The vapour pressure of a liquid determined by laboratory testing in a standard manner: the Reid apparatus at a standard temperature of 380C (1000F) expressed in newtons per square metre or bars, or pounds force per square inch. (105N/m2= 1bar, 1 lb force/in2 = 0. 069 bar = 6894. 76 N/m2). A method used for determining the vapour pressure of a volatile hydrocarbon