588

GLASS-MAKING.

to form the glass upon the end of the tube, and by a dexterous swing or twolengthens it, as shown in I, fig. 511. To extend the neck of that pear, he next rollsover a smooth iron rod, turned round in a horizontal direction, into the shape K ,fi&- 0By further expansion%t the blowing-furnace, he now brings it to the shape i, repsented in fig. 511. _ r gjj

This spheroid having become cool and somewhat stiff, is next carried to the bottom ghole (like fig. 509), to be exposed to the action of flame. A slight wall erected be ^one half of this hole, screens the workman from the heat, but leaves room for the S p r0 ,ppass between it and the posterior wall. The blowing-pipe is made to rest a little w*? r e-the neck of the globe, on a hook fixed in the front wall; and thus may be made easily gtvolve on its axis, and by giving centrifugal force to the globe, while the bottom °* 1 jpart opposite to the pipe, is softened by the heat, it soon assumes the form exhibitm, fig. 511. , 0 n

In this state the flattened globe is removed from the fire, and its rod being resl s0 ]idthe casherbox covered with coal cinders, another workman now applies the end of airon rod tipped with melted glass, called a panto, to the nipple or prominence in jjsmiddle; and thus attaches it to the centre of the globe, while the first workman eoff the globe by touching its tubular neck with an iron chisel dipped in cold water. poleworkman having thereby taken possession of the globe by its bottom or knobbe i gSattached to his punty rod, he now carries it to another circular opening, where he e 1^^it to the action of moderate flame with regular rotation, and thus slowly heats th e ^ juprojecting remains of the former neck, and opens it slightly out, as shown 8 . gge dfig. 511. He next hands it to the flasher, who, resting the iron rod in a .^now^ 1near the side of the orifice A, fig. 509, wheels it rapidly round opposite to a P°flame, till it assumes first the figure o, and finally that of a flat circular table. ^ovesThe flasher then walks off with the table, keeping up a slight rotation as hepjon,along, and when it is sufficiently cool, he turns down his rod into a vertical P . tan tand lays the table flat on a dry block of fire-clay, or bed of sand, when an asnips it off from the panto with a pair of long iron shears, or cracks it oft' with n gedof cold iron. The loose table or plate is lastly lifted up horizontally on a <l° u gn t withiron fork, introduced into the annealing arch fig. 510 and raised on edge; an assis a greata long-kneed fork preventing it from falling too rapidly backwards. In this a boU l

heat of

many tables of glass are piled up in iron frames, and slowly cooled from a neu ;600° to 100° F., which takes about 24 hours; when they are removed. Acircu

late

or table of about 5 feet diameter weighs on an average 9 pounds. . . ca lcia e< ^

4. Flint glass. —This kind of glass is so called because originally made wt coU ntryflints, as the silicious ingredient. The materials at present employed in 1 ,“ wa6 heO ’for the finest flint glass or crystal, are first, Lynn sand, calcined, sifted, pearl"

second, an oxyde of lead, either red lead or litharge; and third, pearJash. water,

ash of commerce must however be purified by digesting it in a very . i f sulphate. 0 ,,which dissolves the carbonate of potash, and leaves the foreign salts, chiefly - g ba" 1 '’potash, muriate of potash, and muriate of soda. The solution of the car n boil e ’allowed to cool and become clear in lead pans, is then run off into a shall 0 e b"j

and evaporated to dryness. Nitre is generally added as a fourth ingredten ^- se froof the glass; and it serves to correct any imperfections which mtg at* 0

accidental combustible particles, or from the lead being not duly oxydize • anL ] man

four substances constitute the main articles; to which we may add arse ^ up , f

ganese, introduced in very small quantities, to purify the color and e '

transparency of the glass. The black oxyde of manganese, when used in * g( j byonly as to peroxydize the iron of the sand, simply removes the ereen tinge c ^ „;veiron; but if more manganese be added than accomplishes that purpose, 1 an e xcepurple tinge to the glass; and in fact, most manufacturers prefer to Jia d by a <alrather than a defect of manganese, since cut glass has its brilliancy ' nc,e exC ess of &*lilach hue. The arsenic is supposed to counteract the injury arising f>' on ‘ ^ 0 palesce Dganese, but is itself very apt on the other hand to communicate some degre