Steam digester Torricelli and further developed by German scientist Otto von Guericke with his Magdeburg hemispheres. Guerike's demonstration was documented by Gaspar Schott, in a book that was read by Robert Boyle. Boyle and his assistant Robert Hooke improved Guericke's air pump design and built their own. From this, through various experiments, they formulated what is called Boyle's law, which states that the volume of a body of an ideal gas is inversely proportional to its pressure. Soon the ideal gas law was formulated. Based on these concepts in 1679 a Boyle's associate, named Denis Papin, built a "bone digester", which is
Standard cubic foot of the label "standard", there is a variety of definitions, mainly depending on the type of gas. Since, for a given volume, the quantity is proportional to the pressure and (absolute) temperature, each definition fixes base values for pressure and temperature. The ideal gas law allows then to compute the quantity per unit of volume for actual pressures and temperatures. Since natural gas is an imprecise mix of various molecular species, chiefly methane but with varying proportions of other gases, a standard cubic foot of natural gas does not represent a precise unit of mass, but only a molecular quantity,