tems considered could be a result of anomalous behavior of the systems or the inherent crudeness of a first-generation model. I t appears, for example, that the model should fit the data for systems where KGLC = K = KNMR, such as is likely for aliphatic alcoholln-electron donor hydrogenbonded complexes (16). T h a t , in itself, would be noteworthy. Nevertheless, in addition to the inconsistencies described above, it presently lacks the support of independent experimental evidence (even inferential) for the existence of local aggregates of A and S in the mixed solvent, or separate clustering of A and S about D when solute is added. A similar two-phase thermodynamic model has been used to interpret solute activity coefficients in nematic liquid-crystalline solvents (32). In t h a t case, however, there was some supporting evidence for solvent clustering from x-ray and light scattering experiments. In short, more experimental evidence and additional refinement are needed before a compelling case can be made for the model. ACKNOWLEDGMENTStimulating discussions and correspondence with J. H.

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Modern instrumental techniques were used for analysing water-based urea-formaldehyde resins. An exhaustive study was made of the silylation of such a resin with BSTFA (N,O-bistrimethylsilyltrifluoroacetamide). From the gas chromatograms the amounts of urea, monomethylol urea and dimethylol urea can be determined quantitatively, thus giving information on the low molecular weight part of the resin. The ratio of low to high molecular weight components as well as the amounts of several low molecular weight compounds can be estimated from a GPC analysis on Sephadex LH 20 in water. A detailed picture of the resin is obtained when freeze-dried samples are subjected to 220 MHz 'H-NMR analysis in DMSO-d6.An overall insight into the composition of these resins can be gained when the results of the mentioned techniques are combined with those of classical chemical analyses. ZUSAMMENFASSUNG: Moderne instrumentelle Methoden wurden zur Analyse von Harnstoff-Formaldehyd-Harzen verwendet. Ein ausfuhrliches Studium der Silylierung des Harzes mittels BSTFA (N,O-Bistrimethylsilyltrifluoracetamid) ermoglicht die quantitative gaschromatographische Bestimmung der niedermolekularen Verbindungen Harnstoff, Monomethylolharnstoff und Dimethylolharnstoff. Das Verhaltnis zwischen nieder-und hochmolekularen Verbindungen sowie die Mengen an niedermolekularen Verbindungen konnen mittels GPC-Analyse auf Sephadex LH 20 in Wasser ermittelt werden.Ein vollstandiges Bild des Harzes erhalt man durch 220 MHz 'H-NMR-Analyse von Losungen von gefriergetrockneten Proben in DMSO-d6. Zusammen mit den Ergebnissen klassischer chemischer Analysen ergeben die Resultate der drei genannten Techniken einen guten Uberblick iiber den Aufbau eines Harnstoff-Formaldehyd-Harzes.

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