An 800 ml stirred jar is described. Its foam producing characteristics are recorded to show how 25 per cent drainage time, shear stress, concentration, stirring time, stirring speed and expansion are inter-related. With other variables kept constant, the time for a foam to commence drainage was found to be a linear function of the expansion, which indicates there is a critical bubble wall thickness below which drainage does not occur. Examples of the use of the apparatus are given.