Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/686

Rh G64 s:tb:aittin__: the mrtiuns to be etched or bitten to the influence of by-lrolluoric acid, the rcmaiuder of the glass being stopped off or pro- tected by a. coating of wax or some pitchy compound.‘ l‘i:1-:<s1-:n (:L_ss.—'l‘he most brilliant effect is produced by cutting, but moulding or pressing is much cheaper, and this branch of the art has nov reached a high state of excellence. Ulass formed by pressing in moulds, known distinctively as pressed glass, is peculiarly an l-English industr_-', principally becattsc it is only tlint glass, or glass possessed of si:nilar properties, that can with advantage be formed in that wa_v. Although mouldc .1 glass has ex- isted from early Roman times, it is only within the present century that the modern industry has been developed, and of late years the trade has assumed important dimensions. A metal that melts at a comparatively moderate heat, and does not quickly pass from the plastic state, is essential for success in pressed glass making, because it has not only accurately to ﬁll all the intricacies of the mould, but it must also be susceptible of fire-polishing. This operation consists of a reheating sullicicnt to melt a thin superﬁcial stratum of the glass, whereby the roughness and obscurity of surface incidental to moulding is removed, and a smooth brilliant effect brought out, inferior only to the sparkling appearance produced by ctttting. The moulds for pressed glass are made of iron or bronze ; with great accuracy of surface ; and they are, in use, kept a little under a red heat. The various segments of the mould are so hinged or connected as to close and leave internally a space representing the form and size of the article to be made, the internal hollow not being pro- duccd by blowing but by the plttnger of the press under which the mould is placed. The required quantity of metal being dropped into the mould, the plunger descends and forces it into all parts of the cavity, completing innnediatcly the formation of the article, which is then ﬁrc-polished by reheating, and afterwards annealed. In this way glass with elaborate facets, bosses, flutings, or other bold orna- ments can be produced with rapidity and case ; and the only bar to great eheapncss is the heavy cost of the lead and potash in flint glass. Several manufacturers both in England and on the Con- tinent, where the pressed glass industry is c.t -nding, now partially supply the place of these costly materials by lime and baryta ; and indeed English pressed glass of excellent quality is now in the market containing ncithcr lead nor potash to any appreciable extent. l3AI‘.YTA GLAss.—Thc high price of red lead, and various disad- vantages connected with its use, have given rise to many efforts to find an efﬁcient substitute for it_in the manufacture of table and ornamental glass. Barium compounds, principally the native sul- phate (common baryta or heavy spar) and the artiﬁcially prepared carbonate, have been more or less experimentally tried ever since 1330 ; but of late years the use of baryta has attracted much atten- tion, and iii several French and Belgian glass-works it is under- stood to have taken its place as a raw material, without, however, much being publicly said regarding the subject. 11. E. Benrath, the scientific director of the Lisette glass—works near Dot-pat has in- vestigated the application of baryta in glass-making with great ful- ness. laryta, it appears, can be used as a partial substitute for the alkalies in glass-making; and indeed it was affirmed by Peligot that carbonate of baryta could altogcthcr supplant either potash or soda, and yield a glass perfectly free of alkali. Such a glass is, how- ever, shown by Benrath to be without practical value ; but he has demonstrated that baryta may be used in the place of either lead or lime, to produce an easily fused dense glass much more brilliant than common glass, and in appearance and properties intermediate between that and flint glass. The qualities of the glass and its usefulness for various purposes can be modiﬁed by using both baryta and lime in varying proportions. There seems little doubt that baryta will occupy an important place in the future of the glass industry. BUTTLE GLASS.—Tl1is department of glass manufacture is of im- portance on account of its enormous extent ; and although the raw materials employed in the trade are coarse and impure, and though the ﬁnished product has little appearance of excellence, the quality of the glass is in the highest degree important. Glass bottles, for example, are used for storing and preserving all manner of liquid substances for food, some of which undergo active chemical change, throughout a pcriod of many years. In such a case it is of the highest consecpicnce that the glass should be capable of resisting the solvent ant corrosive action of acids an-1 other substances which may be imprisoned or generated within the bottle, and sttch an ob- ject is attained by the high proportion of alumina which is foundin bottlc glass. liottle glass varies in tint from the dark-green, almost black, semi-transparent claret bottles to clear and transparent qualities such as are employed for bottling at-rated waters. The dilfercn--e in colour is partially due to the varying purity of the 1Il.ltI'l'l'l.l-i used, and partly to the action of bleaching or oxidizing agents. The nntt-rials ordinarily cmploycd arc common sand, gas- limc, brick-cl.tv, common salt, and soap-boilcrs' waste ; but local I A large proportion of the tbscurin: of the commtwer varieties of glass and of the obscured ornamentation on plate and sheet a-4 w»-ll as on flint ghhs is now produced by means of 'l‘ilglnnan's sand blast described below. (lIJ.iSS [.t..'L':‘:.cTt'I:1:. circmnstances have much influence in determining the class of materials used. In Continental bottle works lava, basalt, and simi- lar rocks of volcanic origin were formerly employed; and in lh-n- tnark and Sweden fluoride of calcimn, left as a waste product of the manufacture of soda from cryolitc, is used with marked :ulvanta_-_rc. For bottle-making the tank furnace with or without compart- ments as already described is much used; but pot furnaces also continue in use. The arrangt-mcnts of a common bottle liousc art- seen in fig. 19, which is a ground-plan indicating a bilateral FIG. 19.——Plan of Bottle House. arrangement of a double bottle house, with the cotnplctc plan of a four-pot furnace and ash arches. The furnace is oblong, similar to the crown furnac.c, but arched over in a barrel shape. lt is erected in the centre of the brick cone, above a cave, which admits the atmosphcre to _the grating. The working holes of this furnace, opposite each pot, for putting in the materials and taking out the liquid glass, are each about 1 foot in diameter. At each angle of the furnace there is also a hole about the same size communicating with the calcining arch, and admitting the flame from the main furnace, which rcvcrberatcs on and calcincs the materials in the arch. lit the ﬁgure, 1 shows the main furnace ; 2, 3, 4, 5, the ash arches for calcining the materials; 6, 7, 8, 9, 10, 11, annealing arches; 12, two-pot arches; 14, clay-house for picking, grinding, sifting, and afterwards working the clay into paste for the pur- pose of manufacturing pots ; 15, mill house for grinding clay ; 16, a. building containing a calcar furnace for experiments, or for pre- paring the materials, when the ash arch attached to the main fur- nace is ltnder repair, including 1, a sand crib, and 2, an ash crib for sifting and mixing the materials, suflieicnt for two houses. The following is an outline of the process of making a common bottle. After the metal has been skimmed, the person who begin.»-. the work is the gathercr, who, heating the pipe, gathers on it a small quantity of metal. After allowing this to cool a. little, he again gathers such a quantity as he conceives to be suflicicnt to make a bottle. This is then handed to the blower, who, while blowing through the tube, rolls the metal 11 ion a stone, at the same time forming the neck of the bottle. Ile t ten puts the metal into a brass or cast-iron mould of the shape of the bottle wanted, and, continuing to blow through the tube, brings it to the desired form. The patent mould now in use is made of brass, the inside finely polished, divided into two pieces, which the workman, b_v prcssing a spring with his foot, opens aml shuts at pleasure. The blower then hands it to the ﬁnisher, who touches the neck of the bottle with a small piece of iron dipt in water, which cuts it completely off from the pipe. He next attaches the punty, on which is a little mctal gathered from the pot, to the bottom of the bottlc, and thereby gives it the shape which it usually presents. This punty may be used for from 18 to 2-1 dozen of bottles. It is occasionally dippcd into sand to prevent its adhcringto the bottle. The finisher then warms the bottle at the furnace, and taking out a small quantity of metal on what is t(‘l'lllt'tl a ring iron, he turns it once round the mouth, forming the ring seen at the mouth of lloltles. llc thcn employs the shears to give shape to the neck. One of thc blades of the shcars has a piece of brass in the centre, tapcrcd like a common cork, which forms the inside mouth ; to the othcr blade is attachc-l a piece of bras.»-., uscd to form the ring. The bottle is thcn lifted by the neck on a fork by a boy, and carried to the