  We present here detailed measurements of the Casimir-Lifshitz force between
two gold surfaces, performed for the first time in both gas (nitrogen) and
liquid (ethanol) enviroments with the same apparatus and on the same spot of
the sample. Furthermore, we study the role of double-layer forces in the
liquid, and we show that these electrostatic effects are important. The later
contributions were precisely subtracted to recover the genuine Casimir force,
and the experimental results are compared with calculations using Lifshitz
theory. Our measurements demonstrate that a carefull account of the actual
optical properties of the surfaces is necessary for an accurate comparison with
the Lifshitz theory predictions at short separations of less than
${200}\si{\nano\meter}
