Principles of equilibrium apparatus development

While these early workers did not have apparatuses suitable for very high pressure, the experimentalists during the first half of the century of hydrates did prove three important principles to guide the development of succeeding apparatuses and methods  

Vigorous agitation is necessary for complete water transformation. With minor exceptions, the early results (as determined by Villard) showed that an increase in agitation caused a decrease in the number of water molecules in the hydrate. 

The following two subsections consider the apparatuses used for most phase equilibria measurements, namely, the three-phase (Lw-H-V and I-H-V) regions, respectively. Similar equipment have been used to measure three-phase (Lw-H-Lhc), and four-phase (Lw-H-V-Lhc) conditions. For two-phase (H-Lhc and H-V) regions, different apparatuses have been used as discussed in Section 6.1.1.4. 

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