Name:______
Glass Lab
Cutting and fire polishing glass tubing
Glass tubing can be broken easily by making a small scratch with a triangular file; this is called “scoring the glass”. After the tubing is scratched, it can be snapped apart at the score. The tubing must be scored only once; multiple scratches will produce jagged edges when broken.
- To score a piece of tubing, make a firm slice with the file perpendicular to the tube: MCS Chemistry Bunsen Burner and Glass Bending Lab page 3
- Place your thumbs opposite the score and apply firm pressure by bending the tubing away from you. The tubing should snap apart. Be mindful of the new edges, they are sharp.
The fresh cut ends can be made smooth by a technique called fire polishing. To fire polish glass tubing, rotate the end in the Bunsen burner using the hottest part of the flame. Heat and rotate the tube until the edges are smooth. You should be able to see this without too much difficulty.
Making glass bends
When glass is heated to high temperatures, it becomes soft and starts to behave like a liquid. To bend glass, we do not want to melt it, we just want to get it soft enough to deform. You may use a wing tip on the burner to increase the area of the flame. The flame spreader makes the flame cooler, so you will need to heat the glass in the flame longer time period to soften it.
Start with a piece of glass tubing approximately 8 inches long. This is long enough to keep your fingers away from the flame. Hold the tubing at the ends and rotate continuously while keeping the middle part of the tube at the top of the inner blue cone.
When the tubing gets soft, it will start to sag due to gravity. Remove from the flame and bend upwards in a smooth continuous motion. Continue to bend until the desired angle is achieved.
When bending the tube, both ends must be in the same plane, otherwise a dogleg bend results.
good bend- flat on tabletoppoor bend- "wobbles"on tabletoppoor bend- partially collapsed
Bend the following shapes:
1. 90° bend (shown above)
2. Gas delivery tube (shown below)
3. Corkscrew (if you are really adept) Use your imagination!
Cut a piece of glass about 60 cm long. A gas delivery tube has three bends, each a different angle: a 90° bend coming out of the flask, another bend of approximately 45° angled downwards, and then another 90° bend up towards the collection bottle on the beehive shelf.
Start with the first right-angle bend, then the smaller angle and finally the bend at the delivery end. Each bend should be heated and bent in turn. If they are sufficiently far away from each other, you should be able to hold the ends of the tube and proceed to the next bend without waiting for everything to cool right down. However, be careful of hot glass.