Some Useful Expedients in Laboratory Glass Working R. H. WRIGHT Uniaersity of New Brunswick, Fredericton, New Brunswick, Canada
T
HE following glass-working tricks have been found very useful, and while they may have been used before they are not mentioned in any of the manuals of laboratory glass blowing with which the writer is familiar. 1.
to the main tube and bent until their ends are properly aligned. The intervening tube which is to bridge the gap is cut to the correct length and held in place a t one
SECURING A SQUARE SEAL IN THE BORE O F A CAPILLARY TUBE
I n sealing the end of the capillary tube of a McLeod gage or a high pressure manometer, and in various other connections, i t is desirable that the bore of the
Flame
:Cut
end by a short length of ruhher tubing which serves also to seal the gap while the other end is heing sealed in the flame. A bit of thin rod is useful in closing pinholes during the process. When one end is sealed, the ruhher is cut away with a knife and the second seal is made, a thin rod being used to fill any gap that may have been left. The blowing is best done through a ruhher tube attached a t A. 3.
c a p i l l q have a uniform cross section right up to the sealed end. When a capillary is sealed in the usual manner, the bore contracts to a conical point, such as is shown in Figure 1A. If, however, a slightly tapering glass rod is made by drawing out a larger piece, this can he thrust into the capillary until it sticks, and a little plug is then cut from i t as shown in Figure 1C. By applying the flame of a blast lamp to the plugged capillary as is shown in Figure ID,a square seal will be obtained with little or no distortion of the bore. See Figure 1B. 2. CLOSED CIRCUITS O F TUBING In making manometers, McLeod gages, flowmeters, and other pieces of apparatus, a closed loop of tubing like that indicated in Figure 2 may he required. The methods of producing such a closed circuit usually recommended require that the piece he softened a t two points simultaneouslyan operation calling for considerable dexterity. The method suggested in Figure 2 avoids this difficulty. The two side tubes are sealed
GROUND JOINTS
Although interchangeable ground joints are available in many sizes and are suited to many purposes, it is sometimes necessary to make a ground joint in the laboratory. The principal difficulties of the usual procedure are in retaining a true circular cross section while producing approximately the same taper in the two parts. These difficulties are avoided by using the procedure shown in Figure 3. A glass tube of the required size is supported near one end in a V-shaped
cut in a board and a t the other end by a one-holed rubber stopper .. held by a rod in the chuck of a variable
71
speed stirring motor.' The glass tube should be lu- centimeters should be heated in the flame of a Meker bricated with a little glycerol where it rotates in the V- burner while the tube is rotating a t a moderate speed. cut. A carbon rod, such as is used in arc lamps, is held When the glass begins to soften, the ring stand carrying the carbon rod is slid along the bench so that the rod slowly presses the glass to the proper taper. A blast lamp held in the hand may be used to supplement the Meker flame. In order to produce the flare shown a t A (Figure 4) or the bulge shown a t B (Figure 4) the speed of rotation of the tube is inaeased considerably and the blast flame played on the glass until it softens enough to be thrown outward by centrifugal force. The success of the procedure depends on the fact in a clamp a t the angle desired for the ground joint, and that the angle a t which the carbon rod is held is not a t such a height that i t presses either the outside or in- altered by sliding the ring stand along the bench or side of the tube to be drawn down or flared. See by moving the clamp which holds the rod up and down Figure 4. The end of the tube for a length of several on the ring stand. Grinding with glycerol and carborundum powder presents no particular difficulty ' The Model 3, Variable Speed Stirrer, made by the Eastern because the two halves of the joint, if properly made, Engineering Company, New Haven, Connecticut, is very conwill have very nearly the same taper. venient.
