GLASS. 



glaziers diamond into the requifite flir.pe. Without mi- 

 nutely detailing tlie fcveral gradations of tht- proccfs, it may 

 be here mentioned, that the workman takes a very large 

 mafs of melted glafs on his hollow iron rod, and by rolling 

 it on an iron plate and.fwinging it backwards and ior wards, 

 caufes it to lengthen, bv its own weiglit, mto a cyhncler, 

 whicli is made hollow and brought to the required tlunneis, 

 by blowino- with a fan of breath, which perfous accuftomed 

 to the bulinefs know how to command. The hollow cylin- 

 der is then opened by holding it to the fire, which, by ex- 

 panding the air confined within it, (the hole of the iron rod 

 being llopped.) burlls it rt the weakeil part, and wlien ftiU 

 foft, it is ripped up through its whole length by iron (hears, 

 opened out into a flat plate, and finilhed by annealing as 



ufual. 1 3 c -..1, 



The large crown glafs of Meffrs. Hammond and bmitli 

 is fuperior in quality as well as in fize to that of any other 

 manufadure. The ufual diameter of the tables in other 

 manufaftures may be taken at 47 or 48 inches, with an 

 occafional variation in a table of one or two inches : and the 



Smith is 60 inches in diameter, and will admit of being cut 

 into fquares of about 33 inclies by 23 inches ; and a little 

 more or lefs. This glafs is almoll free from thofe fpecks, 

 wreaths, &c. which difcolour other glafs, and diftort the 

 obiefts feen through it. It now fupplies the place of 

 German fliect glafs for prints, large fafhes, and exportation 

 to thofe foreign markets where that glafs was formerly in 



ufe. - 



Glass, French, as alfo called Normandy glafs, and ior- 

 merly Lorraine glafs, becaufe it was made in thole provinces : 

 though it has fince been made wholly in the nine glafs 

 works ; five of which were in the forelt of Lyons, four m 

 the country of Eu ; the lall at Beaumont, near Rouen. It 

 is of a thinner kind than our crown clafs ; and, when laid on 

 a piece of white paper, appears of a dirtyifli-green colour. 

 There are but twentj-five tables of this to the cafe. 



Glass, German, is of two kinds, the ivhUe and the green : 

 the firll is of a whitiih colour, but is fubjeft to thofe fmall 

 curved ilreaks, obferved in our NewcalUe glafs, thougli 

 Free from the fpots and blemilhes thereof. The green, 

 befides its colour, is liable to tlie fame ilreaks as the white ; 

 but both of them are llraighter, and lefs warped, than our 

 NewcalUe glafs 



Glas-s, Dutch, is not much unlike our Newcaftle glafs, 

 either in colour or price. It is frequently much warped, 

 like that, and the tables are but fmall. 



Glass, Neivcqfile, is that moll ufed in England. It is of 

 an afli-colour, and much fubjeft to fpecks, Ilreaks, and 

 other blemifhes ; and, befides, is frequently warped. Ley- 

 bourn fays, there are forty-five tables to the cafe, each con- 

 taining five fuperficial feet : fome fay there are but tliirty- 

 five tables, and fix feet in each table. 



Glass, Phia!, is a kind of glafs betwixt the flint glafs 

 and the common bottle, or green glafs. The bell kind may 

 be prepared with a hundred and twenty pounds of wlute 

 {and, fifty pounds of unpurified pearl-alhes, ten pounds of 

 common fait, five pounds of arfenic, and five ounces of 

 manganefe. The compofition for green or common phial 

 clafs, confifts of a hundred and twenty pounds of the cheapeft 

 white fand, eighty pounds of wood aflies, well burnt and 

 fifted, twenty pounds of pearl-allies, fifteen pounds of com- 

 mon fait, and one pound of arfenic. 



Glass, common greiii bottle, is made almoft entirely of 

 fand, lime, and fometimes clay, alkaline allies of any kind, 



as chcapncfs or convenience direft, and more efpeclally of 

 kelp in this country, of barilla, varec, and the other varieties 

 of foda in France, and of wood allies in many parts of Ger- 

 many, and the like. To thcfe ingredients is fometimes 

 added the earth remaining from fahne afhes, after the alkali ' 

 and falts have been extrafted by lixiviation, and in England 

 flags from the iron furnaces. Bottle -glafs is a very hard 

 well-vitrified glafs, which refills the corrofive adlion of all 

 liquids much better than flint glafs. It is ufcd, not only 

 for wine-bottles, but for very large retorts, fubliiiung veiTels, 

 aad pther articles of the chemical apparatus ; and it has for 

 this purpofe the advantage of bearing as much as a pretty 

 full red heat without melting or finking down into a fiiape- 

 Icfs lump, as the lead-glalfes would do. The following 

 compofition is given by Loyfel as a good and cheap material 

 for bottle-glafs ; viz. ico parts of common fand, 30 of 

 varec (a kind of coarfe kelp made on the weflern coalls of 

 France), 160 of the lixiviated earth of afhes, 30 of frcfli 

 wood-afh, or any other kind of alh, 80 of brick-cla)', and 

 any quantity, general'y about 100, of brciken glafs. 'I'his 

 compofition yields no glafs-gall. This kind of glafs is 

 formed of fand of any kind, fluxed by the allies of burnt 

 wood, or of any parts of vegetables ; to which may be 

 added the fcorias or clinkers of forges. When the lofteft 

 fand is ufed, two hundred pounds of wood-alhes will fuffice 

 for a hundied pounds of fand, which are to be ground and 

 mixed together. The compofition witli the clinkers confifts 

 of a hundred and fevcnty pounds of wood-alhes, a hundred 

 pounds of f.nid, and fifty pounds of clinkers, or fcoria;, 

 which are to be ground an4 mixed together. If the clinkers 

 cannot be ground, they mull be broke into fmall pieces, 

 and mixed with the other matter without any grinding. 



A good bottle-glafs, but nearly black and opaque, has 

 been made in France of the decompofed pulverulent bafaltic 

 earth found in the vallies of all bafaltic countries. In France 

 it abounds in the Vivarais, in Languedoc, and Auvergne. 

 The firll glals of this kind appears to have been made in 

 1780 by a M. Ducros at the fuggellion of Chaptal, who 

 finiply melted foine of this balalt without addition in a glafs- 

 pot, and formed of it two very light, black, or rather deep 

 yellow, fliining, perfect bottles. In fubfequent trials by 

 another artill, a mixture of equal parts of bafalt and fand 

 w-as employed, as preferable to the bafalt alone ; but not- 

 withllanding a confiderable demand for bottles of this ma- 

 terial, tlie manufafture was abandoned for want of unifor- 

 mity in the ingredients, which made them often fail. The 

 colour of this glafs was of a green-olive. 



Tlie green colour, tranfmitted by bottle-glafs, when in its 

 perfect Hate, is owing to the iron contained both in the ve- 

 getable aflies and in the fea-fand, which enter into its com- 

 pofition. This glafs affords an inftance of a femi-pellucid 

 fubilance, which exhibits a blue colour by incident hght, 

 and a yellow or orange colour by that which is tranfmitted. 

 See Delaval on the caufe of the permanent colour of opaque 

 bodies. 



Giw^ss, Plate, is the mofl; perfect and beautiful glafs, of 

 which all the kinds of min'ors and looking-glaffes are com- 

 pofed. The materials of which this kind of glafs is made 

 are much the fame as thofe of other works of glafs, I'iz. an 

 alkali fait, and fand. 



To prepare tlie fait, they clean it well of all foreign mat- 

 ters ; pound or grind it with a kind of mill, and finally fift 

 it pretty fine. 



Pearl-aflies, properly purified, will furniili the alkali fait 

 requifite for this purpofe ; but it will be necelfary to add 

 borax, or common fait, in order to facilitate the fufion, and 

 prevent the glafs from fliffcning in that degree of iieat, in 



wliich 



