28

GLASS.— Bottle-Making. Tube-Drawing.

3 feet in height, and nearly the same in diameter.They are filled almost to the edges ; and when thematter has sunk down, and is converted into a glass,more of the composition is put into the pots, andthe fire is urged. The meltings are rapid ; for asmost of the bottle-glass compositions furnish butlittle glass-gall, no time is lost in fining. The pro-cess lasts from seven to eight hours, and when it is. concluded the fire is slackened, that the glass maythicken to the point suitable for working it. Torthis purpose the fire-place is heaped up with smallcoal, draughts are intercepted as much as possible,and care is taken not to touch the fire during theworking of the glass, lest the combustion should bere-excited.

As soon as the working holes are opened, the sur-face of the glass is cleared from sandiver or glass-gall. By dipping the previously warmed pipe intothe pot, a little glass remains attached to the end;after turning this in the air before the hole until itis cooled, and blowing slightly into it to render ithollow, a fresh layer of glass may be attached to itin the pot; to this a third is added in the samemanner, until the ball at the end of the pipe hasaccumulated to a sufficient size. That this ball maybecome uniformly tractable in the subsequent form-ing, it is held by the workman in the flame of thefurnace through the working hole; it is then broughtinto one of the round concavities of the “ marver,”which is wetted or moistened when used. Here theball gradually assumes the form of a thick hollowglobe, or rather pear-shaped vessel.

Thus far advanced, the glass has again becomecool, and is re-heated by insertion into the workinghole, in such a manner that the front part receivesthe chief portion of the heat, and becomes thesofter. The pear-shaped vessel is now lengthenedby the blower, and its form is made somewhat toresemble that of a bottle by a threefold operation :by blowing into the tube with greater force, swing-ing it backwards and forwards in the manner of apendulum, and by a simultaneous constant rotarymotion of the pipe round its axis. ■ As soon as thevessel is of the right size it is inserted in a cylindricalhollow block of wood or iron, placed at the side ofthe workman who is blowing the pear-shaped vessel;and by blowing forcibly into the tube the glass ispressed firmly against the sides of the mould, whilst,by a kind of jerking motion, the neck is drawn outto the proper length. The unfinished bottle, whichas yet has no bottom or mouth, is again warmed inthe working hole in such a manner that the lowerpart only is heated, whilst the other part remainscomparatively cool. In the meantime another work-man or a boy has attached a small quantity of glass tothe ponty or pontil, which is also kept hot in theworking hole. Both workmen now stand oppositeto each other; and whilst the pipe and ponty arekept constantly turning, the latter is forcible pressedagainst the middle of the lower part of the bottle,which is thus forced inwards, and an even edge isproduced, upon which the bottle may stand steadily.The bottle remains for some moments between the

two instruments, until, by the application of coldiron or a drop of water, the neck can be separatedfrom the pipe. This is an operation of constant re-currence in the glass-house, and is effected by asudden change of temperature produced at the pointof separation in the hardened glass, either by thecold application of a drop of water, or by the power-ful heat of a red-hot iron, or thread of liquid glassfrom the pot. The point of separation sometimesrequires to be re-heated, to cause it to fly on theapplication of cold water. The bottle is now sup-ported by the ponty, so that the neck can be warmed,and the sharp edges melted round without softeningthe other parts. A rotating motion is then given tothe red-hot neck, the pipe being rolled backwardsand forwards upon the knees of the workman. Thebottle then revolves upon the axis, and it is onlynecessary to press the pueellas, or an iron instru-ment like a turning chisel, against the mouth towiden or reduce it to any required dimensions ; therim for strengthening the neck is formed from a dropof glass taken from the pot by the edge of the flask,and wrapped round the mouth in the form of athick thread. The bottle, which is now finished,is immediately carried on the ponty-rod to theannealing-oven by a boy, pushed into its properplace, and the ponty-rod is finally detached fromthe bottom of the bottle by a sudden sharp jerk.The place where the ponty was attached is per-ceptible in every bottle blown in this manner, bythe sharp edges where the fracture occurred.

Large round bottles are blown without the useof a mould, and when of a very great size, like thecarboys for sulphuric acid, the aid of steam is calledin, by spirting about an ounce of water into theinterior, and holding the mouth of the pipe withthe thumb.

Tube-drawing .—The operation of “ tube-drawing ”depends on the singular fact, that when a hollowlump of glass, for instance a globe, is drawn outwhilst hot, the cavity in the interior is always pre-served, even when the glass is drawn out to thetenuity of the finest thread.

Whilst one man collects the necessary quantity ofglass on his pipe, and blows this out to a very mas-sive globe, preserving a uniform thickness of thesides as much as possible—the other attaches a dropof glass to a ponty-rod, and warms it on the fire bythe side of the globe. Both instruments are thenremoved from the fire at once, and the ponty-rod ispushed forcibly against the globe in such a manneras to form exactly a straight line with the pipe.This being accomplished, one of the workmen retiresbackwards as quickly as possible, to the distance of50, 60, or 100 feet. In this operation the globe atfirst shrinks, and forms the commencement of thetube, which soon cools, and does not diminish inthickness, whilst the mass of glass is spun out by theconstant drawing from the warm end. Continualrotation of the pipe and ponty-rod is necessary, orthe part of the tube nearest the ground would coolquickest, and the tube thus assume an irregular form.This, however, does not prevent the tube, in conse-