We used polarized light microscopy and optical activity measurements in ord
er to determine the BPIII-Isotropic critical point in CB15-E9 mixtures. The
complete phase diagram is compared with that of mixtures of S,S-4"(methylb
utyl)phenyl-4'-(methylbutyl)biphenylcarboxylate (CE2) and its racemate in w
hich the BPIII-isotropic critical point was first observed, The effect of e
lectric fields on the critical point was also investigated.