This is an optical prism made of acrylic glass and filled with water.
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)