in a sooty flame, is shown by a2.

A Spray Arrester.—This is made by the second method, in which the piece of tube which projects inside the bulb is fused in position first and the outer tube is then joined on. The various stages of making are illustrated by b, b1 and b2, Fig. 9.

A bulb is blown between two tubes by the method given on page 22, the larger tube is then cut off and the small piece of tube introduced into the bulb after having been shaped as shown in by b, Fig. 9. The opening in the bulb is sealed as shown by b1. The sealed part is now heated and the bulb inclined downwards until the inner tube comes in contact with the seal and is fused in position. This operation requires some practice in order to prevent the inner tube either falling through the soft glass or becoming unsymmetrical. The end of the bulb, where the inner tube comes in contact with it, is now perforated by heating and blowing, thus giving the form shown by b2, and the outer tube is joined on. The finished spray arrester is shown by b3. Practice alone will give the power to produce a symmetrical and stable piece of work.

Two Forms of Filter Pump.—That illustrated by d, Fig. 9, is made by the method explained under "An Air Trap on a Barometer Tube." That illustrated by c is made by the method explained under "A Spray Arrester." No new manipulation is involved, and the construction should be clear from a study of the drawings.

Multiple and Branched Internal Seals.—A fuller consideration of these will be found on page 39, but one general principle may well be borne in mind; that, as far as is possible, a tube having both ends fastened inside another tube or bulb should be curved or have a spiral or bulb at some point in its length, otherwise any expansion or contraction will put great strain on the joints.

Sprays.—A spray which is easy to make, easy to adjust, and easy to clean after use is shown by e, Fig. 9. The opening on the top of the bulb is made by melting on a bead of glass, expanding, bursting, and fusing the ragged edges. The two branches which form the spray producing junction are made by the method used for an exhaustion branch and described on page 18.

A spray which can be introduced through the neck of a bottle is shown by h, Fig. 9. The various stages in making this are illustrated by f, and g. If the inner tube is made by drawing out from a larger piece of glass so that two supporting pieces are left on each side of the place where it is intended to make the final bend, that bend can be made in a flat-flame gas burner without causing the inner tube to come in contact with the walls of the outer tube. Care must be taken when joining on the side piece that the inner tube is not heated enough to fuse it. The small hole in the side of the outer tube is produced by heating and bursting.

A Liebig's Condenser.—This consists of a straight glass tube passing through an outer cooling jacket. In practice it is better to make the jacket as a separate piece, and to effect a water-tight junction by means of two short rubber tubes. It may, however, be made with two internal seals of the class described under "A Spray Arrester." There is much less risk of these seals cracking if the inner tube is made in the form of a spiral or has a number of bulbs blown on it in order to give a certain amount of elasticity.

A Double-Surface Condenser.—Fig. 10 shows a condenser of this nature which is supplied by Messrs. Baird and Tatlock. It may be built up in stages as shown by a, b, and c, but the work involved requires considerable skill, and the majority of laboratory workers will find it cheaper to buy than to make.

Fig. 10

A Spherical Condenser.—Such a condenser as that shown by f, Fig 10, involves a method which may find application in a number of cases. The outer bulb is blown from a thick piece of tubing which has been inserted in a smaller piece (see d, Fig. 6); then the inner bulb by similar method. It is now necessary to introduce the smaller bulb into the larger, and for this purpose the larger bulb must be cut into halves. A small but deep cut is made with the file or glass-blowers' knife in the middle of the larger bulb, and at right angles to the axis of the tube on which it is blown. A minute bead of intensely heated glass is now brought in contact with the cut in order to start a crack. This crack may now be led round the bulb as described on page 30. If the work is carried out with care, it is possible to obtain the bulb in two halves as shown by d, and these two halves will correspond so exactly that when the cut edges are placed in contact they will be almost air-tight. The two tubes from the smaller bulb should be cut to such a length that they will just rest inside the larger, and the ends should be expanded. Place the inner bulb in position and fit the two halves of the outer bulb together, taking great care not to chip the edges. If the length of the tubes on the inner bulb has been adjusted properly, the inner bulb will be supported in position by their contact with the tubes on the outer bulb. Now rotate the cracked portion of the outer bulb in front of a blowpipe flame and press the halves together very gently as the glass softens. Expand slightly by blowing if necessary. If a small pin-hole develops at the joint it is sometimes possible to close this with a bead of hot glass; but if the bulb has been cut properly there should be no pin-holes formed. The condenser is finished by joining on the side tubes and sealing the inner tube through by the methods already given. In order to blow bulbs large enough to make a useful condenser, it will be convenient to employ the multiple-jet blowpipe described on page 4.

A Soxhlet-Tube or Extraction Apparatus.—This involves the construction of a re-entrant join where the syphon flows into the lower tube. It is of considerable value as an exercise and the complete apparatus is easy to make.

A large tube is sealed at the bottom and the top is lipped, as in making a test-tube. A smaller tube is then joined on by a method similar to that given on page 18, but without making a perforation in the bottom of the large tube. Heating and expanding by air pressure, first through the large tube, then through the smaller tube and then again through the large tube, will give a satisfactory finish to this part of the work.