Cut glass tube in half without right tools

How to cut glass tube in half without proper tools?

The tube is 1 inch around and 5 ft long I am trying to cut it into smaller 2 ft sections.

This applies to glass bottles too.

WARNINGS:

1. With this procedure (as well as with any pother procedure, i guess), the edges of the glass on the place of the "cut" will most likely be very sharp, and therefore dangerous. Please take the precautionary measure to avoid accidents you yourself and to others.
2. During the process, small shards of glass might be created (and thrown to some distance). Make sure that you are able to clean the area properly before and after the job. If a shard gets into someone's foot, or in someone's food, things can get nasty.
3. The glass will become very hot (hopefully) during the process. Protect yourself wearing some gloves, or some other thermally-insulating material (e.g., towel). Note: Glass shards might get attached to the fibers of the towel!

The procedure

1. Make a mark around the glass tube where you want the cut.
2. Take a sting, preferably of natural fibers (cotton, hemp, flax...). It has to be "thick enough" (not too thin) for the job - experimentation needed. Strings made of polymers will most likely melt during the process.
3. Attach one end of the string to you (maybe your belt), and the other to something else in the room (preferably close to a faucet, maybe the faucet itself, if it is properly secured).
4. Loop the string once around the tube, matching the mark from step 1.
5. Start moving the tube back and forth, with the string tensioned, so the string touches and moves around the tube. This will cause the tube to get hot in that area and its surroundings, so it is a good idea to wear some gloves (or some towel).
6. When you think the glass is hot enough, quickly unwrap the string from around the tube and place the marking on the tube under a jet of cold water.
7. If the glass was hot enough, and the water cold enough, the glass will just break there, and the job is done.
8. If not, repeat steps 5-7 until job done. On step 5, you might need to increase the tension of the string, and the speed of movement, for increasing the friction, and thus, the temperature.