Page:Encyclopædia Britannica, Ninth Edition, v. 10.djvu/683

Rh 1I.-i.*Ui«‘. c'rt'I:E.] coninieiices blowing it, at the same time coiitiiiniiig to tnrii it in the wood block, till he percci'es the diameter to be of the requisite diiiieii- sions (fig. 10), which are usually from 11 to 16 inches. The workinan then rcheats this cylindrical mass, and, when it is suﬂiciciitly softened, coinnieiiccs swinging it over his head, continuing to rchcat and swing till he has made it the desired length, which is commonly about 45 . .-F .'l .‘. . 1 i‘ ll ‘ l! l Ii ~1_'I...J-‘=1'="'!1!i'Im':mlH’lliiilrarri.ll". Fig. 8. Fig. 9 Fig. 10. inches. It is now a cylinder of say 45 inches long by 12 inches in diameter, one end being closed, and the other having the pipe attached to it. The worknian begins to open the end which is closed, for which purpose he encloses the air in the cylinder, by stopping the aperture of the pipe with his finger ; and then placing the close end of the cylinder towards the ﬁre, it becomes softened, while at the szinic time the air within is expanding, and, in about thirty seconds, t.lie softened glass at the extremity of the cylinder gives way, forming an aperture as in ﬁg. 1 '2. The workman then turns the cylinder round very quit-kl y, and, by keeping the opened extremity warm at the same time flashes it out perfectly straight as at g, fig. 13. If the burst edges are ragge i in appearance they are trimmed by cutting with a pair of scissors before ﬁnally expanding. The bursting of the end of a thick licavy cylinder has to be determined by allowing a glowing drop of glass to fall on the spot to be burst before presenting it to the fire. Fig. 11. The other end, which is attached to the pipe, has now to be cutoff, and is done in the following manner. The workman,ha'ing gathered a small quantity of metal on the pontil, draws it out into a thread of about oiie-eiglitli of an inch in diameter, laps it round the pipe end of the cylinder, and, after letting it remain there for about five seconds, withdraws it suddenly, and immediately applies a cold iron to the heated part, which occasions such a sudden contraction, that it cracks off where the hot string of glass has been placed round it. Another method is to draw a senii-cylindrical rod of iron c (ﬁg. 13) heated to redness around the line d of desired fracture, and a drop of water then allowed to fall on the line so drawn determines its fracture. The stages in the development of a cylinder to its full length are illustrated in figs. 9 to 13. Iv'latlcnz'21_q.—The cylinder so blown and detached is now allowed to cool; and, previous to its ﬂattening, the burst extremity being thinner than the remainder, and slightly contracted at its edge, has to be removed to the depth of about 2 inches. For this purpose the cylinder is placed vertically in the jaws of a cutting instrument, having 3. diamond cutter, pressing by a spring, inside the glass(ﬁg. 14). The cutter moves by small wheels on the table on which it is placed, and being pushed around the c_ylinder it makes an accurate cut of uniform height. The cylinder has then to be split longitudinally to allow it to be opened out to a ﬂat shcct. To ac- complish this the practice was fornicrl y to lay the cylinder horizon- tally on a bench, and draw a red-liot iron two or three times along the inner surface at the line of desired fracture. X ow the splitting is done with a dianioiid cutter fixed in the cleft of a stick and (fig. 15) guided from end to end of the cylinder by a :~traiglit-edge K laid within it. The cylinder is now ready to be taken to the flat- 661 toning kiln, which consists of two chambers built together, the one for llatteiiiiig the cylinders, the _othcr for annealing the sheets, the former being kept at a. much higher teniperatnre than the latter. The cylinder, after being gradually reheated, is placed in the centre of the ﬂattening oven, upon a smooth stone, with the split side i1pwai'ds. In a short time it becomes softened with the heat, and ‘MI: ll-; .1 Fig. 15. by its own weight falls out into a ﬂat square sheet of 45 inches by 86. The ﬂattencr, with a. piece of charred wood, rubs it quite smooth, and then places it on edge in the annealing arch, where it remains about three days to be annealed. In the ari'-angcnieiit of the ﬂattening and annealing ovens numer- ous iniprorcineiits have been effected, which have resulted in greatly increased snioothness and uniformity of the glass, and in considerable economy of time and labour in the operations. Fig. 16 shows a section of a ﬂattening (L) and annealing kiln (II) in common use. The split cylinder 0 is introduced and gradually pushed for- ward so as to be i1iiif'orinly heated till it reaches 1’, the flattciiiiigstonc or table, mounted on a movable waggon X. On this waggoii after it has been ﬂattened it is carried into the annealing arch M, as showii by the dotted outline. Here in a less heat it gradually stitfens, till it is ready to be moved by a forked tool to a. horizontal position On the bed of the annealing oven. The waggon then goes back to the ﬂattening arch, and when it is reintroduced with another sheet, that previously flattciicd is ready to be piled up on edge at It, aml 111119- tlic work proceeds till the annealing oven is filled, when it is closed up and allowed to cool down by slow degrees. Chance Lrothers it ('0. of llirniingliani are the iiitroduccrs of a system of C0'l1tl]l1l- ous flattening and annealing furnaces. This they ac_-coniplisli by means of two contiguous circular kilns having re'ol'iiig soles, the