and in other large towns, where the architect can call and compare the qualities of glass supplied under his specification with standards there placed. It was comparatively tay in former years to judge of good glass; now it is almost impossible.