  We have developed an original setup using microfluidic tools allowing one to
produce continuously monodisperse microreactors ($\approx 100$ nL), and to
control their temperatures as they flow in the microdevice. With a specific
microchannels geometry, we are able to apply large temperature quenches to
droplets containing a KNO$_3$ solution (up to 50$^{\circ}$C in 10 s), and then
to follow nucleation kinetics at high supersaturations. By measuring the
probability of crystal presence in the droplets as a function of time, we
estimate the nucleation rate for different supersaturations, and confront our
results to the classical nucleation theory.
