Dielectric properties of ammonium dihydrogen phosphate at very high frequencies

Ammonium dihydrogen phosphate shows no detectable dielectric dispersion between 10 kc/s and 36 Gc/s. Determinations of the permittivity at a frequency of 36 Gc/s are described: the values obtained are || = 14.0 at 21° C and ⊥ = 57.1 at 21.5° C, where || and ⊥ are the values of permittivity when the applied electric field is parallel with or perpendicular to the optical axis. These values are not measurably different from those obtained at lower frequencies by the author (at 1 Mc/s) and by other workers (at 10 kc/s).