  This work describes a new microfluidic device developed for rapid screening
of solubility diagrams. In several parallel channels, hundreds of
nanoliter-volume droplets of a given solution are first stored with a gradual
variation in the solute concentration. Then, the application of a temperature
gradient along these channels enables us to read directly and quantitatively
phase diagrams, concentration vs. temperature. We show, using a solution of
adipic acid, that we can measure ten points of the solubility curve in less
than 1 hr and with only 250 $\mu$L of solution.
