Chapter 3.3 focusses on gas and flow of liquids. We include detailed information on the gas laws, the universal gas law and their clinical applications. We discuss the Dalton and Henry’s laws, the importance of understanding the terms critical temperature and pressure. We then move on to discuss flow, how it can be measured in anaesthetic systems using a number of different pieces of equipment and how understanding the difference between laminar and turbulent flow is important.

Thermodynamics is the science that governs most of the basic, or ‘static’, properties of a system such as a gas. In this chapter we will be focusing on thermodynamics of the dry atmosphere. Water vapour is sufficiently important to deserve a separate chapter. A thermodynamic system is characterised by a small number of state variables, primarily density, pressure, and temperature. After defining these, we will see how they vary as we move up through the atmosphere. Two key equations – the hydrostatic equation and the ideal gas equation – interconnect these variables and their profiles. The First Law of Thermodynamics tells us how the atmosphere responds to an input of heat, as well as a change in pressure, which may come about with elevation (vertical motion). This is the key to the atmosphere’s vertical stability, and (ultimately) to cloud formation.

Chapter 1 introduces basic astronomical terms and concepts used throughout the book.