Boyle's temperature Experiments on different gases over wide ranges of temperature and pressure resulted in the empirical relation,

pv = A + B p + C p² + D p³ + ........

where A, B, C, D etc. are constants, characteristics of each gas, which vary with temperature. They are termed as virial co efficients. Their values diminish rapidly as A > > B > > C and so on. For a perfect gas the first virial coefficient A = RT. As pressure is increased more and more terms become necessary in the relation given above. Under this condition B is the most important term. It is found that B varies in a similar way for all gases, starting with a negative value at low temperature, gradually increasing to zero at a particular temperature and then becoming positive. The temperature at which B = 0, is called Boyle's temperature, because at this temperature the gas obeys Boyle's law over large ranges of pressure.