An experimental method of observing adsorptive length changes in porpoise rods by means of a linear differential transformer and inductance bridge has been developed. The method was used to observe the adsorptive length change behaviour of rods of kaolinite and Vycor, when they were exposed to the vapours of H₂O, CH₃OH, C₂H₅OH, CHCl₃, CCl₄, and C₆H₆. Spreading pressure – length change slopes were measured and the variation in their values for a solid at a particular temperature discussed in terms of the structures of the absorbed phases. An attempt was made to measure the strength of the adsorbate-adsorbent and adsorbate-adsorbate interactions thermodynamically, using the BET c parameter. The effect of particle alignment during extrusion in kaolinite rods was studies by means of ultrasonic and x-ray diffraction techniques.