Eliminating a and b between these relations, we derive P k V k /Tk= 8R, a relation which should hold between the critical constants of any substance.
By actual observations it has been shown that ether, alcohol, many esters of the normal alcohols and fatty acids, benzene, and its halogen substitution products, have critical constants agreeing with this originally empirical law, due to Sydney Young and Thomas; acetic acid behaves abnormally, pointing to associated molecules at the critical point.
Obviously, therefore, liquids are comparable when the pressures, volumes and temperatures are equal fractions of the critical constants.
From the relation between the critical constants Pk Vk/Tk = 37 R or T k /P k = 3 .
