In a high school science class, Riley was given 50 milliliters of water and 50 milliliters of ethanol. His task was to mix them together and then run an experiment on the mixture.

When the teacher came to check on him, however, Riley's mixture only contained 94 milliliters. The teacher accused him of drinking some of the mixture in an attempt to get intoxicated and immediately sent him to the principal. Riley swore that he did NOT drink the mixture and he didn't lose any of the liquids by any means.

What happened to the other 6 milliliters and how could Riley prove his innocence?