The dissocation number is the number of ions or parts that the solute breaks into when dissolved (e.g. 2 for NaCl, or 1 for sugar). Concentration is given in molality, but for weak solutions in water this approximates very closely to molarity.
While theory gives valuse for ideal cases, in reality ebullioscopic constants are measured. Examples include: Acetic acid (3.07), Benzene (2.53), CCl4 (4.95) and water (0.51).