This work investigates five reactions between melamine (M) and formaldehyde (F) at pH = 9.0, and with initial F : M ratios of 2. The samples were analyzed by size exclusion chromatography (SEC), volumetric techniques, and (H-1 and C-13) NMR. Condensation was quantified by the SEC measurements. In the experiments at 38 and 48 degrees C, condensation was almost negligible, and the reversibility of methylolation reactions determined that equilibriums were reached in the ratios between primary, secondary, and tertiary amines. In the experiments at 60, 70, and 90 degrees C, condensation was significant, but in all cases, the mass fraction of single-ringed species was larger than that of species with two or more rings per molecule. The following were estimated by combining the SEC and volumetric measurements: number-average molecular weights, and average functionalities of reactive H's, methylols, methylene bridges, and ether bridges. The dissolution of M in water was essentially instantaneous. The measurements are employed in the next article of this series for adjusting a novel mathematical model. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1030-1041, 2009