the required shape. The production of any constriction in the bore may be avoided by causing some length of tube to take part in the bend, which should never form a sharp angle, but a wellrounded curve, as in the syphon (fig. 6).

Glass tubing may be drawn out to an almost capillary point, as in the jet of a wash bottle, end of a pipette, &c., by heating a portion of it, about a quarter

of an inch long, until it just softens and then steadily pulling until a sufficient constriction is produced, which is afterwards scratched with a file and snapped across. The point may have its edges rounded, and its aperture further diminished if necessary, by holding it in the flame for a few seconds or So. In order to point the extremity of a piece of tubing, another piece of tubing or rod must first be joined to it by the blowpipe, so that the neces

Fig. 6.

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sary extension may be made. It is often advisable to thicken a tube slightly at the spot where it is to be drawn out, by rotating it for some time in the flame, and gently pressing its ends together. In this way the conical aperture may be made both strong and fine.

(15.) Glass-blowing is a valuable accomplishment to the practical chemist, but there are only one or two small operations with which it is actually necessary for the student to become familiar. It will be rarely worth while for him to make his own test-tubes, but he should be able to reseal any that have got accidentally broken. By means of the blowpipe, a piece of waste rod or tubing must first be joined firmly on to two or three projecting points of the broken end, and be made to coincide as nearly as practicable with the axis of the test-tube, as in fig. 7.

Then, at about half an inch or more from its broken end, the tube is to be steadily heated in a large blowpipe-flame, and constantly rotated until a considerable constriction is formed, when gentle extension may be employed. The flame is next to be directed upon what will form the bottom of the tube, just at its Fig. 7.

bend or shoulder, and the extension continued. By this means the end to be pulled away will be left irregularly conical, and that of the new tube well rounded. Finally, the thread of glass proceeding from the cone is to be strongly heated at its junction with the tube until it melts and becomes detached. There is thus always left on the bottom of the tube a little burr or projection of melted glass, which, if sufficiently small, may be made to disappear by heating it and the whole bottom of the tube until the glass is soft, and then blowing into the tube with moderate force while rotating it in the mouth. The burr, if too large for this treatment, may be melted in a small blowpipe-flame, and then have a piece of waste tubing, previously warmed, applied to it, and quickly drawn away, so as to bring the burr with it. In this manner a smaller burr will be left, which may be melted into the bottom of the tube as above described. The mouth of a test-tube may be everted by softening it in the flame, and then bending the edge uniformly outwards with the smooth end of an old file previously heated nearly to redness; or else a conical piece of charcoal may be twisted into the softened mouth of the tube.

Glass tubes sealed at both ends constitute the best means of preserving small specimens, either of liquid or solid. One end of the tube is first sealed as if for a test-tube, save that the small burr need not be interfered with. The other end is then constricted to a greater or less extent, according to the size of the specimen to be introduced, so as to leave a funnel-shaped

Fig. 8.

Fig. 9.

appendage, as in fig. 8. Liquids may be introduced through a very constricted opening by alternately warming and cooling the body of the tube while the liquid is contained in the funnel. After the substance has been introduced, a small blowpipe-flame is gradually brought to bear upon the constriction, and the sealing completed. Very careful heating is. more particularly required when the constriction is moist from the passage of liquid. For practice the student should seal up small tubes filled to within an inch or so of their length with water, spirit, sulphur, sugar, &c. When sealed tubes are used for effecting reactions under pressure, their ends have to be made with great care so as not to be less resisting than the original sides.

When a small bulb has to be blown upon the end of a piece of tubing, the closed end must first be thickened by rotating it in the flame for some time, and pressing it up with a piece of charcoal until enough glass has accumulated. This thick portion has next to be strongly heated, then withdrawn from the flame, and have air quickly but gently blown into it from

the other end, during constant rotation of the tube in the mouth. Or a bulb may be blown in the course of a tube, as in making a bulbed pipette (fig. 9 b), for instance. For this purpose a portion of the tube is to be thickened considerably by rotating it in the

flame for some time and gently pressing the two ends together. The nearest end is then to be closed with a cork, and the thickened portion, having been strongly heated, is to be distended into a bulb by blowing into the tube at the other end, during its rotation in the mouth. In making a pipette, a strong capillary termination should be first formed, and the bulb afterwards blown. The suction orifice may be everted or not at pleasure. The successful blowing of even small bulbs will not be found easy save after considerable practice.

(16.) Connections of tubing and apparatus are made in various ways. Two pieces of tubing of the same diameter may be sealed together, but the operation requires some amount of skill for its performance. The two ends, well adapted and by preference slightly everted, should be heated to softening in the Bunsen or blowpipe flame, and then brought steadily into contact, taking care that the edges exactly coincide. The junction has then to be heated for some time, constantly rotating the tube, and alternately pushing and pulling the free ends, one of which should be stopped with a cork, and the other occasionally blown into, so as to maintain a proper calibre. A piece of wide may be joined to a piece of smaller tubing, by first drawing out the former to a point, and then cutting it across just where its diameter coincides with that of the narrow tube. The two can then be joined together as if originally of equal size. In this way funnel-tubes may be made.

Glass tubes of more or less similar diameter are best connected by means of a short piece of vulcanite tubing, the internal diameter of which should be rather less than the exterior diameter of the glass tubes, so as to grasp them firmly by its contraction without requiring to be tied. In the absence of vulcanite, small connectors may be made of sheet india-rubber, a piece of which of the required size is to be gently warmed, and wrapped round a glass rod or tube; when its opposite edges, having been cut obliquely so as to overlap, and firmly pressed together with the thumbnails, will, if freshly cut and perfectly clean, adhere thoroughly. The removal of the caoutchouc connector, from the tube or rod

on which it has been made, may be facilitated by first moistening the rod in the mouth or afterwards dipping it in water. Glass tubes may often be advantageously connected by a considerable length of vulcanite tubing, which can be closed at will anywhere in its course by pressing it together with a clamp of some kind, or even by tying it tightly with string. A stiff union of two tubes may be made by wrapping a piece of well-soaked bladder or parchment paper several times round their opposed ends, and allowing it to dry on. Or they may be first connected by a piece of vulcanite tubing, and then stiffened by tying on one or two wooden splints made out of lucifer matches. In this way an ordinary funnel may be readily converted into a funnel-tube. An extempore funnel-tube may also be formed by merely resting a small funnel in the suction-orifice of a plain straight pipette (fig. 9 a).

A small tube may be adapted to a considerably larger one, or to the neck of a flask or bottle, by means of a well-fitting perforated cork, the size of which can be readily reduced to any required extent by rasping and filing. A sound cork of slightly conical shape, and of such a size as to require some little force for its insertion, having been softened by pressure between the fingers or rolling under the foot, should be pierced by thrusting the point of a rat-tail file half way through it from each end, and then right through. The hole so made must be enlarged by filing until of a size to fit the tube tightly. When two or more holes have to be made in the same cork, care must be taken to have them all parallel, and as equidistant as possible from one another and from the outside of the cork. For making the necessary perforations variously-sized brass tubes with cutting edges, known as cork-borers, may be used with advantage instead of files. The holes made with them should always be rather too small at first, so as to require some little enlargement by filing. By means of cork-borers, very admirable substitutes for corks may be cut out of solid vulcanite. The end of a tube to be inserted through a perforation should always be rounded off by carefully heating it to redness, so that it may not cut or tear the bore, through which