If you put a LC into an Abbe you'll see 2 lines (one like a shadow and fainter than the other) dividing the light and dark regions. These correspond to the ordinary and extraordinary rays. If you have an Abbe with a polarizer this can help too. See slide 39 in:

June 26th, 2012 Uses of an Abbe refractometer http://tinyurl.com/lbp4szy

Of all the LC's routinely encountered E7 has one of the highest birefringences (0.17 if I recall). There is no sense in trying to carry out homeotropic or homogeneous alignment of the glass prisms of the LC. I wonder though if ITO (as the transparent conductor) was deposited on the prisms of an Abbe whether the LC could be switched by voltage. Maybe someone has done or patented this.

When you plaster the liquid crystal on Abbe refractometer and heat the material over critical temperature, you can only see mean refractive index in isotropic phase. Also, when you decrease temperature below critical tempereature, you obtain mean refactive index for liquid crystalline mesophase, too. But if you apply Lesitine solution solved as 5% on prism before applying LC, below the critical temperature you should see ordinary refractive indices with using polarizor adjusted 90 degree. And than by using that data , you may calculate extraordinary refractive indices for each temperature according to modified foru parameter method. Also, you may benefit from article published by our research group. I hope that I could help.

Article Refractive and birefringent properties and order parameter o...