TECHNIQUES FOR ASSESSING RItEOLOGICAL PROPERTIES 459 Figure 8 Sectilometer for assessing the consistency of solid materials. In another version of this sectilometer (11) the sample is placed on the pan of a spring balance, and the wire, motivated by a constant speed motor, cuts through it at a rate of 0.044 cm/sec. The force exerted on the sample is recorded by the spring balance. COMPRESSION BETWEEN PARALLEL PLATES In this test, solid materials are subjected to alternate compression and relaxation between parallel plates. The technique is less sensitive than that described under Section 4, and involves more structural breakdown. The sample is placed on a solid metal core with a flat surface which is fastened to the base of a metal stand, and a metal plate is brought gently into contact with its surface (Fig. 9). If the sample is of cylindrical shape, the plate should be circular if the sample is a rectangular block, the plate should also be rectangular. The plate is connected by a metal rod to a platform on which weights can be placed. Loading is by means of slotted weights placed around a holder plate which is gently lowered, by a pulley device, on to the platform. In this way damage to the sample is minimized at the moment of loading. A travelling microscope, focussed

46O JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Pulleys •c•/e Figure 9 Compression between parallel plates. on an indicator arm attached to the vertical rod supporting the platform, measures the rate of compression during loading and subsequent recovery when the load is removed. The applied load (F) is converted into stress per unit area (U) by F Ho (XXm) U-A. where H o and H are the height of the sample before and after deformation respectively. U Shear stress (a) -- (XXIV) e Strain (T) -- Ho where e is the non-recovered part of the deformation. (xxv)