however, that these tubes have come into any extensive

use.

This elliptical bore is caused by flattening, in the necessary degree, and before it is drawn out, the short thick tube already described; restoring then its external cylindric form by coating it over with a further portion of melted glass, and rolling it on the iron slab, represented (fig. 5. Chap. IV.) in the foregoing description of the processes pursued in blowing flint glass.

The apparatus usually employed by those who undertake this branch of glass-working is extremely simple. The table is substantially made, and has fixed at its bottom a small double-blast bellows, worked with a footboard, that the artist may himself govern its action, and at the same time have both his hands at liberty for the other operations which he has to conduct. A pipe, proceeding from the bellows, conducts the blast of air to the lamp, which is usually nothing but a bundle of coarse cotton thread, placed in a common tin vessel of a horse-shoe shape, the flame being fed with lumps of tallow heaped up and intermixed with the cotton. A small chimney is hung over the lamp, and at a short distance from the flame, to carry off the smoke, which otherwise would be inconvenient to the workman. The blast pipe is so placed and directed that it throws off the jet of flame from the lamp in a direction contrary to that occupied by the workman, so that all annoyance from this source is equally avoided.

Two or three very simple iron tools, such as files, forceps, scissors, &c., make up the rest of the glassworker's apparatus; while his materials are mostly confined to an assortment of tubes having various bores, and composed of different thicknesses of glass. When employed in making toys or ornaments of glass, tubes of various colours are provided by the workman: these are easily procurable at any glass-house, a good stock of all kinds of tubing being generally kept by the makers. The flame, when most strongly urged by the blowpipe, is about four inches long, having its end of a blunt round

form; its colour, in the part nearest to the wick, is of clear light blue, and beyond this of a pale yellow, the blue portion having by far the greatest heating power.

In proceeding to work, care must be taken to remove all moisture from the tubes, both within and on the outside; they must be heated gradually, to prevent their cracking; and the greater the thickness of the glass, the more necessity there is for caution on this head. Glass is so imperfect a conductor of heat, that where utensils made with it of any considerable thickness have fire applied to them, it is difficult to prevent an unequal degree of expansion, which induces that corresponding inequality of pressure among the different parts under which some will inevitably give way and fly asunder. It is for this reason that glasses intended for use in chemical laboratories can hardly be made too thin, or with too great attention to the equality of their substance, so that heat may be quickly and uniformly transmitted through the

mass.

Glass tubes should be first heated by being held in the flame of the lamp, without employing the blast of air; they should next be brought to the yellow outer edge of the flame when urged by the blowpipe; and, lastly, the fusion must be completed through bringing the glass by slow degrees within the hottest part of the flame.

The power of a blowpipe, such as is usually employed for these purposes, is sufficient for bringing to a white heat a solid lump of glass large enough to form a bulb which will contain three fluid ounces; a size much larger than can be required for purposes to which the lamp is usually applied.

It may be well to describe briefly one or two operations, such as are usually effected by means of the lamp and blowpipe; from which will be made apparent the great facility wherewith this seemingly refractory substance can be moulded, through the agency of heat, according to the will of the workman.

If it be wished to seal a tube hermetically, that is, to

close it effectually at the end by causing the intimate union of its particles, it will suffice that the part be held during a short time in the flame, turning the tube round with the fingers so as to occasion an equal action upon every part by this means the end will presently be so far softened, or partially fused, that the particles will fall in and run together; thus effectually closing the orifice, and producing the appearance of a small button at the extremity. This operation may be hastened, if, when the glass is rendered soft by heat, and before any fusion has ensued, the parts are brought into contact towards their common centre by means of a stout iron needle. In some cases, and particularly when the tube is of any considerable substance, the button thus formed on the end would be inconveniently large, and might besides either fly in cooling, or be accidentally broken. can be remedied by lessening, in the following manner, the quantity of glass whereof it is composed.

This

The end being softened in the flame of the lamp, and another piece of tube of the same size having been equally acted upon, the two ends are to be brought together, and may, by a very little management, be firmly united. If then the tube which is to be sealed is softened a little higher up than the point of union, and the two tubes are pulled gently in opposite directions until they separate, that which is heated will be drawn out with a diminished substance, and may be easily sealed in the part that is required, the joined ends and a portion of the sealed tube remaining attached to the waste piece.

In making some kinds of thermometers, and for various purposes connected with experimental chemistry, it is often required to bend tubes of glass: when these are of small bore, and their substance is tolerably thick, it is only requisite to hold the tube in the weaker part of the flame, in order to soften it through about one or two inches of its length, when it may be slowly and gently brought to the shape required.

Something more than this is needed if the tube be wide and its substance thin. In order to preserve in

such case the particular form of the bore, and to prevent its being much straightened, or perhaps closed at the bend, as it most probably would be if no precaution were taken against it, one end of the tube should be hermetically sealed; and during the time the workman employs himself in bending it at the required part, he should also blow steadily but very gently into the open end. The pressure of his breath employed in this manner, will keep the softened part of the tube distended in the proper degree, so that it cannot collapse during the bending, and the perforation will be maintained in its original form. The closed end of the tube may be readily cut off by first scratching with a file and then breaking it suddenly; an operation which, with a very little care, may be performed without risk of dividing the tube in any other part of its length.

Two tubes may be joined together with tolerable accuracy by heating their ends in the flame, and then bringing them into contact; turning them round in opposite directions with a screwing motion, in order to complete their junction. If it be desired to remove the thickened ring of glass which will thus be produced, one end of the tube must then be previously sealed; and when the union has been fully completed in the way described, and while the glass is yet soft, the workman must blow into the open end, and gently pull the tube at the point of junction, until the ring disappears, and the whole tube becomes equally cylindrical.

In forming hollow bulbs at the end of tubes, such, for instance, as are required in making thermometers, the following process must be used: — -The end whereat the bulb is to be formed must be sealed; and in order to collect at this extremity the needful quantity of glass, it must be pressed while yet quite hot upon some hard surface, by which means that part is somewhat shortened and consolidated into a lump. This must then be held in the most intense flame of the blowpipe until it is quite white hot; being then removed, and the breath applied moderately and steadily to the open end, and

keeping the tube in the mean while with the heated end hanging downwards, the lump will be enlarged into a spherical bulb, the diameter, and consequently the substance, of which can be regulated according to the pleasure of the workman.

It has been already mentioned that glass may be spun into very long and minute threads, with great velocity, when the mass from which it is drawn has been previously heated. For this operation the use of the blowpipe is required, and the manner of its performance is very simple.

The lump of glass being sufficiently softened by the flame, another piece of glass is applied to it, when the two, cohering together, and being then drawn apart, are seen to be connected by minute filaments. A fine thread being thus obtained, its end is applied to a wheel or reel, and the heat of the glass being maintained, while the wheel is turned with considerable velocity, a thread may be drawn continuously out as long as the workman pleases, or until the store of glass is wholly expended.

The thread thus made is extremely flexible and delicately fine. Its firmness depends in a great measure upon the heat whereat the glass is maintained, and upon the velocity wherewith the wheel is turned: the greater these are, the firmer will be the thread.

Glass is only treated in this manner in order to afford a pleasing exemplification of some of its properties, or for purposes of ornament. When it is desired to produce coloured threads, the material employed should be embued with a very deep tint, as, when drawn out in such minute filaments, it would otherwise appear nearly colourless.

The preparation of watch-glasses involves a series of simple but interesting processes. Only a part of these is performed at the glass-house; the remainder being the objects of a separate, and, when viewed with reference to its extent, by no means an unimportant branch of trade and manufacture.