The Triple Point and Solid-to-Solid Phase Transition at ≈ 107 K of n-Butane

At the former IMGC-CNR (now INRiM), the Italian national metrological Institute, a series of pure hydrocarbons were measured in past years to determine with high accuracy for the temperature of their triple point and of their solid-to-solid transition(s) when present. While results on methane, ethane, and propane were published; the 1982 measurements on n-butane were never so far. It seems useful to add these results now to the still scarce existing data for possible inclusion in reference data archives. The paper summarises the experimental setup and results, compared with previous determinations. For the triple point, a temperature T-tp,T-90 = 134.869(2) K was found showing a higher accuracy. For the s.s.t.-I, the temperature was T-90,T-upper-end = 108.2(3) K, where the low accuracy is due to the peculiar s.s.t. properties.

Automated summary

A series of measurements on pure hydrocarbons were conducted at the former IMGC-CNR (now INRiM) to determine the temperature of their triple point and solid-to-solid transition. While results for methane, ethane, and propane were published, the measurements on n-butane in 1982 were not. This paper presents the experimental setup and results, comparing them with previous determinations. The triple point temperature was found to be T-tp,T-90 = 134.869(2) K, showing higher accuracy, while the solid-to-solid transition-I temperature was T-90,T-upper-end = 108.2(3) K with lower accuracy due to its peculiar properties.