Francis C. Frary

“ The glass should become almost soft enough for blowing in a flame that still shows a little yellow near the tip, so that at the highest temperature of the flame it may flow fairly freely and thus easily eliminate irregularities in thickness. If the glass is too hard, the shrinking of the glass, collection of material for a bulb, and in fact most of the working processes will be slower, and the glass will not stay at its working temperature long enough after its removal from the flame to permit it to be properly blown. ”

“ Where gas is not available, an ordinary gasoline blow-torch does very well for all operations requiring a large flame, and a mouth blow-pipe arranged to blow through a kerosene flame does well for a small flame. Several dealers make blow-torches for oil or alcohol which are arranged to give a small well-defined flame, and they would doubtless be very satisfactory for glass-work. Any good bellows will be satisfactory if it does not leak and will give a steady supply of air under sufficient pressure for the maximum size of flame given by the lamp used. ”

“ If some of them appear to be given in excessive detail, the reader will remember that many things which are obvious to the experienced worker are not so to the beginner, and that it is the little details in the manipulation which often spell success or failure in glass-blowing. ”

“ In general, large pieces of glass should be heated very slowly in the smoky flame, and the larger the diameter of the tube the greater the length which must be kept warm to prevent cracking. All large pieces should be carefully heated over their whole circumference to the point where the soot deposit burns off, before being finally cooled. After being thus heated they are cooled in a large smoky flame until well coated with soot, then the flame is gradually reduced in size and the object finally cooled in the hot air above it until it will not set fire to cotton. ”

“ Many laboratories in this country, especially in the west, are located a long way from any professional glass-blower, and the time and money spent in shipping broken apparatus several hundred miles to be mended could often be saved if some of the laboratory force could seal on a new stopcock, replace a broken tube, or make some temporary repairs. Many men in physical or chemical laboratories have occasion to modify some piece of apparatus designed perhaps for other uses, or to design new apparatus. ”

“ 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. ”

“ The tube should always be rotated and kept in a straight line until the glass has set, so that the capillary may have the same axis as the main tube. This capillary or "tail" is often a very necessary handle in glass-blowing, and if it is not straight and true, will continually make trouble.
In drawing out very large tubing, say from one to two inches in diameter, it is often necessary to draw the tube in the flame, proceeding very slowly and at a lower temperature than would be used with small tubing. ”

“ Glass-blowing should be done in a good light, but preferably not in direct sunlight. The operator should be seated in a chair or on a stool of such a height that when working he may comfortably rest one or both elbows on the table. The comfort of the operator has a decided influence on the character of his work; especially in the case of a beginner, who often defeats his purpose by assuming uncomfortable and strained positions. ”

“ Some tubing has occasional knots or lumps of unfused material. The rest of the tube is usually all right, but often the defective part must be cut out. The presence of striations running along the tube is generally an indication of hard, inferior glass. Crookedness and non-uniformity of diameter are troublesome only when long pieces must be used.
Devitrification is one of the worst faults glass can possibly have. It is especially common in old glass, and in glass which has contained acids. ”

“ In rotating the tube, both hands must be used, so that the two ends may revolve at the same rate and the glass in the hot part not be twisted. The rotation is performed by the thumb and first finger of each hand, the other fingers serving to support the tube. As it is almost always necessary to follow rotating and heating a tube by blowing it, the hands should be so placed that it will be easy to bring the right-hand end up to the mouth without shifting the hold on the glass. ”

“ 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. ”

“ Grasping the open end with a pair of crucible tongs, it is cautiously pulled out, a little at a time, usually during rotation in the flame, to make a constriction of moderate wall-thickness, but of sufficient internal diameter to admit the tube containing the substance. After annealing this, cooling and cleaning the tube, the acid and salt are introduced (the former by means of a long-stemmed funnel) and the tube is inclined and rotated about its axis so that the acid wets its surface about half way up from the bottom. ”

“ When so hot that it cannot longer be held in shape, the tube is removed from the flame, and the ends slowly and regularly drawn apart, continuing the rotation of the tube about its axis. By regulating the rate of drawing and the length of tube heated, the desired length and diameter of capillary may be obtained. ”

“ 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 hexagonal carbon can easily be made by carefully filing down an electric light carbon, and finally impregnating it with paraffin or beeswax, and is extremely useful wherever a conical surface has to be formed from the inside of a tube. ”

“ This puts both hands in a position where the tube may be blown and rotated uniformly while its axis is kept horizontal.
Smoothness and exactness are the two things for which the beginner must constantly strive in glass-blowing, and they are only attained by a careful attention to the details of manipulation, with a steady hand and watchful eye. Every move must count, and the exercise must be finished with a minimum of reheating and retouching, for the best results. ”

“ 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. ”

“ Where a ground joint is necessary, however, it is best made in the conical form shown in c, Fig. 17. If the wall of the tube to be used [Pg 52] is not very thick, it is thickened by collecting glass as for a bulb on the ends of two tubes (Exercise No. 6) , and drawing to form cones of suitable shape (a and b, Fig. 17) and of such relative sizes that a will slip about half way into b. In order to make a straight and give it the proper angle, it may be rolled when hot, upon a hot plate of carbon. Blowing during this rolling is often helpful to remove depressions. ”

“ This may be accomplished by doing all heating, shrinking, etc., of the glass in a flame more or less tinged with yellow, and only raising the temperature to the highest point when ready to blow the glass. This kind of devitrification is apparently due to volatilization of the alkalies from the glass in the flame, and it is said that it can be partly remedied or prevented by holding a swab of cotton saturated with a strong solution of common salt in the flame from time to time as the glass is heated. ”

“ The beginner should not leave the first exercise, for example, until he can join together two pieces of tubing so that they form one piece of substantially uniform inner and outer diameter, and without thick or thin spots. ”

“ Steadiness and exact control of both hands are essential in most operations; any uncomfortable or strained position tires the muscles and weakens the control of the operator over them.
In the arrangement of the exercises here presented, several factors have been considered. ”

“ The hands must be held steady, and the tube must be under good control at all times, so that both ends may be rotated at the same angular velocity, even though they may be of different diameters, and the tube be neither drawn apart nor pushed together unless such a motion is expressly desired, as it sometimes is. ”

“ Upon blowing this joint, these thickened walls blow out with the lump, but as they are thinnest next the unchanged tube, they stiffen there first. Then as the thicker parts are still hot, these blow out more, and with the lump make a more or less uniform wall. By this first operation most of the lump will have been removed, provided it was not too large at first, and the tube was hot enough when it was blown. Beginners almost invariably have the glass too cool here, and find difficulty in blowing out a satisfactory bulb. ”

“ 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 [Pg 45] 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. ”

“ The operator must have complete control over the flame, and be able to change its size and character at short notice without giving the work a chance to cool, and often without ceasing to support it with both hands. ”