# Refractive Index of mixtures

1. Apr 13, 2007

### Ogulnius

Is there a general formula to calculate the refractive index of a mixture of two liquids of known refractive index, e.g. water and ethanol, or water and glycerol?

2. Apr 14, 2007

### Gib Z

No. That is because a mixture is not a constant composition - the composition varies throughout the mixture. The index will be different at all these points.

3. Apr 14, 2007

### Gib Z

O unless you want averages, then i guess so. Its been a while since ive done physics, but I think the refractive index is dependent only on density, and you can calculate the average density.

4. Apr 14, 2007

### lpfr

Of course, it is assumed that the liquids are thoroughly mixed and that the mixture is of constant composition.

As a coarse approximation you can use a linear formula:
$$n={ n_1V_1+n_2V_2\over V_1 + V_2 }$$
where n hold for the refractive indexes and V for the volumes.
But this is just an approximation.

Refractive index is not related to density.