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SynopsisDielectric measurements were utilized in the investigation of the polymerization of epoxy resin Epon 826 with diethylenetriamine (DETA) as the crosslinking agent. The time variation of the dissipation factor and of the dielectric constant were measured continuously, while the epoxy system was held at a constant temperature. A range of 11 frequencies (330 cycles/sec.-10 Mcycles/sec.) at three different polymerization temperatures (30, 45, SOOC.) was covered. The test results are given as a set of curves for the dissipation factor and the dielectric constant versus time. Nearly all the dissipation factor curves have the same characteristic shape, with a well-dehed minimum (valley) followed by a maximum (peak). The dielectric constant fa& monotonously from a high initial value to a small h a 1 one that is specific for the fully cured resin. If the time at which the dissipation factor reaches the valley t, and the peak tp are plotted versus the logarithm of the frequency, two straight lines will be obtained. Such a plot can be utilized as an aid in controlling the curing process of cast resins.

Eine Methode zur Dichtebestimmung von Gasen wurde entwickelt, bei welcher das zu untersuchende Gas von einer Schallquelle erregt, und der erzeugte Druck von einem nahen Mikrofon gemessen wird. Man kann zeigen, daß dieser Druck der Gasdichte proportional ist. Schon die mit einer einfachen Versuchsanordnung durchgeführten Messungen ergaben Dichtewerte mit einer Präzision von 0-2% für Dichten über 0,7 kg m~3, die nach einer empirischen Korrektur für alle Dichten gilt. Diese Korrektur verkleinert auch den Fehler der Dichtebestimmung für Dichten über 0,7 kg m -3 auf weniger als 0,2%. Es lassen sich nach dieser Anordnung sehr einfache Dichtemesser sowohl als Industriegeräte und wahrscheinlich auch als Laborgeräte für breite Temperaturund Druckbereiche herstellen.A methodfor the measurement of gas densities has been developed. The gas is exited by a source of sound and the resulting dynamic pressure measured by a microphone nearby. It can be shown that this pressure is proportional to the gas density. Even measurements made with a crude setup yielded results with the precision of 0-2% for densities above 0,7 kg m~3, and with an empirical correction for all densities. This correction also reduces the error of the density determination for densities above 0,7 kg m~3 to less than 0,2% o . Thus it will be possible to construct very simple instruments for industrial and probably laboratory use for a wide range of temperatures and pressures.

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An instrument for the direct measurement of dielectric constant differences between gases of similar polarity is described. The method is based on the pressure dependence of the frequency ratio between two LC oscillators, the capacitive cell of each of which contains one of the gases. A sequence of measurements at different temperatures yields the dipole moment and polarizability differences. A check of the method with a pair of known gases, HC1 and HBr, yielded :[p(HCl)-p(HBr)] = 0.284 D ;[ct(HCl)-a(HBr) ] = -0.95 xThe error in the distortion polarization difference is 0.05 cm3/mol and the dipole moment difference is precise to 0.002 D.