Teacher's Guide to Experiment #3

Glass Labs
Materials:

•Borax obtained from grocery stores may not work for this lab as some contain detergents or soaps).

General Safety Guidelines:

•Use a wire that is a poor conductor of heat and nonreactive at elevated temperatures. Handles could be added to the nichrome wire.

Procedure:

A-6: •If the “glass“ comes out clear enough, you may suggest that they try to use them like a magnifying glass.

•If you want to, have them try a Borax Bead Test, either new wires will have to be handed out or have them make a new loop on the other end of the wire.}

Extension to Part B:

This is a procedure for making a glass swan. With lots of patience and practice, you or your students might want to try this.

Swan Procedure:

1. Place rubber tubing on one end of the glass tubing.

2. Light and adjust burner for a hot flame.

3. Preheat the center of the glass tube and then heat strongly while rotating the tube.

4. As the glass softens, gently push the tubing together just a little. (This allows extra glass for a strong bubble.)

5. Pinch the rubber tube and blow into the glass end until there is a bubble about twice the size of the tubing diameter.

6. While the glass is still hot, make the bubble shape not round by pushing both ends of the tubing at an angle, about 140 degrees relative to each other.

7. Heat either tube near the bubble (body), when soft push the tube back over the bubble (body) to make the neck of the swan. DO NOT HEAT THE BUBBLE

(BODY).

8. Leave a section of the tube, a centimeter or so, at the end of the neck to form the head and heat the tube at this point. (This will make the beak.)

9. When the glass is soft pull it and melt it off.

10. Gently heat the bottom of the bubble (body) with the side of the flame. (This

part of the bubble will then become flat.)

11. Holding the glass by the beak and the other end of the tube, preheat the tail area. (The tube opposite from the beak.) DO NOT HEAT THE BUBBLE

(BODY).

12. When the glass is soft, pull upward and gently twist to form the tail.

13. Melt off excess glass tube and allow to cool.

14. HOW DO YOU MAKE A GOOD ONE ? THE SAME WAY YOU GET TO CARNEGIE HALL .... PRACTICE, PRACTICE, PRACTICE.

Part C Suggestions:

•You might have to seal a piece of Nichrome wire into each end of a 3 cm piece of glass tubing and use this.

•You may want different teams to try different materials such as Pyrex glass, lime glass, leaded glass and or different diameters of the same material. How about other ceramic materials?

•You may also want them to continue recording every 10 seconds while the glass cools and include that data in their graph.

•Electrical resistance should go from more than 20 megaohms at room temperature down to less than one megaohm at 700˚ C.

Sample Data and Analysis: Pyrex Tube

Time	Electrical Resistance
Start	20 MΩ
10 seconds	15.72 MΩ
20 seconds	7.23 MΩ
30 seconds	4.05 MΩ
40 seconds	2.30 MΩ
50 seconds	1.07 MΩ
60 seconds	0.54 MΩ
70 seconds	0.073 MΩ
heat removed
80 seconds	0.23 MΩ
90 seconds	0.95 MΩ
100 seconds	1.85 MΩ
110 seconds	3.17 MΩ
120 seconds	8.22 MΩ
130 seconds	14.78 MΩ
140 seconds	20+ MΩ

Sample Graph:

Answers:

Part A:

1. The glass is transparent and hard but not stable.

2. Answers will vary. Consult CRC Borax Bead Tests Table.

Part B:

1. Pyrex is tough and is heat resistant.

2. Glass is a mixture and does not exhibit long rang crystal structure.

Part C:

1. Different amounts and types of ionic and covalent bonds effect the degree of

electrical conductivity.

2. Yes, at high voltages glass will conduct. A Tesla coil will show this or some

adult toy like the plasma storm ball sold by stores.

3. Yes. It is analogous to resistance in wire. Resistance is directly proportional to

the length and inversely proportional to the diameter.

4. Electronic devices need to be kept within their designated temperature range to

operate as expected.