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woodand a monopoly was granted to Sir Robert Mansell, whowas allowed to import the tine Venetian flint-glasses for drinking,the art of making which was not brought to perfection before thereign of William III . The first glass-plates, for looking-glassesand coach-w indows, were made in 1673, at Lambeth, by the en-couragement of the duke of Buckingham; who, in 1670, intro-duced the manufacture of fine glass into England, by Venetianartists, with amazing success. So that within the last century, theFrench and English have not only equalled, but even excelled, theVenetians, and are now no longer supplied from abroad. TheFrench made a considerable improvement in the art of glass, bythe invention of a method to cast very large plates, till then un-known, and scarce practised yet by any but themselves and theEnglish. This branch was established in Lancashire in 1773, andis now very flourishing.

Of the Materials for making Glass .

The materials, whereof glass is made, are salt and sand, or stones.I. The salt is procured from a sort of ashes brought from the Le-vant , called polverine, or rochetta. They are the ashes of a wa-ter-plant named kali, see Salsola, cut down in summer, dried inthe sun, and burnt in heaps, either on the ground, or on iron-grates; the ashes falling into a pit, grow into a haul mass, or stone,fit for use. It may also be procured from common kelp, or theashes ot the fueus vesiculosus. See Fucus. To extract tin* salt,these ashes are powdered and sifted, then put into boiling water,and there kept till one-third of the water be consumed ; the wholebeing stirred up from time to time, that the ashes may incorporatewith the fluid, and all its salts be extracted: then the vessel is Idl-ed up with new water, and boiled over again, till one-half be con-sumed; what remains is a sort of le.y, strongly impregnated withsalt. This ley, boiled over again in fresh coppers, thickens inabout twenty-four hours, and shoots its salt; which is to be ladledout, as it shoots, into earthen pans, anti thence into wooden vats todrain and dry. This done, it is grossly pounded, and thus putinto a sort of oven, called calcar, to dry. There are also otherplants which yield a salt fit for glass; such as the common thistle,bramble, hops, wormwood, woad, tobacco, fern, and the wholeleguminous tribe, as pease, beans, &c. Peai l-ashes form a leadingflux in the manufacture of glass, and mostly supply the place oftile Levant ashes, the barillas of Spain , and other kinds, formerlyimported for making both glass and soap. There are other fluxesused for different kinds of glass, and for various purposes, as cal-cined lead, nitre, sea-salt, borax, arsenic, smiths-clinkers, andWood-ashes, containing the eartli and lixiviate salts as produced by-incineration. With regard to these several fluxes, we may ob-serve, in general, that the more calx of lead, or other metallicearth, that enters into the composition of any glass, so much theniore fusible, soft, coloured, and dense, this glass is, and recipro-eully. The colours given to glass, by calxes of lead, are shades°f yellow: on the other hand, glasses that contain only saline fluxesPartake of the properties of salts; they are less heavy, less dense,harder, whiter, more brilliant, and more brittle, than the former;a, 'd glasses containing both saline and metallic fluxes also partakethe properties of both these substances. Glasses too saline areeasily susceptible of alteration by the action of air and water: es-pecially those in which alkali prevail; and these are also liable to)e injured by acids. Those that contain too much borax and ar-Se| fic, though at first they appear very beautiful, quickly tarnisha nd become opake w hen exposed to air. By attending to theseProperties of different fluxes, the artist may adjust the proportions°* these to sand, or powdered flints, for the various kinds of glass.

. IF The sand or stone, called by the artists tarso, is the secondJugredient in glass, and that which gives it the body iukI firmness,hese stones, Agricoia observes, must be such as will fuse, aim ofuese such as are white and transparent are best; so that crystalas the precedency of all others. At Venice they chiefly use aort of pebble, found in the Tesino, resembling white marble, andabed cuogolo. Indeed Ant . Neri assures us, that all stones,Much will strike fire with steel, are lit to vitrify: but I)i. Monetthat there are some exceptions from this rule. Hints areadimrable; and when calcined, powdered, and searced, niake aP ‘c white crystalline metal: but the expellee ot pupai ig t» in"rn k “ U,e m “ lers of our glass-houses sparing of their use. _ W hereP l r stones cannot be so conveniently had,v °i- ii.— no. 97.

sand is used. The

b.est for this purpose is that w hich is w hite, small, and shining ; ex-amined by the microscope, it appears to he small fragments ofrock-crystal. For green glass, that which is of a soft texture, andmore gritty; it is to be well washed, which is all the preparation itneeds. Our glass-houses are furnished with white sand, for theircrystal-glasses^ from Lynn in Norfolk, and Maidstone in Kent ,ancl with the coarser, for green glass, from Woolwich.

Of the Furnaces and Implements used in Glassmaking .

In this manufacture there are three sorts of furnaces; the first,called calcar, is for the frit; second for working the glass; thethird, for annealing it, is called the leer. See Plate LXXXIV.

I. The Calcar is an oven ten feet long, seven feet broad, andtwo deep: the fuel, which in Britain is sea-coal, is put into a trenchon one side of the furnace ; and the flame, reverberating from theroof upon the frit, calcines it.

II. The Glass-Furnace, or Working-Furnace, is round, ofthree yards diameter, and two high, or in that proportion. It isdivided into three parts, each of which is vaulted. The lowerpart is properly called the crown, and is made in that form. Itsuse is to keep a brisk fire, which is never put out. The mouthis called the bocca. There are several holes in the arch of thiscrown, through which the flame passes into the second partition,ancl reverberates into the pots filled with the materials. Round theinsides there are eight or more pots placed, and piling pots onthem. The number of pots is alw ays double that of the boccas ormouths, or of the number of workmen, that each may have onepot refined to work out of, and another for metal to refine ill,while he works out of the other. Through the working-holes themetal is taken out of the pots, and the pots are put into the fur-nace ; and these holes are stopped with moveable covers madeof lute and brick, to screen the workman’s eyes from the scorch-ing flames. On each side of the bocca or mouth is a boccarelfjor little hole, out of which coloured glass or finer metal is takenfrom the piling-pot.

III. Above this oven there is the third oven, called the Leer,about five or six yards long, and four feet wide, where the vesselsof glass are annealed or cooled. This part consists of a tower, be-sides the leer, into which the flame ascends from the furnace. Thetower lias two mouths, through which the glasses are put in with afork, and set on the floor or bottom: but they are drawn out oniron pans, called fraches, through the leer, to cool by degrees; sothat they are quite cool by the time they reach the mouth of theleer, which enters the sarosel or room where the glasses are to bestowed.

■ IV. The Furnace for the Green Glass is_square; and ateach angle it has an arch for annealing or cooling glasses. Themetal is wrought on two opposite sides, and on the other two theyhave their colours, into which are made linnet-holes for the fire tocome from the furnace to bake the frit, and to discharge thesmoke. Fires are made in the arches to anneal the work, so thatthe whole process is done in one furnace. These furnaces mustnot be of brick, but of hard sandy stones. In France , they buildthe outside of hrick; and the inner, to bear the five, is made of asort of fullers earth, or tobacco-pipe clay, of which they also makethe melting-pots. In Britain the pots are made of Sturbridgeclay. Mr. Blanccurt observes, that the worst and roughest workin this art is the changing the pots when they are worn out orcracked. In this case, the great working-hole must be uncover-ed ; the faulty pot must betaken out with iron hooks and forks,and a new one must be speedily put in its place, through theflames, by the bauds only. For this work, the man guards him-self with a garment made of skins, in the shape of a pantaloonthat covers him all but his eyes, and is made as wet as possible:the eyes are defended with a proper sort of glass. The principalimplements used by the glass-blower are, a blowing-pipe, fig. 3,which is an iron pipe about two feet long, with rope-yarn wrappedround it at A, where the workman takes hold of it; two or threeiron rods, fig. 4, of the same length ; a pair of blunt shears, tig. 5 •and several different sized ladles, shovels, pokers, &c. ’

Of the Different Kinds of Glass.

The manufactured glass now in use may be divided into threegeneral kinds; 1. white transparent glass; 2. coloured glass; and3. common green, or bottle-glass. Of the first kind there is a7 R great