Studies of Phase Changes in Argon

The influence of the geometry of the sample chamber on the melting behaviour of Ar samples is discussed. Melting curves of Ar samples doped with various small amounts of He, H 2 , Ne, N 2 , CO, O 2 , CH 4 and Kr impurities were determined relative to "pure" samples. It was found that He, H 2 and Ne did not alter the melting curve; N 2 , CO, O 2 and CH 4 lowered the liquidus point of Ar by 2.4, 2.4, 1.8 and 3.0 mK for 100 vppm of these impurities, respectively; Kr increased the scatter of points along the melting curve without noticeably altering the liquidus point. – Values for the triple point temperature and pressure and the boiling point were found to be 83.797 6 K and 516.730 ± 0.010 mmHg (68891.6 N/m 2 ) and 87.294 6 K, respectively. – The vapour pressure of solid and liquid Ar can be described by ln P = A S + ( B S / T ) and ln P = A L + ( B L / T ) + C L T for 81 K ≲ T ≲ 83.8 K and 83.8 K ≲ T ≲ 87.3 K respectively. Numerical values of these constants are compared with some previous determinations. Latent heats of sublimation, vaporization and fusion are calculated to be 7751.6, 6562.0 and 1189.6 joules/mole respectively.