A flow mixing microcalorimetric system we developed recently was appended in this work with a vibrating tube densimeter into a tandem flow arrangement. This new combined apparatus (calo/densimeter) allows simultaneous automatic measurement of mixing enthalpies and densities of highly dilute solutions as a function of composition and, in turn, reliable determination of the solute's infinite dilution partial molar excess enthalpies (H) over bar (E,infinity)(1) and volumes (V) over bar (E,infinity)(1). The performance of the calo/densimeter was verified using 1-propanol in water, and then the apparatus was employed to determine (H) over bar (E,infinity)(1) and (V) over bar (E,infinity)(1) of several ionic liquid precursors (N-methylimidazole, N-methylpiperidine, N-methylmorpholine, 2-picoline, 3-picoline, and 2,6-lutidine) in water and methanol at 298.15 K. The changes of enthalpy associated with solvation and the transfer of the solutes from water to methanol were evaluated. The thermodynamic behavior observed for individual solutes was compared and briefly discussed in terms of molecular interactions.