Natural gas is a mixture of 21 components and it is widely used in industries and homes. Knowledge of its thermodynamic properties is essential for designing appropriate processes and equipment. This paper presents simple but precise correlations of how to compute important thermodynamic properties of natural gas. As measuring natural gas composition is costly and may not be effective for real time process, the correlations are developed based on measurable real time properties. The real time properties are temperature, pressure and specific gravity of the natural gas. Calculations with these correlations are compared with measured values. The validations show that the average absolute percent deviation (AAPD) for compressibility factor calculations is 0.674%, for density is 2.55%, for Joule-Thomson coefficient is 4.16%. Furthermore, in this work, new correlations are presented for computing thermal properties of natural gas such as enthalpy, internal energy and entropy. Due to the lack of experimental data for these properties, the validation is done for pure methane. The validation shows that AAPD is 1.31%, 1.56% and 0.4% for enthalpy, internal energy and entropy respectively. The comparisons show that the correlations could predict natural gas properties with an error that is acceptable for most engineering applications.

This article is part one of a discussion that attempts to examine the state of research on the history of the police in the Second Republic of Poland as presented in to‑date historiography. My interest includes literature concerning both the State Police and the Police of the Silesian Voivodeship, two organisations independent from each other. The 1989/1990 timeline is obviously not accidental, as it was of great significance for the way research on public security organs in the interwar period was conducted.
The recent 100‑year anniversary of the National Police created an excellent opportunity to assess the achievements pertaining to its history and the organisation modelled on it, i.e., the Police of the Silesian Voivodeship (PWŚl). Although their history has been the subject of several studies, it is worth taking a closer look at them trying to assess both the problems addressed and the quality of these studies. The author has made an attempt to carry out a quantitative and qualitative analysis of the existing literature, which is to lead to the identification of significant accomplishments, as well as to highlighting unexplored possibilities.
The author has chosen scientific publications as a basis for his analyses. Publications of an occupational nature, that is, manuals, specialist materials, handbooks, course books, etc., remain outside the area of the author’s interest.
The resulting analysis leads to the conclusion that it was not until the late 1980s that the one‑sided image of the pre‑war police, constructed through the discourse of repression against the “progressive” communist and workers’ movements, began to be abandoned. However, still dominating was the factual history, unfortunately not preceded by theoretical reflections.