-
A SIMPLE METHOD FOR REPAIRING BROKEN TEST TUBES
I t is a common thing in the average laboratory to discard a test tube as soon as it is broken. Although test tubes are not as valuable as other chemical apparatus, it is an absolute waste to throw away any test tube which is capable of repair, and many of the so-called ruined tubes can be easily and quickly fixed. I t takes skill, patience, and much practice to become an efficientglass blower, but the simple operations necessary for the repair of a test tube can be learned in a few minutes. Besides being interesting and helpful a small saving isrealized; consequently, the return fully justifies
ID'
3
FILL H€K
6
the time and labor spent. The following method applies only to those test tubes which have had the end knocked out or broken off. The broken end of the tube is first fused with a piece of scrap tubing. This can be done by holding the two ends in a flame until the ends are a bright cherry red. They are then pressed quickly together and allowed to cool. The next step consists of heating the test tube about one-half inch from the point of fusion or just above the last part of the break. The tube should be rotated in the same spot until it begins to contract (1). I t will become thick and it should be allowed to draw itself slowly apart, so that the glass a t the end becomes thicker than that of the rest of the tube. After a bit the tube will become very narrow and will melt in two (2).
VOL.6, No. 11
REPAIRING BROKEN TESTTUBES
1987
The tube is then allowed to cool and the small piece of solid glass a t the end of the tube is filed off so as to leaqe less glass to be ironed out later (3). The tube should be rotated continually while in the flame. The tube is now slowly reheated by putting only the small tip in a remote part of the flame. This precaution must be taken in order to insure against breaking the tube by too fast reheating and thereby mining an otherwise good job. Heating the point also serves to close any possible hole which might have resulted from the filing operation. When the point and about an eighth of an inch of the tube are red, the tube is taken to the mouth and gently blown so that the globule which forms on the end is partly removed (4). Too much blowing a t this point will force out the end too far, and the glass will either burst or become too thin to be manageable. The point is again placed in the flame androtated. This is continued until the point has contracted back to where i t was before the blowing. The tube is then removed and blown. Only a very light pressure should be used. This step should be repeated three or four times or until all of the original globule a t the end has been absorbed. A little more of the tube may be heated each time the step is repeated (5). The tube is again heated, this time with the entire end in the flame. When the entire end is bright red, the tube is held in a vertical position and blown until the end is rounded out (6). Great pains should be taken not to blow too hard. Too much pressure will result in a large end which is very difficult to remove. If the above steps are carried out, the test tube will have an end which is as strong if not stronger than that of the original tube. With practice the operator can become expert enough to make a repair which defies detection as a piece of mended work. Remember that continuous rotation of the tube and gentle blowing are essential to good work.
