Despite it's far to be a perfect prism, you can use it for personal or classroom basic optical experiments.
As it is filled with water, its refractive index is of about 1.33.
If it was entirely made of glass or acrylic glass, its refractive index would be about 1.5.
Actually, in this prism, four refractions occurs :
1 - air (1.0) to glass (1.5)
2 - glass (1.5) to water (1.33)
3 - water (1.33) to glass (1.5)
4 - glass (1.5) to air (1.0)
Step 1: What do you need ?
- tools required to cut acrylic glass
- transparent adhesive tape (scotch-tape)
- something to glue acrylic glass
- a tool to drill acrylic glass
- a rubber stopper (or anything that will do the job)
- a funnel ( see here if required : http://www.instructables.com/id/Improvised-Tiny-Funnel/ )
- It is, of course, possible to use real glass instead of acrylic glass. Though, it would be difficult to drill it.