  Using a system composed of a Quadrupole and Ioffe Configuration (QUIC) trap
loaded from a slowed atomic beam, we have performed experiments to observe the
Bose-Einstein Condensation of Na atoms. In order to obtain the atomic
distribution in the trap, we use an in situ out of resonance absorption image
through a probe beam, to determine temperature and density. The phase space
density (D) is calculated using the density profile and the temperature. We
have followed D as a function of the final evaporation frequency. The results
show that at 1.65 MHz we crossed the value for D expected to correspond to the
critical point to start de Bose-Condensation of the sample. Due to the low
number of atoms remaining in the trap at the critical point, the interaction
produces minor effects and therefore an ideal gas model explains well the
observations. We analyze the obtained low number in terms of efficiency of
evaporation. The utility of an in situ detection is illustrated by measuring
the harmonic gas pressure of the trapped gas in the route to condensation.
