Bernard D. Bolas

“ From two to five minutes, heating at a distance of about eight inches in front of the flame will be found sufficient in most cases, and another minute should be taken in bringing the tube into the flame. Gradual heating is important, but even heating is still more important and this can only be obtained by uniform and steady rotation. Until the student can rotate a tube steadily without thinking about it, real progress in glass-blowing is impossible. ”

“ If, as will doubtless happen at times, a piece of work gives trouble and it is necessary to pause and consider the whole question, or if for any other reason it is necessary to stop during the construction of a partially finished join or other operation, great care should be taken not to allow the work to cool. A large, brush-like flame may be produced by increasing the amount of gas admitted to the blowpipe, and the work should be held just in front of the current of hot air produced by such a flame. ”

“ An interesting vacuum tube is made which has no electrodes, but contains a quantity of mercury. When the tube is rocked so as to cause friction between the mercury and the glass sufficient charge is produced to cause the tube to glow. ”

“ In the case of a blowpipe burning oil or wax fuel the flame may be a trifle more ragged without disadvantage.
Bellows and Blowing.—The bellows should be adjusted to deliver air at constant pressure, either by insertion of a tap or, better, by attention to the wind reservoir if necessary. The movement of the foot in blowing should be steady, not jerky.
Heating Glass.—The tube or rod should be heated cautiously until it has reached its softening point in its thickest part. Steady rotation of the glass during the heating is almost essential. ”

“ If the blowpipe is to be used with gas, the form of burner described under. "A Simple Form of Blowpipe" will be found quite satisfactory.
The Use of Oil, or Other Non-Gaseous Fuels.—Although gas, when available, is usually preferred on account of its convenience, there are several other fuels which give a hotter flame. They have, also, the additional advantage of not requiring any connecting pipes; but each has its own disadvantage.
One liquid fuel deserves special mention as [Pg 87] being rather less desirable than the others; this is alcohol. ”

“ A very light spring holds the bulb in position.
This valve is fitted into a metal or glass T piece, one limb of which leads to the air reservoir and the other limb leads to the blowpipe jet; the limb containing the valve leads to the tube through which the air is blown in.
A convenient reservoir may be made from a fairly large football bladder. A network of string should be fitted over the outside of the bladder and the strings should terminate in a hook on which a weight can be hung, in order to provide a means of adjusting the pressure at which the air is delivered to the jet. ”

“ Larger Holes in Glass.—The method of drilling with a hard steel rod is not highly satisfactory for anything but small holes. When a larger hole, say one of an eighth of an inch or more, is needed it is better to use a copper or brass tube. This tube may be held in an American hand-drill, but a mixture of carborundum or emery and water is supplied to the rotating end. Tube or drill must be lifted at frequent intervals in order to allow a fresh supply of the grinding material to reach the end. ”

“ Care should be taken not to employ so soft a lubricant or so large an excess as to cause it to run down the stirrer into the liquid which is being stirred.
Leading a Crack.—It sometimes happens that a large bulb or specially thin-walled tube has to be divided. In such a case it is scarcely practicable to use the method recommended for small tubes on page 12, but it is quite easy to lead a crack in any desired direction. A convenient starting point is a file cut; this is touched with hot glass until a crack is initiated. ”

“ Glass-blowing is neither very easy nor very difficult; there are operations so easy that the youngest laboratory boy should be able to repeat them successfully after once having been shown the way, there are operations so difficult that years are needed to train eye and hand and judgment to carry them out ”

“ A support for such a blowpipe may be cut out of a piece of brass or tin-plate, and should be fastened to a small, flat, wooden board. A source of flame may consist of an ordinary brass elbow, such as is used on gas fittings, and into which a piece of thin brass tube (the body of a fish-tail burner from which the perforated non-metallic plug has been removed will serve quite well) has been fitted. It is an advantage to flatten the brass tube somewhat and to file the flattened end to a slope which corresponds with the angle at which the blowpipe jet enters the burner. ”

“ Thermometer Bulbs.—If the thermometer is to be filled with mercury, it is desirable to use a rubber bulb for blowing, as moisture is liable to condense inside the tube when the mouth is used, and this moisture will cause the mercury thread to break. In any case, a slight pressure should be maintained inside the thermometer tube while it is in the flame; otherwise the fine capillary tube will close and it will be very difficult to expand the heated glass into a bulb. ”

“ Yet a surprisingly large number of scientific workers fail even to join a glass tube or make a T piece that will not crack spontaneously, and the fault is rather one of understanding than of lack of ability to carry out the necessary manipulation. ”

“ If the inner tube is made by drawing out from a larger piece of glass so [Pg 37] 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. ”

“ Methods of Manufacture.—When the student has familiarised himself with the more common operations and processes used in glass-blowing, he will be in a position to increase his skill and knowledge of special methods by a critical examination of various examples of commercial work. ”

“ Although very convenient in use, it has the disadvantage of being rather too highly inflammable and capable of burning without a wick, thus involving a certain fire risk; the flame is scarcely visible in a bright light, and the heat given by either the ordinary flame or the blowpipe flame produced from alcohol is considerably less than that from a similar flame in which coal gas is used. For small work, however, the facility with which a spirit lamp may be lighted may more than counterbalance these disadvantages at times. ”

“ The presence of aluminum compounds appears to have some influence on the tendency of the glass to resist devitrification. Soda-glass, as a rule, is more liable to crack by sudden heating than lead-glass, and articles made from soda-glass often tend to crack spontaneously if badly made or, in the case of heavier and thicker articles, if insufficiently annealed. [Pg 57]
Combustion-Glass.—Is usually a glass containing more calcium silicate and potassium silicate than the ordinary "soft" soda-glass. ”

“ As a rule, soda-glass will need more annealing than lead-glass.
Drilling Glass.—Small holes may be drilled in glass by means of a rod of hard steel which has been broken off, thus giving a more or less irregular and crystalline end.
There are several conditions necessary to enable the drilling of small holes to be carried out successfully:—the first of these is that the "drill" should be driven at a high speed. ”

“ There is no need, however, to purchase an expensive table for laboratory use. All the work described in this book can quite well be done with a simple foot bellows and a quick-change blowpipe. Nearly all of it can be done with a single jet blowpipe, such as that described [Pg 7] first, or even with the still simpler apparatus mentioned on page 84, but I do not advise the beginner to practise with quite so simple a form at first, and for that reason have postponed a description of it until the last chapter. ”

“ The thermometer may be filled by the following method:—When the straight tube has been made the first dumb-bell is introduced and shaken down well towards the lower bulb, the tube is now bent to its final shape and the whole thermometer filled with alcohol as described on page 44. Now heat the thermometer to a little above the maximum temperature that it is intended to record, and pour clean mercury into the open bulb while holding the thermometer vertically. Allow to cool, and the mercury will be sucked down. ”

“ Such a bellows may be obtained at almost any jewellers' supply dealer in Clerkenwell, but it not infrequently happens that the spring in the wind [Pg 6] chamber is too strong for glass-blowing, and hence the air supply tends to vary in pressure. This can be improved by fitting a weaker spring, but an easier way and one that usually gives fairly satisfactory results, is to place an ordinary screw-clip on the rubber tube leading from the bellows to the blowpipe, and to tighten this until an even blast is obtained. ”

“ A very crude form of ground-in stopper may be made by drawing out the neck and the mass of glass which is intended to form the stopper to approximately corresponding angles, wetting the surfaces with a mixture of the abrasive material and water, and grinding the stopper in by hand. ”

“ The use of such a blowing-tube avoids the inconvenience of raising the work to the mouth when internal air-pressure is required. One end of the rubber tube is retained in the mouth during work.
General Notes.—A large amount of glass-blowing is spoiled through carelessness in arranging the work beforehand. The student should have every detail of his manipulation clearly in mind before he commences the work; [Pg 103] he should not trust to evolving the method during the actual manipulation. ”

“ If any liquid is to be introduced, it may now be done by inserting a thin rubber or other tube through the opening and running the liquid in. A glass tube should be used with caution for introducing the liquid, as any hard substance will tend to scratch the inside of the glass and cause cracking. The final closure is made by melting the drawn-out extension in the blowpipe flame; the finished seal being shown by g, Fig. ”

“ There is a wide choice of apparatus, from a simple mouth-blowpipe and a candle flame to a power-driven blower and a multiple-jet heating device. All are useful, and all have their special applications, but, for the present, we will consider the ordinary types of bellows and blowpipes, such as one usually finds in a chemical or physical laboratory.
The usual, or Herepath, type of gas blowpipe consists of an outer tube through which coal gas can be passed and an inner tube through which a stream of air may be blown. Such a blowpipe is shown in section by Fig. ”

“ Animal and Vegetable Oils.—Almost any oil may be used as a fuel, but many tend to become hard and gummy if allowed to stand in the air for any considerable time. When this happens, the wick becomes clogged and it is impossible to obtain a good flame. A number of the oils tend, also, to produce rather strongly smelling smoke. ”

“ Exceedingly good graduations may be made by the edge of a small, thin, abrasive wheel which is mounted on the end of a small mandrel and driven by a flexible shaft from an electric motor or any other convenient source of power. ”

“ Filling may be carried out as follows:—Fit a small funnel to the open end of the capillary by means of a rubber tube, and pour into the funnel rather more than enough of the liquid to be used than is required to fill the bulb. ”

“ Once having mastered the underlying reason, he can evolve schemes of manipulation to suit his own particular needs, although, as a rule, those given in the following pages will be found to embody the result of many years' experience. ”

“ Rubber Blowing Tube.—In complicated work it is often convenient to use a thin rubber blowing-tube which is connected with the work either by a cork and piece of glass tubing or by fitting over a drawn-out end. ”

“ Letcher, and is shown by e, and in section by f Fig. 1. It is only necessary to rotate the desired jet into position in order to connect it with both gas and air supplies. A small bye-pass ignites the gas, and adjustment of gas and air may be made by a partial rotation of the cylinder which carries the jets.
For specially heavy work, where it is needed to heat a large mass of glass, a multiple blowpipe jet of the pattern invented by my father, Thomas Bolas, as the result of a suggestion derived from a study of the jet used in Griffin's gas furnace, is of considerable value. ”

“ Such a form, although highly satisfactory in action, needs constant watching while in action, as should the mercury funnel become empty air will enter the exhausted vessel. Obviously, the fall-tube must be made not less than thirty [Pg 50] inches long; the measurement being taken from the junction of the exhaustion branch with the fall-tube to the top of the turned-up end.
Fig. 12
A Macleod Pump.—One form of this is illustrated by b, Fig. 12. It has the advantage [Pg 51] that the mercury reservoir may be allowed to become empty without affecting the vacuum in the vessel being exhausted. ”

“ Great care must be taken in the [Pg 69] final grinding that there is no accumulation of abrasive material in the transverse hole of the plug; if this is allowed to occur there will be a ring ground out of the socket where the holes move, and the tightness of the finished stopcock will be lost.
Marking Glass.—As a preliminary to a consideration of the methods of graduating and calibrating glass apparatus, it is convenient to consider the various methods which are available for marking glass. ”

“ It is well, therefore, to avoid keeping such solutions longer than is necessary, and to bear in mind that any deposit [Pg 79] formed by solutions containing both silver and ammonia may have explosive properties, especially when dry. ”

“ These are,—file, glass-knife, small turn-pin, large turn-pin, carbon cones, carbon plate, rubber tube of small diameter, various sizes of corks, and an asbestos heat reflector. For ordinary work, an annealing oven is not necessary, but one is described on page 60 in connection with the special cases where annealing is desirable.
Fig. 3 illustrates the tools and appliances. a is an end view of the desirable form of file, and shows the best method of grinding the edges in order to obtain a highly satisfactory tool. ”