The two pieces of tubing to be used each have one end cut square and the other sealed in the usual manner. The longer of the two is now heated at the point at which the joint is to be made, until it begins to color the flame. A small flame is used, and the tube rotated until the flame begins to be colored, when the rotation is stopped, and only one spot heated until a spot the diameter of the tube to be sealed on has become red hot and begun to shrink. This is now gently blown out into a small bulb, as in a, Fig. 7, and it will be noted that this bulb will have walls tapering from the thick walls of the tube to a very thin wall at the top. The sides of this bulb, below the dotted line, are to form the small side tube to which the main side tube is to be sealed. The top of the bulb is now softened by directing a small flame directly upon it, and as soon as it shrinks to the level indicated by the dotted line, it is removed from the flame and quickly blown out to form a thin bulb, as indicated in b, Fig. 7. This will usually be so very thin that a stroke of the file or glass-knife will break it off at the dotted line, leaving the side tube, to which the short piece of tubing is now sealed according to the second method (Exercise No 2). In doing this, care is taken to direct the flame partly on the main tube in the two crotches, so that both tubes blow out a little and give space for the gases to turn in, as indicated in c, Fig. 7, and at the same time increase the mechanical strength of the job. On the other hand, care is taken not to deform the main tube, and not to produce such a bulge or bulb at the joint as will prevent the finished tube from lying flat on a table.
Discussion.—Most beginners tend to err in the first steps of this operation, by blowing too hard and too long when blowing out the little bulb. The result is a large, very thin bulb, which breaks off in such a way as to leave a hole in the main tube, occupying nearly half the circumference of the tube at that point, instead of the neat side tube which they should have. It is not difficult to seal a tube on this side tube, but it is very difficult to seal a tube into a hole in another tube. Care should be taken here, as in the two previous exercises, that the lump obtained at the joint when the two tubes are put together is made as small as possible, and reduced if possible by gently drawing on the side tube as soon as the tubes have actually joined. It is much easier to prevent the formation of a lump at the joint than it is to remove the lump after it is formed. The remarks previously made about blowing quickly after removing the work from the flame apply here with especial force. A "tee" tube, from its very nature, is exposed to a good many strains, so care must be taken that the walls of the joint are of uniform thickness with the rest of the tube.
The beginner will find it easiest to make this tube out of two pieces of the same tube, about 1⁄4 inch in diameter. Larger or smaller tubing is usually more difficult. If tubing much more than 1⁄4 inch is used, the whole joint, including part of the main tube, must be heated nearly to the softening point at the close of the operation, and well annealed, as described in Chapter 1 (page 3) or it will be almost certain to crack. In the larger sizes of tube it will be necessary to heat the whole circumference of the main tube frequently during the operation, to prevent it from cracking.
In sealing a small tube on the side of a large one, it is usually advisable, after warming the spot where the joint is to be made, to attach a small drop of glass to the tube at that point, and direct the flame upon that, thus supplying at the same time both a definite point to be heated and an extra supply of glass for the little side tube which is desired. In this way it is also easier to blow out a side tube with a sufficiently small diameter. If the diameter of this tube should be much greater than that of the small tube, the latter may be enlarged with a carbon or a flanging tool.
EXERCISE NO. 4
To Join Two Tubes of Different Diameters
In this case the first method (Exercise No. 1) is to be used whenever possible, as it gives a much smoother joint than the second method. The directions given will describe the adaptation of this method to the problem: if the second method must be used on account of awkward shape, etc., of the work, the modifications required will be obvious to any one who has learned to make the joint by the first method.
After sealing or corking one end of the larger tube, the
other end is drawn out to form a tail as described on page
9, taking care to have the tube uniformly heated, and
to draw the tail rapidly enough so that the cone is short,
as indicated in a, Fig. 8. The tube is now rotated, a
small flame directed against the cone at right angles
to an element of it, and it is allowed to shrink a little,
as indicated in b, Fig. 8, so that its walls will thicken.
When the tail is cut off, at the dotted line, the diameter
of the opening and the thickness of the walls at that point
should correspond with the dimensions of the tube to be
sealed on. As the glass is hot, the scratch for cutting it
must be made with a file (moisten the edge!), and it
often will not break square across. Before proceeding
to seal on the small tube, any large projections on the
cut end are best removed, by warming the cut surface a
little, directing the small flame upon each projection in
turn and touching it with a warm scrap of glass. It will
adhere to this and may then be removed by rotating this
scrap a little so as to wind up the projection on it, and
then drawing it off, while the flame is still playing on the
spot. This must be done rapidly and care taken not to
soften the main part of the cone.
The large tube is now taken in the left hand, the small one in the right, the ends heated and joined in the usual manner, taking care not to get any larger lump at the joint than necessary. A small flame is now directed on the cone at right angles to its elements as before, and the tube rotated so as to heat the whole circumference. The flame should be just large enough to heat the whole of the cone. As the latter shrinks, the lump at the joint is brought into the edge of the flame, and it and a very little of the small tube allowed to shrink with the cone.
When well shrunk and heated to blowing temperature the joint is removed from the flame and blown gently with careful rotation, pushing the tubes together a little when the blowing is about finished, so that the cone becomes a short thick half-bulb, as shown in d, Fig. 8. This corresponds to the first thick bulb in the first method (d, Fig. 6), and is treated similarly. It is again heated and shrunk, taking care not to involve either the large tube or the small one in the shrinking, blown quickly to about the same shape as before, (d, Fig. 8), and then gently drawn out into a smooth cone (e), exactly as in the first exercise. Care should be taken not to draw too rapidly or too far, as then the resulting cone (f) is weaker than it should be, and does not look well.
Discussion.—The beginner will find that this operation is best learned on two tubes which are not too nearly of the same diameter. A tube about 5⁄8 inch in diameter and one a little less than 1⁄4 inch will be suitable. Both should have moderately heavy walls (1⁄16 inch or a trifle over for the large tube, and a trifle less for the small one) but the large tube should not be too heavy or else it will be hard to prevent melting down too much of the small tube, and getting this drawn out too thin during the process. One of the troublesome features of this exercise is the difficulty of rotating two tubes of different diameters with the same angular velocity, so as not to twist the joint. Another difficulty is found in getting the cone uniformly heated to blowing temperature without overheating and overshrinking the small tube. The reason for this is obviously the much greater circumference of the cone, especially at its large end, so that relatively much less of it is being heated at any time. The beginner is also inclined to start with too long a cone, or else heat so much of the large tube that part of its glass is included in the cone, with the result that in order to get the right wall-thickness the cone must be made too long (g, Fig. 8). This does not look well, and usually will be irregular in shape.
EXERCISE NO. 5
Tube for Condensing Sulphur Dioxide
This is useful as a test of mastery of the preceding
exercise. A piece of 3⁄16 or 7⁄32 inch tubing is joined
to each end of a piece of tubing 5⁄8 by about 5 inches, and
two constrictions made in the large tube, by the method
described on page 10. The small tubes are then bent
in the same plane, as shown, and their ends fire-polished
(Fig. 9).
EXERCISE NO. 6
Bulb at the End of a Tube
For this exercise tubing of 1⁄4 inch diameter and moderately
strong walls is selected. A tail is drawn out on one
end of the tube, and a piece of tubing about nine or ten
inches long is cut off. The tail should be carefully drawn
in the axis of the tube, and in the same straight line with
it, as it is to be used as a handle in assembling the glass
for the bulb. This tail must be long enough so that it
can be conveniently held in the left hand, as described on
page 13, and rotated about the same axis as the main
tube. Holding the main tube in the right hand and the
tail in the left, the tube is rotated in a large flame so
that a piece of it, beginning where the tail stops and
extending about an inch to the right, may be uniformly
heated to the highest temperature at which it can be
kept in shape. As soon as
this temperature is reached,
the tube is removed from the
flame, continuing the rotation
and taking care not to draw
out the heated part, and
gently blown. The rotation
is carefully continued during
the blowing, holding the tube
in approximately a horizontal
position. As soon as the tube
has expanded a little the tail
is pushed gently toward the
main tube, continuing the
gentle blowing. If this is
properly done, the heated
piece of tube will become a
short bulb of about double its
original diameter, and about
the same wall thickness as the
original tube. It will have
somewhat the appearance of
a, Fig. 10, when properly manipulated.
The tube is now reheated as before, taking care this time that the heating extends over all that part of the bulb to the right of the dotted line in the figure, as well as part of the main tube adjoining. If this heating has been properly placed, when the operation of blowing and pushing together is repeated the result will be to lengthen the bulb into a uniform cylinder, as shown in b, Fig. 10. Otherwise the result will be a series of bulbs, as in c, Fig. 10, separated by thickened ridges which will be almost impossible of removal later and will disfigure the final bulb. This operation of heating, blowing and pushing together is repeated several times, until the cylinder becomes as long as can be conveniently handled (about 1-1⁄4 inches to 1-1⁄2 inches). If more glass is needed than is then contained in the cylinder, the latter may now be heated as a whole, and blown and pushed gently into a shorter cylinder of a slightly greater diameter, and more glass then added as before.
When enough glass has been collected for the bulb, it is all well heated and blown gently a couple of times, pushing the mass together as required, until a thick bulb like d, Fig. 10, is obtained. The tail must now be removed at the point indicated by the dotted line. To do this, a very fine flame is directed on the point where the tail joins the bulb, and the tube well rotated as the glass softens at that point. When sufficiently soft, the work is raised a little, so that the flame instead of striking the glass squarely at the point indicated passes below and tangential to it. The tail is now drawn off slowly, continuing the rotation, raising the work just out of the flame whenever the thread of glass drawn off becomes too thin, and lowering it again to the point where the flame just touches it when the glass stiffens a little. By this means the tail may be drawn off without leaving an appreciable lump behind, as indicated in e and f, Fig. 10. When as much of the extra glass has been removed as is practicable, the flame is brought to play squarely upon the little lump left, the last of the tail removed, and the lump heated and gently blown to a small excrescence on the main bulb. The whole end of the latter is now heated until it begins to shrink a little, and gently blown to make it uniform in thickness. The whole bulb is then heated in a flame of the proper size, so that it all may shrink to about two-thirds of its diameter. The flame must be very carefully chosen and directed, so as to shrink all the bulb, right up to the main tube, but not soften the latter. As soon as this stage is reached, the bulb is removed from the flame, continuing the even rotation, and blown to the desired size, preferably by a series of gentle puffs following one another at very short intervals. During the blowing, the main tube is held in a horizontal position, and any tendency of the bulb to fall out of line is corrected by the rotation. If the shape of the bulb or its size are not satisfactory, it may be shrunk again and reblown. Such shrinking should begin in a large yellow flame, with just enough air to give it direction. The amount of air may be gradually increased as the bulb shrinks and the walls become thick enough to bear it without collapsing. If the bulb starts to collapse at any time, it must be immediately blown enough to regain its convex surface, before the shrinking proceeds further.
Discussion.—In collecting the glass for the bulb, enough must be gathered to give the walls the desired strength. Since the area of a sphere is proportional to the cube of its diameter, it is evident that doubling the size of a bulb diminishes the thickness of its walls to a very large extent. The limit of diameter for a strong bulb on ordinary 1⁄4-inch tubing, collecting the glass as above, is about 1-1⁄2 inches, and the beginner will do well not to blow his bulbs more than an inch in diameter.
The collection of the glass is one of the most important parts of the process. If the mass of glass be twisted, furrowed or ridged, or lop-sided, it is very difficult to get a good, even, spherical bulb, no matter how many times it is shrunk and blown. The greatest care should therefore be taken to get a uniform cylinder, on the same axis as the main tube; and to this end the rotation of the tube must be carried on very evenly. For method of holding the tube, see page 14.
If a very large bulb is required, it will often be economical to seal on the end of the tube a short piece of a large tube, provided with the proper tail, and use the glass in the large tube for the bulb instead of attempting to collect it from the small tube. In this case part of the small tube will usually be included in the bulb, so that the joint comes in the latter, and not where it joins the tube. As the amount of glass carried on the end of the tube increases in weight and size the difficulties of heating it uniformly, keeping it in the proper position and handling it increase rapidly.
In collecting glass, it is usually best not to leave the part of the cylinder next the tube with too thick walls. This is always the coolest part during the preparation for blowing the bulb, consequently it does not get blown out, and causes an ugly thickened appearance on that end of the bulb.
If the bulb grows too long or pear-shaped, it may be easily shortened by heating to the blowing temperature, and then blowing gently with the main tube in a vertical position, and the bulb at the top of it. Gravity will then shorten the bulb nicely.
The finished bulb should be a nearly perfect sphere, with the axis of the tube passing through its center, and the portion of the tube adjoining the bulb must not be distorted, twisted, or blown out. In order to prevent the distortion of the tube, care must be taken that it is never heated quite to its softening point during the process.
EXERCISE NO. 7
Blowing a Bulb in a Tube
The tube is selected and one end closed as in the previous exercise, but it should be cut a little longer, say about twelve inches. Beginning at a point about four inches from the closed end, glass is collected and blown into a thick-walled bulb, exactly as in the previous exercise. Greater care must be taken, however, that the cylinder collected and this thick bulb are of uniform thickness and set squarely in the axis of the tube. Instead of removing the tail, the bulb must be blown in this case with both pieces of tubing attached, and care must be taken that they "line up" properly, i.e., are in the same straight line, and that this line passes as near as may be through the center of the bulb. The tube is held in approximately horizontal position during the blowing of the bulb, as in the previous case, and especial care taken with the rotation. Both pieces of tube must of course be rotated at the same rate, and their softened ends must be kept at exactly the proper distance from each other, so that the bulb may be spherical and not elongated. If the blowing of the bulb be quickly and accurately done, it may usually be completed before the glass is quite set, and the alignment of the two tubes may then be rectified while looking straight through the bore of the tube.
Discussion.—The two points of greatest importance are the collection of the glass, and the uniform rotation of the tube. A larger tube may be sealed in the middle of a small one when a large amount of glass is necessary. The piece of tubing used for the exercise must be long enough so that the fingers may be kept on a cool part of the glass without getting uncomfortably near the ends of the tube. It should not be any longer than necessary, however, as the extra weight and length make the manipulation of the hot glass more difficult.
When a string of bulbs are required on the same tube, a piece of glass 18 inches long may be used at the start, and the first bulb made near the closed end, as described. Each succeeding bulb will then be in plain view during the blowing, and when the open end becomes too short for comfort, it may be dried out, cut off, and another piece joined to it, starting as in the first method (Exercise No. 1), but instead of drawing out the thick bulb to a tube, it is made part of the glass collected for the next bulb. If the string of bulbs becomes awkward to handle on account of its length and weight, it may be made in several parts and these later sealed together by the second method, preferably blowing through a rubber tube attached to the open end, as described on page 22.
Very neat small bulbs may be made on tubing of a diameter of 3⁄16 inch or a little less, but the beginner is advised to start with tubing of about 1⁄4 inch diameter. The use of tubing with too thick walls usually produces bulbs which are thick-walled at the point where they leave the tube, but inclined to be too thin at the point of maximum diameter (perpendicular to the axis of the tube) where most of the strain comes and strength is particularly needed.
CHAPTER IV
Advanced Exercises
EXERCISE NO. 8
Sealing a Tube Through Another Tube
First Method—Making a Gas-washing Tube
This first method can be used whenever one can work
through an open end opposite to the end of the tube
where the joint is to be made. To illustrate it, take a
piece of rather thin-walled tubing, about 3⁄4 inch in
diameter, and some pieces of rather strong tubing a little
less than 1⁄4 inch in diameter. Draw off the large tube
in a short cone, then draw off the tail as in the making of
the bulb on the end of the tube, blow out the little lump
slightly, shrink the whole cone a little and blow gently to
form a rounded end like that on a test-tube, with walls
about the thickness of those of the rest of the tube. Cut
this tube to a suitable length, say about six inches, and provide
two corks which will fit the open end of it. Now cut
a piece of the small tubing of the proper length to form
the piece which is to be inside the large tube. For practice
purposes, this piece should be about an inch shorter
than the large tube. Flange one end of this tube a little,
and anneal the flange well in the smoky flame. Bore one
of the corks so that a piece of the small tubing will fit it,
and cut a couple of notches in the side of this cork so that
air can pass between it and the glass. Pass a short piece
of the small tubing through this cork, and attach the
flanged piece of small tube to this by means of a short
piece of rubber tubing, so that when the whole is inserted
in the large tube it is arranged as in a, Fig. 11. The piece
of glass tubing projecting out through the cork is now cut
off so as to leave an end about 1⁄2 inch long when the
cork is firmly seated and the inner tube pushed into
contact with the center of the end of the large tube, as
shown in the drawing. Care should be taken that the
little rubber tube which joins the two pieces is arranged
as in the figure; i.e., most of it on the piece of tubing which
passes through the cork, and very little on the other
piece, so that when the cork is removed after the small
tube has been sealed through the large one, the rubber
tube may easily come with it. Select a short piece of the
small tubing of suitable length for the piece which is to
be on the outside of the large tube as a continuation of
the piece inside, and another piece for the delivery tube.
A small bulb may be blown in the latter at a point about
2-1⁄2 inches from the closed end, and the open end cut
off about 1-1⁄2 inches from the bulb. A cork or cork-boring
of suitable size to stopper the small tube is prepared,
and laid ready with the other (unbored) cork for
the large tube.
When everything is in readiness, the rounded end of the large tube is slowly heated until it softens and joins firmly to the small tube inside. After it has shrunk down well, it is blown out to its original size, placing the whole end of the large tube, cork and all, in the mouth. Now with a fine-pointed flame the glass covering the end of the small tube is heated to the softening temperature, and then is blown out to an excrescence by blowing on the end of the small tube which passes through the cork. The end of this excrescence is heated and blown off in the usual way, so as to leave the small tube sealed on the inside of the large one and opening through it into this short tube which has been blown out. The end of the small tube which passes through the cork is now closed with the cork prepared for it, and the short outer tube is joined to the tube that has just been blown out, so that the joint appears like b, Fig. 11. Use the first method (Exercise No. 1) for this joint. Reheat the whole of the end of the tube nearly to the softening temperature, anneal it a little, and allow to cool a few seconds until well set. Now remove the cork, short glass tube and rubber tube from the open end of the large tube and insert the solid cork in their place. Warm the joint and the whole of that end of the tube again carefully up to about the softening point, then seal on the side tube for the delivery of the gas in the usual way, taking care that the whole of the end and the joint are kept warm meanwhile. When thoroughly sealed, the delivery tube is bent up parallel to the tube through which the gas enters, and then out at right angles to it, as shown in c. The whole of the end of the tube is now cautiously reheated and then cooled slowly to anneal it.
The cork may now be removed from the open end of the large tube, this end heated in a large flame, caught together with a scrap of glass tubing and drawn off into a cone so that the base of the cone is about opposite the end of the inner tube. The lump of glass is drawn off the point of this cone and it is reblown to form a rounded end, as previously described.
After this cools, the tube through which the gas enters may be heated at the proper point and bent at right angles to form the finished apparatus as shown in d. The ends of the small tube are cut off square and fire-polished.
Discussion.—After the joint has once been made, great care must be taken that it is kept hot during all the subsequent manipulations, and if it becomes somewhat cool at any time it must be reheated very slowly. It is obvious that the rate of heating and cooling of the inner tube will be slower than that of the outer tube, and this will readily produce stresses which tend to crack the tube at the joint. The amount of heating and cooling which such a joint will stand depends upon its form. The beginner should examine such a joint on regular factory-made apparatus, and note the uniformity of wall-thickness and the "clean-cut" appearance of the joint, as a model for his imitation. A ragged joint, where the line of joining of the inner and outer tubes wavers instead of going squarely around the tube, is almost sure to crack during the cooling and heating unless extra precautions are taken with it. The presence of a small lump of glass at any point on the joint affords an excellent starting place for a crack, as do also the points on a ragged joint where the inner tube comes farther down on the outer tube than at other points.
In order to insure a joint which is square and not ragged, it is essential that the angle between the inner and outer tubes at the joint be very nearly a right angle. For this reason the two tubes should not be of too near the same size, or if this cannot be avoided, a small bulb should be blown on the end where the joint is to be made. If this bulb be made with the same wall-thickness as the rest of the tube, and somewhat pear-shaped, it may be drawn out to the same size as the rest of the tube, if necessary, after the joint has been made.
This method is used wherever possible in preference to the second method (Exercise No. 9), as it is easier to get a good joint with it. It may also be used where it is desired to seal the tube through the side of a tube, or for a tube sealed through the wall of a bulb, as in a Geissler potash bulb or similar apparatus. Where there is not space to join the inner tube to the blowing tube by a rubber tube, this joint may be made with a small piece of gummed paper, which can readily be broken when desired.
EXERCISE NO. 9
Sealing a Tube Through Another Tube
Second Method—Making a Suction Pump
Select a piece of tubing 3⁄8 to 1⁄2 inch in diameter,
with walls about 1⁄16 inch or a little less in thickness,
heat a place about 4 inches from one end and draw it
out so that when cut off at the proper point it will look
like a, Fig. 12; the open end of the drawn out part being
small enough to slip inside another piece of the original
tube. A small thick-walled bulb is now blown as
indicated by the dotted lines, and annealed. A piece of
the original tubing is now prepared, 7 or 8 inches long,
with one end cut square off and the other closed. A
piece of 1⁄4-inch tubing about 2 inches long, and drawn out
at one end to a tail several inches long is also prepared, to
form the inlet tube for the air. Another piece of the
3⁄8-inch tube is prepared, about 4 inches long, and provided
with a tail drawn out as indicated in b, so that when
cut off at about 2-1⁄2 or 3 inches from the main tube its
inner diameter may be slightly less than that of the narrowest
point of the tube a. A small thick-walled bulb
is blown at the point indicated by the dotted lines, and
annealed. Care must be taken in drawing the capillary
and blowing the bulb in both a and b that the capillary
tubes are in the axis of the main tube, and in the same
straight line with it.
The open end of the 8-inch piece of tube and the bulb of the piece a are now warmed together, the end of the tube only moderately and the bulb to about its softening temperature. The tube a is now inserted in the open end of the large tube, and the bulb softened with a suitable flame and pressed into good contact with the tube. It is then reheated, including the joint, blown a little and pulled out to form a straight tube in line with the main tube. By warming the joint a little, and proper rotation, the capillary may be brought into the same straight line with the rest of the tube.
Keeping this joint hot, a place about an inch from it on the tube a is warmed, and the piece of 1⁄4-inch tubing previously prepared is sealed on at that point. The joint is then well annealed and allowed to cool.
The tube a is now cut at such a place that when b is inserted in the open end the point will come near the end of the constriction of a, as shown in c. Care is taken to get a clean square cut. The side tube is now cut off about an inch from the main tube and corked. Tube b is sealed into the open end of a, in the same way as a was sealed into the large tube, and the joint carefully annealed.
Discussion.—As in the first method, the secret of success lies in getting a square joint, and having the inner tube leave the outer one at nearly right angles. All the remarks about annealing, lumps, etc., made under the previous method apply here.
This method may be applied in sealing a small tube
into the end of a large one, the latter being either drawn
to a cone and cut off at the desired diameter, or else
given a rounded end like a test-tube and a hole the proper
size blown in the center of it. A suitable thick-walled
bulb is to be blown on the small tube, as in the case
described above. This method is also used in making
the Kjeldahl trap (a, Fig. 13), the small tube to be
inserted being first drawn, the thick bulb blown at its
point of union with the main tube, and then the small
tube bent and cut. The large bulb is best made with
rather heavy wall, being either blown in the middle of
a tube, and one piece of the tube drawn or cut off, or
else made on the end of a tube. In the latter case a drop
of glass must be put on the point where the joint is to
be, so as to get a hole of the proper size with enough glass
around it to prevent it from growing larger when it is
heated. The author prefers to blow the bulb in the
middle of the tube, draw off one end of the bulb, and
blow out the desired hole where the tube was drawn off.
The whole bulb must generally be reheated and blown
a little at the end of the process, and well annealed.
The suction pump can also be made on 1⁄4-inch tubing, and one joint saved if desired, by constricting the tube to form the raceway for the water and air, as shown in b, Fig. 13. (See page 10 for method.) But it is more difficult to make a square joint on such small tubing.
CHAPTER V
Modified Methods and Special Operations
CAPILLARY TUBING
This is commonly used in many forms of apparatus
for gas analysis, and one is often called upon to join two
pieces or to make a tee on it. The methods are nearly
the same as with other tubing, except that more care and
patience are required. The work must be done much
more slowly on account of the thickness of the walls, and
open ends of the tube must always
be enlarged before joining them to
anything. This is best done by carefully
sealing the end and then blowing,
with several suitable reheatings, to
form a pear-shaped bulb as in a, Fig.
14. The end of this is then heated
and blown off, and the piece is ready
to be joined to another similar end, or
to a piece of ordinary tubing if desired.
The joints are best not blown
too much, as thick walls shrink very slowly. Much may
be done by gently pushing the tube together or pulling
it apart in the flame, to remove lumps and irregularities.
It is necessary that the bore of the joint be approximately
that of the main tube, and care must be
taken that the latter is not constricted at the point
where the joint begins.
Especial care must be taken to warm the tube slowly when starting and cool it slowly when through, as the thick walls frequently crack if not carefully handled. For this reason the whole neighborhood of the joint must be heated somewhat so that there may not be stresses set up between the heated and unheated portions.
In making the tee (b, Fig. 14) the inability to blow the joint makes itself decidedly felt, but if the side tube is properly enlarged as previously described, a good joint can be made by alternately pulling and pushing on the end of the side tube, and shrinking well.
Very fine capillary tubing should be blown with a rubber bulb instead of the mouth, so as not to get moisture into the tube. The rubber bulb may also be used to advantage on some of the coarser capillary tubing.
When a bulb is to be joined to a piece of capillary tubing, the joint is preferably made before blowing the bulb, and will then be taken up a little way on the bulb during the process. Care must of course be taken not to constrict the capillary; the pear-shaped bulb blown on the end (a, Fig. 14) may well extend back a little further than usual into the tube so as to prevent this. If a bulb is required in the middle of a capillary tube, the latter is usually best cut and a piece of ordinary tubing of suitable size sealed in to provide material for the bulb.
GLASS ROD
Joints, tees, etc., in glass rod are made on the same principle as in tubing, except that of course they cannot be blown, and regularity must be obtained by accumulating a small mass of uniformly heated glass, and then drawing it to a suitable rod, on the same principle as Exercise No. 1.
Great care must be taken in heating and cooling this, as in the case of the capillary tubing, and for the same reasons.
By joining pieces side by side, pressing with carbon plates or a plate and a rod, and other suitable manipulations, stirrers, spatulas, and other objects may easily be made from rod, and its manipulation is relatively easy on account of the fact that one does not have to worry about the bore of the tube. But the same general rule about not having thick and thin spots in contact, and making all changes in diameter on a taper if possible instead of abruptly, applies here. Thick pieces will cool and contract at different rates from thin ones, and cracks are likely to develop where they join. Work which has been formed with any tool must always be heated to the softening point afterward before allowing it to cool in order to remove the stresses caused by the contact of the tool with the hot glass.
When it is necessary to join a piece of rod to the side of a piece of tubing, the end of the rod is made very hot while the wall of the tube at the spot desired is heated to just below the softening temperature. The rod can then be pressed into firm union with the tube and drawn a little to remove the excess of glass without deforming the tube.
MENDING STOPCOCKS
Mending the Plug.—The plug of the stopcock occasionally
falls out and is broken. If the break is in the
main part of the plug, nothing can be done except to
search for a spare plug of suitable size and grind it to
fit, as described below. If only the little cross-piece at
the end is broken off, it can easily be replaced. In
most ordinary stopcocks the plug is solid, but the little
handle is hollow. What has been said above regarding
care in heating and cooling glass rod applies with especial
force here. It is usually best to wind the whole of the
plug with several thicknesses of asbestos cord, leaving
bare only the end where the handle is to be joined. This
diminishes the danger of cracking the plug by too rapid
heating, and also makes it more comfortable to hold. A
piece of rather thick-walled tubing of suitable diameter is
chosen, drawn out so as to have a suitable taper (taking
care to heat enough of the tube so that the capillary tail
has good wall-thickness and strength), and then a
corresponding taper is drawn to form the other side
of the handle. The result is shown in Fig. 15, a. The
capillary tail is now heated and bent back to form a
handle which will be in the same straight line as the axis
of the plug (b, Fig. 15) and the main part of the tube
drawn off at the dotted line, making a neat seal at that
point. The broken end of the plug is now slowly warmed
in the smoky flame, the heat gradually increased by a
gentle stream of air from the bellows, and the point at
which this handle is to be attached finally brought to
the temperature at which the glass flows freely. In the
mean time, the little handle has been warmed almost to
the softening point. It is now quickly pushed into place
(c, Fig. 15), taking care that its axis is parallel to the hole
in the plug, and then drawn away from the plug just
enough to make a graceful neck instead of the bulging one
indicated by the arrow in the figure. With a fine pointed
flame the little tail is now drawn off at the point indicated
by the dotted line (c, Fig. 15) and the whole carefully annealed.
If necessary, the handle can be blown a little
before the tail is removed. Local heating and blowing at
the point where the handle joins the plug is often necessary
in order to make a smooth job.
Regrinding.—This is sometimes necessary to make stopcocks tight, when the grinding has not been properly done in the factory. For this, a very little fine flour of emery or carborundum is the best and quickest. If this is not at hand, some clean sand may be ground in an agate mortar, and if possible sieved. Only material which passes the 100-mesh sieve should be used. It will be ground still finer in the process. For the final polishing, a little infusorial earth or even kaolin will do.
The surface to be ground is moistened with water and dusted over with a little of the abrasive. The plug is now inserted in the stopcock, and turned with a gentle pressure. This turning should be in the same direction for several revolutions, then in the opposite direction for several more revolutions, etc. As the abrasive becomes finer during the grinding, a little more may be added if necessary. In general, only a little grinding will be required, and one small pinch of carborundum or emery will be ample. The beginner usually grinds too much, and with too coarse material. As the grinding surface becomes dry, water is added drop by drop, and the grinding continued until the abrasive seems to be reduced to an impalpable powder, most of which has been squeezed out of the stopcock. The two surfaces in the stopcock are usually grinding upon each other at this stage, and inspection will show whether the contact between them is uniformly good. If not, the grinding must be continued with a little fresh abrasive. If contact appears to be good, the surfaces are ground together for a little with practically no abrasive, so as to polish them, and the joint is then washed out and tested.
In grinding in a new plug to replace a broken one, the plug selected should have practically the same taper as the seat into which it is to be ground, and should be a very little too large. Care must be taken to so distribute the abrasive material as to grind mostly on the places where the plug fits tightly.
Sealing on a New Tube.—It frequently happens that one of the tubes of the stopcock is broken off close to the cock itself, and a new one must be joined to the stub of the old one. With care, this may often be successfully done even where the break is within 1⁄4 inch of the stopcock. The first step is to clean and dry the stopcock, remove the plug, cork the open ends of the stopcock sleeve and the other tube, and wind a couple of layers of asbestos cord carefully over the sleeve and the most of the corks which close it. A suitable tube, having as near as possible the same diameter and wall strength as the one broken off, is selected and a piece the desired length cut off. The broken end of the tube on the stopcock is now squared off as well as possible, by cutting or by heating and drawing off the projections, and the new tube sealed on, usually with the first method (Exercise No. 1). If the break is very close to the stopcock, very little reheating and blowing can be done, on account of the danger of getting the stopcock sleeve out of shape, and the work must be heated very slowly to prevent cracking. The main reliance is then placed on making a good joint when the tubes are brought together, and then drawing out this joint a little, at once, to get an even wall.
CLOSED CIRCUITS OF TUBING.
In some pieces of apparatus closed circuits of circular or rectangular shape are required. A similar problem is involved in apparatus like the ordinary Soxhlet extractor, where a small tube is joined to the side of a large one, bent to form a siphon, and attached again to a continuation of the original large tube. The difficulty in all such cases is to provide for the contraction taking place as the last joint cools. If part of the circuit has the shape of the letter S, or is a spiral, the natural springiness of the glass will take care of this. If not, the side of the circuit opposite to the joint and parallel to it must be heated also, the two being finally heated together to the softening point after the joint is completed, and then allowed to cool together.
To make the last joint, the rest of the tube is made in approximately the desired form, the two pieces which are to be joined to make the last joint being just enough out of the desired position to allow them to pass one another. The final joint is preferably made in the middle of a straight piece of tube, not at a tee. The two pieces which are to be joined are bent so as to just pass each other, marked at the right point with the glass-knife, and cut there, preferably with a small bead of hot glass. One or both of these tubes are now warmed to the softening point in such a place that the tubes can be made to meet properly, and the two cut ends pressed together. They are now warmed in the flame, and joined together, either by simultaneously warming the opposite side of the circuit or some other suitable part, so as to allow the two ends to be pushed together again after they are softened, or by gently touching the places that do not unite with a hot bead of glass, and using the glass to fill up the crack where the ends do not quite meet. Care must be taken not to leave knots or lumps of glass in the finished joint, and the latter should be well reblown, and if necessary left as a small bulb or enlargement, rather than have it have too thick walls.
SPIRALS
Spirals of glass tubing are probably best made free-hand
before the blow-pipe, unless one has a great many of
them to make, and extreme accuracy is desired. To
begin with, a piece of tubing of the desired size (say 3⁄16
inch in diameter) and a convenient length (about two feet)
is selected, one end closed, and a right-angle bend made
about six inches from the closed end. Holding the closed
end in the left hand and the long open one in the right,
the spiral is begun. The short closed end is to be parallel
to the axis of the spiral, and preferably in that axis.
Using a moderate-sized flame, of somewhat yellow color,
and taking care to heat the whole circumference of the
tube, the long open end is wound little by little into a
spiral having the short end a (Fig. 16) as an axis. The
bend at b, where the tube changes from the radius to the
circumference of the circle, must be rather short, but
the tube must not be flattened or constricted here.
Especial pains is to be taken with the first turn of the
spiral (b to c, Fig. 16), as the shape of this determines the
diameter of the whole spiral, and serves as a guide for the
rest of the turns. The winding of the tube is best accomplished,
after a portion has been softened, by slowly
turning the short end a a little about its own axis, while
the long open end remains where it was. This winds
the tube into a spiral, just as if there were a solid cylinder
in the center of it, and this cylinder was being turned
about its axis, and was winding up the soft glass upon its
circumference. As the cylinder is not actually there, the
curve of the turns must be carefully estimated by the
eye, so that the spiral may be uniform and moderately
smooth. When the original piece of tube has been used
up, another piece is sealed on to the open end, and the
operation continued as far as may be required.