In one aspect, an apparatus for determining a property of a fluid is disclosed that in one embodiment may include a transparent member having an axis and a first end substantially perpendicular to the axis and a second end having an outer surface at a first angle to the axis, a light source directing light at the first end, a detector placed spaced from the second end, the space between the second end and the detector containing a fluid, wherein the detector detects light exiting from the outer surface at a second angle to the axis and passing through the fluid, and a controller for determining the second angle from the light detected by the detector. A processor determines the bulk fluid refractive index from the light detected by the detector and a property of the fluid therefrom.